While the origin of negative BOLD response in fMRI has been debated, we present an explanatory biophysical model that accounts for imaging and physiological parameters, including vascular-orientation, CBV change, TR, TE, inflow and even different oxygenation levels in arterial and venous compartments. This model shows that it is possible for negative BOLD to arise from both arterial and venous sources even in the presence of neural-activity increase. This abstract suggests part of the negative BOLD response originates simply from the vascular origin of the signal.
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