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Abstract

Previous studies demonstrated negative BOLD response beyond the stimulated regions in V1, V2 and V3 in humans and anesthetized monkeys. Here we demonstrate negative BOLD response in alert monkey early visual areas. Monkeys were trained to stay still during 20 s long trials. Each trial began with 3 s in which a blank gray image was presented, followed by the presentation of a fixation spot (0.15 degrees radius) for 3 s, and a stimulus for 4 s. The stimulus consisted of rotating checkers pattern bound between eccentricities of 2 and 4 degrees. The animals fixated within 1 degree from the fixation spot. A blank gray image was presented during the last 10 s of each trial. A surface coil (40 mm diameter) was positioned in proximity to the operculum of one hemisphere. fMRI was conducted in a vertical bore Bruker 7T magnet, using a GE-EPI sequence.
Increased activity (2.5) was observed within the V1, V2, and V3 representations of the stimulated regions in the visual space. Negative BOLD response was detected in these areas in regions corresponding to more peripheral eccentricities. We are currently conducting experiments to further characterize this negative BOLD response.