Copyright 1988 by the American Psychological Association, Inc.
0735-7044/8S/$00.75
Behavioral Neuroscience
1988, Vol. 102, No. 2, 222-227
Variations in Human Corpus Callosum Do Not Predict
Gender: A Study Using Magnetic Resonance Imaging
Lanning Houston
William Byne and Ruth Bleier
Department of Neurophysiolpgy
University of Wisconsin-Madison
Department of Radiology
University of Wisconsin-Madison
Controversy exists in the neuropsychological literature concerning the existence of genderassociated differences in cognitive functioning and in hemispheric lateralizatiou of cognitive
functions. A recent study, based on 14 brains obtained at autopsy, reported sex differences in the
splenium of the human corpus callosum and suggested that the larger splenium in females reflects
less hemispheric lateralization, or "specialization," than the male brain for visuospatial functions.
Our measurements of the human corpus callosum using magnetic resonance images of 37 living
subjects failed to confirm reported sex differences in the splenium. A marginally significant sexrelated difference in minimum body width and an age-related decrease in anteroposterior distance
were found. Most striking were the large variations in callosal size and shape among individuals
regardless of age or gender. Existing knowledge of the functions of the corpus callosum does not
permit correlations between variations in callosal size and shape and variations in cognitive
functions.
A recent study of the human corpus callosum which used
measurements of 14 brains obtained at autopsy has reported
finding the splenium, the posterior portion of the corpus
callosum, to be larger and more bulbous in females than in
males (de Lacoste-Utamsing & Holloway, 1982). The authors
considered this finding to be the first reported evidence for
sex differences in human brain morphology and to have
important implications for our understanding of human evolution as well as for neuropsychological research on sex
differences in hemispheric lateralization of cognitive functions.
Despite a lack of consensus in the neuropsychological literature on the evidence for gender-related differences either
in cognitive functions or in hemispheric lateralization of
cognitive functions (Caplan, MacPherson, & Tobin, 1985;
Fairweather, 1976; McGlone, 1980), the dominant theory
holds that males process visuospatial information predominantly with the right hemisphere and that females use both
hemispheres more symmetrically in visuospatial functions
and, thus, are said to be less lateralized than males (McGlone,
1980). De Lacoste-Utamsing and Holloway (1982) suggested
This research was supported by National Institutes of Health grants
NSI6643 to Ruth Bleier and HD03352 to the Waisman Center on
Mental Retardation and Human Development. William Byne was a
predoctoral fellow in the Neuroscience Training Program at the time
of this study.
We are grateful to Inge Siggelkow for her assistance in this research,
to Cliff Gillman for computer and statistical consultations, to Shirley
Hunsaker for photographic assistance, and to Yvonne Slusser for
reproduction of the tracings. We thank John Brugge, Janet Hyde,
and Richard Reale for their very helpful comments on this article.
Lanning Houston is now at 9240 University Avenue, Coon Rapids,
Minnesota 55433.
Correspondence concerning this article should be addressed to
William Byne, who is now at Box 52, Albert Einstein College of
Medicine, 1300 Morris Park Avenue, Bronx, New York 10461.
that their finding provides evidence for an anatomical basis
for this hypothetical gender-related difference in hemispheric
lateralization of visuospatial functions.
It seemed important to follow up that report with measurements on a larger series of subjects in view of the small sample
size in that study (5 females, 9 males) and a number of
unstated, possibly relevant variables (method of selection of
the brains from autopsy specimens, age of subjects, cause of
death, extent of postmortem changes). Furthermore, though
the authors reported a bimodal distribution of the values for
maximum splenial width (0.9-1.4 cm for males and 1.4-1.8
cm for females), there was no statistically significant sex
difference in the area of the posterior fifth, defined by the
authors as representing splenial surface area (p = .08).
