Corpus callosum
Image: Life Sciences Database/Wikimedia

The two hemispheres in your brain are connected by a thick bundle of nerve fibres called the corpus callosum that ensures both sides of the brain can communicate and send signals to each other.

A combination of sensory, motor and cognitive information is constantly being transferred between hemispheres via this neural highway.

There are approximately 300 million axons (nerve fibres) in an average corpus callosum. It is located in the white matter of the cerebrum and is around 10cm long at the midline. This neural bridge is the largest white matter structure in the brain and only evolved in placental mammals.

If the corpus callosum is severed, the brain’s hemispheres are not able to communicate properly, and the loss of a range of functions can occur – for example, changes to visual perception, speech and memory. Surgical severing of the corpus callosum is a last-resort method for untreatable epilepsy, to stop seizures spreading across the brain.

Corpus callosum agenesis

There’s a common developmental disorder which affects the corpus callosum, causing it to be either malformed or even missing altogether. This usually happens at a critical period during pregnancy from 12-16 weeks gestation. It is estimated that this disorder, called corpus callosum agenesis or dysgenesis, affects around 1 in 4000 people, leading to a range of physical, intellectual, and social disabilities.

QBI researchers have been looking for the causes of this agenesis, to understand why it occurs and to help with early diagnosis and targeted care for children and adults affected by the disorder. So far the scientists have discovered that there is a particular type of glial cell in foetal brains that plays a role in the development of the corpus callosum. Disruption to these cells is one source of the disorder.

Scientists at QBI have also been investigating the genetics of corpus callosum agenesis. The researchers found that mutations in a gene called DCC led to malformation of the corpus callosum. The same gene is also linked to what’s known as mirror movement disorder, in which people involuntarily move one limb in coordination with the other - such as wanting to only lift your left hand but being unable to stop the right one from lifting as well. Depending on where along the DCC gene the mutations occur, a person can have one or both of the disorders together.

Some people with corpus callosum agenesis are high functioning, and although they face some challenges, they are able to live full and productive lives. Researchers are interested in how the brains of these people are re-wired to compensate for the loss of this massive brain connection. This work will help researchers to understand the process of brain plasticity and how the brain could re-wire itself during foetal life.