Menstuff® has compiled the following information on the Corpus
Callosum, the massive formation of nerve fibers bridging the two
cerebral hemispheres. Most (but certainly not all) communication
between regions in different halves of the brain are carried over the
corpus callosum.
Sexual dimorphism
Of much more substantial popular impact was a 1982 Science article (de Lacoste-Utamsing and Holloway) claiming to be the first report of a reliable sex difference in human brain morphology and arguing for relevance to cognitive gender differences. This paper appears to be the source of a large number of lay explanations of perceived male-female difference in behaviour: for example Newsweek 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.
Source: en.wikipedia.org/wiki/Corpus_callosum#External_links
History
Anatomy
Each hemisphere contains neurons which project callosal axons not
only to homologous (homotopic) areas in the contralateral hemisphere
but also to heterologous (heterotopic) areas. There are approximately
200,000,000 callosal axons in humans! The corpus callosum is
undoubtedly the most important commissure to connect the two
hemispheres, not only by virtue of its size, but also due to the
wealth of its neural connections. It is through these projections
that information is shared between the two halves of the brain. Very
little is known about the neural signals that pass between the
hemispheres, but recent studies have used modern tract tracing
techniques to determine precisely the sites of origin and termination
of neurons which project across the corpus callosum. Using a
retrograde tracer (horseradish peroxidase), Lomber et al. (1994) were
able to link the functional divisions of the cerebral cortex to fiber
trajectory through the corpus callosum. The motor cortex sends fibers
through the rostrum and genu of the corpus callosum. The adjacent
somatosensory cortex projects fibers through the anterior half of the
corpus callosum whereas axons arising from auditory regions pass
through the posterior two-thirds of the corpus callosum and the
dorsal splenium. Axons from the limbic cortex also help to form these
regions of the corpus callosum. Finally, axons from visual cortices
which occupy the greatest single fraction of the cortical mantle pass
through the largest portion of the corpus callosum; the fibers are
present throughout the splenium and extend well into the body and the
anterior portion. Ramifications of the axonal breakdown of the corpus
callosum are discussed in out section on new developements.
Source: www.macalester.edu/psychology/whathap/UBNRP/Split_Brain/Corpus%20Callosum.html
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