The BOLD contrast is widely used to study brain function. Under externally-applied stimuli, positive BOLD responses (PBR) are generally attributed to local increases in brain activity. Negative BOLD responses (NBR) are also frequently observed, but their underlying neurovascular-coupling mechanisms are less well-understood. Here, we study the NBR to contrast-varying visual stimuli. Both intra-modal (located in regions directly associated with the stimulus) and cross-modal responses (located in functionally-distinct regions) are analyzed.