The corpus callosum (CC), with over 300 million fibers, is the largest white matter fiber bundle in the human brain. (It is easily identifiable in conventional MRI scans.) Topographically, it is centered along the midsagittal plane with radiations that extend to the prefrontal and frontal cortex in the anterior brain, the sensory-motor cortex in the middle and the parietal, temporal and occipital lobes in the posterior half of the brain.
This large and heterogeneous collection of fibers is responsible for interhemispheric communication. Michael Gazzaniga, a neuroscientist at Dartmouth College, has being studying the nature of this left brain- right brain communication for over 30 years. Here he explains some of his fascinating findings to Alan Alda, former hawkeye, now host of Scientific American Frontiers. And this is one of Gazzaniga's papers. (A similar account of the mysterious workings of the brain first got me interested in brain imaging. The book in question was V.S. Ramachandran's Phantoms in the Brain.)
Because of the important role it plays, the CC is the focus of many studies. Some are concerned with changes in the shape, size or structure of the CC. These changes may occur due to aging or degenerative disease. On one end of the spectrum, work is being done to provide tools to measure and monitor these changes. At the other end are the clinical studies. An example of a clinical study might be one that links the different stages of the disease or aging process with physical alterations.