Differential activation of right and left posterior sylvian regions by semantic and phonological tasks: a positron-emission tomography study in normal human subjects.

A previous study of brain activation in normal subjects during a phonological (Phonemes) task and a lexical semantic (Words) task using positron-emission tomography [3] is complemented by new data after a method for image realignment was applied [17]. The pattern of cerebral blood flow increases associated with Words compared with Phonemes, involved several foci of activation but these were not exclusively distributed in the left hemisphere as it also included the right angular gyrus, suggesting a participation of the right hemisphere in lexical semantic processes. Conversely, by comparison to Words, Phonemes activated left-sided perisylvian regions, involving the inferior part of the left supramarginal gyrus, in accordance with previous results on verbal short-term memory [12].