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corpus callosum

The corpus callosum is an area of the brain that is fairly likely to be attacked in multiple sclerosis.

The corpus callosum is one of the two main connections between the two halves (hemispheres) of the brain (the other one is the anterior commissure). The corpus callosum consists of a tract of very many nerve cells (neurons). The long extensions of these neurons (the axons) project from each hemisphere into the other. In midsagittal section (an imaginary slice through the head from the top and along the line of the nose), the corpus callosum looks like a thick arc located in the centre of the brain. See this diagram:

The job of the corpus callosum is to route communication between the two hemispheres. Humans, to a great extent, and great apes, to a much lesser extent, have developed an asymmetry of the brain whereby the two hemispheres are specialised in different functions and this, perhaps, is partly responsible for our great intellectual abilities. The corpus callosum is the channel through which nerve transmissions between the two pass. Although it is unclear exactly what the roles of these transmissions are, it is clear that motor, sensory, visual and other functions are involved.

The corpus callosum principally consists of about two hundred million white matter axons, some of which are normally myelinated (sheathed by an insulating substance called myelin) and some are not. The upper surface has a relatively thin layer of grey matter. The underside of the corpus callosum forms the roof of the lateral and third ventricles.

In multiple sclerosis, the corpus callosum is relatively likely to be attacked. One neurologist I saw, said that the lesions that I have in my corpus callosum were highly indicative of MS, since lesions there are almost always associated with multiple sclerosis in a person of my age.

The corpus callosum is not a brain region in which lesions are associated with specific psychological or neurological symptoms. Indeed, people with a severed corpus callosum (a very radical treatment for severe epilepsy) do not lose their intelligence nor their sense of self. Such cases have shown that the brain is a very plastic organ capable of reassigning functions from one area to another.

On the other hand, there is some MRI evidence that multiple sclerosis lesions in this area are better correlated with cognitive dysfunction than with physical problems. Based on the effects of tumours in this region, impaired judgment and defective memory are potential symptoms of damage to the forward part of the corpus callosum and behavioural changes are possible with damage to the rear part - all of these dysfunctions are observed in some people with MS.

Corpus Callosum Links:
Corpus Callosum
The Human Corpus Callosum
Gray's Anatomy - The Corpus Callosum
Model-guided Segmentation of Corpus Callosum in MR Images


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