Spatial variation of the negative BOLD response in human primary visual cortex

The negative hemodynamic response functions (nHRF), temporal dynamics of the negative BOLD response (NBR) evoked by a brief stimulus, have been reported as an inverted version of the corresponding positive HRF (pHRF). With a careful delineation of the nHRF from the stimulus representation (SR), we found that the nHRF adjacent to the SR was not the inverted version of the corresponding pHRF. We also characterized the nHRF with respect to the depth and found inverse proportion of the nHRF amplitudes between contralateral and ipsilateral sides, which can indicate different underlying mechanisms of the nHRF.