Cerebral Dominance and Anatomic Asymmetry

Among Paul Broca's important contributions one of the most dramatic was the demonstration that aphasias resulted almost exclusively from lesions of the left hemisphere. This phenomenon of cerebral dominance — i.e., the superiority of one cerebral hemisphere in acquiring certain kinds of learned behavior — is a distinctive biologic attribute of man, and is, as far as is now known, either absent or poorly developed in any other mammal. For many years it was assumed that dominance existed only for speech and handedness, which were regarded as tightly linked. But the last 30 years have shown that each hemisphere is . . .