Two monkeys were trained on a contour-detection task (see Experimental Procedures). In each trial, the monkeys were

presented with one of two visual stimuli and were required to discriminate between a contour and a noncontour stimulus (Figure 1A). The stimulus in the contour trials was comprised from a circular contour (“circle”) embedded within an array of randomly oriented and positioned Gabor elements (“background”). In the noncontour trials, the stimulus was composed from background alone, with the background elements identical to the contour condition, while the circle elements were randomly rotated along the circle path (Figure 1A; Experimental Procedures). The monkeys could easily perform the task (reaching a

detection performance PD0332991 datasheet of 80%–91%), while we imaged the population responses in V1 at high spatial and temporal resolution using voltage-sensitive dye imaging (VSDI). The dye signal measures the sum of membrane potential from all neuronal elements in the imaged area. Therefore, the voltage-sensitive dye (VSD) signal from each pixel sums the membrane potential from neuronal selleckchem populations (rather than single cells) emphasizing subthreshold synaptic potentials (Grinvald and Hildesheim, 2004). Data analysis was performed on a total of 30 and 22 recording sessions from two hemispheres of two monkeys. To study the population responses in the contour and noncontour trials, we first needed to retinotopically map the visual stimuli onto the V1 area (see Experimental Procedures). The stimulus part that is mapped onto V1 imaged area is approximately outlined by a yellow rectangle in Figures 1A and 1B. This part of the stimulus includes few Gabor elements comprising part of the circle and the background. To map these elements onto the imaged area, we performed another set of experiments, where the monkeys were passively fixating

and briefly presented on each trial with one or two individual Gabor elements comprising parts of the circle or background (Figure 1C, top row). The VSDI-activation maps, i.e., population-response maps, evoked by the Gabor elements belonging to the circle (C1–C3) and background (Bg1–Bg3) allow easy visualization and accurate localization of individual Gabor elements on V1 (Figure 1C, bottom row). Figure 1D shows Linifanib (ABT-869) an early-activation map evoked by the contour stimulus, where the activation patches over V1 clearly corresponded to the individual Gabor elements in the circle and background. We defined two regions of interest (ROIs; Figure 1D): (1) A circle area (C) was defined by contouring the area in V1 that was activated by the circle elements (C1–C3). (2) A background area (Bg) was defined by contouring the area in V1 that was activated by the background elements (Bg1–Bg3). The retinotopic mapping enabled us to analyze the population responses (VSDI amplitude) in the circle and background area evoked in the contour-detection task.