Brain (1999), 122, 329–338
Brain activation during maintenance of standing
postures in humans
Yasuomi Ouchi,1 Hiroyuki Okada,2 Etsuji Yoshikawa,2 Shuji Nobezawa1 and Masami Futatsubashi2
1Positron
Medical Center, Hamamatsu Medical Center and
Research Laboratory, Hamamatsu Photonics K.K.,
Hamakita, Japan
2Central
Correspondence to: Yasuomi Ouchi MD, Positron Medical
Center, Hamamatsu Medical Center, 5000 Hirakuchi,
Hamakita 434-0041, Japan
Summary
The regulatory mechanism of bipedal standing in humans
remains to be elucidated. We investigated neural
substrates for maintaining standing postures in humans
using PET with our mobile gantry PET system. Normal
volunteers were instructed to adopt several postures:
supine with eyes open toward a target; standing with feet
together and eyes open or eyes closed; and standing on
one foot or with two feet in a tandem relationship with
eyes open toward the target. Compared with the supine
posture, standing with feet together activated the
cerebellar anterior lobe and the right visual cortex
(Brodmann area 18/19), and standing on one foot
increased cerebral blood flow in the cerebellar anterior
vermis and the posterior lobe lateral cortex ipsilateral
to the weight-bearing side. Standing in tandem was
accompanied by activation within the visual association
cortex, the anterior and posterior vermis as well as within
the midbrain. Standing with eyes closed activated the
prefrontal cortex (Brodmann area 8/9). Our findings
confirmed that the cerebellar vermis efferent system
plays an important role in maintenance of standing
posture and suggested that the visual association cortex
may subserve regulating postural equilibrium while
standing.
Keywords: postural balance; brain activation; PET; statistical parametric mapping
Abbreviations: ANCOVA 5 analysis of covariance; ANOVA 5 analysis of variance; BA 5 Brodmann area;
rCBF 5 regional cerebral blood flow; SPM 5 statistical parametric mapping
Introduction
The mapping of human brain regions responsible for
maintenance of standing posture is an unprecedented study,
which may be comparable with the first report, in which
the investigators used single photon emission tomography
(SPECT) and described a focal increase in regional cerebral
blood flow (rCBF) in the hand somatosensory area by simple
finger movement (Lassen et al., 1977; Roland et al., 1980).
Standing itself may be classified as simple behaviour, but
maintenance of the postural balance requires rapid processing
of signals from the visual, vestibular and somatosensory
systems (Nashner, 1976). Alterations in these sensory
functions relating to standing postures in human brain could
never be studied with ordinary tomographic scanners. To
date, the role of the sensory information for postural control
has been investigated with a movement kinematic method
by measuring body sway in conditions in which a certain
sensory input was changed or limited.
It is common clinically that patients with vestibular deficits
can show gait ataxia, abnormal head and body righting
reactions, and difficulties in balancing on one leg and in
heel-to-toe stance (Horak et al., 1988). The movement kinetic
© Oxford University Press 1999
studies stressed that somatosensory as well as vestibular
information was important in selection of postural movement
adjustment according to the environmental context (Diener
et al., 1984; Horak et al., 1990). It was also reported that
vision ameliorated the fluctuation of the body position caused
by standing with a narrow stance width or with eyes closed
(Day et al., 1993). For elderly people, disequilibrium can be
a common problem, as revealed by posturography (Fife and
Baloh, 1993). Their instability can be triggered easily by
malfunctioning responses to visual cues (Nashner et al.,
1982), vestibular (Norre et al., 1987) and proprioceptive
reflexes (Lord et al., 1991). Previous clinicopathological
studies suggested that the cerebellum plays a central role in
controlling postural balance (Holmes, 1922a, b) and that both
the spinocerebellum and vestibulocerebellum participate in
this sensory processing (Parent, 1996). Despite these lines of
evidence, no conventional radiological scanners are suitable
for mapping functional topography in the cerebellum involved
in the postural equilibrium system for standing in humans.
