INTRACRANIAL FLOW PARAMETERS DURING CHANG ES IN CEREBRAL FUNCTION ANDCOGNITIVE CEREBRAL PERFORMANCE

Extensive studies have revealed a close relationship between neuronal activity and regional cerebral blood flow. However, SPECT and PET, the technologies most commonly used in these studies, are of limited valu e for assessment of the dynamics of cerebral blood flow changes at dif ferent states of functional brain activity. The introduction of transc ranial Doppler sonography and the extended application of stimuli pres entation and perception have now been added to the investigator's arma mentarium. Simple sensory stimulation (visual, acoustic and tactile) a nd complex mental tasks (viewing of complex pictures, tactile differen tiation of objects) changed the blood flow velocity in the basal intra cranial arteries. These changes corresponded to the current concepts o f functional cortical organization. The magnitude of the flow velocity increases upon visual stimulation was dependent on the complexity of the stimuli used, and was up to 38 % in our studies. The introduction of continuous and bilateral simultaneous Doppler recordings, the calcu lation of mean flow velocity from cardiac cycle to cardiac cycle and a specially designed averaging method for data analysis allowed effecti ve elimination of non-specific influences and made it possible to demo nstrate rapid changes of perfusion in both middle cerebral artery terr itories in direct response to hemisphere-specific tasks. These changes were correlated with known functional cerebral asymmetries. A languag e task, for instance, was associated with a significantly larger flow velocity increase in the middle cerebral artery of the dominant hemisp here than in the corresponding artery of the non-dominant hemisphere ( 5.2 +/- 1,8 % vs 3.0 +/- 1.8 %, p < 0.001). The excellent time resolut ion of this technology made it possible to record hemodynamic changes taking place in response to modifications of neuronal activity within less than 1 s. The shortest time interval between stimulus presentatio n and the first significant increase in flow velocity was on average 7 17 +/- 191 ms. The latency of less than Is suggest that the coupling b etween alterations of neuronal activity and the regional cerebral bloo d now response is mediated by an remarkably rapid mechanism.