Shift-invariant linearity and spatial variation of the negative BOLD response in human with high spatiotemporal functional MRI

Motivation: Many fMRI studies have observed a negative BOLD response (NBR) that is often associated with neural suppression. However, the temporal dynamics of the NBR remains unclear. Goal(s): Here, we investigate temporal linearity of the NBR and characterize spatial variations of the BOLD negative hemodynamic response function (nHRF) along cortical surface. Approach: We examine temporal linearity of the NBR with a unilateral visual stimulus with various stimulus durations, then use the same stimulus with 2-s duration for spatial variation of nHRF. Results: We found unique nHRF dynamics varying gradually along cortical surface, and non-linear behavior of the NBR with different stimulus duration. Impact: The unique dynamics of the NBR can confound linear analyses of event-related fMRI experiments. In addition, our results with shift-invariant experiments with different stimulus durations suggest that temporal linearity does not hold for the NBR.