HEMISPHERIC LATERALIZATION OF COGNITIVE EVOKED BLOOD-FLOW VELOCITY CHANGES ASSESSED BY SIMULTANEOUS BILATERAL TRANSCRANIAL DOPPLER SONOGRAPHY

The newly developed method of simultaneous bilateral transcranial Dopp ler sonography (sbTCD) provides a reliable tool for the assessment of hemispheric differences in changes of cerebral blood flow velocities e voked by cognition. Lateralized increase of flow velocity in the middl e cerebral arteries (MCA) could be detected in response to specific ta sks predominantly processed in either the left or the right hemisphere in all 57 subjects tested. During language processing 83% of right-ha nders exhibited a significantly higher increase in left-hemispheric bl ood flow velocity ((x) over bar = 4.5 +/- 2.7%). Among left-handers th is was observed in only 57%. A bilateral increase in flow velocity wit h no significant side differences was found with calculation. Moreover , flow velocity increments in the MCA exceeded those in the anterior c erebral artery (ACA) indicating that the cortical areas most important for arithmetics are supplied by the MCA. Thus, sbTCD is a promising m ethod for the assessment of hemispheric lateralization of higher corti cal functions as well as for the localization of active brain areas su pplied by the MCA or ACA. In comparison to other methods, the measurem ent of hemodynamic parameters by sbTCD has the advantage of better tim e resolution in the range of seconds and of noninvasiveness which allo ws intrasubject averaging and longitudinal studies.