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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
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:
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