Our study of the corpus callosum using magnetic resonance
images (MRI) of the callosum in living subjects fails to confirm the splenial dimorphism that was previously reported
but describes a marginally significant sex-associated difference
in minimum body width, an age-associated decrease in callosal anteroposterior distance, and Age x Sex interactions in
total area and area of the rostral 4/5 of the corpus callosum.
The most striking finding was the large variation among
individuals irrespective of sex and age.
Method
Magnetic Resonance Imaging
Magnetic resonance imaging makes it possible to examine the
corpora callosa of a large number of living subjects. Routine cranial
MRI examination frequently includes the sagittal images of the corpus
callosum. For this study, measurements were made on all MRIs
selected as suitable from those filed in the MRI unit (University of
Wisconsin). The subjects of the MRIs were normal volunteers (used
as controls for the evaluation of MRIs) or patients referred for
suspected or known central nervous system disease. Because the study
was retrospective, based on MRIs already on file, information about
222
223
VARIATIONS IN CORPUS CALLOSUM DO NOT PREDICT GENDER
the subjects was limited to that available in their MRI files. Thus
possibly relevant data, such as hand preference, were not available.
Patients were excluded only when the pathologic process affected, or
theoretically could affect, the corpus callosum (e.g., hydrocephalus or
tumor) and when the entire corpus callosum was not on a single slice
as a consequence of an oblique imaging plane. The MRIs were taken
for clinical purposes, and the positioning was done in accordance
with clinical criteria, by direct observation, concerning the true midsagittal plane. Magnetic resonance images were eliminated if there
was any visible evidence of deviation from the midsagittal plane.
Thus, although small deviations probably escaped detection, these
errors would not be consistent in any direction by sex or age but
rather would be a random error across the entire population studied.
Such errors could be expected to be of no greater magnitude than
those introduced randomly by the pathologist's knife in samples of
autopsy specimens.
In total, MRIs from 22 females and 15 males were used. The
female subjects ranged in age from 14 to 68 years with a mean age of
35.9; the male subjects ranged in age from 16 to 68 years with a mean
age of 46.5. For an additional and preliminary analysis of possible
age-related differences, subjects were also divided into under 40 and
over 40 years of age. Nine females and 10 males were over 40 years
of age.
A General Electric 1.5 Tesla human magnetic resonance unit was
used, and midline sagittal images were obtained using a partial
saturation pulse sequence with repetition time of 600 ms. Slices were
10 mm thick and were acquired using a 128 X 256 data matrix.
Measurements of Corpus Callosum
Tracings of the perimeter of the corpus callosum were made from
each MRI scan at a magnification of 1.1 to 1.3, and the accompanying
5-cm scale was traced in order to correct for differences in magnification. From these tracings, the parameters investigated by
d'e Lacoste-Utamsing and Holloway (1982) were measured: anteriorposterior distance (AP), maximum splenial width, total cross-sectional
area, and the areas of the posterior fifth (the splenium, approximately)
and anterior 4/5. Areal determinations were made with computer
assistance. Maximum splenial width was defined as the length of the
longest line through the splenium that could be drawn perpendicular
to a segment of its dorsal surface. In addition to parameters investigated in the original study (de Lacoste-Utamsing & Holloway, 1982),
we also examined the circularity of the splenium, the minimum width
of the body of the callosum, and the proportion of the total callosum
occupied by its caudal fifth. Circularity was examined because of the
previous report that the callosum is more bulbous in women than in
men. Circularity was defined by the following formula: circularity =
(4 pi x area)//)2, where p is the perimeter of the splenium. A line
indicating the rostral border of the posterior fifth of the callosum was
used as the anterior margin of the perimeter of the splenium. Circularity equals 1 for a circle and is less than 1 for any other shape. All
tracings and measurements were done without knowledge of the age
or sex of the subjects.
Statistical analyses were carried out with computer assistance and
involved two-way (Sex x Age) analysis of variance (ANOVA) for overall
comparisons and t tests when the ANOVA indicated a significant Sex
X Age interaction.
