The Variability of Human, BOLD Hemodynamic Responses

TLDR

Cerebral hemodynamic responses to brief neural activity are delayed and dispersed, and their specific shape matters for BOLD fMRI design and analysis. The study aims to examine the characteristics and variability of hemodynamic responses from the central sulcus during an event‑related simple reaction time task. Using fMRI scanning, the authors assess how subject, day, and within‑day scanning session contribute to variability in the evoked hemodynamic response shape. They find substantial inter‑subject variability but reduced variability across multiple scans within the same subject, with implications for sensitivity and specificity of event‑related fMRI analyses.

Abstract

Cerebral hemodynamic responses to brief periods of neural activity are delayed 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 fMRI scanning, we examine here the characteristics and variability of hemodynamic responses from the central sulcus in human subjects during an event-related, simple reaction time task. Specifically, we determine the contribution of subject, day, and scanning session (within a day) to variability in the shape of evoked hemodynamic response. We find that while there is significant and substantial variability in the shape of responses collected across subjects, responses collected during multiple scans within a single subject are less variable. The results are discussed in terms of the impact of response variability upon sensitivity and specificity of analyses of event-related fMRI designs.