corpus callosum

Brain: Corpus callosum
Corpus callosum from above. (Anterior portion is at the top of the image.)
Median sagittal section of brain (person faces to the left). Corpus callosum visible at center, in light gray.)
Gray's	subject #189 828
NeuroNames	hier-173
MeSH	Corpus+Callosum
NeuroLex ID	birnlex_1087

The corpus callosum is a structure of the mammalian brain in the longitudinal fissure that connects the left and right cerebral hemispheres. It facilitates communication between the two hemispheres. It is the largest white matter structure in the brain, consisting of 200-250 million contralateral axonal projections. It is a wide, flat bundle of axons beneath the cortex. Much of the inter-hemispheric communication in the brain is conducted across the corpus callosum.

Monotremes and marsupials do not have a corpus callosum.

Review

The posterior portion of the corpus callosum is called the splenium; the anterior is called the genu (or "knee"); between the two is the truncus, the 'body' of the corpus callosum. The rostrum is the portion of the corpus callosum that projects posteriorly following from the anteriormost genu.

Thinner axons in the genu interconnect prefrontal cortex areas between the two sides of the brain. Those in the posterior body of the corpus callosum interconnect parietal lobe areas. Thicker axons in the midbody of the corpus callosum and in the splenium interconnect areas of the motor, somatosensory, and visual cortex.^[1]

Evolution

In primates, axon diameter, and hence its conduction velocity has increased in the corpus callosum with increased brain size and so maintained the speed of communication between the two cerebral hemispheres particularly between its primary motor and sensory areas. However this scaling between increased brain size and increased myelination of corpus callosum axons has not occurred between chimpanzees and humans.^[1] This has resulted in humans having double the delay time of communication between the two sides of its brain compared to that of macaques.^[1]

Sexual dimorphism

There are disputed claims about the difference of the size of the human corpus callosum in men and women and the relationship of any such differences to gender differences in human behaviour and cognition.

R B Bean, a Philadelphia anatomist, suggested in 1906 that the "exceptional size of the corpus callosum may mean exceptional intellectual activity" and claimed differences in size between males and females and between races, although these were refuted by Franklin Mall, the director of his own laboratory.^[2]

Of much more substantial popular impact was a 1982 Science article claiming to be the first report of a reliable sex difference in human brain morphology, and arguing for relevance to cognitive gender differences.^[3] This paper appears to be the source of a large number of lay explanations of perceived male-female difference in behaviour: For example Time magazine was reported to state in 1992 that the corpus callosum is "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 women’s intuition."^[4] There is scientific dispute not only about the implications of anatomical difference, but whether such a difference actually exists. A substantial review paper 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.^[2] Bishop and Wahlstein found that "the widespread belief that women have a larger splenium than men and consequently think differently is untenable." However, more recent studies using new analysis and imaging techniques (e.g. diffusion-tensor imaging) revealed morphological and microstructural sex differences in human corpus callosum.^[5][6][7] A 2006 Serbian study found variations in morphology correlated with sex, but in ways too complex for simple direct comparison.^[8] Whether,^{[citation needed]} and to what extent, these morphological differences are associated with behavioural and cognitive differences between men and women remains unclear.

Other correlations

The front portion of the corpus callosum has been reported to be significantly larger in musicians than non-musicians,^[9] and to be slightly larger in left-handed and ambidextrous people than right-handed people. ^[10]

Epilepsy

The symptoms of refractory epilepsy can be reduced by cutting the corpus callosum in an operation known as a corpus callosotomy. ^[11]

Pathology

• Alien hand syndrome
• A complete or partial absence of it in humans is called agenesis of the corpus callosum.
• Split-brain
• Septo-optic dysplasia (deMorsier syndrome)
• Alexia without agraphia (seen with damage to splenium of corpus callosum)

External links

Wikimedia Commons has media related to: Corpus callosum

• BrainMaps at UCDavis corpus callosum

• Comparative Neuroscience at Wikiversity
• NIF Search - Corpus callosum via the Neuroscience Information Framework

Additional images

Mesal aspect of a brain sectioned in the median sagittal plane.	Coronal section of brain immediately in front of pons.	Coronal section of brain through intermediate mass of third ventricle.	Coronal section of lateral and third ventricles.
Central part and anterior and posterior cornua of lateral ventricles exposed from above.	Coronal section through anterior cornua of lateral ventricles.	Coronal section of brain through anterior commissure.	Diagram showing the positions of the three principal subarachnoid cisternæ.
Medial view of a halved human brain

References