Brain (2001), 124, 176–208
Cortical innervation of the facial nucleus in the
non-human primate
A new interpretation of the effects of stroke and
related subtotal brain trauma on the muscles of facial
expression
Robert J. Morecraft, Jennifer L. Louie, James L. Herrick and Kimberly S. Stilwell-Morecraft
Division of Basic Biomedical Sciences, The University of
South Dakota School of Medicine, Vermillion, South
Dakota, USA
Correspondence to: Dr Robert J. Morecraft, Division of
Basic Biomedical Sciences, The University of South Dakota
School of Medicine, Vermillion, SD 57069, USA
E-mail: [email protected]
Summary
The corticobulbar projection to musculotopically defined
subsectors of the facial nucleus was studied from the face
representation of the primary (M1), supplementary (M2),
rostral cingulate (M3), caudal cingulate (M4) and ventral
lateral pre- (LPMCv) motor cortices in the rhesus monkey.
We also investigated the corticofacial projection from the
face/arm transitional region of the dorsal lateral premotor
cortex (LPMCd). The corticobulbar projection was
defined by injecting anterograde tracers into the face
representation of each motor cortex. In the same animals,
the musculotopic organization of the facial nucleus was
defined by injecting fluorescent retrograde tracers into
individual muscles of the upper and lower face. The facial
nucleus received input from all face representations. M1
and LPMCv gave rise to the heaviest projection with
progressively diminished intensity occurring in the M2,
M3, M4 and LPMCd projections, respectively. Injections
in all cortical face representations labelled terminals in
all nuclear subdivisions (dorsal, intermediate, medial and
lateral). However, significant differences occurred in the
proportion of labelled boutons found within each
functionally characterized subdivision. M1, LPMCv,
LPMCd and M4 projected primarily to the contralateral
lateral subnucleus, which innervated the perioral
musculature. M2 projected bilaterally to the medial
subnucleus, which supplied the auricular musculature.
M3 projected bilaterally to the dorsal and intermediate
subnuclei, which innervated the frontalis and orbicularis
oculi muscles, respectively. Our results indicate that the
various cortical face representations may mediate
different elements of facial expression. Corticofacial
afferents from M1, M4, LPMCv and LPMCd innervate
primarily the contralateral lower facial muscles. Bilateral
innervation of the upper face is supplied by M2 and
M3. The widespread origin of these projections indicates
selective vulnerability of corticofacial control following
subtotal brain injury. The finding that all face
representations innervate all nuclear subdivisions, to some
degree, suggests that each motor area may participate in
motor recovery in the event that one or more of these
motor areas are spared following subtotal brain injury.
Finally, the fact that a component of the corticofacial
projection innervating both upper and lower facial
musculature arises from the limbic proisocortices (M3
and M4) and frontal isocortices (M1, M2, LPMCv and
LPMCd) suggests a potential anatomical substrate that
may contribute to the clinical dissociation of emotional
and volitional facial movement.
Keywords: brainstem; cranial nerves; limbic cortex; motor cortex
Abbreviations: BDA ⫽ biotinylated dextran amine; DY ⫽ diamidino-yellow; FB ⫽ fast blue; FD ⫽ fluorescein dextran;
FR ⫽ fluoro ruby; LPMCd ⫽ dorsal lateral premotor cortex (or area 6V); LPMCv ⫽ ventral lateral premotor cortex (or area
6V); LYD ⫽ lucifer yellow dextran; M1 ⫽ primary motor cortex; M2 ⫽ supplementary motor area (or medial area 6); M3 ⫽
rostral cingulate motor cortex (or area 24c); M4 ⫽ caudal cingulate motor cortex (or area 23c); MCA ⫽ middle cerebral
artery; PB ⫽ phosphate buffer; PHA-L ⫽ Phaseolus vulgaris leucoagglutinin
© Oxford University Press 2001
Cortical innervation of the facial nucleus
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Introduction
The complex nature of facial expression has greatly influenced
the notion that the cerebral cortex plays an important role in
mediating facial movement (Duchenne, 1862; Darwin, 1872;
Jackson, 1884; James, 1890; Denny-Brown, 1950; Damasio,
1994). Underscoring this relationship are the many alterations
in facial expression that follow subtotal brain injury and
occur in psychiatric illness and cranial–cervical dystonia.
Despite the critical nature of these disorders, we know little
about how the cerebral cortex and facial nucleus interact
structurally, and how alterations in this interaction may
disrupt our ability to appropriately control the muscles of
facial expression. For example, over the past century little
has changed in the way we interpret the most common poststroke condition, in which occlusion of the middle cerebral
artery and its branches results in paralysis of the contralateral
lower face, but sparing of the upper face. The clinical
consequences remain explained by the suggestion that the
upper facial musculature receives bilateral innervation from
the primary motor cortex (M1) and the lower face only
contralateral innervation from M1 (Papez, 1927; Pearson,
1946; Reed and Sheppard, 1976; Brodal, 1981; WilsonPauwels et al., 1988; Adams et al., 1997; Kandel et al.,
2000). The continued teaching of this tenet is quite surprising,
considering the fact that neuronal tracing studies conducted
in human and non-human primates do not fully support the
classic interpretation (Kuypers, 1958a, b; Jenny and Saper,
1987). For example, it has been shown that parts of the facial
nucleus innervating the lower facial musculature receive
heavy contralateral input from M1. However, parts of the
facial nucleus containing motor neurones innervating the
upper facial musculature receive little input from M1.
Contributing further to the enigma is evidence indicating that
the supplementary motor area (M2 or medial area 6), which
contains a face representation, may not innervate the facial
nucleus (Jürgens, 1984).
Further associated with the mysteries underlying facial
deficits following localized brain damage are numerous
behavioural and clinical observations that have demonstrated
a dissociation between voluntary and emotional facial
movements (Darwin, 1872; Jackson, 1884; Wilson, 1924;
Monrad-Krohn, 1924, 1939; Allen, 1931; Karnosh, 1945;
Podolsky, 1945; Brown, 1967; Brodal, 1981; Duchenne,
1990; Hopf et al., 1992; Damasio, 1994, 1995; Topper et al.,
1995; Husain, 1997; Ross and Mathiesen, 1998; Urban
et al., 1998; Hopf et al., 2000). The most frequently reported
example is ‘volitional facial paralysis’. This occurs in patients
who present with impaired voluntary movement in their
lower facial muscles contralateral to a cortical or subcortical
lesion but overcome the paralysis when responding to an
emotionally provocative or humorous remark. Volitional
facial paresis has been associated with lesions involving M1
and the underlying subcortical white matter (Hopf et al.,
1992). Similarly, but less commonly encountered, is a
condition where emotionally affiliated facial movement is
not only spared but excessive. In contrast to this is the
inverse condition historically known as ‘amimia’, or more
commonly known as ‘emotional facial paralysis’. This
disorder is characterized by an inability to smile on one side
of the face; however, voluntary control over the same set of
facial muscles is largely unaffected. Emotional facial paresis
has been reported in patients with lesions involving the
midline cortex, insula, thalamus, striatocapsular region and
pons (Laplane et al., 1977; Hopf et al., 1992, 2000; Damasio,
1994; Urban et al., 1998). Collectively, these observations
have led to the hypothesis that separate neural systems may
mediate emotional and voluntary facial movements. Closely
related is the recent suggestion that the anterior cingulate
cortex may mediate emotionally associated movements in
the upper face and the lateral frontal cortices volitional
movements in the lower face (Damasio, 1994). However,
specific neural systems that may form an integrated network
between voluntary and emotional portions of the cortex and
musculotopically defined parts of the facial nucleus have not
been localized.
Several lines of research have revealed that there are at
least five cortical face representations in the human and nonhuman primate brain, with each face representation being
affiliated with five distinct cortical motor areas. (Fig. 1A and
B) (Ferrier, 1886; Horsley and Schäfer, 1888; Penfield and
Welch, 1951; Woolsey et al., 1952, 1979; Bates, 1953; Luschei
et al., 1971; Muakkassa and Strick, 1979; McGuinness
et al., 1980; Sirisko and Sessle, 1983; Luppino et al., 1991;
Morecraft and Van Hoesen, 1992; Paus et al., 1993; Tanji,
1994; Godschalk et al., 1995; West and Larson, 1995;
Morecraft et al., 1996; Picard and Strick, 1996; Tokuno et al.,
1997; Wu et al., 2000; Morecraft and Yeterian, 2001). They
include the face representation of the primary motor cortex
(M1-areas F1 and F4), ventral lateral-premotor cortex
(LPMCv-area 6V), supplementary motor cortex (M2-area
6m), rostral cingulate motor cortex (M3-area 24c) and caudal
cingulate motor cortex (M4-area 23c). The fact that there is
widespread face representation at the cortical level raises the
possibility that each face representation may innervate the
facial nucleus, i.e. much like all cortical arm representations,
selectively innervate brachial levels of the spinal cord and
leg representations the lumbosacral levels (Biber et al., 1978;
Murray and Coulter, 1981; Hutchins et al., 1988; Galea and
Darian-Smith, 1994; Luppino et al., 1994; Rouiller et al.,
1994; Morecraft et al., 1997). It is possible to speculate that
all cortical face representations may not only innervate
the facial nucleus but also preferentially target subsectors
controlling different groups of facial muscles, this premise
being based upon the fact that the various subsectors of
the primate facial nucleus are musculotopically organized
(Fig. 1C) (Jenny and Saper, 1987; Satoda et al., 1987; Porter
et al., 1989; Welt and Abbs, 1990; VanderWerf et al., 1998)
and the fact that M1 preferentially innervates only the
contralateral lateral subnucleus (Jenny and Saper, 1987).
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Fig. 1 (A) Schematic diagrams of the medial (top) and lateral (bottom) surfaces of the cerebral cortex of the rhesus monkey depicting the
basic organization of the frontal lobe and adjacent cingulate cortex. (B) Enlarged representation of A illustrating the basic somatotopical
organization of the motor cortices. (C) Transverse section through the lower pons illustrating the location of the facial nucleus (top), the
major nuclear subdivisions (bottom right) and the basic musculotopic organization (bottom left). A ⫽ arm; as ⫽ arcuate sulcus; cf ⫽
calcarine fissure; cgs ⫽ cingulate sulcus; cs ⫽ central sulcus; Ea ⫽ ear; F ⫽ face; FEF ⫽ frontal eye fields; Fr ⫽ frontalis; ios ⫽
inferior occipital sulcus; ips ⫽ intraparietal sulcus; L ⫽ leg; lf ⫽ lateral fissure; LL ⫽ lower lip; LPMCd ⫽ dorsal lateral premotor
cortex; LPMCv ⫽ ventral lateral premotor cortex; ls ⫽ lunate sulcus; M1 ⫽ primary motor cortex; M2 ⫽ supplementary motor cortex;
M3 ⫽ rostral cingulate motor cortex; M4 ⫽ caudal cingulate motor cortex; OO ⫽ orbicularis oculi; P ⫽ platysma; pre-SMA ⫽ presupplementary motor cortex; rs ⫽ rhinal sulcus; SEF ⫽ supplementary eye field; sts ⫽ superior temporal sulcus; poms ⫽ medial parietooccipital sulcus; sts ⫽ superior temporal sulcus; UL ⫽ upper lip.
Finally, defining the organization of the corticofacial
projection from M3 and M4, whose origins are embedded in
the proisocortical portion of the ‘emotive’ limbic lobe, may
assist in interpreting the clinical observations that have long
suggested a dissociation of voluntary and emotional facial
movements.
The occurrence of altered facial expressions that
accompany subtotal brain trauma and present in psychiatric
illness and cranial–cervical dystonia implies that a strong
and highly organized structural linkage occurs between the
cerebral cortex and the facial nucleus. The fact that selective
muscle groups are adversely affected following localized
brain damage indicates that the various cortical face
representations may preferentially influence different groups
of facial muscles. To advance our understanding of these
important neurological issues, we studied the organization of
the descending projection from the face representation of
five major cortical motor areas to musculotopically defined
subsectors of the facial nucleus. In addition, we investigated
a potential corticofacial projection from the ventral part of
the dorsal lateral premotor cortex (LPMCd), which primarily
gives rise to arm movements following stimulation, but
occasionally face movements. Our findings provide new
insight to the long-standing question of cortical innervation
of the upper and lower facial musculature. Together, these
observations offer a new and alternative explanation for the
clinical deficits that occur following localized cortical damage
to the lateral and medial regions of the cerebral hemisphere.
Material and methods
The corticobulbar projection to the facial nucleus was studied
in seven adult rhesus monkeys (Macaca mulatta). All
protocols received Institutional Animal Care and Use
Cortical innervation of the facial nucleus
179
Fig. 2 Plate of low-power bright-field photomicrographs of representative BDA injection sites in different motor fields, following tissue
processing for immunohistochemical visualization. (A) Coronal section illustrating the ventral lateral premotor cortex (LPMCv) injection
site in case SDM 22. (B) Coronal section depicting the rostral cingulate motor cortex (M3) injection site in case SDM 9. (C) Horizontal
section showing the M3 injection site in case SDM 14. Scale bar in B ⫽ 5 mm and is applicable to all plates. CgS ⫽ cingulate sulcus;
ILAS ⫽ inferior limb of the arcuate sulcus; PS ⫽ principle sulcus; SLAS ⫽ superior limb of the arcuate sulcus.
Committee approval and were conducted in accordance with
USDA and the Society for Neurosciences guidelines. Each
monkey was immobilized with ketamine hydrochloride
(10 mg/kg) then anaesthetized intravenously with
pentobarbital (2.5–4 mg/kg/h). The head was shaved,
scrubbed with betadine and the animal placed into a NIH
head holder or Kopf stereotaxic head holder.
Surgery
The lateral surface of the cerebral cortex was exposed as
described previously (Morecraft and Van Hoesen, 1992;
Morecraft et al., 1992). Bridging cortical veins draining into
the superior sagittal sinus were cauterized to expose the
medial wall of the cerebral cortex. Intracortical
microstimulation was used to localize the arm and face
representations in M1, LPMCd, LPMCv and M2. Standard
anatomical landmarks were used to localize the face
representation in M3 and M4. Graded pressure injections
(0.2–0.3 µl per penetration) of anterograde neuronal tracers
were made into the various cortical face representations using
a Hamilton microsyringe inserted 2–3 mm below the cortical
surface under microscopic guidance. To minimize white
matter involvement following M2 injections, the superior
frontal lobule was gently retracted laterally and the tip of the
needle was inserted directly into the intended grey matter
lining the vertical wall without involving cortex on the
dorsomedial convexity and its underlying white matter. For
injections into the lower bank of the cingulate sulcus (e.g.
