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The corpus callosum
(call ō sum) is the largest connective pathway in a human brain. It is made of more
than 200 million nerve fibers that connect the left and right sides
(hemispheres) of the brain.
If we cut a brain in half
down the middle, we would also cut through the fibers of the corpus
callosum. When looking at the middle side of one half of the brain, for
example, in magnetic resonance imaging (MRI), the corpus callosum looks like a cross-section of a mushroom cap at the center of the brain.
Each
hemisphere of the brain is specialized to control movement and feeling
in the opposite half of the body, and each hemisphere specializes in
processing certain types of information (such as language or spatial
patterns). Thus, to coordinate movement or to think about complex
information, the hemispheres must communicate with each other. The
corpus callosum is the main connector that allows that communication.
In
a typical infant brain, the corpus callosum develops between 12 to 16
weeks after conception (near the end of the first trimester). While the
entire structure develops prior to birth, the fibers of the corpus
callosum continue to become more and more effective and efficient on
into adolescence. By the time a child is approximately 12 years of age,
the corpus callosum functions essentially as it will in adulthood,
allowing rapid interaction between the two sides of the brain. From
this age on (and typically earlier) as the corpus callosum becomes
increasingly functional in their typically developing peers, children
with ACC appear to fall behind developmentally because the corpus
callosum is absent.
Parents often ask if the corpus
callosum is the only path between the hemispheres of the brain. It
isn't the only path, but it is by far the most important. Some much
smaller connections are usually present in ACC. The anterior commissure
is the largest and most useful of these other pathways. However, it
only has about 50,000 nerve fibers, a far cry from the more than 200
million fibers in the corpus callosum.
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