Results
Measurements of Corpus Callosum and Analysis by
Gender
The measurements (Table 1) indicate that there was a
marginally significant main effect of sex for minimum width
only, with the width being smaller in men, F(l, 33) = 4.45, p
= .04. There was no significant main effect of sex on any of
the other parameters examined, Fs(l, 33) = 2.48, 0.43, 3.23,
3.12, 0.04, 1.67, 2.95; ps = .12, .52, .08, .09, .85, .21, .10,
respectively, for total area, posterior fifth area, ratio of posterior fifth to total area, anterior 4/5, AP, maximum splenial
width, and circularity.
Analysis by Age
There was a significant main effect of age only for the AP
distance, F( 1, 33) = 7.58, p <. 01, with the distance being less
in subjects over 40 (SEM = 7.12 ± 0.10) than in subjects
under 40 (SEM = 7.53 ± 0.013). There was no significant
main effect of age on any of the other parameters: Fs(l, 33)
= 0.89, 0.25, 1.13, 1.04, 0.10, 1.96, 0.10; ps = .35, .62, .30,
Table 1
Measurements of Human Corpus Callosum
Group
Women
<40
>40
All
Men
<40
>40
All
P/T
Anterior
4/5
(mm2)
Minimum
width (cm)a
AP (cm)b
Splenial
width (cm)
Circular
168 ±9
174+11
170 ±7
0.288 ± 0.009
0.281 ±0.011
0.285 ± 0.007
415 + 20
454 ± 40
431 + 20
0.395 ±0.031
0.423 ± 0.039
0.407 + 0.024
7.44 + 0.15
7.26+0.15
7.36 ±0.11
1 .09 + 0.05
1.23 + 0.12
1.15 ±0.06
0.718 + 0.03
0.722 ± 0.04
0.720 + 0.02
172+ 14
154 ± 16
160 ± 36
0.290 + 0.013
0.326 ±0.015
0.314 + 0.011
429 + 51
324 ± 26"
359 + 27
0.354 ± 0.056
0.301 ±0.031
0.319 ±0.028
7.77 ± 0.27
6.99 ±0.1 4
7.25 ±0.16
1.00 ±0.06
1.10 ±0.06
1.07 + 0.05
0.688 ± 0.03
0.640 ± 0.04
0.649 + 0.03
«
Total
area
(mm2)
Posterior
1/5
(mm 2 )
13
9
22
583 ± 27
628 ± 49
601 ± 25
5
10
15
602 ± 63
478 + 35C
5 19 ±34
Note. Mean values ± standard errors for callosal measurements comparing women with men and also under-40-year-old group (<40) with
over-40-year-old group (>40). P/T = ratio of posterior fifth to total area. AP = anterior-posterior distance.
" Main effect of sex, F(l, 33) = 4.45, p = .04.
b
Main effect of age, F(1, 33) = 7.58, p < .01.
c
Significantly different from under-40-year-old women, /(22) = 2.45, p = .02, and over-40-year-old-women, ((18) = 2.54, p = .02. Difference
from under-40-year-old men approaches significance, ((14) = 1.88, p = .08 (see Footnote 1).
" Significantly different from under-40-year-old women, ((22) = 2.88, p< .01, and over-40-year-old women, ((18) = 2.77, p = .01. Difference
from under-40-year-old men approaches significance, ((14) = 2.08, p = .058 (see Footnote I).
224
W. BYNE, R. BLEIER, AND L. HOUSTON
.32, .75, .17, .76, respectively, for total area, posterior fifth,
ratio posterior fifth to total, anterior 4/5, minimum width,
maximum splenial width, and circularity.