M3 and M4) the arachnoid matter bridging over the cingulate
sulcus was removed and the superior frontal lobule was
retracted laterally exposing cortex in the lower bank. The
needle tip was then inserted directly into the cingulate cortex,
avoiding the adjacent frontal cortex (Fig. 2B and C). The
location of each stimulation point and injection site was
recorded on a JVC videocassette recorder (HR-S9400U,
Dage-MTI, Inc., Michigan City, Ind., USA) directly connected
to a three-chip colour camera (MTI DC-330, JVC, Aurora,
Ill., USA) that was mounted on the photo/video port of the
surgical microscope (Stortz M-703F, Olympus, Minneapolis,
Minn., USA). These images were metrically calibrated and
captured with respect to anatomical landmarks (e.g. sulci)
and used for developing an accurate post-mortem
reconstruction of the brain surface, the location of each
physiological stimulation point and the penetration point
of each tract tracer injection. Intramuscular injections of
fluorescent retrograde neuronal tracers were made in upper
and lower facial muscles in four of the seven monkeys
studied by using a microsyringe inserted into a 20 g needle,
which was then inserted into the muscle tissue. Each muscle
was localized using the criteria of Huber (Huber, 1933).
Intracortical microstimulation
A monopolar tungsten microelectrode (impedance 1.0–
2.0 MΩ) was attached to a Grass S88 stimulator and a
constant current stimulus isolation unit. The system was
grounded and the electrode was lowered to a depth of 100 µm
and advanced at 500-µm intervals. Cortex was mapped with
a train duration of 50–100 ms and a pulse duration of 0.2 ms
delivered at 330 Hz. Stimulation points were spaced 0.5–
2.5 mm apart to minimize tissue damage. The lowest level
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of current needed to evoke movement was considered the
movement threshold. During all experiments, applied current
levels were continuously monitored by measuring the voltage
with the use of a digital storage oscilloscope (LG Precision
Co., Ltd, Ceritos, Calif., USA) and determining the system
resistance. The current values ranged between 3 and 80 µA
Cortical innervation of the facial nucleus
(Figs 3–6). All movements at threshold were discrete and
confined to a specific body part (e.g. upper lip, tongue,
wrist, finger).
Experimental design
Cortical and intramuscular injections
In all monkeys, anterograde tracers were injected into various
cortical face representations to study the patterns of terminal
labelling in the facial nucleus (Figs 2–6). Injections and
representative volumes were made according to the relative
size of each face representation and to minimize arm
representation involvement when possible. The anterograde
tracers used were 10% biotinylated dextran amine (BDA),
10% lucifer yellow dextran (LYD), 2.5% Phaseolus vulgaris
leucoagglutinin (PHA-L), 10% fluorescein dextran (FD) and
10% fluoro ruby (FR). The FD injectate was composed of
an equal mixture of 3000 and 10 000 MW volumes, as was
the FR injectate. In monkeys SDM 14, 19, 20 and 22, specific
facial muscles were injected with the retrograde tracers 4%
fast blue (FB) and 4% diamidino-yellow (DY). This enabled
us to examine the topographical relationship between
corticofacial terminals and the general organization of facial
lower motor neurones. The specific injection site parameters
in each experiment are described below.
Monkey SDM 9. FB was injected into the face representation
of M1 (four penetrations; total volume 0.8 µl) (see Fig. 1 of
Morecraft et al., 1996). In the contralateral hemisphere, BDA
was injected into the face area of M3 (two penetrations; total
volume 0.4 µl), positioned directly above the genu of the
corpus callosum (Fig. 2B).
Monkey SDM 10. FB was injected into the arm representation
of M2 (one penetration; total volume 0.2 µl) and DY was
injected into the face representation of M2 (one penetration;
total volume 0.2 µl) (see Fig. 3 of Morecraft et al., 1996).
On the contralateral hemisphere, BDA was injected into the
rostral half of M4 (one penetration; total volume 0.4 µl),
positioned at coronal levels involving the arcuate spur to
levels extending 2 mm caudal to this landmark.
Monkey SDM 14. All cortical injections were made into the
right hemisphere (Figs 2C and 3A). PHA-L was injected into
the face representation of M1 (four penetrations; total volume
0.8 µl) and FD was injected into the physiologically defined
181
face representation of LPMCv (total volume 0.8 µl). On the
medial wall of the hemisphere, LYD (total volume 0.6 µl) was
injected into the face representation of M2, and BDA was
injected into the rostral portion of M3 (lower bank of the
cingulate sulcus) corresponding to coronal levels including the
genu of the corpus callosum (two penetrations; total volume
0.6 µl) (Fig. 2C). Finally, FR (one penetration; total volume
0.4 µl) was injected into the rostral portion of M4 located at
coronal levels including the arcuate spur. In the upper facial
musculature located contralateral to the cortical injections, DY
was injected into the frontalis/corrugator supercilii complex
(three penetrations; 10 µl total volume) and FB was injected
into the upper and lower orbital and preseptal portions of
the orbicularis oculi (six penetrations; 10 µl total volume)
(Fig. 3B). In the lower facial musculature located ipsilateral to
the cortical injections, DY was injected into the upper
orbicularis oris (upper lip) (three penetrations; 10 µl total
volume) and FB was injected into lower orbicularis oris (lower
lip) (three penetrations; 10 µl total volume) (Fig. 3B).
Monkey SDM 19. All cortical injections were made in the
right hemisphere (Fig. 4A). LYD was injected into the face
representation of M1 (four penetrations; total volume 1.2 µl)
and FD was injected into the arm representation of M1 (four
penetrations; total volume 0.9 µl). FR was then injected into
the arm representation of M2 (two penetrations; total volume
0.6 µl). However, during surgery a large bridging vessel
required ligation over the rostral part of M2, yielding the
underlying cortex (face area) unresponsive to stimulating
current. Therefore, the face area was approximated as being
localized immediately anterior to the physiologically defined
arm representation and caudal to the pre-SMA (M2 presupplementary motor area) which resides in the superior
frontal gyrus in a plane above the genu of the corpus callosum
(Fig. 1A). BDA was injected into the face area of M2
(two penetrations; total volume 0.6 µl). In the upper facial
musculature located contralateral to the cortical injections,
DY was injected into the frontalis–corrugator supercilii
complex (three penetrations; 10 µl total volume) and FB was
injected into the upper and lower orbital and preseptal
portions of the orbicularis oculi (six penetrations; 10 µl total
volume) (Fig. 4B). In the lower facial musculature located
ipsilateral to the cortical injections, DY was injected into the
upper orbicularis oris (three penetrations; 10 µl total volume)
Fig. 3 Summary diagrams of the experimental design in monkey SDM 14. (A) Corticobulbar terminals were studied in the facial nucleus
following cortical injections (black irregular spheres) made into five face representations in the right cerebral cortex. The view of the
medial wall is a mirror image, thus illustrating the right medial wall injection sites. Top pullout depicts the location of the LYD injection
in M2 in relation to physiological mapping, the BDA injection in M3 and the FR injection in M4. Bottom pullout demonstrates the
location of the PHA-L injection in M1 and the FD injection in the LPMCv in relation to physiological mapping. Each black dot
represents a stimulation point labelled with corresponding threshold level (µA) and body part where the movement was observed. (B) In
the same monkey, the musculotopic organization in the facial nucleus was studied following injections of retrograde dyes into selected
facial muscles. In the left upper face, DY was injected into the frontalis (squares) and fast blue (FB) was injected into orbicularis oculi
(x). In the right lower face, DY was injected into the upper lip (triangles) and FB was injected into the lower lip (inverted triangles).
ac ⫽ anterior commissure; cc ⫽ corpus callosum; cf ⫽ calcarine fissure; D ⫽ digits; Ea ⫽ ear; ecs ⫽ ectocalcarine sulcus; El ⫽ elbow;
ilas ⫽ inferior limb of the arcuate sulcus; ipcd ⫽ inferior precentral dimple; J ⫽ jaw; NR ⫽ no response; ps ⫽ principal sulcus; Sh ⫽
shoulder; spcd ⫽ superior precentral dimple; Th ⫽ thumb; To ⫽ tongue; Wr ⫽ wrist. For other conventions see Fig. 1.
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Fig. 4 Summary diagrams illustrating the experimental design in monkey SDM 19. (A) Corticobulbar terminals were studied in the facial
nucleus following cortical injections (black irregular spheres) made into two face representations in the right cerebral cortex. The view of
the medial wall is a mirror image. The top pullout depicts the location of the BDA injection into M2. FR was also injected into the arm
representation of M2. The bottom pullout demonstrates the location of the LYD injection in M1 and the FD injection in the arm
representation of M1. Each black dot represents a stimulation point labelled with corresponding threshold level (µA) and body part
where the movement was observed. (B) In the same monkey, the musculotopic organization in the facial nucleus was studied following
injections of retrograde dyes into selected facial muscles. In the left upper face, DY was injected into the frontalis (squares) and FB was
injected into orbicularis oculi (x). In the right lower face, DY was injected into the upper lip (triangles) and FB was injected into the
lower lip (inverted triangles). For abbreviations see Figs 1 and 3.
Cortical innervation of the facial nucleus
and FB was injected into the lower orbicularis oris (three
penetrations; 10 µl total volume) (Fig. 4B).
Monkey SDM 20. All cortical injections were made in the right
hemisphere. BDA was injected into the face representation of
M1 (two penetrations; total volume 1.0 µl) and LYD was
injected into the arm representation of M1 (two penetrations;
total volume 1.0 µl). FR was injected into cortex lining the
lower bank of the cingulate (M3) from a location established
at coronal levels, including the genu of the corpus callosum,
to a caudal location corresponding to a coronal plane located
2 mm rostral to the genu of the arcuate sulcus (10 penetrations;
total volume 10 µl). FB was injected bilaterally into the
orbital, preseptal and pretarsal portions of the orbicularis
oculi (10 penetrations; total volume 25 µl).
Monkey SDM 22. All cortical injections were made in the
right hemisphere (Fig. 5A). On the lateral wall, FR was
injected into the face representation of M1 (four penetrations;
total volume 1.2 µl), and BDA was injected into the face
representation of LPMCv (four penetrations; total volume
1.2 µl). FR was injected into the face area of M2 (four
penetrations; total volume 0.4 µl). PHA-L was injected into
the face area of M3 (two penetrations; total volume 0.5 µl)
and LYD was injected into the face area of M4 (one
penetration; total volume 0.4 µl). In the upper facial
musculature contralateral to the cortical injections, FB was
injected into the upper and lower orbital, preseptal and
pretarsal portions of the orbicularis oculi (seven penetrations;
10 µl total volume) and DY was injected into the orbitoauricularis muscle (two penetrations; 10 µl total volume)
(Fig. 5B). In the lower facial musculature located ipsilateral
to the cortical injections, FB was injected into the upper
orbicularis oris (three penetrations; 10 µl total volume) and
DY was injected into the lower orbicularis oris (three
penetrations; 10 µl total volume) (Fig. 5B).
Monkey SDM 23. FD was injected into the ventral part of
the arm area of LPMCd as defined using microstimulation
(three penetrations; total volume 1.0 µl) (Fig. 6).
Tissue processing
Following a survival period of 21–30 days each monkey was
deeply anaesthetized with Nembutal and perfused with 300–
500 ml of 0.9% saline solution followed by 2 l of 4%
paraformaldehyde in 0.1 M phosphate buffer (PB), then 1 l
of 10% sucrose in 0.1 M PB. The perfusion was completed
by an infusion of a 10% then 30% solution of sucrose in
0.1 M PB. The brain was removed, placed in 30% sucrose
in 0.1 M PB and stored for 2–4 days at 4°C. Post-mortem
photographs and electronic images were taken of the dorsal,
ventral, lateral and medial surfaces of the cerebral cortex,
brainstem and spinal cord. Each injected facial muscle in
monkeys SDM 14, 19, 20 and 22 as well as the adjacent
non-injected muscles were dissected and placed in 30%
sucrose in 0.1 M PB, stored at 4°C.
The cortex was frozen then sectioned coronally (monkeys
SDM 9, 10, 20 and 22) or horizontally (monkeys SDM 14,
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19 and 23) on an American Optical sliding microtome (AO
860) at a thickness of 50 µm in cycles of 10. The brainstem
was frozen with dry ice and cut transversely (perpendicular
to its long axis) at a thickness of 50 µm in cycles of five. In
monkey 5, brainstem serial sections were cut with a vibratome
at a thickness of 200–300 µm. Finally, each muscle was
frozen sectioned and examined for tracer localization (Vander
Werf et al., 1996, 1998).
The first section of each cortical and brainstem series was
mounted on subbed slides, dried overnight, coverslipped with
DPX mounting medium (Aldrich Chemicals, Milwaukee,
Wis., USA) and used for fluorescent analysis (Morecraft and
Van Hoesen, 1992, 1993, 1998; Morecraft et al., 1993)
(Fig. 7). After analysis, each fluorescent section was stained
for Nissl substance using thionin. The second section in each
series was processed for BDA using the avidin–biotin method
(Fig. 8). Following successive rinses in PB, the sections were
incubated in 0.05% DAB (diaminobenzidine tetrachloride)
and 1% nickel ammonium sulphate for 10 min. Then, 0.009%
hydrogen peroxide was added and the tissue incubated for
another 10–15 min, rinsed in PB, serially dehydrated, mounted
on subbed slides and coverslipped using Permount (Fisher
Chemicals, Denver, Co., USA). The BDA injection site,
axons and cells stained by nickel-enhanced DAB appeared
blue-black upon visualization.
