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Corpus callosum from above
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Median sagittal section of brain The relations of the Pia Mater are indicated by the red color ("Corpus callosum" visible at center, in light gray)
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The is the largest
White Matter structure in the
Mammal ian
Brain . It consists mostly of
Contralateral Axon projections. It appears as a wide, flat region just
Ventral to (below) the
Cortex . It is missing in
Monotreme s and
Marsupial s. It is made up of 200-250 million nerve fibers.
The corpus callosum connects the left and right
Cerebral Hemisphere s. Most (but certainly not all) communication between regions in different halves of the brain are carried over the corpus callosum. The posterior portion of the corpus callosum is called the ; the anterior is called the '''genu''' (or "knee"); between the two is the body. The most anterior part is the '''rostrum'''.
Agenesis Of The Corpus Callosum is a complete or partial absence of the corpus callosum in humans.
In humans, disputed claims have been made about the importance for gender difference of a difference in size between the corpus callosum in males and females, and analogous racial claims. RB Bean, a Philadelphia anatomist, suggested in
1906 that the ‘‘exceptional size of the corpus callosum may mean exceptional intellectual activity” and claimed gender differences which were refuted by Franklin Mall, the director of his own laboratory (Bishop and Wahlsten, 1997).
Of much more substantial popular impact was a '' stated in
1992 that the corpus callosum was ‘‘Often wider in the brains of women than in those of men, it may allow for greater cross talk between the hemispheres—possibly the basis for woman’s "
Intuition ”. It has also been used, for example, as the explanation of an increased single-task orientation of male, relative to female, learners; a smaller male organ is said to make it harder for the left and right sides of the brain to work together and to explain a feminine ability to multitask.
The relationship between known gender-specific biology (such as males having, in general, higher
Testosterone levels than females) and claims about behaviour (such as human males being more competitive) remains a highly contested one. Unusually, the scientific dispute in the case of the corpus callosum is not about the implications of biological difference, but whether such a
difference actually exists. A substantial review paper (Bishop and Wahlsten, 1997) performed a meta-analysis of 49 studies and found, contrary to de Lacoste-Utamsing and Holloway, that males have a ''larger'' corpus callosum, a relationship that is true whether or not account is taken of larger male brain size. Bishop and Wahlstein found that "(t)he widespread belief that women have a larger splenium than men and consequently think differently is untenable."
There is no current evidence that difference in male and female cognitive behaviour can be explained by differences in the size of the corpus callosum.
- de Lacoste-Utamsing, C., Holloway, R. L. "Sexual dimorphism in the human corpus callosum." ''Science'', 216, 1431–1432, 1982.
- Bishop, K.M. and D. Wahlsten. "Sex Differences in the Human Corpus Callosum: Myth or Reality?", ''Neuroscience and Biobehavioral Reviews'', Vol. 21, No. 5, pp. 581–601, 1997.
