Split Brain Experiments

In some severe cases of epilepsy, patients have undergone a callosotomy, which is a procedure where the corpus collosum (a set of nerve fibres connecting the two cerebral hemispheres) is severed. This has proven successful in controlling severe seizures (1). Tests carried out on these ‘split-brain’ patients have yielded some interesting results. In the 1960s, Michael Gazzaniga and Roger Sperry designed tests for investigating how the separation of the hemispheres had effected the mental capacities of the patients. When presenting visual or tactile information to the right visual field (left hemisphere) of the patients (who, as most people, had a left-brain dominance for language processing), they were able to verbalise and write what they saw or felt. When the same information was presented to the left visual field (right hemisphere), they were unable to elicit the same verbal and written responses. Despite not having the same verbal capacities, when the patients were asked to give non-verbal responses to the visual and tactile information presented to the right hemisphere, they were able to do so. For example, when an object such as a cigarette was presented, the split-brain patients were able to match it to an image of an ashtray, when given several images to choose from. Based on these types of tests, researchers have concluded that, despite there being sub-cortical connections between the two hemispheres, some aspects of mental functioning work independently within each hemisphere (2).

1. Gazzaniga, M. S. (2005). “Forty-five years of split-brain research and still going strong“. [Review]. Nature Reviews Neuroscience, 6(8), 653-U651.

2. Gazzaniga, M. S. (1967) “The split brain in man“. Sci. Am.217, 24–29.