A brief look into the work of Roger Sperry and his experiments with Split-brain patients, which led him to receive the Nobel prize in Physiology & Medicine in 1981.
Split-brain operations were first carried out in the 1940’s, to try and prevent attacks in a severe form of epilepsy that could not be treated by medication. This type of epilepsy involves an electrical discharge beginning in a specific area of the brain which then spreads quickly to other areas of the brain eventually attacking the forebrain, resulting in intense seizures that can lead to violent falls and potential serious injury with a loss of consciousness during an attack and amnesia throughout and after the attack. The split brain operation was devised to try and stop this spread from one side of the brain to the other and involved cutting the corpus callosum.
The Corpus callosum is a large mass of fibres connecting cortical areas on one side of the brain with cortical areas on the other side; it is the largest pathway in the brain and ensures communication between the two hemispheres of the brain. When the corpus callosum is severed in epileptic patients the electrical discharges are confined to one hemisphere, ensuring the epilepsy to be greatly reduced and leaving intact all other functions such as sensory, motor and cognitive functioning.
Roger Sperry became intrigued by this; he thought that the removal of the largest pathway in the brain must affect behaviour. He decided to devise a test based on the complex anatomy of the visual system; this system is more complex than any other system in the human body as the eyes are not directly crossed, the left side of each retina is connected to the left side of the brain and the right side of each retina is connected to the right side of the brain, since the retinal image is inverted the left side of the visual field connects to the right side of the brain and the right side of the visual field connects to the left side. In split-brain patients an image cannot pass to the other hemisphere as the corpus callosum has been cut.
The standard split-brain study devised by Sperry, involved a split-brain patient sitting in front of a screen that hides his or her hands from view. Behind the screen there are a few objects that the patient cannot see, the patient would focus their eyes on the centre of the screen and a word would be flashed up on the screen in their left visual field. The information from the left visual field is received by the non-verbal right hemisphere of the brain resulting in the patient not being able to tell the experimenter what they saw. The patient would then be asked to reach behind the screen with their left hand and pick out the object that corresponded with the word previously flashed on the screen. As the right hemisphere controls movement of the left side of the body, the left hand was able to pick out the correct object, even though the patient was unaware that they saw a word. As long as the object in the left hand is behind the screen and hidden from view, they were not able to say what the object was. This early study confirmed to Sperry that the left hemisphere controls reading and speech and the right hemisphere is not able to process verbal stimuli.