Sex x Age Analysis
Men over 40, but not those under 40, had smaller total and
anterior 4/5 areas than did women in either age group. Thus
there was a marginally significant Sex X Age interaction for
the total area, F(\, 33) = 4.09, p - .05, and a significant
interaction for the anterior 4/5, F(l, 33) = 4.91, p = .03 (see
Footnote 1 for other age-group comparisons).' There were no
other significant Sex x Age interactions: Fs(l, 33) = 0.98,
2.65, 1.09, 2.92, 0.06, 0.17; ps = .33, .11, .30, .10, .81, .68,
respectively, for posterior fifth, ratio posterior fifth to total,
minimum width, AP, splenial width, and circularity.
Individual Variations in Corpus Callosum
The most striking and perhaps most potentially informative
finding in our study is the range of variation in size and shape
of the corpus callosum among individuals, regardless of sex
or age, as shown by the tracings in Figure 1. It is not possible
to predict either sex or age by the shape or size of any
individual corpus callosum. A bulbous splenium is common
in both sexes as is a narrowing of the body, and a nonbulbous
splenium may be seen in females as well as males (Figure 1).
Similarly, with respect to age, although a general trend toward
decreased length appears to occur with age, there are large
and small corpora callosa at both ends of the age range. A
decrease in callosal size may theoretically occur with agerelated neuronal loss, although this has yet to be demonstrated.
Discussion
Other Studies of Human Corpus Callosum
The failure to confirm the reported finding of a larger
splenium in females has also been reported elsewhere in five
recent studies of the corpus callosum (Demeter, Ringo, &
Doty, 1985; Kertesz, Polk, Howell, & Black, 1987; Oppenheim, Lee, Nass, & Gazzinega, 1987; Weber & Weis, 1986;
Witelson, 1985); all reports were based on larger numbers of
brains obtained at autopsy than were used in the original
study. Witelson's study (1985) found that the corpus callosum
is 11 % larger in left-handed and ambidextrous people (mixedhanders) than in those with right-hand preference. The difference was in total, anterior half, and posterior half areas, but
not in the posterior fifth. The study found no significant sexrelated differences in any of these measurements of the callosum. The results suggested, however, that there may be a
complex interaction between sex and hand preference, with
mixed-handed males tending to have a relatively larger posterior half. A more recent investigation of the relation between
handedness and the corpus callosum using MRI in 79 subjects
found no significant differences in size of corpus callosum
between right- and left-handed subjects (Nasrallah, Andreasen, Coffman, Olson, Dunn, & Ehrhardt, 1986).
Since the completion of the present study, Holloway and
de Lacoste (1986) have published the results of a study designed the replicate and extend their original finding of splenial sexual dimorphisms. The replication study found the
cross-sectional area of the entire callosum and the maximal
splenial width to be larger in females than in males. The crosssectional area of the splenium (defined as the posterior 1/5 of
the callosum in their original study) was either not measured
or found not to be dimorphic in the replication study. Similarly, the area of the splenium is not discussed in another of
their recent studies that concluded that the splenial dimorphism is established by the 26th week of gestation (de Lacoste,
Holloway, & Woodward, 1986). The distinction between
splenial size (i.e., area) and maximum width is crucial to the
authors' suggestion that "the larger female splenium could
imply that more fibers connect the posterior portions of
cerebral cortex" in females than in males (Holloway &
de Lacoste, 1986, p. 90), as well as to the authors' summary
statement that they found "that the splenial portion of the
corpus callosum was larger and more bulbous in females than
in males" (p. 87). To have meaning in the context of these
two sentences, larger must be taken to indicate a larger area
and not simply the single-dimensional linear measurement,
maximum width. Yet no data are provided indicating a larger
area in females.