Previous animal studies on cerebellar functions for body
balance stressed that the cerebellar vermis located in the
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medial longitudinal cortical zone (spinocerebellum),
considered important for co-ordinating body movement with
respect to gravity and head movement in space, played a
role in integrating the senses such as tactile proprioception
from the feet (Chambers and Sprague, 1955; Leicht and
Schmidt, 1977; Leicht et al., 1977). Similarly, the human
cerebellar vermis seems to co-ordinate the timing in keeping
the centre of gravity within the limits required for stable
upright standing (Diener et al., 1989), and this co-ordination
deteriorates with the age-related shrinkage of the vermis
(Koller et al., 1983). These lesion deficit studies supported
the idea that the vermis contributes to controlling upright
posture during locomotion and standing. Thus, the cerebellar
vermis is considered an integral centre of the neural
mechanism for proper maintenance of equilibrium and
posture. Previous brain activation studies on the cerebellar
motor system showed that the central lobule in the anterior
cerebellum was activated by foot movements performed in
the supine position (Nitschke et al., 1996; Wessel and
Nitschke, 1997). Moving the feet in the supine position,
however, is essentially different from the motor function
related to maintaining the standing posture with the feet.
The purpose of this study was to investigate neural
substrates which are related to the process of maintaining
standing postures, such as standing on one foot, standing
with feet in a tandem position and standing with eyes closed,
using PET with H215O.
Methods
Subjects
Eight healthy, right-handed (right-footed) female volunteers
(31.8 6 6.5 years, mean 6 SD) participated in the present
PET experiment. Before the study, the participants rehearsed
the standing postures required, and the height of the scanner’s
gantry was adjusted to each subject’s stature for optimal
imaging. The present study was approved by the Ethics
Committee of the Hamamatsu Medical Center, and written
informed consent was obtained from all participants after the
nature and possible risks of the experiment were explained.
Fig. 1 Task design: (A) supine with eyes open; (B) standing with
feet together and with eyes open; (C) standing on one foot and
with eyes open; (D) standing with feet in a tandem relationship
and with eyes open; (E) standing with feet together and with eyes
closed.
having the left heel directly in front of the right toes (Task
D). All tasks except for Task E required volunteers to
stare at the target during PET measurement. Their ocular
movements during measurements were monitored by
videotaping. PET measurements in which marked ocular
movement was observed in the replay checked just after the
PET scan were discarded, and the same scan was repeated.
As physiological parameters, blood pressure and pulse rate
were measured before and after each PET scan.
Before PET measurement, a preliminary study was
performed to investigate the magnitude of sway in each
standing posture by measuring maximal lateral deviation of
the head in the lateral direction and counting the number of
sidesteps (collapse of posture) within a period of 60 s (Table
1). Each subject stood upright in a series of postures against
the wall with a lattice measuring scale on it. Although the
situation in the present PET study was not the same as that
in this preliminary study in terms of fixation of the head, no
significant differences [P . 0.05, one-way ANOVA (analysis
of variance) with Scheffe’s F test] in the magnitude of sway
were observed among standing-related tasks except for Task
E. This result permitted further comparison among standing
tasks in the present PET study. However, care was necessary
in interpreting results from Task E-involved comparisons
because head fixation might be expected to influence standing
posture significantly.
PET procedure
Experimental design
The study consisted of five different tasks. The control task
was to adopt the supine posture (Fig. 1A, Task A) and stare
at a target (a round object) hanging 1 m ahead of the subject.
