The brain is an incredibly complex structure. In general, the left hemisphere of the brain controls the right side of the body whilst the right hemisphere controls the left side of the body. Although the brain’s hemispheres work together, it is clear that certain areas of the brain have more specific functions. (Localisation of function).
The left hemisphere contains structures linked with: Logic & language
The right hemisphere contains structures linked with: Creativity & visuo-spatial perception
Our understanding of this has developed due to several studies-a lot of them involving split-brain patients.
The corpus callosum is a vital structure that connects both hemispheres of the brain allowing them to communicate with each other. Split-brain is a specific syndrome where the corpus callosum is severed to an extent. Surgical removal of the corpus callosum (corpus callosotomy) is a rare procedure and is a last resort for severe types of seizures. Effectively, this prevents the nerves from sending seizure signals between the two hemispheres of the brain.
The first patient to undergo a full corpus callosotomy was Patient W.J. in 1962. He was injured during World War II and suffered from grand mal seizures (violent muscle contractions and constant loss of consciousness). His operation was a success and led to a major decrease in the number of seizures he got.
Kim Peek was an American savant who was naturally born without a corpus callosum. Kim Peek was incredible at speed reading and retention. He could read both pages of an open book simultaneously, using each eye for the two pages. He was able to give a full account of any book he read and he didn’t give two different accounts for each two pages he read. It is speculated that he may have developed additional subcortical connections for information transfer between the two hemispheres.
In this way, he was different to those who went through a complete callosotomy. For these individuals, a sort of split personality can form.
Sperry and Gazzaniga
Sperry and Gazzaniga are considered the pioneers of split-brain studies. They asked several split-brain patients to partake in different tasks. For example, some participants were asked to describe what they saw. When the stimulus word was exposed to the right visual field, it would be processed by the left hemisphere and the participant would say the word. Therefore, highlighting that the left hemisphere is associated with language. If the same word was exposed to the left visual field, then the right hemisphere would process the information. Now the participant was unable to describe the word due to the lack of language centres in the right hemisphere. They were able to select an object that matched the word showing the presence of tactile understanding. These tasks, amongst many others, highlighted the localisation of function within the brain.
Take a look at this video:
So there we have it, a quick run through of the split-brain phenomenon. Incredibly fascinating stuff that has heavily contributed to our understanding of the brain and has had a positive impact on severely epileptic patients.
Thank you for reading!