We do not know how to reconcile the discrepant findings
among different laboratories, but procedural differences do
not appear to be a primary factor. It should be noted, however,
that our procedure for determining AP was the same as that
of other groups that failed to detect splenial dimorphisms
(Weber & Weis, 1986; Oppenheim et al., 1987; Witelson,
1985), but different from the method used by de Lacoste et
al. (1986). Their method for determining AP is illustrated
explicitly in their most recent publication; however, in that
study (de Lacoste et al., 1986), the method for determining
maximum splenial width differed from the method used in
their previous studies (de Lacoste-Utamsing & Holloway,
1982; Holloway & de Lacoste, 1986), and it is not clear
whether or not they consistently used the same procedure for
measuring AP. Although differences in the method of determining AP could influence determinations of splenial crosssectional area (since the splenium is operationally defined as
the posterior 1/5 of the callosum), such differences would not
influence determinations of maximal splenial width. And, as
noted previously, Holloway and de Lacoste (de Lacoste et al.,
1986; Holloway & de Lacoste, 1986) apparently failed to
confirm the existence of a significant sexual dimorphism in
splenial size (i.e., cross-sectional area) in their most recent
publications, perhaps understandable in view of the questionable statistical significance (p = .08) in the sexual dimorphism
originally reported in splenial area (de Lacoste-Utamsing &
Holloway, 1982).
1
p values for measurements comparing all age/sex groups are as
follows (see Table 1 for abbreviations). For total callosal area, <40 W
vs. >40 W = .39, <40 W vs. <40 M = .75, <40 W vs. >40 M = .023,
>40 W vs. <40 M = .75, >40 W vs. >40 M = .021, and >40 M vs.
<40 M = .08. For anterior 4/5, <40 W vs. >40 W = .35, <40 W vs.
<40 M = .74, <40 W vs. >40 M = .009, >40 W vs. <40 M = .72,
>40 W vs. >40 M = .013, and >40 M vs. <40 M = .058.
VARIATIONS IN CORPUS CALLOSUM DO NOT PREDICT GENDER
225
callosal terminals (Berlucchi, 1981; Caminiti & Sbriccoli,
1985).
Organization and Functions of Corpus Callosum
Figure 1. Drawings of corpora callosa measured in this study. (The
splenium is to the left. For each sex, drawings were arranged in order
of age and alternate drawings were selected for illustration here; the
youngest is at the top. The lower five callosa in both groups are from
subjects 40 years of age and over. The line indicates 1.33cm.)
Experimental neuroanatomical and electrophysiological
studies indicate the complexity of the patterns of both intrahemispheric and Interhemispheric corticocortical connections, yet, the implications of these connections for cognitive
functioning are not known. To summarize briefly, experimental work has shown that an orderly combination of intrahemispheric and interhemispheric (callosal) inputs to cortical
areas results in the construction of a continuous representation of the visual fields across the vertical meridian and a
continuous representation of the body surface across its midline (Antonini, Berlucchi, & Lepore, 1983; Jones, Coulter, &
Wise, 1979; Killackey, Gould, Cusick, Pons, & Kass, 1983).
In the auditory system of the cat, the corpus callosum has
been found to connect similar portions of the frequency
representations in the four tonotopically organized fields (A,
Al, P, and VP) of the two hemispheres. In addition, corticocortical projections have been found to be particularly dense
in regions where the neuronal responses to binaural stimulation are greater than the response to stimulation of either ear
alone at a given frequency and intensity (Imig, Reale, Brugge,
Morel, & Adrian, 1986).
Goldman-Rakic and Schwartz (1982) suggested that the
pattern of interdigitation of contralateral and ipsilateral cortical columnar projections to frontal association cortex may
provide for the bilateral integration of spatial and temporal
information underlying the cognitive and behavioral functions associated with frontal cortex.
Corpus Callosum and Cognitive Functions
Relation Between Callosal Size and Shape and
Functional Hemispheric Symmetry
De Lacoste-Utamsing and Holloway (1982) suggested that
sex differences in the size and shape of the splenium reflect
sex differences in hemispheric lateralization of visuospatial
functions. Specifically, they suggested that a larger splenium
implies more structural and functional hemispheric symmetry. If particular variations in callosal size or shape are to be
interpreted to indicate differences in some parameter of cognitive functioning, then such interpretations must be based
upon known correlations between callosal morphology and
cognitive functions. To date no evidence exists for such
correlations.