Subsequently, subjects were instructed to adopt different
standing postures: (i) standing with feet together and eyes
open and focused on the target (Fig. 1B, Task B); (ii) standing
on one foot with eyes open and focused (Fig. 1C, Task C);
(iii) standing in a tandem posture with eyes open and focused
(Fig. 1D, Task D); and (iv) standing with feet together and
eyes closed (Fig. 1E, Task E). Since all participants were
right-footed, the one-legged posture consisted of standing on
the right foot (Task C), and standing in tandem consisted of
We used a high-resolution PET scanner (SHR2400,
Hamamatsu Photonics, Hamakita, Japan) with spatial resolution of 2.7 mm (full-width at half-maximum) transaxially
and 5.5 mm axially and with 80 mm axial field of view
(Yamashita et al., 1990). This PET system had a mobile
gantry which enabled vertical movement (up to 165 cm from
the bottom) and tilting (–20° to 190°). The restricted axial
field of view obliged us to determine beforehand the scanning
area required in the PET study on the mid-sagittal image
obtained by MRI (see below) (Ouchi et al., 1997). By tilting
the PET gantry, the axial field of view could cover the area
from the middle frontal gyrus to the lower part of the
cerebellum. After backprojection and filtering (Hanning filter,
Brain and standing postures
331
Table 1 Postural stability in preliminary measurements (60 s duration)
Posture
Standing
Standing
Standing
Standing
Maximal sway (mm)
with feet together
on one foot
in tandem
with feet together (eyes closed)
17.9
20.1
20.4
21.7
6
6
6
6
1.8
2.3
1.9
1.7*
No. of sidesteps
0.0
0.3
0.1
0.0
6
6
6
6
0.0
0.5
0.3
0.0
Values are expressed as mean 6 SD. *P , 0.01 versus standing with feet together and eyes open
(one-way ANOVA).
cut-off frequency 0.2 cycles per pixel), image resolution was
8.0 3 8.0 3 6.5 mm full-width at half-maximum. The voxel
of each reconstructed image measured 1.45 3 1.45 3 8 mm.
The head was fixed using a specially made thermoplastic
face mask and head holder which was fitted firmly to the
urethane holder receiver attached to the internal surface of
the gantry hole of the PET scanner. After fixation of the
head in the holder, a 20 min transmission scan was obtained
in the supine position. After the first emission scan in the
supine posture with eyes open and focused on a target
hanging 1 m ahead (Task A), the head holder was removed
temporarily from the receiver and the position of the gantry
was set optimally for each volunteer’s head height before
performing a series of standing tasks (Tasks B–E). Each
participant wore the face mask and head holder during the
study consisting of a total of eight PET measurements. The
order of conditions was counterbalanced except for Task A:
A-B-C-D-E-D-C-B, or A-E-D-C-B-B-C-D. For each PET
scan, individuals received a 555 MBq bolus of H215O through
the left cubital vein by an automated injector. A 90 s PET
scan commenced 30 s after the start of bolus injection and
60 s after completion of each standing posture. Relative
rCBF images were integrated over a period of 60 s from
when the tracer first entered the cerebral circulation after
bolus injection (Raichle et al., 1983). Since the head position
was marked three-dimensionally with laser lights attached to
the gantry in both supine and standing postures, the head
position was realigned satisfactorily to the position of the
first scan. During interscan intervals, volunteers were released
temporarily from the head fixation to the gantry and allowed
to rest on a chair.
MRI procedure
MRI was performed to determine the scanning brain area in
the axial direction using a static magnet (0.3 T MRP7000AD,
Hitachi, Japan) with the following acquisition parameters:
three-dimensional mode sampling, TR/TE (200/23), 75° flip
angle, 2 mm slice thickness with no gap and 256 3 256
matrices. The spatial relationship between the locus of the
centre of the magnetic field and that of PET images was
calibrated in advance. This calibration permitted us to perform
PET scans parallel to an arbitrarily sectioned MRI plane and
to select the brain area concerned in an axial direction by
tilting PET detector rings (Ouchi et al., 1997). The same
thermoplastic face mask and head holder were used during
both MRI and PET measurements.
