Two male adult macaque monkeys were used in this study. Standard operant conditioning techniques were used to train the subjects to fixate and to press buttons for a small liquid reward. Eye movements were recorded using the EyeLink II video tracking system Proton pump inhibitor (SR Research, Osgoode, Ontario, Canada) running at 500 Hz. When the monkeys were ready for recordings, we implanted custom chambers that allowed for a dorsal access to ITC (Horsley-Clark coordinates, +15 anterior, +20 lateral). Based on reconstructed

electrode trajectories, we believe most of our recordings took place from the lateral convexity of ITC, ventral to the lower bank of the superior temporal sulcus (STS) and lateral to the perirhinal cortex (Figure S2). Recordings were obtained with fine tungsten microelectrodes (Alpha Omega Engineering, Alpharetta, GA, USA, or Frederic Haer Company, Bowdoinham, ME, USA). Single units were isolated online using a threshold and dual-amplitude windows, while analog signals were streamed to disk for offline

analysis. All stimuli used were taken from Hemera Photo-Objects Vols. 1, 2, and 3 (Hemera Technologies), subtended about 2° × 2° of visual angle at a viewing distance of 90 cm, and were presented centrally on top of a uniform gray background. Both monkeys were familiarized with the same set of 125 stimuli (Figure S1A). During the familiarization phase the monkeys saw the images in either a passive fixation task or in a delayed match-to-sample task. When the familiarization click here phase was completed, we began the recordings. All recordings were obtained during a passive fixation task in which eye position was constrained to be within 1° of the center of the screen, as ten stimuli (no repeats) were presented. At the end of the stimulus presentation epoch, an extrafoveal square target was presented (eccentricity = 6°) to which the monkey had to saccade to obtain its juice reward. Because the goal of this experiment was to compare neuronal responses to familiar and novel stimuli, for every recording

session we selected a new set of 125 never before seen stimuli. Although the selection process Ribavirin was random, we used the scale invariant feature transform and the dot product of normalized color histograms to eliminate from this novel set stimuli which looked either too similar to the familiar ones or to one another (see Supplemental Experimental Procedures). We attempted to record from every well-isolated and visually responsive unit in ITC. To avoid a neuronal selection bias, the vast majority of visually responsive units (n = 40/50, 80% for monkey D; n = 35/38, 92% for monkey I) were found and isolated with an independent set of 50 initially novel stimuli that gradually became familiar as the recording sessions accumulated. Thus, the results presented here are not a consequence of selecting units that we knew ahead of time would be responsive to familiar items.