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 phono logical (Phonemes) task and a lexical semantic (Words) task using posi tron-emission tomography [3] is complemented by new data after a metho d for image realignment was applied [17]. The pattern of cerebral bloo d flow increases associated with Words compared with Phonemes, involve d several foci of activation but these were not exclusively distribute d 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 lef t-sided perisylvian regions, involving the inferior part of the left s upramarginal gyrus, in accordance with previous results on verbal shor t-term memory [12].