The corpus callosum is a wide, flat bundle of neural fibers beneath the cortex in the eutherian brain at the longitudinal fissure. It connects the left and right cerebral hemispheres and facilitates inter- hemispheric communication. It is the largest white matter structure in the brain, consisting of 200–250 million contra lateral-axonal projections.
Agenesis of the corpus callosum (AgCC)
Agenesis of the corpus callosum (AgCC) is a rare birth defect (congenital disorder) in which there is a complete or partial absence of the corpus callosum. It occurs when the corpus callosum fails to develop normally, typically during pregnancy. The development of the fibers which would otherwise form the corpus callosum become longitudinally oriented within each hemisphere and form structures called probst bundles.
Initial symptoms of ACC usually include seizures, which may be followed by feeding problems and delays in holding the head erect, sitting, standing, and walking. Other possible symptoms may include impairments in mental and physical development, hand-eye coordination, and visual and auditory memory.
People born with AgCC still show normal communication between two halves of the brains
Neuroscientists at the California Institute of Technology (Caltech) have found that people who are born with AgCC, still show remarkably normal communication across the gap between the two halves of their brains. Their findings are published in a paper in the October’19 in The Journal of Neuroscience.
According to J. Michael Tyszka, lead author of the paper and Associate Director of the Caltech Brain Imaging Center, many areas of the brain display slowly varying patterns of activity that are similar...
to one another. The fact that these areas are synchronized is probably due to presence of interconnected network called a resting-state network. Much to their surprise, Tyszka and his team found that these resting-state networks look essentially normal in people with AgCC, despite the lack of connectivity.
Tyszka observed “This was a real surprise. We expected to see a lot less coupling between the left and right brain in this group – after all, they are missing about 200 million connections that would normally be there. How do they manage to have normal communication between the left and right sides of the brain without the corpus callosum?”
The researchers used functional magnetic resonance imaging ( fMRI) to demonstrate that synchronized activity between the left and right brain survives even this sort of radical rewiring of the nerve connections between the two hemispheres. The presence of symmetric patterns of activity in individuals born without a corpus callosum shows the brain’s remarkable plasticity and ability to compensate.
About a third of people with AgCC also have autism, and altered connectivity in the corpus callosum has been found in autism. The remarkable compensation in brain functional networks found may thus have important implications also for understanding the function of the brains of people with autism.