Increased activity in human visual cortex during directed attention in theabsence of visual stimulation

When subjects direct attention to a particular location in a visual scene, responses in the visual cortex to stimuli presented at that location are en hanced, and the suppressive influences of nearby distracters are reduced. W hat is the top-down signal that modulates the response to an attended versu s an unattended stimulus? Here, we demonstrate increased activity related t o attention in the absence of visual stimulation in extrastriate cortex whe n subjects covertly directed attention to a peripheral location expecting t he onset of visual stimuli. Frontal and parietal areas showed a stronger si gnal increase during this expectation than did visual areas. The increased activity in visual cortex in the absence of visual stimulation may reflect a top-down bias of neural signals in favor of the attended location, which derives from a fronto-parietal network.