Monkeys SDM 14, 19 and 22 received injections of
multiple anterograde tracers (e.g. BDA, LYD, PHA-L, FR
and FD). In these experiments, BDA was processed alone in
a complete series of tissue sections as indicated above,
mounted on glass slides and coverslipped. In additional
serial sets of unprocessed tissue sections through the cortex,
brainstem and spinal cord, double labelling immunohistochemistry was performed (Fig. 8F). In all of the double
labelling experiments, BDA was reacted first according to
the above protocol with the exception that BDA was stained
brown using DAB in the absence of nickel ammonium
sulphate (Fig. 8B and C). After reacting for BDA, the same
tissue sections were then incubated in avidin–biotin blocking
reagent (Vector SP-2001), rinsed in 10% normal goat serum
for 2 h then incubated overnight, with the appropriate
biotinylated antibody directed against a second neuronal tract
tracer (e.g. biotinylated anti-LYD). The tissue was then
incubated in a solution of avidin–biotinylated peroxidase
complex, rinsed in buffer and stained blue using the Vector
SG peroxidase substrate kit (Vector SK-4700). Thus, BDA
was colourized brown and the second tracer (e.g. LYD) was
stained blue in the same tissue sections (Fig. 8A and F). All
sections were rinsed, dehydrated, mounted and coverslipped
on glass slides. This process was conducted on another set
of serial sections staining BDA brown with DAB, then
another anterograde tracer blue (e.g. PHA-L), again using
the appropriate antibody and blue reaction process to visualize
the second tracer (e.g. biotinylated anti-PHA-L). FR and FD
were also processed immunohistochemically in the same
manner (e.g. BDA brown then FR blue). In these series, FR
and FD labelling was verified by comparing the locations of
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Fig. 5 Diagrams illustrating the experimental design in monkey SDM 22. (A) Corticobulbar terminals were studied in the facial nucleus
following cortical injections (black irregular spheres) made into five face representations in the right cerebral cortex. The view of the
medial wall is a mirror image. The top pullout depicts the location of the FR injection into M2, the PHA-L injection into M3 and the
LYD injection into M4. The bottom pullout demonstrates the location of the FD injection in M1 and BDA injection into LPMCv. Each
black dot represents a stimulation point labelled with corresponding threshold level (µA) and body part where the movement was
observed. (B) In the same monkey, the musculotopic organization in the facial nucleus was studied following injections of retrograde
dyes into selected facial muscles. In the left upper face, DY was injected into the orbital auricularis (squares) and FB was injected into
orbicularis oculi (x). In the right lower face, DY was injected into the upper lip (triangles) and FB was injected into the lower lip
(inverted triangles). For abbreviations see Figs 1 and 3.
Cortical innervation of the facial nucleus
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Fig. 6 Diagrams illustrating the experimental design in monkey SDM 23. (A) Corticobulbar terminals
were studied in the facial nucleus following an injection of FD (irregular black spheres) made into arm/
face area of LPMCd in the right cerebral cortex. The pullout demonstrates the location of the FD
injection in relation to physiological mapping. Each black dot represents a stimulation point labelled
with corresponding threshold level (µA) and body part where the movement was observed. For
abbreviations see Figs 1 and 3.
immunochemically localized reaction products to fluorescent
labelling in the non-reacted fluorescent series. The specific
antibodies used for each anterograde tracer were biotinylated
anti-Lucifer Yellow rabbit IgG fraction, biotinylated antiPHA-L rabbit IgG fraction, biotinylated anti-FR rabbit IgG
fraction and biotinylated anti-FD rabbit IgG fraction (all
from Vector Laboratories, Burlingame, Calif., USA). The
remaining cortical tissue sections were stained for myelin
using the gold chloride method (Schmued, 1990) and
cytochrome oxidase for evaluating histochemical boundaries
of the frontal motor areas (Matelli et al., 1985).
Data analysis
Fluorescent material was studied using epi-fluorescent
illumination and immunohistochemically processed material
was examined under bright-field illumination. Data from all
tissue sections were collected with the use of a conventional
Hewlett Packard X-Y plotter (HP-7045B, Hewlett Packard,
Palo Alto, Calif., USA) that was attached to the x–y axes of
a microscope stage (Olympus BX60, Minneapolis, Mass.,
USA). The outline of the tissue section, anatomical landmarks
such as blood vessels and ventricles, the white and grey
matter interfaces, periphery of the injection sites, and
transported tracing substances were plotted in each tissue
section. The criterion of Condé was used to assess the
effectiveness of the fluorescent injection sites (Condé, 1987).
Accordingly, zones 0–II were interpreted as corresponding to
the effective uptake site. For immunohistochemically
developed material, the effective injection site was defined
by the heavily stained area that surrounds the point of
tracer administration and extends to the edge of the deposit.
The edge of the injection site corresponding to the region
where the dense precipitate diminishes, neurones and
labelled axons are distinguishable, and the intensity of
fibre staining is similar to fibre staining intensity occurring
in local, primary projection targets (Fig. 2). Cortical
sections were spaced at intervals of 500 µm. Nissl-,
myelin- and cytochrome-stained sections were used for
plotting architectonic boundaries directly onto the chartings.
Brainstem tissue sections were analysed at intervals of
250 µm. Fluorescent labelling (retrogradely labelled motor
neurones with FB and DY and corticofacial terminals
labelled with FD and FR) and immunohistochemically
developed sections (BDA, LYD, PHA-L, FD and FR) were
also plotted using the x–y plotter. To study in greater detail
facial nucleus labelling patterns in immunohistochemically
processed sections, axon varicosities in the nucleus were
charted a second time, using maximum range conditions
of the x–y recorder or with a drawing tube. White and
grey matter borders were added to the brainstem chartings
using Nissl-stained sections. In monkey SDM 20,
vibratomed sections through the brainstem were charted
for FR terminals. FR labelling in the facial nucleus was
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Fig. 7 Plate of photomicrographs showing examples of fluorescent dye-labelled facial motor neurones following intramuscular injections.
(A) DY labelled neurone in the medial subnucleus following an injection in the orbito-auricularis in case SDM 22. (B) FB-labelled
neurones in the intermediate subnucleus following an injection into the orbicularis oculi in SDM 14. (C) DY-labelled neurone in the
lateral subnucleus following an injection into the upper lip in SDM 19. (D) FB-labelled neurone in the lateral subnucleus following an
injection into the lower lip in SDM 22. Scale bar in D is applicable to all plates.
verified in this case using a Bio-Rad 1024 confocal
microscope (Bio-Rad Laboratories, Hercules, Calif., USA).
The terminal projection from representative cases of each
motor area (M1, LPMCv, LPMCd, M2, M3 and M4) was
quantified within the facial nucleus using immunohistochemically processed material (Fig. 9). To accomplish
this, the total number of labelled boutons was counted in
every immunohistochemically reacted serial section through
the ipsilateral and contralateral facial nucleus (e.g. at 250 µm
intervals through a rostrocaudal distance of 1.7–2.2 mm).
Terminal boutons were further categorized by ipsilateral and
contralateral nuclear subdivision (medial, lateral, dorsal and
intermediate). Terminal boutons, or axon varocosities,
represent putative synaptic contacts between a projection
axon and local neurones (Wouterlood and Groenewegen,
1985). The total number of boutons in each subdivision of
each side was divided by the total number of boutons counted
in the entire case. The ratio was converted to a percentage
and expressed by subdivision in each side.
The cortex was reconstructed using surface drawings
developed from metrically calibrated photographs and video
images taken of the brain prior to tissue sectioning (Figs
3–6). Nissl-, myelin- and cytochrome-oxidase-stained tissue
sections were used to delineate architectonic areas of the
frontal lobe and cingulate gyrus. A physiological map of the
cortical surface illustrating the locations of the stimulation
points, electrolytic lesions, sulci and vessels was constructed
from images taken during surgery of each penetration point
and surrounding landmark. The stimulation map was
superimposed on the injection site map (Figs 3–6). The
brainstem sections were reconstructed by stacking each serial
section in a caudal to rostral sequence depicting terminal
Cortical innervation of the facial nucleus
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Fig. 8 Plate of photomicrographs illustrating terminal labelling in the facial nucleus following injections of anterograde tracers in the
various face representations in the cerebral cortex. Unlabelled arrows identify examples of terminal boutons. (A) LYD fibres and
terminals (blue reaction product) in the lateral subnuclei following an injection of LYD in M1 in case SDM 19 (⫻40). (B) BDA fibres
and terminals (brown reaction product) in the lateral subnucleus following an injection in LPMCv in case SDM 22 (⫻40). (C) BDA
fibres and boutons (brown reaction product) found in the medial nucleus following an injection of BDA in M2 in case SDM 19 (⫻40).
(D) FR fibres and terminals (red reaction product) found in the medial subnucleus following an injection of FR in M2 in case SDM 22
(⫻40). (E) BDA fibres and terminals (brown reaction product) in the intermediate subnucleus following an injection of BDA in M3 in
case SDM 14 (⫻60). (F) LYD fibres and terminals (blue reaction product) in the lateral subnucleus following an injection of LYD in M4
in case SDM 22 (⫻40). The brown reaction product in the same tissue section represents BDA-labelled fibres that occurred as a result of
the BDA injection in LPMCv in the same cerebral hemisphere (see B).
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Fig. 9 Histograms showing the percentage of boutons found in each subnucleus of each side in representative cases involving each motor
area. The data from M1 (SDM19-LYD), LPMCv (SDM22-BDA), LPMCd (SDM23-FD), M2 (SDM19-BDA), M3 (SDM14-BDA) and
M4 (SDM22-LYD) is further illustrated in serial cross-sections through the facial nucleus in Figs 10, 11, 12, 13, 14 and 15, respectively.
labelling in all cases and motor neuronal labelling in selected
cases (Figs 10–15).
Cytoarchitectonic organization of the facial
nucleus
The facial nucleus can be subdivided into several distinct
cellular groups or subnuclei (Papez, 1927; Courville, 1966;
Jenny and Saper, 1987; Satoda et al., 1987; Baker et al.,
1994). In this report, the organization of the monkey facial
nucleus was determined according to the criteria of Jenny
and Saper (Jenny and Saper, 1987) using Nissl-stained
sections to facilitate comparison of our work with previously
published results on the corticofacial projection. Thus, the
nucleus was subdivided into intermediate, dorsal, medial
and lateral subsectors (Fig. 1C, right). Furthermore, patterns
of motor neurone labelling following injection of retrograde
tracers in the facial muscles and organization of corticofacial
terminals following injections into cortex correlated well
with the basic designation of intermediate, dorsal, medial
Cortical innervation of the facial nucleus
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Fig. 10 A series of line drawings through the facial nucleus in case SDM 19 following an injection of LYD into the face representation
of M1 and injections of retrograde tracers into representative upper and lower facial muscles. Illustrated on the tissue sections are the
locations of anterograde and retrograde labelling in each subnucleus.
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Fig. 11 A series of line drawings through the facial nucleus in case SDM 22 following an injection of BDA into the face representation
of LPMCv and injections of retrograde tracers into representative upper and lower facial muscles. Illustrated on the tissue sections of the
facial nucleus are the locations of anterograde and retrograde labelling in each subnucleus.
Cortical innervation of the facial nucleus
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Fig. 12 A series of line drawings through the facial nucleus (top) and spinal cord (bottom) in case SDM 23 following an injection of FD
into the arm representation of LPMCd. Illustrated on the representative tissue sections is anterograde labelling (black dots).
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Fig. 13 A series of line drawings through the facial nucleus in case SDM 19 following an injection of BDA into the face representation
of M2 and injections of retrograde tracers into representative upper and lower facial muscles. Illustrated on the tissue sections of the
facial nucleus are the locations of anterograde and retrograde labelling in each subnucleus.
Cortical innervation of the facial nucleus
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Fig. 14 A series of line drawings through the facial nucleus in case SDM 14 following an injection of BDA into the face representation
of M3 and injections of retrograde tracers into representative upper and lower facial muscles. Illustrated on the tissue sections of the
facial nucleus are the locations of anterograde and retrograde labelling in each subnucleus.
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Fig. 15 A series of line drawings through the facial nucleus in case SDM 22 following an injection of LYD into the face representation
of M4 and injections of retrograde tracers into representative upper and lower facial muscles. Illustrated on the tissue sections of the
facial nucleus are the locations of anterograde and retrograde labelling in each subnucleus.
Cortical innervation of the facial nucleus
and lateral subsectors (Fig. 1C, left). Cell sparse bands,
packing, somal diameter and staining intensity were
considered for parcellation.
Definition and characterization of cortical face
areas
The face area of M1 is located rostral to the ventral extent
of the central sulcus and on average has a low physiological
threshold for excitability (Fig. 1A and B) (Weinrich and
Wise, 1982; Huang et al., 1988; Huntley and Jones, 1991;
Murray and Sessle, 1992; Preuss et al., 1996) (Fig. 1B). The
caudal portion of the M1 face area corresponds to area 4 in
Nissl-stained sections (Brodmann, 1909; Barbas and Pandya,
1987; Preuss and Goldman-Rakic, 1991) and area F1 in
cytochrome oxidase preparations (Matelli et al., 1985, 1991).
The rostral portion corresponds to the caudal portion of area
6V in Nissl-stained sections (Barbas and Pandya, 1987;
Preuss and Goldman-Rakic, 1991) and area F4 in cytochromeoxidase-stained sections (Matelli et al., 1985, 1991).
Immediately anterior and adjacent to the face representation
of M1 is the face area of the ventral lateral premotor cortex
(LPMCv) (Fig. 1B). This cortex corresponds to the rostral
portion of area 6V (Barbas and Pandya, 1987; Preuss and
Goldman-Rakic, 1991) as well as area F5 (Matelli et al., 1985,
1991). Physiologically, the face representation of LPMCv has
a higher threshold of excitability in unanaesthetized monkeys
when compared with the caudal portion of M1 (Rizzolatti
et al., 1988; Preuss et al., 1996). Electrophysiological
evidence indicates the arm and face representations overlap
in the dorsal portion of LPMCv (Gentilucci et al., 1988;
Rizzolatti et al., 1988; Godschalk et al., 1995; Preuss et al.,
1996). Within this transitional cortex, arm movements are
heavily represented, but face movements are occasionally
evoked. Similarly, the ventral part of LPMCd is primarily
related to arm movements and less so to face movements
(Godschalk et al., 1995; Preuss et al., 1996). Histologically,
the ventral part of LPMCd corresponds to area 6D in Nissl
preparations and area F2 in cytochrome oxidase preparations.
This overlap in somatotopy was taken into consideration in
our experimental design as we investigated the corticofacial
projection from the ventral part of LPMCv as well as the
corticofacial projection from the ventral portion of LPMCd.
