Between-task habituation in functional transcranial Doppler ultrasonography

We investigated the variability of absolute brood flow velocity (BFV) and t ask-induced BFV change over consecutive cognitive tasks and compared two me thods of baseline determination that are used to calculate relative BFV cha nges. Bilateral transcranial Doppler ultrasonography recordings of BFV in t he middle cerebral arteries was performed in 90 right-handed volunteers dur ing 13 cognitive tasks and their preceding rest periods. Both absolute BFV and elicited BFV changes between rest and activation significantly decrease d over successive tasks. Instead of calculating an averaged baseline value, our results suggest that the rest phase immediately preceding the activati on phase should be selected for baseline measurement. The between-task habi tuation effect could be due to a fading of attentional resources during the sustained and demanding performance. (C) 1999 Lippincott Williams & Wilkin s.