Data analysis
Statistical parametric mapping (SPM) software (SPM96;
Wellcome Department of Cognitive Neurology, London,
UK) implemented in Matlab (Mathworks Inc., Sherborn,
Mass., USA) on a HyperSPARC ss-20 workstation (Sun
Microsystems Co., Montain View, Calif., USA) was used to
realign all PET scans to the first emission scan to correct for
head movement (Friston et al., 1995a, b). After realignment,
all images were transformed into a standard stereotaxic
anatomical space (Talairach and Tournoux, 1988) and filtered
with an isotropic Gaussian kernel of 8 mm full-width at halfmaximum to increase the signal-to-noise ratio and to allow for
the gyral anatomical differences among individuals. The effect
of variance due to global cerebral blood flow was removed by
using voxel-by-voxel ANCOVA (analysis of covariance) with
the global flow normalized to 50 ml/100 g/min as a
confounding covariate. This process generated normalized
mean rCBF values on a voxel-by-voxel basis for each task.
Comparison of adjusted mean rCBF in a specific task with
that in the control task was performed on a voxel-by-voxel
basis with t-statisitics. The appropriate design matrix was
used to specify these comparisons. The resultant set of voxel
values for each contrast constituted a t-statistic SPM{t},
which was then transformed to a unit normal distribution
(SPM{z}) map (Friston et al., 1995b). We reported significant
activation areas consisting of clusters of voxels which had
the peak height: P , 0.05 with a correction for multiple
comparison (Friston et al., 1995b).
Results
Physiological changes during PET
measurements (Table 2)
There were no significant differences in systemic blood
pressure or pulse rate before and after each PET measurement
under any of the experimental conditions (P . 0.05, repeated
ANOVA). Neither significant reduction in blood pressure nor
increase in pulse rate were observed during standing.
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Y. Ouchi et al.
Table 2 Physiological data for each condition
Posture
Systolic blood pressure
Pre-scan
Supine
Standing
Standing
Standing
Standing
with feet together
on one foot
in tandem
with feet together (eyes closed)
122.0
121.6
123.0
123.2
121.3
6
6
6
6
6
Pulse rate
Post-scan
17.7
17.3
17.7
17.9
16.2
124.7
127.9
129.3
130.9
125.8
6
6
6
6
6
Pre-scan
18.7
19.8
20.6
21.8
19.1
78.0
79.8
78.3
78.3
79.6
6
6
6
6
6
Post-scan
6.9
8.2
7.4
8.7
8.0
80.0
82.3
80.8
80.7
81.8
6
6
6
6
6
7.7
10.1
8.4
8.8
8.5
Values are expressed as mean 6 SD.
Table 3 Coordinates and Z scores for significant activation during standing postures(P , 0.05, corrected) compared with
supine position
Posture
Brain region
Coordinates
x
y
z
Z
%∆CBF
Standing with feet together
R lingual/inferior occipital gyri (BA 17/18)
R cerebellar anterior lobe (culmen)
Cerebellar anterior vermis
26
24
22
290
280
272
24
216
210
4.69
4.29
3.91
4.3
4.0
3.0
Standing on one (R) foot
R cerebellar anterior lobe (culmen)
Cerebellar anterior vermis
R cerebellar posterior lobe (lateral cortex)
20
26
46
234
256
242
224
220
228
4.84
4.56
3.94
4.4
4.1
3.1
Standing with feet in tandem
R cerebellar anterior vermis
R inferior occipital gyrus (BA 18)
R inferior temporal gyrus (BA 37)
Cerebellar posterior vermis
16
24
56
4
280
286
258
258
210
22
26
240
4.95
4.80
4.53
3.91
4.5
4.4
4.0
3.2
BA 5 Brodmann area; R 5 right; L 5 left. These standing conditions required subjects to keep eyes focused on the target during PET
measurements.
