In fact, the late suppression (starting ∼140 ms after stimulus onset) as well as the link to perceptual processes fit well with late effects of a top-down feedback into V1. It is commonly thought that feedback connections from higher visual areas (Bullier et al., 2001; Li et al., 2006) are mainly excitatory. Some of these excitatory feedback input can influence local inhibitory neurons and thus induce a feedback inhibition (Isaacson and Scanziani, 2011). Another possible explanation is that background suppression is mediated

by a decreased excitatory feedback: a background input whose role is to reduce the gains of single neurons (Chance et al., 2002). Additional studies are required to better understand the source of the background suppressive phenomenon. In summary, we have shown that during contour integration there is a strong divergence of V1 population responses processing the contour or the noisy background. GS-7340 solubility dmso The neuronal population in the contour area increases its response amplitude and is positively correlated with behavior, while the background displays opposing characteristics, suppressed activity, and a negative correlation with behavior. These opposing 3-Methyladenine molecular weight processes increase the difference in neuronal activity between the contour and the noisy background and thus

may improve contour segregation from a noisy background and facilitate its perception. Additional information appears in Supplemental Experimental Procedures. Two adult monkeys (Macaca fascicularis; S, L) were Thalidomide trained on a contour-detection task. The trial started when the animal fixated on a small fixation point displayed on a uniform gray background. After a random fixation interval, a contour or noncontour stimulus appeared on the screen for 250–1,000 ms. The animal maintained fixation until the stimulus and fixation point were turned off. At this point, two small lateral targets appeared, one on each side

of the screen, and the animal was required to indicate its visual perception by performing a rightward saccade for a contour report and leftward saccade for noncontour report. A trial was classified as correct only if the animal maintained fixation throughout the trial, responded with a saccade to the correct target, and fixated on the target for an additional 400 ms. The animal was rewarded with a drop of juice for each correct trial. In each recording session, the contour and noncontour stimuli appeared in 80% of the trials, while the remaining 20% trials were fixation-alone trials (no stimulus presentation, blank condition). These trials were used to remove the heart beat artifact in the VSDI analysis (see VSDI analysis below). Detection performance is defined as the number of correct trials divided by total number of trials (sum of contour and noncontour trials). The average detection performance was 91% (2% misses, i.e.