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Sperry, Roger Wolcott

brain left nerve severed

(1913–94) US neurobiologist: made important studies of brain function.

Sperry was a student of psychology at Oberlin College and of zoology at Chicago, and worked in several centres before joining the California Institute of Technology in 1954 as professor of psychobiology. His ingenious experimentation challenged previous theories of brain function and led to new ones.

Although a mammal cannot repair a severed optic nerve, an amphibian can. Sperry studied this regeneration and found that, even with obstacles in its path, the new nerve would find its way to its original synaptic connection in the brain. Again, if the optic nerve of a salamander was severed, and the eye removed and replaced after a rotation of 180°, the animal when offered food on its right side would aim to the left, showing that the fibres had remade their old functional connection.

Sperry did much work on the brain in higher animals. The brain consists of two similar halves (containing roughly 109 interconnected cells) with many nerve fibres (commissures) linking the two sides. It was well known that the two halves controlled muscles on the opposite side of the body. Sperry examined animals in which all commissures were severed to give a ‘split brain’, and found (surprisingly) that in many ways monkeys and cats so modified behave as if they had two brains. Human patients are sometimes commissurotomized to prevent severe epilepsy spreading, and Sperry found that such split-brain patients, although normal in many ways, show that usually the right hemisphere specializes in non-verbal processes (eg emotions and spatial relationships) while the left (as has long been known) is dominant in language processing. If a split-brain person picks up an unseen object (for example, a pencil) in the left hand, the ‘feel’ goes to the right hemisphere; but the person could not say what was held, as ‘putting it into words’ calls for links with the left hemisphere. A woman shown a picture of a nude woman in her left visual field only said she saw nothing, but she blushed and giggled. Sperry’s results point to discrete pathways in the brain carrying specific types of information, and have implications for theories of consciousness. He shared a Nobel Prize in 1981.

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