What is known about the cortical topographic organization
of callosal neurons does not permit any assumptions of correlations between callosal size or shape and the number of
callosal axons or degree of symmetry of hemispheric projections. Although virtually all cytoarchitectonic areas of the
cortex send and receive callosal projections, patches of callosal
neurons and terminals are arranged in register, surrounded
by neurons with no or few callosal connections (Berlucchi,
1981). Callosal terminations occur on neurons that do not
project to the corpus callosum, and some areas of the cerebral
cortex that send axons through the callosum do not receive
Despite the body of information gained experimentally in
recent years concerning the organization and functions of
some callosal neurons, relatively little is still known about the
functions of the callosum in animals. Neither is there a basis
for predicting how variations in cortical callosal representation may affect size or shape of the callosum nor, conversely,
what variations in callosal size or shape imply for cortical
representation and functions. What is known experimentally
about the corpus callosum cannot, in any case, be extrapolated
to cognitive functions or abilities of the human brain or to
the question of possible assymetries in hemispheric processing
Of information. We are, furthermore, still lacking in the
knowledge concerning the functions of the human corpus
callosum that would be necessary to formulate a theory concerning its role in cognitive functioning.
Furthermore, the effort to correlate small statistical morphological variations with cognitive functions represents the
application of very crude measures of unknown significance
(e.g., splenial size) to very complex, subtle, and incompletely
understood phenomena (e.g., visuospatial ability). Within
neuropsychology, there is no consensus or rigor in the definition of the term, visuospatial ability, nor is there any reason
to consider visuospatial ability to be a unitary skill or concept
rather than a complex of elements (Caplan et al., 1985). Yet,
226
W. BYNE, R. BLEIER, AND L. HOUSTON
what mechanisms, structures, and processes together comprise
whatever aspects of visuospatial ability that are measured by
a variety of neuropsychological instruments cannot be defined
or described at the present time.
Because, in addition, it is estimated that only about 2% of
cortical neurons send their axons through the callosum (Berlucchi, 1981), it is unlikely that even a more complete knowledge of callosal functions and morphological variations can
provide a basis for theories of cognitive functions or of individual differences in cognitive abilities.
Influences on Callosal Size and Shape
In two recent studies, de Lacoste-Utamsing and Holloway
have suggested that their finding of sex-related differences in
callosal size in adult and fetal brains provides evidence that
the gonadal steroids and/or genetic sex have an important
role in the differentiation of central neural structures that are
associated with cognitive functions (de Lacoste et al., 1986;
Holloway & de Lacoste, 1986). For this hypothesis, the authors rely on the validity of the highly speculative theory
(Geschwind & Behan, 1982) that fetal testosterone causes
delayed left hemispheric development and consequent right
hemispheric dominance. Serious questions have been raised,
however, concerning the validity of both the theory and the
study (of an association between left-handedness, dyslexia,
and immune disorders) that prompted the theory (Bleier,
Houston, & Byne, 1986; Satz & Soper, 1986).
It seems likely that the large variations in size and shape
that we have found among individual corpora callosa may be
the result of complex interactions among any number of
prenatal and postnatal influences, which may include genetic,
hormonal, and other biological factors as well as environmental and experiential influences. However, differences in callosal shape may simply reflect effects of prenatal and perinatal
mechanical forces and be of no greater apparent significance
than variations in gyral and sulcal patterns.
Differences in postnatal cortical development may be influenced by significant individual variations in postnatal sensory
and motor experiences as well as other environmental factors.
