Behavioral and Anatomical Correlates of Corpus Callosum Size
Christine
1
Chiarello ,
Suzanne
1
Welcome ,
University of California,
Laura K.
1
Riverside ,
2
Halderman ,
University of
Stephen
2
Pittsburgh ,
CDIC
4
Towler ,
3
Riverside ,
Ronald
3
Otto ,
University of Florida,
4
Leonard
& Christiana M.
4
Gainesville
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It is known that individuals vary widely in the area of the corpus callosum. Some
proposed correlates of this variation include:
• Sex:
•Males have larger absolute corpus callosum size, but not when brain volume
is controlled (Bishop & Wahlsten, 1997)
•Consistency of Handedness:
•Some find no significant differences in callosal area between consistent and
non-consistent right-handers (Preuss, 2002; Hines, et al., 1992)
•In males only, non-consistent right-handers may have larger callosa,
especially isthmus (Wistelson & Goldsmith, 1991)
•Degree of Behavioral Lateralization:
•Several dichotic listening studies have found negative associations between
left hemisphere asymmetry and callosal area (Westerhausen, et al., 2006;
Yazgan, 1995; Hines, et al., 1992)
•Brain Asymmetry
•In males, but not females, asymmetry of Sylvian fissure negatively correlated
with size of isthmus (Aboitiz, Scheibel, & Zaidel, 1992)
No prior studies of the corpus callosum have investigated both behavioral and
anatomical asymmetries. In the current large-scale study, we re-examine
sex/handedness differences in callosal area and correlations with behavioral and
anatomical asymmetries.
Method
PARTICIPANTS:
• 100 male, 100 female native English speakers
• 18-34 years of age
• 103 consistent-handed (exclusive preference for one hand), 97 mixed handed
DVF TASKS:
• Lexical Decision
• Masked Word Recognition (2 AFC procedure)
• Word Naming (administered twice with different stimuli)
• Nonword Naming
• Semantic (manmade vs natural) Decision
• Verb Generation
• Category Generation
•Composite asymmetry score across all 7 tasks calculated separately for accuracy and
reaction time
BRAIN MEASUREMENTS FROM MRI:
• Area of corpus callosum: total, rostrum, genu, anterior body, middle body, posterior body,
isthmus, and splenium
•Asymmetry of posterior (planum temporale and primary Heshl’s gyrus) and frontal (pars
opercularis) anatomy
Multiple regression was used to control for brain volume in all analyses
Results
Groups characterized by consistency of handedness and sex do not
differ in callosal area, degree of behavioral asymmetry, or degree of
brain asymmetry
2
Female mixed-handers
with greater lefthemisphere advantages
have larger callosa when
brain size and average
accuracy are controlled
Composite Accuracy Asymmetry
Introduction
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Corrected Corpus Callosum Area
Male
Consistent
(N=44)
Male
Mixed
(N=56)
Female
Consistent
(N=59)
Female
Mixed
(N=41)
Callosum Area
5.58
5.71
5.75
5.64
Accuracy Asym
.111
-.005
-.081
.005
Middle
Posterior
RT Asym
.112
-.060
-.053
.038
Body
Body
Planum Temporale
Asym.
.087
-.208
.027
.152
For this group, relationships between behavioral asymmetry and area hold for all
regions of the callosum except the splenium, and account for between 9 and 29
percent of variance in regional area, as shown below
Anterior
Body
29.3
9.1
0.4
16.8
Heschl’s Asym.
-.019
.011
-.049
.075
Pars Opercularis Asym
.157
-.138
.019
-.008
Genu
Relationships between asymmetries and area of corpus callosum
differ between groups:
•Mixed-handed females show strongest relationship between behavioral
(accuracy) asymmetry and callosal area
•No groups show relationship between RT asymmetry and callosal area
•Degree of leftward-asymmetry of temporal areas positively associated
(pink) with callosal area in some groups
•Degree of leftward asymmetry of frontal areas negatively associated
(yellow) with callosal area in males only
•No relationship between callosal area and either behavioral or anatomical
asymmetry in female consistent-handers
Male
Consistent
Male Mixed
Female
Consistent
Female
Mixed
NS
NS
NS
Total, genu,
rostrum, ant.
body, mid.
body, post.
body, isthmus
RT Asym
NS
NS
NS
NS
Planum Temporale
Asym.
Rostrum
NS
NS
NS
Heschl’s Asym.
Isthmus
NS
NS
Post. body
Pars Opercularis Asym
Ant. Body
Isthmus,
Splenium
NS
NS
Acknowledgment
This research was supported by NIDCD grant 5R01DC6957.
Splenium
22.4
16.5
Accuracy Asym
18.9
Isthmus
Rostrum
Conclusions
•Corpus callosum size, when adjusted for brain volume, does not differ between sex or handedness
groups.
•Instead, sex and handedness may be important moderators of relationship between asymmetry and
callosal area.
•Frontal asymmetries were associated with smaller callosa, but only in males.
•In contrast, correlations with behavioral asymmetry or posterior anatomical asymmetries were
always positive - greater asymmetry was associated with larger callosa. This is consistent with an
inhibitory role for the corpus callosum.
References
Aboitiz, F., Scheibel, A.B., & Zaidel, E. (1992) Morphometry of the sylvian fissure and the corpus callosum,
with emphasis on sex differences. Brain, 115 (5), 1521-41.
Bishop, K.M. & Wahlsten, D. (1997) Sex difference in the human corpus callosum: myth or reality?
Neurosci Biobehav Rev, 21 (5), 581-601.
Hines, M., Chiu, L., McAdams, L.A., Bentler, P.M., & Lipcamon, J. (1992) Cognition and the corpus
callosum: verbal fluency, visuospatial ability, and language lateralization related to midsagittal suface areas
of callosal subregions. Behav Neurosci, 106(1), 3-14.
Preuss, U.W., Meisenzahl, E.M., Frodl, T., Zetzsche, T. Holder, J., Leinsinger, G., Hergerl, U., Hahn, K., &
Moller, H.J. (2002) Handedness and corpus callosum morphology. Psychiatry Res., 116(1-2), 33-42.
Westerhausen, R., Woerner, W., Kreuder, F., Schweiger, E., Hugdahl, K., & Wittling, W. (2006) The role of
the corpus callosum in dichotic listening: a combined morphological and diffusion tensor imaging study.
Neuropsychology, 20 (3), 272-9.
Wistelson, S.F. & Goldsmith, C.H. (1991) The relationship of hand preference to anatomy of the corpus callosum
in men. Brain Res, 545(1-2), 175-82.
Yazgan, M.Y., Wexler, B.E., Kinsbourne, M., Peterson, B., & Leckman, J.F. (1995) Functional significance
of individual variations in callosal area. Neuropsychologia, 33(6), 769-79.