YouTube hosts a classic video of one of the famous ‘split-brain’ patients who had his corpus callosum surgically cut to treat otherwise untreatable epilepsy, effectively separating the two hemispheres of the brain.
This procedure is intended to stop seizures spreading across the brain and its effects were first studied in depth by Roger Sperry, who won a Nobel prize for his work demonstrating that the patients experienced, in certain situations, a sort of split consciousness.
Split-brain patients have been incredibly important in cognitive neuroscience, because the procedure prevents information travelling from one side of the cortex to the other.
The left-most and right-most areas of your vision go directly to the opposite hemisphere, and the same goes for touch information from your hands. Information from the left hand goes to your right hemisphere and vice versa.
In people who have an intact corpus callosum, the information is then communicated to the other hemisphere as well, so the whole brain has access. In split-brain patients, only one hemisphere has access.
Sperry worked with neuropsychologist Michael Gazzaniga who used this effect to demonstrate how each hemisphere could be specialised for different functions.
In the video, Gazzaniga runs Joe, a split-brain patient, through one of these experiments and demonstrates various interesting effects.
For example, it shows how Joe can read words that appear to the right because they get transmitted to the left hemisphere which is specialised for language.
However, Joe can’t read words that appear to the left, because they get transmitted to the language-limited right hemisphere, but he can draw what the word describes with the appropriate hand, because the right hemisphere is specialised for spatial functions.
He can then look at his own picture, making the information available to the left hemisphere, and only then can he name it.
There have been many variations on these experiments that have demonstrated a number of curious effects about brain specialisation and consciousness, some of which are described in a Scientific American article by Gazzaniga.
One of the most interesting things is that the patients don’t feel that their conscious mind is any different, but their split consciousness can be demonstrated experimentally, as shown in the video.