TRANSCRANIAL DOPPLER ULTRASONIC ASSESSMENT OF MIDDLE CEREBRAL-ARTERY BLOOD-FLOW VELOCITY CHANGES DURING VERBAL AND VISUOSPATIAL COGNITIVE TASKS

Hemisphere specific changes of blood flow velocity in the right and le ft middle cerebral artery (MCA) induced by cognitive demands of verbal and nonverbal tasks were examined by means of a newly developed techn ique of simultaneous bilateral transcranial ultrasonic Doppler sonogra phy (TCD). Thirty-one right-handed healthy volunteers served as subjec ts. Identical stimulus and response procedures were used with all task s to avoid possible differential effects of these conditions on blood Bow velocity. Compared to the preceding resting phase, the increase in flow velocity induced by each of the verbal tasks (sentence completio n, similar or contrasting word meanings, similarities) proved to be si gnificantly higher in the left than in the right MCA. Among the non-ve rbal visuospatial tasks only the ''identical pictures'' (perceptual sp eed) task led to a complementary higher increase in right MCA blood Bo w velocity. No such asymmetry in blood flow acceleration was observed, however, with the tasks ''figure assembly'' and ''cube comparison'' w hich require visualization and mental rotation of figures. The finding s underline the recently emerging uncertainty in neuropsychological re search with regard to the functional specialization of the right hemis phere.