At birth, callosal neurons are distributed uniformly across the
visual, auditory, and somatosensory cortex in kittens and
rodents, unlike the mosaic pattern of distribution in adults
(Feng & Brugge, 1983; Innocenti, Fiore, & Caminiti, 1977;
Ivy & Killackey, 1981). The restriction of callosal projections
characteristic of the adult pattern is thought to result from
selective elimination of callosal collaterals and/or neurons in
the postnatal period. At birth, the corpus callosum of the
rhesus monkey, for example, has three times the adult number
of axons, which is attained at about 6 months of age (LaMantia & Rakic, 1984). There is little knowledge of the factors
involved in the restriction of the diffuse neonatal pattern to
the patchy adult pattern of distribution of callosal neurons or
in the elimination of callosal axonal collaterals during postnatal development. Although changes from the continuous to
discontinuous pattern of callosal neurons have been reported
to occur prenatally in the rhesus monkey (Killackey & Chalupa, 1986), it appears also to be the case that specific patterns
of callosal connections can be shaped by sensory experience.
Experimental manipulations in kittens, such as ocular enucleation, induction of squint, and suturing of the eyelids, have
been followed by changes in the number, packing density,
and distribution of labeled callosally projecting cortical neurons and in the density of labeled callosal terminals within
the cortex (Innocenti & Frost, 1979; Innocenti, Frost, & Hies,
1985; Lund, Mitchell, & Henry, 1978). However, it is not
known how or whether these changes are reflected in callosal
structure.
In summary, large variations in callosal size and shape exist
among individuals of each sex and of each age group. Although the range of callosal size and shape is similar between
the sexes and between age groups, this study found a modest
tendency for the minimum width of the callosal body to be
larger in women, and for the AP distance to be larger in
persons under 40 years of age than over. Virtually nothing is
known about the relation of callosal size or projections to
cognitive functions and abilities or about the cortical structural and functional bases for individual cognitive differences.
Thus it is premature to propose functional or evolutionary
implications either for the sizable variations in callosal size
and shape among individuals or for the few small differences
that may appear between groups characterized by some attribute, such as age, gender, or handedness. It is clear, however, that at this level of analysis, individual variability far
overshadows any other trend in callosal morphology that has
thus far been investigated.
References
Antonini, A., Berlucchi, G., & Lepore, F. (1983). Physiological organization of callosal connections of a visual lateral suprasylvian
cortical area in the cat. Journal of Neurophysiology, 49, 902-921.
Berlucchi, G. (1981). Recent advances in the analysis of the neural
substrates of interhemispheric communication. In O. Pompeiano
& C. Ajmone Marsan (Eds.), Brain mechanisms and perceptual
awareness (pp. 133-152). New York. Raven Press.
Bleier, R., Houston, L., & Byne, W. (1986). Can the corpus callosum
predict gender, age, handedness, or cognitive differences? Trends
in Neurosciences, 9, 391-394.
Caminiti, R., & Sbriccoli, A. (1985). The callosal system of the
superior parietal lobule in the monkey. Journal of Comparative
Neurology, 237, 85-99.
Caplan, P. J., MacPherson, G. M., & Tobin, P. (1985). Do sex-related
differences in spatial abilities exist? American Psychologist, 40,
786-799.
de Lacoste-Utamsing, C., & Holloway, R. L. (1982). Science, 216,
1431-1432.
de Lacoste M. C., Holloway, R. L., & Woodward, D. J. (1986). Sex
differences in the fetal human corpus callosum. Human Neurobiology, 5, 93-96.
Demeter, S., Ringo, J., &. Doty, R. W. (1985). Sexual dimorphisms
in the human corpus callosum. Abstracts Society for Neuroscience,
11, 868.
Fairweather, H. (1976). Sex differences in cognition. Cognition, 4,
231-280.
Feng, J. Z., & Brugge, J. F. (1983). Postnatal development of auditory
callosal connections in the kitten. Journal of Comparative Neurology, 214,4(6-426.
Geschwind, N., & Behan, P. (1982). Left-handedness: Association
with immune disease, migraine, and developmental learning dis-
VARIATIONS IN CORPUS CALLOSUM DO NOT PREDICT GENDER
order. Proceedings of Che National Academy of Science, 79, 50975100.
Goldman-Rakic, P., & Schwartz, M. L. (1982). Interdigitation of
contralateral and ipsilateral columnar projections to frontal association cortex in primates. Science, 216, 755-757.