Brain activation during standing postures
compared with the supine position (P , 0.05,
corrected) (Table 3)
Nomenclature in the cerebellum (Ito, 1984) was based on
the MRI atlas (Courchesne et al., 1989). Comparison of
bipedal standing with the supine posture showed significant
rCBF increases in the right primary and secondary visual
cortex [Brodmann area (BA)17/18], the left cerebellar anterior
lobe (culmen) and the anterior vermis (Fig. 2A).
Comparison of standing on one foot (right) with the
supine posture showed significant activation in the rightsided cerebellar anterior lobe (culmen) and the anterior
vermis, and the right posterior lobe (Fig. 2B).
Compared with the supine posture, standing with feet
together in a tandem relationship activated the cerebellar
anterior and posterior vermis, and the inferior occipital (BA
18) and temporal cortex (BA 37), considered to be the visual
association cortex (Fig. 2C).
Brain activation for balancing in upright
postures: comparison of standing in tandem
posture with standing with feet together
(P , 0.05, corrected) (Table 4, Fig. 3)
Compared with the upright posture with feet together, standing
with the feet in tandem activated focal regions in the medial
longitudinal cerebellar zone (vermis) and the left midbrain
corresponding to the red nucleus. This vermal zone included
the central lobule and culmen anteriorly and the uvula
and nodulus posteriorly. Activation, albeit not statistically
significant (Z 5 3.01), was also seen in the left thalamus.
Brain activation during standing with eyes
closed, compared with standing with eyes open
(P , 0.05, corrected) (Table 5, Fig. 4)
Shifting from the eyes open to eyes closed condition during
bipedal standing (‘Romberg manoeuvre’) resulted in
significant activation in the bilateral middle frontal gyri
(BA 9 and 8).
Discussion
The present study was performed to determine the brain
topography for maintenance of postural balance during
standing in humans. However, there were several methodological limitations of the present study. First, fixation of the
head sacrificed a free and natural standing style intrinsic to
each subject and impaired the subjects’ ability to correct for
imbalance during standing. It was unpredictable to what
extent volunteers depended on the head fixation system
during standing, but our preliminary study measuring the
Brain and standing postures
333
Fig. 2 Results of SPM in comparisons of several standing postures with the supine position (P , 0.01,
corrected) with the eyes open. (A) Standing with feet together versus supine; (B) standing on one foot
versus supine; (C) standing with feet in a tandem relationship versus supine. Details of coordinates and
Z-values are given in Table 3.
Table 4 Activated foci in balancing posture: standing with feet in tandem versus with feet
together
Brain region
R cerebellar anterior vermis
L midbrain (red nucleus)
L cerebellar anterior vermis
Cerebellar posterior vermis
Coordinates
x
y
z
8
26
216
24
240
218
244
252
28
24
210
246
Z
%∆CBF
4.28
4.04
3.94
3.91
3.7
3.3
3.1
2.9
R 5 right; L 5 left.
sway magnitude while adopting different standing postures
showed that there were no significant differences in sway
level among postures with eyes open. These differences in
sway magnitude indicated that different stimuli caused by
altering upright posture could cause focal brain activation in
the areas contributing to each postural regulation. This
was supported by the PET activation study showing that
different types of movement of a unilateral upper limb
resulted in alterations in activated intensity and foci in the
brain (Colebatch et al., 1991). Secondly, the removal of head
fixation between scans could have caused positional errors
which might have resulted in errors on final analyses.
However, the use of the face mask and head holder which
covered the volunteer’s craniofacial part throughout the PET
334
Y. Ouchi et al.
Fig. 3 Significant rCBF increases in a comparison of standing in tandem (Task D) with standing upright (Task B) were observed in the
anterior and posterior vermis and the midbrain corresponding to the red nucleus. Weak (not significant) activation of the left thalamus
was also observed. The numerals denote z-directional distance from the AC–PC (anterior–posterior commissural) line on Talairach’s
standardized brain atlas. The coloured bar indicates Z-values from 0 to 5.
