To assess cognitively-related regional asymmetries of brain function, regional cerebral blood flow (rCBF) was determined by the xenon inhalation method while normal subjects performed 10 different tasks and also while they were at rest. In addition to healthy subjects, patients with schizophrenia were also studied. A total of 447 rCBF studies were carried out during the following conditions: the Wisconsin Card Sort Test, a numbers matching test, a symbols matching test, Raven's Progressive Matrices, an auditory discrimination test, an auditory control task, two versions of a visual continuous performance task, line orientation, semantic classification, and resting. On the whole, those tasks that seem to require or allow for internal verbalisation resulted in the greatest activation of the left hemisphere compared with the right; right hemisphere activation predominated only in the two tasks primarily involving attention and vigilance. Furthermore, a consistent regional topography of normal cerebral functional laterality was seen: under most conditions left prefrontal cortical activity exceeded that of right prefrontal cortex; during all non-auditory tasks, parieto-occipital cortical activity had an opposite pattern-greater right than left. During most conditions the schizophrenic patients displayed the same pattern. While several cognitively specific between-group differences were found, no single cortical region was consistently implicated and no specific direction of abnormal asymmetry predominated. These data suggest that there is a predominant task-independent functional pattern of cortical activity emphasising relatively greater left anterior and right posterior activation. This pattern may reflect the verbal and attentional primacy of these areas, respectively.
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