Holloway, R. L., & de Lacoste, M. C. (1986). Sexual dimorphism in
the human corpus callosum: An extension and replication study.
Human Neurobiology, 5, 87-91.
Imig, T. J., Reale, R. A., Brugge, J. F., Morel, A., & Adrian, H. A.
(1986). Topography of corticocortical connections related to tonotopic and binaural maps of cat auditory cortex. In M. F. Lepore,
M. Ptito, & H. H. Jasper (Eds.), Two hemispheres—One brain (pp.
103-116). New York. Alan R. Liss.
Innocenti, G. M., Fiore, L., & Caminiti, R. (1977). Exuberant projection into the corpus callosum from the visual cortex of newborn
cats. Neuroscience Letters, 4, 237-242.
Innocenti, G. M., & Frost, D. O. (1979). Effects of visual experience
on the maturation of the efferent system to the corpus callosum.
Nature, 280, 231-233.
Innocenti, G. M., Frost, D. O., & Illes, J. (1985). Maturation of visual
callosal connections in visually deprived kittens: A challenging
critical period. Journal of Neuroscience, 5, 255-267.
Ivy, G. O., & Killackey, H. (1981). The ontogeny of the distribution
of callosal projection neurons in the rat parietal cortex. Journal of
Comparative Neurology, 195, 367-389.
Jones, E. G., Coulter, J. D., & Wise, S. P. (1979). Commisural
columns in the sensory-motor cortex of monkeys. Journal of Comparative Neurology, 188, 113-136.
Kertesz, A., Polk, M., Howell, J., & Black, S. E. (1987). Cerebral
dominance, sex, and callosal size in MRI. Neurology, 37, 13851388.
Killackey, H. P., & Chalupa, L. M. (1986). Ontogenetic change in
the distribution of callosal projection neurons in the postcentral
gyrus of the fetal rhesus monkey. Journal of Comparative Neurology, 244,331-348.
227
Killackey, H. P., Gould III, H. J., Cusick, D. C., Pons, T. P., & Kass,
J. H. (1983). The relation of corpus callosum connections to
architectonic fields and body surface maps in sensorimotor cortex
of new and old world monkeys. Journal ofComparative Neurology,
219, 384-419.
LaMantia, A.-S., & Rakic, P. (1984). The number, size, myelination,
and regional variation of axons in the corpus callosum and anterior
commissure of the developing rhesus monkey. Abstracts Society
for Neuroscience, 10, 1081.
Lund, R. D., Mitchell, D. E., & Henry, G. H. (1978). Squint-induced
modification of callosal connections in cats. Brain Research, 144,
169-172.
McGlone, J. (1980). Sex differences in human brain asymmetry: A
critical survey. The Behavioral and Brain Sciences, 3, 215-263.
Nasrallah, N. A., Andreasen, N. C., Coffman, J. A., Olson, S. C.,
Dunn, V., & Ehrhardt, J. C. (1986). The corpus callosum is not
larger in left-handers. Abstract Society for Neuroscience, 12, 720.
Oppenheim, J. S., Lee, B. C. P., Nass, R., & Gazzinega, M. S. (1987).
No sex related differences in human corpus callosum based on
magnetic resonance imagery. Annals of Neurology, 21, 604-606.
Satz, P., & Soper, H. V. (1986). Left-handedness, dyslexia, and
autoimmune disorder: A critique. Journal of Clinical and Experimental Neuropsychology, 8, 453-458.
Weber, G., & Weis, S. (1986). Morphometric analysis of the human
corpus callosum fails to reveal sex-related differences. Journal fur
Hirnforschung, 2, 237-240.
Witelson, S. F. (1985). The brain connection: The corpus callosum
is larger in left-handers. Science, 229, 665-668.
Received November 26, 1986
Revision received February 13, 1987
Accepted February 20, 1987 •