Table 5 Activated foci during ‘Romberg test’: standing with eyes closed versus eyes open
Brain region
L middle frontal gyrus (BA 9)
R middle frontal gyrus (BA 8)
Coordinates
x
y
z
226
30
48
40
34
42
Z
%∆CBF
4.58
3.91
3.9
3.0
BA 5 Brodmann area; R 5 right; L 5 left.
examination and a three-directional laser marker permitted
maintenance of the initial position and allowed further
analysis using SPM96. Thirdly, our scanner’s axial field of
view was insufficient to cover the whole brain, and therefore
we had to exclude the brain region covering the primary
somatosensory foot area. An animal experiment showing that
a cat lacking the cerebrum was able to walk (Miller et al.,
1975) suggested that the cerebral cortex was not involved in
walking control. However, there was anatomical evidence of
ascending efferent fibres from cerebellar nuclei projecting to
the contralateral primary motor area (Parent, 1996), along
with evidence of significant activations in the foot area while
walking in humans revealed by our previous SPECT study
(Fukuyama et al., 1997). Thus, the primary foot somatosensory area cannot be neglected as a candidate for postural
control. Fourthly, physiological conditions, especially in the
brain haemodynamics, may be altered by shifting from the
supine position to the standing position. However, stabilization of systemic blood pressure and pulse rate of each subject
measured before and after each scan reduced this possibility.
In addition, ANCOVA eliminated the confounding effect
from the global cerebral blood flow change during statistical
analysis in SPM96.
The present study showed that the activated brain areas
during upright standing in humans were localized to specific
divisions of the cerebellum (the anterior lobe and the medial
longitudinal zone, i.e. vermis) and the visual cortex. Our
preliminary sway measurement study showed that compared
with normal bipedal standing, balancing unipedal and tandem
directional upright postures scored a little worse (Table 1).
Brain and standing postures
335
Fig. 4 Significant rCBF increases in a comparison of bipedal standing with eyes closed (Task E) versus that with eyes open (Task B)
were found in the bilateral middle frontal gyri (BA 8/9).
This might indicate that the latter postures could possibly
require more accurate co-ordinating responses to postural
adjustment for shifting the centre of gravity (Mitchell, 1971;
Richardson et al., 1996). Our results showing anterior lobe
and medial cerebellum activation during standing supported
the observations of previous human lesion studies which
indicated that medial cerebellar lesions disturbed balance and
gait, while the lateral cerebellar lesions impaired motor coordination in the distal extremities (Ivry et al., 1988; Diener
et al., 1989). Thus, our findings confirmed that the cerebellar
anterior lobe, specifically the anterior vermis, plays a central
role in upright postural equilibrium during standing in
humans.
Functionally, the vermal and paravermal cortical areas are
specific parts of the cerebellum encompassing fastigial nuclei
which are concerned primarily with mechanisms that modify
extensor muscle tone for postural control (Chambers and
Sprague, 1955; Ito, 1984) and interposed nuclei (emboliform
and globose) for facilitation of flexor muscle tone for proper
maintenance of posture via the rubrospinal tract (Courville,
1966; Flumerfelt et al., 1973). Vestibular nuclei project to
the uvula, nodulus and flocculus which, in part, comprise
the posterior vermis and contribute to postural equilibrium
(Kotchabhakdi and Walberg, 1978; Carpenter, 1988). These
findings might be supported by the present result that comparison of the bipedal posture with feet in a tandem relation-
ship with the normal bipedal posture showed significantly
activated foci rostrocaudally in the cerebellar medial longitudinal areas (Fig. 3). Activation in the anterior vermis and
the midbrain corresponding to the red nucleus along with
weak thalamic activation (Fig. 3) suggested that the
cerebellar–rubrothalamic projection system (Appelberg,
1960; Eager, 1963; Tolbert et al., 1978) may function as a
regulatory neuronal output to adjust upright balance during
standing. The posterior vermal activation in the present study
might reflect augmentation of vestibulo-ocular responses
because the posterior vermis (nodulus and uvula) plays an
important role in habituating and stabilizing the vestibuloocular reflex in head positioning (Waespe et al., 1985). It
was reported that alterations in platform angle disturbed
correct information from the vestibular system, resulting in
collapse of upright posture in aged subjects (Diener et al.,
1986; Norre et al., 1987). Adopting such a distorted platform
in the present study would have caused explicit activation in
the vestibulocerebellum.
