[Intracranial blood flow parameters in cerebral functional changes and cognitive 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 value for assessment of the dynamics of cerebral blood flow changes at different states of functional brain activity. The introduction of transcranial Doppler sonography and the extended application of stimuli presentation and perception have now been added to the investigator's armamentarium. Simple sensory stimulation (visual, acoustic and tactile) and complex mental tasks (viewing of complex pictures, tactile differentiation of objects) changed the blood flow velocity in the basal intracranial arteries. These changes corresponded to the current concepts of 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 calculation of mean flow velocity from cardiac cycle to cardiac cycle and a specially designed averaging method for data analysis allowed effective elimination of non-specific influences and made it possible to demonstrate rapid changes of perfusion in both middle cerebral artery territories in direct response to hemisphere-specific tasks. These changes were correlated with known functional cerebral asymmetries. A language task, for instance, was associated with a significantly larger flow velocity increase in the middle cerebral artery of the dominant hemisphere 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 resolution 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 presentation and the first significant increase in flow velocity was on average 717 +/- 191 ms. The latency of less than 1 s suggest that the coupling between alterations of neuronal activity and the regional cerebral blood flow response is mediated by an remarkably rapid mechanism.