The face representation of M2 lies within the rostral portion
of medial area 6 (Mitz and Wise, 1987; McGuire et al.,
1991; Preuss and Goldman-Rakic, 1991; Godschalk et al.,
1995; Morecraft et al., 1996). This same location corresponds
to area F3 using cytochrome oxidase staining (Matelli et al.,
1985, 1991; Luppino et al., 1993). The face representation
of M2 is relatively smaller than the lateral face areas and
has, on average, a higher threshold of movement excitation
when compared with the average threshold values of cortex
residing in the caudal portion of M1 (Mitz and Wise, 1987;
Luppino et al., 1991; Huntley and Jones, 1991). The face
area of M2 lies 1–3 mm rostral to a coronal plane established
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through the genu of the arcuate sulcus (Mitz and Wise, 1987;
Matsuzaka and Tanji, 1996; Morecraft et al., 1996). Rostral
to area F3 is area F6, which corresponds to the pre-SMA
(Matelli et al., 1985; Luppino et al., 1991). The pre-SMA is
related primarily to complex arm movements (Alexander and
Crutcher, 1990; Matsuzaka and Tanji, 1996) and is much less
excitable than adjacent area F3 (Luppino et al., 1991). The
cingulate motor cortex lines the depths of the cingulate sulcus
and is formed by the rostral and caudal cingulate motor
cortices (Biber et al., 1978; Muakkassa and Strick, 1979;
Morecraft and Van Hoesen, 1988, 1992; Hutchins et al.,
1988; Dum and Strick, 1991; Devinsky et al., 1995;
Nimchinsky et al., 1996). The rostral cingulate motor cortex
(M3) corresponds cytoarchitecturally to area 24c (Vogt et al.,
1987; Dum and Strick, 1991; Morecraft and Van Hoesen,
1992; Morecraft et al., 1996). The face area of M3 is located
in the rostral portion of area 24c, in coronal levels that
include the genu of the corpus callosum (Muakkassa and
Strick, 1979; Morecraft and Van Hoesen, 1992; Morecraft
et al., 1996; Tokuno et al., 1997). The genu and its anterior
limit were visualized during surgical exposure to assist in
localizing the M3 face area. The caudal cingulate motor area
(M4) corresponds cytoarchitecturally to area 23c (Vogt et al.,
1987; Hutchins et al., 1988; Dum and Strick, 1991; Morecraft
and Van Hoesen, 1992; Morecraft et al., 1996). The face
representation of M4 is located in the rostral part of area 23c
(Morecraft et al., 1996; Tokuno et al., 1997). This general
area gives rise to face movements using intracortical
microstimulation in the unanaesthetized monkey (Luppino
et al., 1991; Godchalk et al., 1995). Anatomically, this
location corresponds to coronal levels that include the anterior
commissure medially and spur of the arcuate sulcus laterally
(Morecraft and Van Hoesen, 1992; Morecraft et al., 1996;
Nimchinsky et al., 1996; Tokuno et al., 1997). If the spur is
absent, the location of the M4 face area was approximated
1.0–2.0 mm caudal to the genu of the arcuate sulcus.
Results
Retrograde labelling of facial motor neurones
Labelled neurones were found in the facial nucleus in all
monkeys receiving injections of FB and DY into the facial
muscles (Figs 3–6). All injections of retrograde tracer placed
into the frontalis–corrugator muscle complex labelled motor
neurones in the dorsal subnucleus (Figs 10, 13 and 14, right).
Occasionally, a few labelled cells appeared in the medial
edge of the intermediate subnucleus. Labelled neurones
occurred in the dorsal region of the medial subnucleus
following injections in the orbito-auricularis muscle (Figs 11
and 15, right). Injections in the orbicularis oculi muscle
consistently labelled neurones that were confined to the
intermediate subnucleus (Figs 10, 11 and 13–15, right).
Injections in upper orbicularis oris muscle labelled motor
neurones in the dorsolateral sector of the lateral subnucleus
(Figs 10, 11 and 13–15, left) and injections in the lower
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orbicularis oris muscle labelled neurones in the ventrolateral
sector of the lateral subnucleus (Figs 10, 11 and 13–15, left).
Location of cortical injection sites
In all cases presented in this report, the injection sites were
evaluated for somatotopic affiliation on the basis of multiple
criteria. First, the location and peripheral extent of the
injection sites made in M1, M2, LPMCv and LPMCd were
reconstructed in direct relation to all electrophysiological
stimulation points. Secondly, matching Nissl and cytochrome
oxidase sections were used to evaluate histological boundaries
in each motor area. The face areas of M1, LPMCv and
LPMCd correlated to the ventral extent of each respective
histological region. The face areas of M2, M3 and M4
correlated to the rostral extent of each respective histological
region. Thirdly, corticocortical interconnections amongst the
various injection sites in the same animal were evaluated
for topographical reciprocity. For example, cortical arm
representations are selectively interconnected, as are cortical
face representations (Pandya and Vignolo, 1971; Muakkassa
and Strick, 1979; Morecraft and Van Hoesen, 1988, 1992;
Luppino et al., 1994; Nimchinsky et al., 1996; Tokuno et al.,
1997). Fourthly, descending projections from each injection
site to the facial nucleus and spinal cord were analysed.
Injection site involvement of cortical face areas was supported
by the presence of projections to the facial nucleus (Kuypers,
1958a, b; Jenny and Saper, 1987; Morecraft et al., 1996).
Injection site involvement of cortical arm areas was supported
by the presence of direct projections to the brachial spinal
cord (Biber et al., 1978; Hutchins et al., 1988; Dum and
Strick, 1991; Galea and Darian-Smith, 1994; Rouiller et al.,
1994; Luppino et al., 1994; Morecraft et al., 1997).
Monkey SDM 9. The BDA injection site in M3 was confined
to the face representation as determined by FB tracer transport
from M1 to the BDA injection site in M3 (Fig. 2B) [also
see Morecraft et al. (1996), Fig. 1]. This was verified by the
presence of BDA labelling in the facial nucleus [see Morecraft
et al. (1996), Fig. 4]. No BDA labelling was found in the
spinal cord, indicating no BDA involvement of the M3 arm
representation.
Monkey SDM 10. The BDA injection site involved the
arm and face representations of M4 as determined by the
corticocortical projection patterns and the fact that BDA
labelling was found in both the facial nucleus and spinal
cord (see Morecraft et al., 1996, Figs 3 and 4).
Monkey SDM 14. The PHA-L injection in M1, FD injection
in LPMCv and LYD injection in M2 were all confined to
the physiologically defined face representation of each motor
area (Fig. 3A). All injections produced terminal labelling in
the facial nucleus (Fig. 14) with the exception of PHA-L,
which only labelled descending fibres. A few terminals were
found in the spinal cord from the LPMCv injection, indicating
minimal involvement of the adjacent arm representation. At
the cortical level these injection sites were found to be
topographically interconnected with each other as well as
with the BDA injection in the rostral part of M3 (face area)
and FR injection site in the rostral part of M4 (face area).
Anatomically, the M3 injection site corresponded to coronal
levels including the genu of the corpus callosum. This
injection produced terminal labelling in the facial nucleus
verifying the involvement of the M3 face area (Fig. 8E). The
anatomical location of the M4 injection site corresponded to
coronal levels including the arcuate spur as well as the
anterior commissure. Terminal labelling was found in the
facial nucleus and very light labelling was found in the spinal
cord that was largely confined to the region of the spinal
accessory nucleus.
Monkey SDM 19. On the lateral surface of the hemisphere
(Fig. 4A, bottom), the LYD and FD injection sites were
confined to the physiologically defined face and arm
representations of M1, respectively. The LYD injection
labelled terminals in the facial nucleus (Figs 8A and 10) and
the FD injection labelled terminals in the spinal cord. On the
medial wall of the hemisphere (Fig. 4A, top), the FR injection
site was confined to the arm representation of M2, which
was verified by physiological reconstruction, and its heavy
projections to the arm area of M1 and the spinal cord. The
BDA injection site was located in the rostral part of M2.
This injection gave rise to heavy projections to the face
representation of M1 as well as the facial nucleus, indicating
primary involvement of the face representation of M2
(Fig. 8C). Light labelling was found in the arm representation
of M1 as well as the spinal cord, indicating minimal
involvement of the arm representation of M2.
Monkey SDM 20. The BDA and LYD injection sites were
restricted to the physiologically mapped face and arm
representations of M1, respectively. Projections from these
injection sites were analysed in the cortical region of M3 for
the purpose of evaluating the somatotopic affiliation of the
FR injection site placed in M3. The FR injection was large
by design, involving most of M3 including its face and arm
representations. This was supported by the finding that the
M1 face injection labelled terminals in the rostral part of M3
(face area of M3) and the M1 arm injection labelled terminals
immediately caudal to this field (arm area of M3). This was
subsequently verified by the finding of FR labelling in both
the facial nucleus and spinal cord.
Monkey SDM 22. On the lateral surface of the hemisphere
(Fig. 5A, bottom), the FD and BDA injection sites were
found to be confined to the physiologically mapped face
representations in M1 and LPMCv, respectively, and each
gave rise to terminal labelling in the facial nucleus (Figs 8B
and 11). On the medial surface of the hemisphere (Fig. 5A,
top), the PHA-L injection was confined to the face
representation of M3 as determined by its anatomical location
and projections to the face areas of M1, LPMCv and
M2. However, this injection did not label terminals at
mesencephalic and pontine levels, only fibres. The LYD
injection site in M4 involved the face area and to a minimal
extent the arm area (Fig. 5A, top). Its somatotopically
affiliated projections to the face areas of M1, LPMCv and
Cortical innervation of the facial nucleus
M2 as well as its projection to the facial nucleus verified
this deduction (Figs 8F and 15). Light labelling in the
dorsomedial part of the spinal grey indicated minimal injectate
involvement of the arm representation of M4.
Monkey SDM 23. The FD injection site was confined to
the physiologically defined arm representation of LPMCd
(Fig. 6). Heavy labelling occurred in the spinal cord (Fig. 12,
bottom) and very light labelling was found in the facial
nucleus (Fig. 12, top). This indicated overlap between the
arm and face representations of the lateral premotor cortices
(e.g. intermingling of corticospinal and corticofacial
neurones) with arm representation predominating in this
location.
Topographical organization of anterograde
projections to the facial nucleus
Thirteen anterograde injection sites involving the various
face representations were used for analysis. All face
representations were found to project to the facial nucleus
but major differences were found in the topographical
distribution of each projection. In all cases, labelling took
the form of concentrated patches and occurred throughout
most of the rostral and caudal extent of the facial nucleus
(Figs 10–15). The results from individual injection sites
described below are identified by monkey (e.g. SDM19) and
tract tracing compound (e.g. LYD).
Corticofacial projections from M1
Two injection sites were evaluated (SDM19-LYD and
SDM22-FD). Both gave rise to similar and extensive patterns
of labelling in the facial nucleus. The overall projection was
characterized by a contralateral predominance, where the
primary target was the contralateral lateral subnucleus.
Terminal boutons were counted in each nuclear subsector in
injection SDM19-LYD (Figs 4, 8A, 9 and 10). In this case,
3065 boutons were found bilaterally. The most extensive
distribution of labelled boutons occupied the contralateral
lateral subnucleus (55.38%). This took the form of dense
patches of label in both the dorsal and ventral portions of
the lateral subnucleus, where motor neurones innervating the
upper and lower perioral musculature, respectively, were
located (Fig. 10). Comparatively lighter and patchy labelling
occupied the ipsilateral lateral subnucleus (15.09%). Sparse
terminal labelling was also found in the intermediate
(ipsilateral, 5.62%; contralateral, 9.21%), medial (ipsilateral,
6.41%; contralateral, 4.29%) and dorsal (ipsilateral, 1.41%;
contralateral, 2.59%) subnuclei.
Corticofacial projections from LPMCv (area 6V)
Two injection sites were studied (SDM14-FD and SDM22BDA) (Figs 3, 5, 8B, 9 and 11). A total number of 3731
boutons were counted bilaterally in injection SDM22-BDA.
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Much like the M1 projection, the LPMCv projection was
characterized by a contralateral predominance, with the
primary target being the contralateral lateral subnucleus
(42.97%). Surprisingly, a substantial number of labelled
boutons occurred in the ipsilateral lateral subnucleus
(29.64%), suggesting a significant influence of LPMCv
projection on the ipsilateral lower facial musculature. In both
lateral subnuclei, labelling was densely distributed in the
dorsal and ventral regions where lower motor neurones
innervating the upper and lower perioral musculature were
localized (Fig. 11). Much lighter axonal labelling occurred
in the remaining subnuclei with a slight predominance
in the contralateral projection (ipsilateral intermediate, 2.09%;
contralateral intermediate, 7.64%; ipsilateral dorsal, 1.39%;
contralateral dorsal, 3.16%; ipsilateral medial, 4.37%;
contralateral medial, 8.74%).
Corticofacial projections from LPMCd (area 6D)
The LPMCd injection site (SDM23-FD) gave rise to the
weakest projection to the facial nucleus, totalling 264 boutons
(Figs 6, 9 and 12). Labelling was diffuse with large labelfree zones located between small clusters or patches of
terminal fields (Fig. 12). The projection was primarily to the
contralateral lateral subnucleus (28.02%) with a moderate
projection ending in the ipsilateral lateral subnucleus
(20.88%). A relatively moderate projection, similar in
intensity to the ipsilateral projection to the lateral subnucleus,
occurred in the contralateral medial subnucleus (15.33%).
Few boutons were found in the ipsilateral medial subnucleus
(5.55%). The dorsal and intermediate subnuclei also received
a comparatively minor projection that was slightly more
contralateral in its intensity (ipsilateral dorsal, 8.79%;
contralateral dorsal, 10.99%; ipsilateral intermediate, 4.40%;
contralateral intermediate, 6.04%).
Corticofacial projections from M2 (area 6m)
Three injection sites involving the face representation of M2
gave rise to similar patterns of terminal labelling in the
facial nucleus (SDM14-LYD, SDM19-BDA and SDM22-FR)
(Figs 3–5, 8C and D and 13). All the injection sites in M2
produced dense terminal labelling in the medial subnucleus,
where lower motor neurones innervating the orbito-auricular
muscle were localized in our study (Fig. 13), and the posterior
auricular muscle in other studies (Jenny and Saper, 1987;
Welt and Abbs, 1990). The injection in SDM19-BDA was
the largest by design, producing 2738 boutons and was
selected as the representative M2 injection site. In this case,
axon varicosities were concentrated bilaterally in the medial
subnucleus (ipsilateral, 30.86%; contralateral, 29.52%). A
lighter, but also bilateral projection occurred in the lateral
(ipsilateral, 7.41%; contralateral, 9.57%), dorsal (ipsilateral,
6.17%; contralateral, 5.51%) and intermediate (ipsilateral,
5.59%; contralateral, 5.37%) subnuclei.
