The variability of human, BOLD hemodynamic responses

Cerebral hemodynamic responses to brief periods of neural activity are dela yed and dispersed in time. The specific shape of these responses is of some importance to the design and analysis of blood oxygenation level-dependent (BOLD), functional magnetic resonance imaging (fMRI) experiments. Using fM RI scanning, we examine here the characteristics and variability of hemodyn amic responses from the central sulcus in human subjects during an event-re lated, simple reaction time task. Specifically, we determine the contributi on of subject, day, and scanning session (within a day) to variability in t he shape of evoked hemodynamic response. We find that while there is signif icant and substantial variability in the shape of responses collected acros s subjects, responses collected during multiple scans within a single subje ct are less variable. The results are discussed in terms of the impact of r esponse variability upon sensitivity and specificity of analyses of event-r elated fMRI designs. (C) 1998 Academic Press.