The corpus callosum, the largest fibre structure in the brain, is a network of some 800 million axons that serves as a link between the two hemispheres of the brain. "Each hemisphere has its own specialty: speech and phonology are linked to the left hemisphere, and the right hemisphere is the seat of spatial analysis. But the two hemispheres do not work independently of one another: a communication link between them is needed so they can picture the world globally; the link is the corpus callosum," explains Maryse Lassonde, Professor in the Department of Psychology at Université de Montréal and holder of the Canada Research Chair in developmental neuropsychology.

Yes some people are born without a corpus callosum. "Congenital agenesis of the corpus callosum" is actually quite common, affecting one child in every 100 on average. In Quebec, the Saguenay region has an especially high rate. But this anomaly does not have any devastating consequences for children, according to Professor Lassonde. Absence of the corpus callosum at birth would only result in a slowing of psychomotor functions. In a new demonstration of neural plasticity, the neuropsychologist discovered an astonishing faculty in her work with the blind: the brain of a person who grows up with a major handicap, such as blindness or absence of corpus callosum, can reorganize itself to compensate for the deficiency. Advances in our knowledge of agenesis of corpus callosum hold out great hope for many parents. "Using prenatal ultrasound, we can diagnose agenesis of corpus callosum in the fetus very early on. Because I work on this problem, I receive many messages from women asking if they should interrupt their pregnancy for this reason. I recently received a photograph of a young child in perfect health. The prenatal diagnosis had identified agenesis of corpus callosum and the parents wanted to know my opinion on a possible abortion. I advised against it. I am pleased that they took my advice!" says Maryse Lassonde.

While agenesis of corpus callosum causes little serious damage in children, it can be serious if a lesion occurs in an adult. "An adult who has had the corpus callosum sectioned suffers a total disconnection between the two hemispheres: the right hand literally does not know what the left hand is doing," the researcher notes. However, this fact can be useful in some circumstances: ablation of the corpus callosum is one of the recommended treatments for epilepsy, a disturbance of the brain's electrical activity. The goal of surgery is to prevent epilepsy from propagating from one hemisphere of the brain to the other. Infantile epilepsy, which was a secondary aspect of Maryse Lassonde's work, has now become a priority for her. And the new Research Chair should propel her work forward byleaps and bounds.

Researcher: Maryse Lassonde
Telephone: (514) 343-6959
Funding: Canadian Foundation for Innovation, Natural Sciences and Engineering Research Council