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R. J. Morecraft et al.
Corticofacial projections from M3 (area 24c)
Three injections involving the face representation of M3
were studied (SDM9-BDA, SDM14-BDA and SDM20-FR)
(Fig. 4). All cases gave rise to a general pattern of labelling
that was dispersed throughout the dorsomedial region of the
facial nucleus. Specifically, this projection was mainly located
in the intermediate and dorsal subnuclei, where lower motor
neurones innervating the upper facial muscles were located
and the medial portion of the medial subnucleus where
auricular muscles were represented (Figs 8E and 14). Overall,
this projection was characterized as being predominantly
bilateral, with slightly more ipsilateral labelling distributed
within the intermediate subnucleus in some cases. There was
also a moderate gradient in the overall density of terminal
labelling, where the boutons were slightly more numerous in
the intermediate subnucleus. Comparatively fewer labelled
profiles were found in the dorsal subnuclei and fewer boutons
were localized in the medial and lateral subnuclei. For
example, a total of 759 boutons were counted in the
corticofacial projection in injection SDM14-BDA. The
majority of boutons were observed in the ipsilateral
intermediate subnucleus (24.82%) with fewer boutons found
in the contralateral intermediate subnucleus (21.20%). A
moderate number of boutons were found in the dorsal
subnucleus (ipsilateral, 11.19%; contralateral, 16.20%).
Progressively fewer boutons occurred in the medial
(ipsilateral, 9.48%; contralateral, 8.16%) and lateral
(ipsilateral, 4.74%; contralateral, 4.21%) subnuclei.
Corticofacial projections from M4 (area 23c)
Three injection sites involving the face representation of M4
were analysed for corticofacial projections (SDM10-BDA,
SDM14-FR and SDM22-LYD) (Figs 3 and 5). All injections
in the face representation of M4 produced similar patterns
of axonal label in the facial nucleus that were concentrated
in the dorsal portion of the lateral subnucleus (Figs 8F
and 15). This location contained labelled motor neurones
following muscular injections in the upper portion of the
orbicularis oris. A total of 638 boutons were found bilaterally
in case SDM22-LYD. Of these, the largest number of labelled
boutons was concentrated in the contralateral lateral
subnucleus (43.86%), with significantly fewer labelled
terminal profiles occurring in the ipsilateral lateral subnucleus
(3.29%). The remaining projections were comparatively
lighter and predominantly contralateral in the intermediate
(ipsilateral, 2.19%; contralateral, 14.89%), dorsal (ipsilateral,
3.45%; contralateral, 12.70%) and medial (ipsilateral, 8.46%;
contralateral, 11.16%) subnuclei.
Discussion
The contemporary viewpoint on cortical innervation of the
facial nucleus has deep roots in neurological history dating
back for more than a century. Along with the corticospinal
projection, the corticofacial projection is often used as a
classical example for teaching the basic principles of lesion
localization as well as diagnosing the upper motor neurone
syndrome. The premise of our existing knowledge of this
projection is based upon the interpretation of upper motor
neurone facial palsy following the most common cortical
stroke. Specifically, this view is formed in the context of
unilateral destruction of M1 following middle cerebral artery
(MCA) occlusion and the suggestion that each M1 supplies
upper facial motor neurones with a significant bilateral
projection and lower facial motor neurones with only a
contralateral projection. Presumably, the bilateral projection
is responsible for upper face sparing and the contralateral
projection underlying the deficit. Results from the present
study do not fully support this interpretation but, importantly,
provide an alternative explanation for the common clinical
occurrence of upper face sparing following MCA infarction.
This report also advances new information that may assist
in interpreting facial deficits following midline brain injury.
Furthermore, the present observations shed new light on
multiple supranuclear projection systems that may participate
in functional recovery of facial movement following localized
cortical damage. Finally, our results are discussed and
interpreted in the context of localization of emotional and
volitional facial paresis.
Cortical innervation of the facial nucleus
The corticofacial projection from M1
Following injections of anterograde tracer into the face region
of M1 we found labelling in all subdivisions of the facial
nucleus that would be in agreement with previous
observations in the monkey (Kuypers, 1958b; Jenny and
Saper, 1987) (Figs 9 and 10). Also in agreement with these
reports was our finding of a substantial projection from M1
to the contralateral lateral subnucleus, which innervates the
lower facial musculature (Fig. 16). The heavy labelling found
in the lateral subnucleus and comparative light labelling
found in the remaining subnuclei correlate with the common
motor responses evoked in the contralateral lower facial
muscles and weak, but occasionally notable, activity in the
upper facial muscles following intracortical microstimulation
in monkey (McGuinness et al., 1980; Sirisko and Sessle,
1983; Huang et al., 1988; Murray and Sessle, 1992). Similarly,
this would correspond to the movement patterns elicited
using epicortical and magnetic transcranial stimulation of
M1 in humans (Penfield and Welch, 1951; Woolsey et al.,
1979; Cohen and Hallett, 1988; Cruccu et al., 1990; Cocito
et al., 1993; Urban et al., 1997). The weak but consistent
projection to the intermediate and dorsal subnuclei may
underlie the mild weakness in upper facial movement
occasionally reported in the literature (Mills, 1889a; MonradKrohn, 1924; Kojima et al., 1997). Our observations support
the classical observation of contralateral lower facial paralysis
following damage to M1. However, in agreement with Jenny
Cortical innervation of the facial nucleus
Fig. 16 Summary diagram illustrating cortical face areas giving
rise to contralateral innervation of the lateral subnucleus. The
lateral subnucleus, in turn, was found to innervate the lower facial
musculature. These observations support the classic teaching that
middle cerebral artery occlusion that involves M1 and or LPMCv
gives rise to paralysis of the contralateral lower facial
musculature.
and Saper (1987), our results do not suggest that sparing of
the upper facial muscles is due to significant bilateral
projections to upper facial lower motor neurones arising from
M1 located in the undamaged hemisphere.
The corticofacial projection from LPMCv and
LPMCd
The corticofacial projection from LPMCv and LPMCd was
found to be primarily contralateral and target the lateral
subnucleus (Figs 9, 11, 12 and 16). This would correlate
with the limited physiological observations indicating that
mouth movements are primarily represented in the ventral
lateral premotor region of macaque monkeys (Gentilucci
et al., 1988). The finding of a relatively moderate ipsilateral
projection from LPMCv to the lateral subnucleus suggests a
potentially significant ipsilateral influence on lower facial
motor neurones from the lateral surface of the hemisphere.
These observations indicate that the overall extent of a
199
cortical lesion affecting the lateral convexity may correlate
with the degree of facial paralysis, on the one hand, and the
potential for motor recovery on the other. For example, our
results suggest that a large unilateral lesion damaging both
M1 and the adjacent LPMCv are likely to give rise to severe
deficits in the contralateral lower facial musculature with a
poor prognostic outcome in terms of motor recovery. In
contrast, a more limited lesion leaving one of these areas
intact may yield milder deficits in the contralateral lower
face and correlate with greater potential for motor recovery.
Our findings also suggest that recovery in the contralateral
lower facial muscles following unilateral destruction of
M1 and or LPMCv may be facilitated through the intact
contralateral projection from M4 to the lateral subnucleus.
Furthermore, the intact ipsilateral projection to the lateral
subnucleus from LPMCv in the undamaged hemisphere may
play an important role in the recovery process that follows
MCA infarction.
We found a greater number of labelled boutons in the
facial nucleus following injections in LPMCv (SDM22-BDA)
than in M1 (SDM19-LYD), which was not anticipated based
upon what is known about the relative density of the
corticospinal projection from M1 and LPMCv (Figs 10 and
11). Although it is possible that the LPMCv projection may
be slightly heavier, this result may be attributable to several
experimental factors. It is possible that the rate of uptake
and transport of BDA and LYD are somewhat different.
Indeed, caution must be exercised when comparing the
intensity of two projection systems determined with two
different neuronal tract tracers. However, we consistently
found robust labelling in many primary subcortical targets
such as the pontine nuclei and medullary reticular formation
in all of our experiments using both of these dextran tracers
as well as with FR and FD. Another potential factor may be
related to the finding that the LPMCv injection site was
slightly larger in the dorsal and ventral dimension than both
M1 injection sites studied. Thus, the LPMCv injection
site may have involved a greater number of corticofacial
projection neurones. Importantly, the facial nucleus in case
SDM22-BDA was larger along the longitudinal axis (e.g.
superior–inferior dimension) than the facial nucleus in both
M1 cases. This resulted in an additional tissue section to
examine in case SDM22 (e.g. note seven facial nucleus levels
in Fig. 10 and eight levels in Fig. 11). Also adding to the
total number of labelled boutons in the LPMCv case was the
comparatively significant ipsilateral projection to the lateral
nucleus. Indeed, future experiments are needed to address
the relative strength of each projection using alternative
methodologies. Notwithstanding, our findings indicate that
the corticofacial projection from LPMCv appears to be quite
important anatomically and possibly functionally.
The corticofacial projection from M2
We found the M2 projection to the facial nucleus to be
moderate in intensity and to target preferentially and
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R. J. Morecraft et al.
representation of M2 and the highly sensitive
immunohistochemical detection method used in our study.
The potential clinical implications of the preferential
projection to auricular lower motor neurones are unclear for
several reasons. First, human auricular musculature is not as
developed and specialized as demonstrated in the rhesus
monkey (Huber, 1933; Williams et al., 1989). Secondly, a
clear or commonly noted facial deficit does not appear to
accompany localized M2 lesions. For example, an absence
of cranial nerve abnormalities in patients with localized M2
lesions has been reported previously (Meador et al., 1986;
Chan and Ross, 1988). Thirdly, pathologically confirmed
lesions affecting the superior frontal lobule (M2) that produce
facial deficits also involve adjacent portions of the cingulate
cortex. Under these circumstances patients have been
characterized as having a blunted facial expression and
weakness in the lower face, which is particularly notable
when smiling (Laplane et al., 1977; Masdeu et al., 1978).
The above, in conjunction with our observations, suggests a
careful re-evaluation of the potential role of M2 in mediating
facial expression.
The corticofacial projection from M3 and M4
Fig. 17 Summary diagram illustrating cortical face areas giving
rise to bilateral innervation of the intermediate, dorsal and medial
subnuclei. These subnuclei were all found to innervate upper
facial musculature. Our findings suggest that sparing of the upper
facial musculature following middle cerebral artery infarction is
due to sparing of the projection from M2 and M3, which reside in
the territory of the anterior cerebral artery. The present findings
and the fact that the rostral cingulate motor cortex (M3) receives
widespread limbic and prefrontal inputs (Morecraft and Van
Hoesen, 1993, 1998; Morecraft et al., 1998, 2000), and is itself
considered one of the higher-order motor areas in the cortex
(Shima et al., 1991; Shima and Tanji, 1998), supports the view
that M3 may be involved in mediating upper facial expression of
higher-order emotions (Damasio, 1994). FN, facial nucleus.
bilaterally the medial subnucleus (Figs 9, 13 and 17). The
medial subnucleus, in turn, was found to contain lower
motor neurones supplying the auricular musculature. Possibly
related to this finding are observations in monkeys
demonstrating that neurones in M2 are responsive to auditory
stimuli in addition to other forms of sensory cues (Kurata
and Tanji, 1985). Our finding of a corticofacial projection
from M2 is in disagreement with an earlier study (Jürgens,
1984) that did not localize a facial nucleus projection from
M2. This discrepancy could be due to the possibility that
the injection in Jürgens’ study did not involve the face
Our findings support previous observations of a direct
projection from M3 and M4 to the facial nucleus (Morecraft
et al., 1996) and extend this finding by demonstrating the
topographical organization of each projection. In the present
study, we found the projections from M3 and M4 to be very
different in terms of their primary subnuclear target as well
as their mode of laterality. The corticofacial projection from
M3 ended bilaterally, within the dorsal and intermediate
subnuclei, which were found to innervate the orbicularis
oculi and frontalis–corrugator muscular complex, respectively
(Figs 9, 14 and 17). This complex consists of anatomically
interdigitating, histochemically unique and functionally
complementary circumorbital musculature (Freilinger et al.,
1990; Goodmurphy and Ovalle, 1999). The contralateral
portion of the projection found in our study would, in part,
support Damasio’s observation of weakness occurring in the
contralateral orbicularis oculi in patients with unilateral
anterior cingulate damage (Damasio, 1994). The fact that the
projection in the monkey was bilateral raises the possibility
that there may be species differences in the laterality of the
projection to the upper face.
The difficulty in interpreting deficits in the upper facial
musculature following anterior cingulate damage may, in
part, be associated with the potential bilateral nature of this
projection found in our study and the fact that facial paralysis
in patients is commonly assessed on the basis of asymmetry.
For example, in applying our non-human primate data to the
human, it suggests that unilateral destruction would yield
deficits similar in magnitude in the ipsilateral and contralateral
orbicularis oculi and frontalis–corrugator musculature.
Presumably, the bilateral M3 projection to the upper face
from the intact hemisphere may mask significant facial
Cortical innervation of the facial nucleus
deficits and contribute to rapid compensatory mechanisms
underlying motor recovery.
We have emphasized the lack of experimental support
affiliated with the classic interpretation of upper face sparing
following superficial MCA infarctions. Since the origin of
the M3 projection described in our study is located within
the vascular territory of the anterior cerebral artery, we
suggest that bilateral sparing of the upper face following
superficial MCA occlusion is due, in part, to sparing of
anterior cingulate projection to the dorsal and medial regions
of the facial nucleus.
The topography of the corticofacial projection from M4 was
very similar to the general distribution found in experiments
conducted on M1, LPMCv and LPMCd as it preferentially
targeted the contralateral subnucleus (Figs 9, 15 and 16).
Furthermore, the projection from M4 was highly specific in
that it ended within the dorsolateral sector of the lateral
subnucleus, which consistently contained motor neurones
innervating the upper, but not the lower lip. Theoretically,
this observation indicates that damage to the human caudal
cingulate motor region may impair elevation of the
contralateral upper lip. This finding may underlie the clinical
observations of Laplane and co-workers who carefully noted
contralateral lower facial weakness only when smiling,
following unilateral resection of M2 and the midportion of
the adjoining cingulate cortex (Laplane, 1977).