The lack of lower brainstem (vestibular nuclei) activation
in the present study might be partly due to use of the head
fixation and restriction of the ocular movement by gaze
fixation. The important contribution of vision to proprioception is that of sensing the movement of the head in space.
In cats, the visual proprioceptive neurons responding to
moving objects in a specific direction were localized in the
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Y. Ouchi et al.
rostral pontine region (Baker et al., 1976). This brainstem
region might also be important in humans for visual
proprioceptive control because a human lesion study showed
that lesions of the pontomedullary vestibular nuclei and the
rostral tegmentum disturbed the pattern of co-ordinated
eye–head roll motion (Brandt and Dieterich, 1987). Thus,
activations in the lower brainstem would have been expected
in the condition permitting a volunteer to perform self-paced
postures without any head fixation.
The present study showed significant activation in the
visual cortex on comparison of standing postures with the
supine condition. Monitoring of ocular movement by videotape ensured that this activation in the visual cortex was not
ascribed to saccadic eye movement during standing. However,
this method was not sufficient to monitor minute ocular
motions or changes in optic focus. Therefore, it is possible
that there might be electrooculographic or retinoscopic ocular
adjustment for stereopsis during standing because the stereoscopic processing requires activities of area 18 in the right
hemisphere (Ptito et al., 1993; Nagahama et al., 1996). In
the present study, the activated cortical areas outside the
cerebellum were chiefly confined to the human V2–V3 areas
(McKeefry et al., 1997). It was reported that areas V2–V3
were involved in the processing of the stereoscopic or
disparity vision and orientation discrimination (Clarke and
Miklossy, 1990). Interestingly, standing in tandem showed
significant activation in the fusiform gyrus corresponding to
V5 for motion vision (Zeki et al., 1991). These findings
suggested that standing with the eyes open itself may
accompany concurrent activation of the visual cortical fields
which may subserve stereopsis and motion vision to maintain
proper standing posture. This speculation was supported by
the clinical evidence that distortion of visual input caused
deterioration of postural balance during standing (Wolfson
et al., 1992).
Comparison of standing with eyes closed versus eyes
open showed significant activation in the bilateral middle
frontal gyri (BA 8/9), a little anterior ventral to the reported
frontal eye field (Paus, 1996) (Fig. 4). The frontal eye field
and the supplementary eye field (medial part of the superior
frontal gyrus) were shown to be activated during imagined
saccade without eye movement (Bodis-Wollner et al., 1997).
In addition, an imaginary mental task activated area 8 and
its reciprocally connected dorsolateral prefrontal cortex (BA
9/46) (Cohen et al., 1996). These results suggested that
standing with eyes closed may resemble mental imagery
resulting in significant activation in the BA 8/9 in the present
study. Clinically, this type of manoeuvre, i.e. shifting from
eyes open to eyes closed during standing with feet together,
is known as the ‘Romberg test’ and categorized as a
neurological test for sensory ataxia (Haerer, 1992).
Conclusions
We identified functional brain fields associated with
equilibrium of upright posture during standing in humans.
Our findings confirmed the idea that the cerebellar vermis
efferent system is involved in the active maintenance of body
balance, and suggested that the visual association cortex
contributes to its stability possibly by monitoring threedimensional orientation in space while standing.
Acknowledgement
We thank Mr Toshihiko Kanno for his technical assistance.
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Received June 8, 1998. Revised August 27, 1998
Second revision on September 30, 1998. Accepted October 5, 1998