There is increasing evidence that white matter (WM) elicits robust blood oxygenation level-dependent (BOLD) responses to task in functional MRI. However, the detection of BOLD signals in WM has usually assumed a canonical hemodynamic response function (HRF) as in gray matter (GM), which contributes to low sensitivity in detection of WM activation. We demonstrate in this work that the HRFs in WM possess reduced magnitudes, delayed onsets and prolonged initial dips in WM tracts that are connected with task activated GM, thus calling for alternate data analyses in exploring WM activity.