Musculotopic organization of the facial nucleus
The topographic representation of the peripheral branches of
the facial nerve in the macaque facial motor nucleus have
been reported in several previous studies (Jenny and Saper,
1987; Satoda et al., 1987; Porter et al., 1989; Welt and Abbs,
1990; Baker et al., 1994; VanderWerf et al., 1998). The present
study was not intended to re-examine the musculotopic
organization of the primate facial nucleus but to include
intramuscular injections in our design to strengthen our
deductions regarding topographical association formed
between each descending corticofacial projection and lower
motor neurone organization. However, the general patterns
of retrogradedly labelled motor neurones found in our study
are consistent with most of the reported observations in the
macaque monkey. For example, injections of fluorescent dyes
into the orbicularis oculi consistently labelled motor neurones
in the intermediate subnuclei (Figs 10, 11 and 13–15). This
observation would be in agreement with several recent studies
(Porter et al., 1989; Welt and Abbs, 1990; Baker et al., 1994;
Huffman et al., 1996; VanderWerf et al., 1998). However,
we did not find labelled motor neurones in the contralateral
intermediate subnucleus following unilateral injections in the
orbicularis oculi as reported by Porter and co-workers (1989).
Injections located in the frontalis muscle labelled neurones
primarily in the dorsal subnucleus, with few labelled neurones
occurring in the adjacent portion of the intermediate
subnucleus (Figs 10, 13 and 14). This finding would be in
agreement with both Jenny and Saper (1987) and Welt and
201
Abbs (1990). However, we were unable to find labelled
neurones in the dorsal part of the lateral subnucleus as
reported by Jenny and Saper (1987). We found the motor
neuronal population devoted to upper lip innervation to be
located in the dorsal portion of the lateral subnucleus and
lower lip innervation to be located in the ventral portion of
the lateral subnucleus (Figs 10, 11 and 13–15). This finding
would parallel the topographical observations of perioral
innervation demonstrated by Welt and Abbs (Welt and
Abbs, 1990).
Face representation in the cerebral cortex
Multiple face areas have been localized in the human cerebral
cortex that appear to have homologous counterparts in the
monkey cortex (Mills, 1889b; Penfield and Welch, 1951;
Woolsey et al., 1952, 1979; Muakkassa and Strick, 1979;
Morecraft et al., 1996; Picard and Strick, 1996). For example,
non-human primate face areas have been identified in M1,
LPMCv, M2 and M4 using intracortical microstimulation
(Gentilucci et al., 1988; Godschalk et al., 1995; Preuss et al.,
1996). Patterns of corticocortical interconnections have also
been supportive by demonstrating that the face areas of M1,
LPMCv, M2, M3 and M4 are selectively interconnected at
the cortical level (Muakkassa and Strick, 1979; Morecraft
and Van Hoesen, 1992; Morecraft et al., 1996; Tokuno et al.,
1997). Our results reinforce and extend the concept of cortical
face representation by demonstrating that each major face
area sends direct corticobulbar projections to the facial
nucleus. Furthermore, our observations suggest that each
cortical face representation may, in part, function
independently from M1 by preferentially influencing different
facial movements. However, it is important to recognize that
integrated facial movements may be heavily mediated at the
cortical level through reciprocal corticocortical projections
forming interconnecting matrices amongst all the face areas
studied.
The various patterns of descending projections to the facial
nucleus and spinal cord from LPMCv and LPMCd suggest
that some overlap occurs between face and arm
representations in the lateral premotor region. For example,
injections located in the ventral portion of LPMCv gave rise
to a heavy projection to the facial nucleus but also a small
projection to the spinal cord (Fig. 11). This observation
indicates that corticofacial and corticospinal neurones are
probably intermingled in the LPMCv, with corticofacial
projections predominating. We found the inverse relationship
to occur when investigating the descending projection from
LPMCd. For example, an injection into LPMCd gave rise to
a heavy corticospinal projection and a light corticofacial
projection (Fig. 12). In contrast to both projection patterns
of the lateral premotor cortex (LPMC), we failed to find
corticospinal projections following tracer injection in the face
area of M1, only corticofacial projections. Therefore, it
appears that the anatomical and functional border between
the face and arm representations in LPMC is less distinct
202
R. J. Morecraft et al.
than that found in M1. These observations parallel the
intermingled somatotopy of lateral area 6 found using
intracortical microstimulation (Gentilucci et al., 1988;
Rizzolatti et al., 1988; Godschalk et al., 1995) and lack of
intermingled somatotopy characterizing the ventral part of
M1 using the same experimental approach (McGuinness
et al., 1980; Sirisko and Sessle, 1983; Huang et al., 1988;
Huntley and Jones, 1991). The integrated somatotopy in the
lateral premotor region may, in part, form a basis for unit
recordings suggesting this area plays an important role in
mediating combined movements of the hand and mouth
(Rizzolatti et al., 1988).
Clinical dissociation of emotional and voluntary
facial movements
Formulated largely on the basis of clinical correlates is the
suggestion that separate neural systems exist for mediating
voluntary and emotional facial movements (Darwin, 1872;
Jackson, 1884; Wilson, 1924; Monrad-Krohn, 1924, 1939;
Allen, 1931; Karnosh, 1945; Podolsky, 1945; Brown,
1967; Brodal, 1981; Rinn, 1984; Duchenne, 1990; Weddell,
1990; Arroyo et al., 1993; Weller, 1993; Damasio, 1994,
1995; Topper et al., 1995; McConachie and King, 1997;
Ross and Mathiesen, 1998; Urban et al., 1998; Hopf et al.,
2000). Although our comments related to this issue must be
tempered since our findings reflect only structural patterns,
they may contribute key pieces of information to develop
new and testable hypotheses designed to advance our
understanding of this clinically derived tenet. Of particular
significance was our finding of a bilateral projection from
M3 to the upper facial musculature and a contralateral
projection from M4 to the lower facial musculature. These
diverse systems may represent important descending
projections contributing to a complex neural network
subserving emotional expression of facial movement. For
example, the origin of the corticofacial projection from M3
and M4 is located in the dorsal edge of the cingulate cortex.
The cingulate cortex, in turn, has long been viewed as a
critical component of the ‘emotive’ limbic lobe (Broca, 1878;
Papez, 1927; MacLean, 1954; Baleydier and Maugiere, 1980;
Damasio and Van Hoesen, 1983; Mesulam, 1988; Pardo
et al., 1993; Devinsky et al., 1995; George et al., 1995;
Ketter et al., 1996; Van Hoesen et al., 1996) and both
cingulate motor cortices receive powerful and widespread
prefrontal and limbic lobe inputs (Bates and Goldman-Rakic,
1993; Morecraft and Van Hoesen, 1993; Lu et al., 1994;
Morecraft and Van Hoesen, 1998; Morecraft et al., 2000).
Furthermore, the amygdala, which plays a critical role in
regulating emotional processes (Kling and Brothers, 1992;
Damasio, 1994, 1995; Adolphs et al., 1995; LeDoux, 1996;
Rolls, 1999) projects not only to the cingulate motor field
(Amaral and Price, 1984) but to its somatotopic
representations in a highly specific manner (Morecraft et al.,
1998). Specifically, we have found that the amygdalo-
cingulate motor projection targets primarily the face area of
M3 and to a much lesser extent the remaining somatotopic
representations in M3 and M4 (Morecraft et al., 1998).
Therefore, there is good ground to consider the possibility that
blunted emotional expression in the upper facial musculature
accompanying anterior cingulate damage (Critchley, 1930;
Laplane et al., 1981; Damasio, 1994) may, in part, be a result
of disconnecting the limbic lobe and amygdala projections
to the rostral cingulate motor area which, in turn, projects
bilaterally to the dorsomedial region of the facial nucleus. It
is also possible that flattened facial expression in patients
with anterior cingulate damage is a general consequence of
disruption of the cingulate motor cortex, which forms a
pivotal interface between the limbic lobe and many cortical
and subcortical motor targets such as the isocortical motor
fields, basal ganglia and facial nucleus as reported here (Van
Hoesen et al., 1993; Morecraft and Van Hoesen, 1998). The
above would, in part, lend structural support to the behavioural
view suggesting that the anterior cingulate controls emotionrelated movements in the face (Damasio, 1994). Finally,
functional imaging data as well as observations from naturally
occurring and surgically guided lesions affecting the anterior
cingulate region have demonstrated that the anterior cingulate
cortex encodes pain and perceived unpleasantness (Foltz and
White, 1962; Hurt and Ballantine, 1974; Davis et al., 1997;
Rainville et al., 1997; Lenz et al., 1998; Cohen et al., 1999).
Our observations suggest that bilateral contraction of the
upper face, a hallmark response directly associated with the
perception of pain in man (Darwin, 1872) may in part be
mediated by descending corticofacial projections emanating
directly from the rostral cingulate motor cortex.
Our observations indicate that the corticofacial projection
from M4 to the dorsolateral portion of the lateral subnucleus
may be associated with the classical observation of preserved
reflex smiling in the presence of contralateral paralysis in
the lower facial musculature following damage to the lateral
face areas (M1 and LPMCv). As shown in our study and in
agreement with others, the dorsolateral region of the lateral
subnucleus contains lower motor neurones supplying the
upper perioral musculature. More speculative, but possibly
associated, are the observations from patients with localized
cingulate seizures suggesting that the cingulate cortex plays
an important role in regulating the expression of laughter
(Arroyo et al., 1993; McConachie and King, 1997).
Although our series of experiments identifies several new
upper motor neurone pathways that may be involved in
mediating volitional and emotional facial responses, it is
important to recognize that structures interconnected with
the origin of each corticobulbar projection, such as the
thalamus, insula and temporal lobe, are likely to contribute
as well to the appropriate execution of volitional and
emotional facial movement. This supposition is based upon
the fact that each upper motor neurone projection field
must be activated or influenced by neural inputs from their
‘extended’ projection system. In support of this would be the
observation that emotional facial paralysis occurs following
Cortical innervation of the facial nucleus
damage to the insula, thalamus and striatocapsular region
(Hopf et al., 1992). Therefore, the projections described in
our report must be considered in the context of potential
large-scale neural systems mediating complex behaviours
(Pandya and Kuypers, 1969; Jones and Powell, 1970;
Mesulam and Greswind, 1978; Goldman-Rakic, 1988; Gloor,
1990; Mesulam, 1990, 1998; Morecraft et al., 1993).
Study limitations
It is important to note that our deductions regarding cortical
innervation of the facial musculature are based upon the
topographical association formed between anterogradely
labelled boutons and retrogradely labelled groups of facial
motor neurones. Thus, our study does not reveal whether
monosynaptic contacts directly link these projection systems.
However, our findings provide critical baseline data to initiate
experiments designed to examine the microcircuitry of these
important neural systems.
Our predictions regarding the potential clinical implications
of our data have been developed on the theoretical basis of
cortical damage that is restricted to the origin of each
corticobulbar projection. However, it is important to recognize
the possibility that subcortical lesions are likely to disrupt
the various descending projection systems as they pass
inferiorly to reach the facial nucleus. We are aware that this
issue is particularly critical when considering the fact that
each pathway courses through different regions of the corona
radiata and internal capsule (unpublished observations),
where each pathway is selectively vulnerable to different
forms of localized insult. Due to the extensive scope of this
data and its potential clinical correlates, this material will be
described in a subsequent report.
Finally, although we have identified several new pathways
that interconnect the cerebral cortex with specific parts of
the facial nucleus controlling upper facial musculature, it is
important to recognize that numerous subcortical pathways
are likely to contribute as well to mediating activity in the
upper facial musculature. These would include the retrorubral,
medullary reticular, spinal trigeminal, parvocellular reticular,
lateral tegmental and nucleus ambiguus projections to the
dorsal and medial subregions of the facial nucleus (Holstege
et al., 1977, 1986; Isokawa-Akesson and Komisaruk, 1987).
Conclusions
The facial nucleus received input from all face representations
studied underscoring their recognition as cortical face
representations and potential roles in regulating facial
movement. M1 and LPMCv gave rise to the heaviest
corticofacial projection. In comparison, M2 gave rise to a
moderate projection, whereas the projection from M3 and
M4 was lighter. Evidence for a weak corticofacial projection
from LPMCd was found, but the corticospinal projection was
more prominent from this region of cortex. Injections in all
cortical face representations labelled terminals in all nuclear
203
subdivisions (dorsal, intermediate, medial and lateral).
However, significant differences occurred in the proportion
of labelled boutons found within each musculotopically
characterized subdivision. M1, LPMC and M4 projected
primarily to the contralateral lateral subnucleus, which
innervated the lower facial musculature (Fig. 16). M2
projected bilaterally to the medial subnucleus which supplied
the orbito-auricularis as determined in our study (Fig. 17)
and the posterior auricularis musculature as reported by
others (Jenny and Saper, 1987; Satoda et al., 1987; Welt and
Abbs, 1990). M3 projected bilaterally to the dorsal and
intermediate subnuclei, which innervated the frontalis and
orbicularis oculi muscles, respectively (Fig. 17).
Potential disturbances in the projection patterns found in
the present study could take the form of highly predictable
deficits in facial expression in the event that selective insult
disrupts the origin or descending axons of each corticofacial
projection. Our results suggest that unilateral damage to the
lateral motor cortices (LPMC and M1) is likely to lead to
deficits in the contralateral lower facial muscles as classically
interpreted. Recovery may occur, in part, from the
contralateral projection from M4 within the damaged
hemisphere as well as the moderate ipsilateral projection
from LPMCv within the undamaged hemisphere. Our findings
also suggest that upper facial sparing following lateral cortical
damage is due to sparing of the bilateral projection from M2
and M3, which reside medially and originate from the cortical
territory supplied by the anterior cerebral artery. Disturbances
affecting the reported circuitry in the form of excessive
stimulation, which may occur from inappropriate sensory
stimulation, or in the absence of an appropriate inhibitory
influence might yield excessive muscle contractions in
isolated groups of muscles, such as that which characterizes
the various forms of cranial–cervical dystonia.
Acknowledgements
This work was supported by NIH grants NS 33003 and NS
36397, the South Dakota Health Research Foundation and a
grant from the Benign Essential Blepharospasm Research
Foundation (R.J.M.).
