Convergent evoked potential and cerebral blood flow evidence of task-specific hemispheric differences.

Two independent measures of cerebral activation, probe evoked potentials (EPs) and regional cerebral blood flow (rCBF) were used to assess the relative contribution of the left and right parietal areas during a task requiring mental rotation of geometric figures. The objective of the study was to ascertain the degree of concordance in these two measures in revealing task-specific hemispheric activation. Since rCBF is a direct measure of regional metabolic rate and has been shown to reflect expected task-specific hemispheric asymmetries, its concordance with probe EP data could serve to validate the assumptions underlying interpretation of the latter. EPs to strobe flashes and rCBF were simultaneously measured in 19 dextral normal adults during a mental rotation task and during a control task involving similar stimulation and response requirements. A high degree of concordance in these two measures was obtained, with both revealing significantly greater activation of the right parietal region during the mental rotation task. Besides supporting the notion of predominant right hemisphere involvement in this type of visuo-spatial operation, this study suggests that either measure may be used as a reliable index of task-specific regional cerebral asymmetries.