References
Adams RD, Victor M, Ropper AH. Principles of neurology. 6th ed.
New York: McGraw-Hill; 1997. p. 1378.
Adolphs R, Tranel D, Damasio H, Damasio AR. Fear and the
human amygdala. J Neurosci 1995; 15: 5879–91.
Alexander GE, Crutcher MD. Preparation for movement: neural
representations of intended direction in three motor areas of the
monkey. J Neurophysiol 1990; 64: 133–50.
Allen IM. The dissociation of voluntary and emotional movements
of the face with special reference to emotional paresis as a physical
sign. J Neurol Psychopath 1931; 12: 24–39.
204
R. J. Morecraft et al.
Amaral DG, Price JL. Amygdalo-cortical projections in the monkey
(Macaca fascicularis). J Comp Neurol 1984; 230: 465–96.
Arroyo S, Lesser RP, Gordon B, Uematsu S, Hart J, Schwerdt P,
et al. Mirth, laughter and gelastic seizures. Brain 1993; 116: 757–80.
Baker RS, Stava MW, Nelson KR, May PJ, Huffman MD, Porter
JD. Aberrant reinnervation of facial musculature in a subhuman
primate: a correlative analysis of eyelid kinematics, muscle
synkinesis, and motoneuron localization. Neurology 1994; 44:
2165–73.
Baleydier C, Mauguiere F. The duality of the cingulate gyrus in
monkey: neuroanatomical study and functional hypothesis. Brain
1980; 103: 525–54.
Barbas H, Pandya DN. Architecture and frontal cortical connections
of the premotor cortex (area 6) in the rhesus monkey. J Comp
Neurol 1987; 256: 211–28.
Cruccu G, Berardelli A, Inghilleri M, Manfredi M. Corticobulbar
projections to upper and lower facial motoneurons. A study by
magnetic transcranial stimulation in man. Neurosci Lett 1990; 117:
68–73.
Damasio AR. Descartes’ error: emotion, reason, and the human
brain. New York: Grosset/Putnam; 1994. p. 139–43.
Damasio AR. Toward a neurobiology of emotion and feeling:
operational concepts and hypotheses. Neuroscientist 1995; 1: 19–25.
Damasio AR, Van Hoesen GW. Emotional disturbances associated
with focal lesions of the limbic frontal lobe. In: Heilman KM, Satz
P, editors. Neuropsychology of human emotion. New York: Guilford
Press; 1983. p. 85–110.
Darwin C. The expression of the emotions in man and animals.
London: John Murray; 1872.
Bates JAV. Stimulation of the medial surface of the human cerebral
hemisphere after hemispherectomy. Brain 1953; 76: 405–47.
Davis KD, Taylor SJ, Crawley AP, Wood ML, Mikulis DJ. Functional
MRI of pain- and attention-related activations in the human cingulate
cortex. J Neurophysiol 1997; 77: 3370–80.
Bates JF, Goldman-Rakic PS. Prefrontal connections of medial
motor areas in the rhesus monkey. J Comp Neurol 1993; 336: 211–28.
Denny-Brown D. Disintegration of motor function resulting from
cerebral lesions. J Nerv Ment Dis 1950; 112: 1–45.
Biber MP, Kneisley LW, LaVail JH. Cortical neurons projecting to
the cervical and lumbar enlargements of the spinal cord in young
adult rhesus monkeys. Exp Neurol 1978; 59: 492–508.
Devinsky O, Morrell MJ, Vogt BA. Contributions of anterior
cingulate cortex to behaviour. [Review]. Brain 1995; 118: 279–306.
Broca P. Anatomie comparée des circonvolutions cérébrales: le
grand lobe limbique et la scissure limbique dans la série des
mammifères. Rev Anthropol 1878; 1: 385–498.
Brodal A. Neurological anatomy in relation to clinical medicine.
3rd ed. New York: Oxford University Press; 1981. p. 495–508.
Brodmann K . Vergleichende Lokalisationslehre der Grosshirnrinde.
Leipzig: Barth; 1909.
Brown JW. Physiology and phylogenesis of emotional expression.
[Review]. Brain Res 1967; 5: 1–14.
Chan J-L, Ross ED. Left-handed mirror writing following right
anterior cerebral artery infarction: evidence for nonmirror
transformation of motor programs by right supplementary motor
area. Neurology 1988; 38: 59–63.
Cocito D, Cassano D, De Mattei M. Motor evoked potentials in
orbicularis oris muscle: no evidence of ipsilateral corticonuclear
projections [letter]. Muscle Nerve 1993; 16: 1268–9.
Duchenne GB. The mechanism of human facial expression. (1862)
Edited and translated by Cuthbertson RA. New York: Cambridge
University Press; 1990.
Dum RP, Strick PL. The origin of corticospinal projections from
the premotor areas in the frontal lobe. J Neurosci 1991; 11: 667–89.
Ferrier D. The functions of the brain. 2nd ed. London: Smith, Elder;
1886. p. 235–67.
Foltz EL, White LE. Pain ‘relief’ by frontal cingulumotomy.
J Neurosurg 1962; 19: 89–100.
Freilinger G, Happak W, Burggasser G, Gruber H. Histochemical
mapping and fiber size analysis of mimic muscles. Plast Reconstr
Surg 1990; 86: 422–8.
Galea MP, Darian-Smith I. Multiple corticospinal neuron populations
in the macaque monkey are specified by their unique cortical origins,
spinal terminations, and connections. Cereb Cortex 1994; 4: 166–94.
Cohen LG, Hallett M. Noninvasive mapping of human motor cortex.
Neurology 1988; 38: 904–9.
Gentilucci M, Fogassi L, Luppino G, Matelli M, Camarda R,
Rizzolatti G. Functional organization of inferior area 6 in the
macaque monkey. I. Somatotopy and the control of proximal
movements. Exp Brain Res 1988; 71: 475–90.
Cohen RA, Kaplan RF, Moser DJ, Jenkins MA, Wilkinson H.
Impairments of attention after cingulotomy. Neurology 1999; 53:
819–24.
George MS, Ketter TA, Parekh PI, Horwitz B, Herscovitch P, Post
RM. Brain activity during transient sadness and happiness in healthy
women. Am J Psychiatry 1995; 152: 341–51.
Condé F. Further studies on the use of the fluorescent tracers fast
blue and diamidino yellow: effective uptake area and cellular storage
sites. J Neurosci Methods 1987; 21: 31–43.
Gloor P. Experiential phenomena of temporal lobe epilepsy. Facts
and hypotheses. [Review]. Brain 1990; 113: 1673–94.
Courville J. The nucleus of the facial nerve: the relation between
cellular groups and peripheral branches of the nerve. Brain Res
1966; 1: 338–54.
Critchley M. The anterior cerebral artery and its syndromes. Brain
1930; 53: 120–65.
Godschalk M, Mitz AR, van Duin B, van der Burg H. Somatotopy
of monkey premotor cortex examined with microstimulation.
Neurosci Res 1995; 23: 269–79.
Goldman-Rakic PS. Topography of cognition: parallel distributed
networks in primate association cortex. [Review]. Annu Rev
Neurosci 1988; 11: 137–56.
Cortical innervation of the facial nucleus
205
Goodmurphy CW, Ovalle WK. Morphological study of two human
facial muscles: orbicularis oculi and corrugator supercilii. Clin Anat
1999; 12: 1–11.
Jones EG, Powell TP, An anatomical study of converging sensory
pathways within the cerebral cortex of the monkey. Brain 1970; 93:
793–820.
Holstege G, Kuypers HGJM, Dekker JJ. The organization of the
bulbar fibre connections to the trigeminal, facial and hypoglossal
motor nuclei. Brain 1977; 100: 265–86.
Jürgens U. The efferent and afferent connections of the
supplementary motor area. Brain Res 1984; 300: 63–81.
Holstege G, van Ham JJ, Tan J. Afferent projections to the orbicularis
oculi motoneuronal cell group. An autoradiographical tracing study
in the cat. Brain Res 1986; 374: 306–20.
Hopf HC, Muller-Forell W, Hopf NJ. Localization of emotional and
volitional facial paresis. [Review]. Neurology 1992; 42: 1918–23.
Hopf HC, Fitzek C, Marx J, Urban PP, Thomke F. Emotional facial
paresis of pontine origin. Neurology 2000; 54: 1217.
Horsley VAH, Schäfer EA. A record of experiments upon the
functions of the cerebral cortex. Phil Trans R Soc 1888; 179B: 1–45.
Huang CS, Sirisko MA, Hiraba H, Murray GM, Sessle BJ.
Organization of the primate face motor cortex as revealed by
intracortical microstimulation and electrophysiological identification
of afferent inputs and corticobulbar projections. J Neurophysiol
1988; 59: 796–818.
Huber E. The facial musculature and its innervation. In: Hartman
CG, Straus WL, editors. The anatomy of the rhesus monkey (Macaca
mulatta). Baltimore: Williams and Wilkins; 1933. p. 176–88.
Huffman MD, Baker RS, Stava MW, Chuke JC, Rouholiman BR,
Porter JD. Kinematic analysis of eyelid movements in patients
recovering from unilateral facial nerve palsy. Neurology 1996; 46:
1079–85.
Huntley GW, Jones EG. Relationship of intrinsic connections to
forelimb movement representations in monkey motor cortex: a
correlative anatomic and physiological study. J Neurophysiol 1991;
66: 390–413.
Hurt RW, Ballantine HT Jr. Stereotactic anterior cingulate lesions
for persistent pain: a report on 68 cases. Clin Neurosurg 1974; 21:
334–51.
Husain AM. Neurological picture: mimetic smile. J Neurol
Neurosurg Psychiatry 1997; 63: 144.
Hutchins KD, Martino AM, Strick PL. Corticospinal projections
from the medial wall of the hemisphere. Exp Brain Res 1988; 71:
667–72.
Isokawa-Akesson M, Komisaruk BR. Difference in projections to
the lateral and medial facial nucleus: anatomically separate pathways
for rhythmical vibrissa movements in rats. Exp Brain Res 1987;
65: 385–98.
Jackson JH. The Croonian lectures on evolution and dissolution of
the nervous system. Lecture I. BMJ 1884; 1: 591–93.
Kandel ER, Schwartz JH, Jessell TM. Principles of neural science.
4th ed. New York: McGraw-Hill; 2000.
Karnosh LJ. Amimia or emotional paralysis of the face. Dis Nerv
Syst 1945; 6: 106–8.
Ketter TA, Andreason PJ, George MS, Lee C, Gill DS, Parekh PI,
et al. Anterior paralimbic mediation of procaine-induced emotional
and psychsensory experiences. Arch Gen Psychiatry 1996; 53:
59–69.
Kling AS, Brothers LA. The amygdala and social behavior. In:
Aggleton JP, editor. The amygdala: neurobiological aspects of
emotion, memory, and mental dysfunction. New York: Wiley-Liss;
1992. p. 353–77.
Kojima Y, Kaga K, Shindo M, Hirose A. Electromyographic
examination of patients with unilateral cortical facial paralysis.
Otolaryngol Head Neck Surg 1997; 117: S121–4.
Kurata K, Tanji J. Contrasting neuronal activity in supplementary
and precentral motor cortex of monkeys. II. Responses to movement
triggering vs. nontriggering sensory signals. J Neurophysiol 1985;
53: 142–52.
Kuypers HGJM. Corticobulbar connexions to the pons and lower
brain-stem in man. An anatomical study. Brain 1958a; 81: 364–88.
Kuypers HGJM. Some projections from the peri-central cortex to
the pons and lower brain-stem in monkey and chimpanzee. J Comp
Neurol 1958b; 110: 221–55.
Laplane D, Talairach J, Meininger V, Bancaud J, Orgogozo JM.
Clinical consequences of corticectomies involving the
supplementary motor area in man. J Neurol Sci 1977; 34: 301–14.
Laplane D, Degos JD, Baulac M, Gray F. Bilateral infarction of the
anterior cingulate gyri and of the fornices. J Neurol Sci 1981; 51:
289–300.
LeDoux JE. The emotional brain. New York: Simon and Schuster;
1996.
Lenz FA, Rios M, Zirh A, Chau D, Krauss G, Lesser RP. Painful
stimuli evoke potentials recorded over the human anterior cingulate
gyrus. J Neurophysiol 1998; 79: 2231–4.
Lu MT, Preston JB, Strick PL. Interconnections between the
prefrontal cortex and the premotor areas in the frontal lobe. J Comp
Neurol 1994; 341: 375–92.
James W. The principles of psychology, Vol. 2. London:
Macmillan; 1890.
Luppino G, Matelli M, Camarda RM, Gallese V, Rizzolatti G.
Multiple representations of body movements in mesial area 6 and
the adjacent cingulate cortex: an intracortical microstimulation study
in the macaque monkey. J Comp Neurol 1991; 311: 463–82.
Jenny AB, Saper CB. Organization of the facial nucleus and
corticofacial projection in the monkey: a reconsideration of the
upper motor neuron facial palsy. Neurology 1987; 37: 930–9.
Luppino G, Matelli M, Camarda R, Rizzolatti G. Corticocortical
connections of area F3 (SMA-proper) and area F6 (pre-SMA) in
the macaque monkey. J Comp Neurol 1993; 338: 114–40.
206
R. J. Morecraft et al.
Luppino G, Matelli M, Camarda R, Rizzolatti G. Corticospinal
projections from mesial frontal and cingulate areas in the monkey.
Neuroreport 1994; 5: 2545–8.
Mitz AR, Wise SP. The somatotopic organization of the
supplementary motor area: intracortical microstimulation mapping.
J Neurosci 1987; 7: 1010–21.
Luschei ES, Garthwaite CR, Armstrong ME. Relationship of firing
patterns of units in face area of monkey precentral cortex to
conditioned jaw movements. J Neurophysiol 1971; 34: 552–61.
Monrad-Krohn GH. On the dissociation of voluntary and emotional
innervation in facial paresis of central origin. Brain 1924; 47: 22–35.
MacLean PD. The limbic system and its hippocampal formation.
J Neurosurg 1954; 11: 29–44.
Monrad-Krohn GH. On facial dissociation. Acta Psychiat Neurol
1939; 14: 557–66.
Masdeu JC, Schoene WC, Funkenstein H. Aphasia following
infarction of the left supplementary motor area: a clinicopathologic
study. Neurology 1978; 28: 1220–3.
Morecraft RJ, Van Hoesen GW. Somatotopical organization of
cingulate projections to the primary and supplementary motor
cortices in the old-world monkey [abstract]. Soc Neurosci Abstr
1988; 14: 820.
Matelli M, Luppino G, Rizzolatti G. Patterns of cytochrome oxidase
activity in the frontal agranular cortex of the macaque monkey.
Behav Brain Res 1985; 18: 125–36.
Morecraft RJ, Van Hoesen GW. Cingulate input to the primary and
supplementary motor cortices in the rhesus monkey: evidence for
somatotopy in areas 24c and 23c. J Comp Neurol 1992; 322: 471–89.
Matelli M, Luppino G, Rizzolatti G. Architecture of superior and
mesial area 6 and the adjacent cingulate cortex in the macaque
monkey. J Comp Neurol 1991; 311: 445–62.
Morecraft RJ, Van Hoesen GW. Frontal granular cortex input to the
cingulate (M3), supplementary (M2) and primary (M1) motor
cortices in the rhesus monkey. J Comp Neurol 1993; 337: 669–89.
Matsuzaka Y, Tanji J. Changing directions of forthcoming arm
movements: neuronal activity in the presupplementary and
supplementary motor area of monkey cerebral cortex. J Neurophysiol
1996; 76: 2327–42.
Morecraft RJ, Van Hoesen GW. Convergence of limbic input to the
cingulate motor cortex in the rhesus monkey. Brain Res Bull 1998;
45: 209–32.
McConachie NS, King MD. Gelastic seizures in a child with focal
cortical dysplasia of the cingulate gyrus. Neuroradiology 1997; 39:
44–5.
McGuinness E, Sivertsen D, Allman JM. Organization of the face
representation in macaque motor cortex. J Comp Neurol 1980; 193:
591–608.
McGuire PK, Bates JF, Goldman-Rakic PS. Interhemispheric
integration: I. Symmetry and convergence of the corticocortical
connections of the left and the right principal sulcus (PS) and the
left and the right supplementary motor area (SMA) in the rhesus
monkey. Cereb Cortex 1991; 1: 390–407.
Meador KJ, Watson RT, Bowers D, Heilman KM. Hypometria with
hemispatial and limb motor neglect. Brain 1986; 109: 293–305.
Mesulam MM. Patterns in behavioral neuroanatomy: association
areas, the limbic system, and hemispheric specialization. In:
Mesulam MM, editor. Principles of behavioral neurology. 4th ed.
Philadelphia: F.A. Davis; 1988. p. 1–70.
Mesulam MM. Large-scale neurocognitive networks and distributed
processing for attention, language, and memory. [Review]. Ann
Neurol 1990; 28: 597–613.
Mesulam MM. From sensation to cognition. [Review]. Brain 1998;
121: 1013–52.
Mesulam MM, Geschwind N. On the possible role of neocortex and
its limbic connections in the process of attention and schizophrenia:
clinical cases of inattention in man and experimental anatomy in
monkey. J Psychiatr Res 1978; 14: 249–59.
Mills CK. Cerebral localisation in its practical relations [I]. Brain
1889a; 12: 233–88.
Mills CK. Cerebral localisation in its practical relations [II]. Brain
1889b; 12: 358–406.
Morecraft RJ, Yeterian EH. Prefrontal cortex. In: Ramachandran
VS, editor. Encyclopedia of the human brain. [Review]. San Diego:
Academic Press. In press 2001.
Morecraft RJ, Geula C, Mesulam MM. Cytoarchitecture and neural
afferents of orbitofrontal cortex in the brain of the monkey. J Comp
Neurol 1992; 323: 341–58.
Morecraft RJ, Geula C, Mesulam MM. Architecture of connectivity
within a cingulo-fronto-parietal neurocognitive network for directed
attention. Arch Neurol 1993; 50: 279–84.
Morecraft RJ, Schroeder CM, Keifer J. Organization of face
representation in the cingulate cortex of the rhesus monkey.
Neuroreport 1996; 7: 1343–8.
Morecraft RJ, Louie JL, Schroeder CM, Avramov K. Segregated
parallel inputs to the brachial spinal cord from the cingulate motor
cortex in the monkey. Neuroreport 1997; 8: 3933–8.
Morecraft RJ, Avramov K, Schroeder CM, Stilwell-Morecraft KS,
Van Hoesen GW. Amygdala connections with the cingulate motor
cortex: preferential innervation of the face representation of M3
(area 24c) in the rhesus monkey [abstract]. Soc Neurosci Abstr
1998; 24: 653.
Morecraft RJ, Rockland KS, Van Hoesen GW. Localization of area
prostriata and its projection to the cingulate motor cortex in the
rhesus monkey. Cereb Cortex 2000; 10: 192–203.
Muakkassa KF, Strick PL. Frontal lobe inputs to primate motor
cortex: evidence for four somatotopically organized ‘premotor’
areas. Brain Res 1979; 177: 176–82.
Murray EA, Coulter JD. Organization of corticospinal neurons in
the monkey. J Comp Neurol 1981; 195: 339–65.
Murray GM, Sessel BJ. Functional properties of single neurons in
the face primary motor cortex of the primate: I. Input and output
features of tongue motor cortex. J Neurophysiol 1992; 67: 747–58.
Cortical innervation of the facial nucleus
Nimchinsky EA, Hof PR, Young WG, Morrison JH. Neurochemical,
morphologic, and laminar characterization of cortical projection
neurons in the cingulate motor areas of the macaque monkey.
J Comp Neurol 1996; 374: 136–60.
Pandya DN, Kuypers HG. Cortico-cortical connections in the rhesus
monkey. Brain Res 1969; 13: 13–36.
Pandya DN, Vignolo LA. Intra- and interhemispheric projections
of the precentral, premotor and arcuate areas in the rhesus monkey.
Brain Res 1971; 26: 217–33.
207
Ross RT, Mathiesen R. Images in clinical medicine. Volitional and
emotional supranuclear facial weakness. N Engl J Med 1998;
338: 1515.
Rouiller EM, Babalian A, Kazennikov O, Moret V, Yu XH,
Wiesendanger M. Transcallosal connections of the distal forelimb
representations of the primary and supplementary motor cortical
areas in macaque monkeys. Exp Brain Res 1994; 102: 227–43.
Papez JW. Subdivisions of the facial nucleus. J Comp Neurol 1927;
43: 159–91.
Satoda T, Takahashi O, Tashiro T, Matsushima R, Uemura-Sumi
M, Mizuno N. Representation of the main branches of the facial
nerve within the facial nucleus of the Japanese monkey (Macaca
fuscata). Neurosci Lett 1987; 78: 283–7.
Pardo JV, Pardo PJ, Raichle ME. Neural correlates of self-induced
dysphoria. Am J Psychiatry 1993; 150: 713–9.
Schmued LC. A rapid, sensitive histochemical stain for myelin in
frozen brain sections. J Histochem Cytochem 1990; 38: 717–20.
Paus T, Petrides M, Evans AC, Meyer E. Role of the human anterior
cingulate cortex in the control of oculomotor, manual, and speech
responses: a positron emission tomography study. J Neurophysiol
1993; 70: 453–69.
Shima K, Aya K, Mushiake H, Inase M, Aizawa H, Tanji J. Two
movement-related foci in the primate cingulate cortex observed in
signal-triggered and self-paced forelimb movements. J Neurophysiol
1991; 65: 188–202.
Pearson AA. The development of the motor nuclei of the facial
nerve in man. J Comp Neurol 1946; 85: 461–76.
Shima K, Tanji J. Role for cingulate motor area cells in voluntary
movement selection based on reward. Science 1998; 282: 1335–8.
Penfield W, Welch K. The supplementary motor area of the cerebral
cortex: a clinical and experimental study. Arch Neurol Psychiat
1951; 66: 289–317.
Sirisko MA, Sessle BJ. Corticobulbar projections and orofacial and
muscle afferent inputs of neurons in primate sensorimotor cerebral
cortex. Exp Neurol 1983; 82: 716–20.
Picard N, Strick PL. Motor areas of the medial wall: a review of
their location and functional activation. [Review]. Cereb Cortex
1996; 6: 342–53.
Tanji J. The supplementary motor area in the cerebral cortex.
[Review]. Neurosci Res 1994; 19: 251–68.
Podolsky E. The emotions and the cerebrum. Dis Nerv Syst 1945;
6: 312–4.
Tokuno H, Takada M, Nambu A, Inase M. Reevaluation of ipsilateral
corticocortical inputs to the orofacial region of the primary motor
cortex in the macaque monkey. J Comp Neurol 1997; 389: 34–48.
Porter JD, Burns LA, May PJ. Morphological substrate for eyelid
movements: innervation and structure of primate levator palpebrae
superioris and orbicularis oculi muscles. J Comp Neurol 1989; 287:
64–81.
Topper R, Kosinski C, Mull M. Volitional type of facial palsy
associated with pontine ischaemia. J Neurol Neurosurg Psychiatry
1995; 58: 732–4.
Preuss TM, Goldman-Rakic PS. Myelo- and cytoarchitecture of the
granular frontal cortex and surrounding regions in the strepsirhine
primate Galago and the anthropoid primate Macaca. J Comp Neurol
1991; 310: 429–74.
Preuss TM, Stepniewska I, Kaas JH. Movement representation
in the dorsal and ventral premotor areas of owl monkeys: a
microstimulation study. J Comp Neurol 1996; 371: 649–76.
Rainville P, Duncan GH, Price DD, Carrier B, Bushnell MC. Pain
affect encoded in human anterior cingulate but not somatosensory
cortex. Science 1997; 277: 968–71.
Reed GM, Sheppard VF. Basic structures of the head and neck.
Philadelphia: W.B. Saunders; 1976. p. 314–37.
Rinn WE. The neuropsychology of facial expression: a review of
the neurological and psychological mechanisms for producing facial
expressions. [Review]. Psychol Bull 1984: 95: 52–77.
Rizzolatti G, Camarda R, Fogassi L, Gentilucci M, Luppino G,
Matelli M. Functional organization of inferior area 6 in the macaque
monkey. II. Area F5 and the control of distal movements. Exp Brain
Res 1988; 71: 491–507.
Rolls ET. The brain and emotion. Oxford: Oxford University
Press; 1999.
Urban PP, Beer S, Hopf HC. Cortico-bulbar fibers to orofacial
muscles:
recordings
with
enoral
surface
electrodes.
Electroencephalogr Clin Neurophysiol 1997; 105: 8–14.
Urban PP, Wicht S, Marx J, Mitrovic S, Fitzek C, Hopf HC. Isolated
voluntary facial paresis due to pontine ischemia. Neurology 1998;
50: 1859–62.
Van Hoesen GW, Morecraft RJ, Vogt BA. Connections of the monkey
cingulate cortex. In: Vogt BA, Gabriel M, editors. Neurobiology of
cingulate cortex and limbic thalamus. Boston: Birkhäuser; 1993. p.
249–84.
Van Hoesen GW, Morecraft RJ, Semendeferi K. Functional
neuroanatomy of the limbic system and prefrontal cortex. In: Fogel
BS, Schiffer RB, Rao SM, editors. Neuropsychiatry. Baltimore:
Williams and Wilkins; 1996. p. 113–44.
VanderWerf F, Baljet B, Prins M, Ruskell GL, Otto JA. Innervation
of the palpebral conjunctiva and the superior tarsal muscle in the
cynomolgus monkey: a retrograde fluorescent tracing study. J Anat
1996; 189: 285–92.
VanderWerf F, Aramideh M, Otto JA, Ongerboer de Visser BW.
Retrograde tracing studies of subdivisions of the orbicularis oculi
muscle in the rhesus monkey. Exp Brain Res 1998; 121: 433–41.
208
R. J. Morecraft et al.
Vogt BA, Pandya DN, Rosene DL. Cingulate cortex of the rhesus
monkey: I. Cytoarchitecture and thalamic afferents. J Comp Neurol
1987; 262: 256–70.
Weddell RA, Miller JD, Trevarthen C. Voluntary emotional facial
expressions in patients with focal cerebral lesions. Neuropsychologia
1990; 28: 49–60.
Weinrich W, Wise SP. The premotor cortex of the monkey. J Neurosci
1982; 2: 1329–45.
Weller M. Anterior opercular cortex lesions cause dissociated lower
cranial nerve palsies and anarthria but no aphasia: Foix-ChavanyMarie syndrome and ‘automatic voluntary dissociation’ revisited
[editorial]. J Neurol 1993; 240: 199–208.
Welt C, Abbs JH. Musculotopic organization of the facial motor
nucleus in Macaca fascicularis: a morphometric and retrograde
tracing study with cholera toxin B-HRP. J Comp Neurol 1990; 291:
621–36.
West RA, Larson CR. Neurons of the anterior mesial cortex related
to faciovocal activity in the awake monkey. J Neurophysiol 1995;
74: 1856–69.
Williams PL, Warwick R, Dyson M, Bannister LH. Gray’s anatomy.
37th ed. Edinburgh: Churchill Livingstone; 1989.
Wilson SAK. Some problems in neurology. No. II. Pathological
laughing and crying. J Neurol Psychopath 1924; 4: 299–333.
Wilson-Pauwels L, Akesson EJ, Stewart PA. Cranial nerves: anatomy
and clinical comments. Toronto: B.C. Decker; 1988. p. 81–96.
Woolsey CN, Settlage PH, Meyer DR, Sencer W, Hamuy TP, Travis
AM. Patterns of localization in precentral and ‘supplementary’
motor areas and their relation to the concept of a premotor area.
Res Publ Assoc Res Nerv Ment Dis 1952; 30: 238–64.
Woolsey CN, Erickson TC, Gilson WE. Localization in somatic
sensory and motor areas of human cerebral cortex as determined
by direct recording of evoked potentials and electrical stimulation.
J Neurosurg 1979; 51: 476–506.
Wouterlood FG, Groenewegen HJ. Neuroanatomical tracing by use
of Phaseolus vulgaris-leucoagglutinin (PHA-L): electron microscopy
of PHA-L-filled neuronal somata, dendrites, axons and axon
terminals. Brain Res 1985; 326: 188–91.
Wu CW, Bichot NP, Kaas JH. Converging evidence from
microstimulation, architecture, and connections for multiple motor
areas in the frontal and cingulate cortex of prosimian primates.
J Comp Neurol 2000; 423: 140–77.
Received April 11, 2000. Revised August 9, 2000.
Accepted September 8, 2000