Reward Association Affects Neuronal Responses to Visual Stimuli in Macaque TE and Perirhinal Cortices

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To study the roles of the perirhinal cortex (PRh) and temporal cortex (area TE) in stimulus-reward associations, we recorded spike activities of cells from PRh and TE in two monkeys performing a visually cued go/no-go task. Each visual cue indicated the required motor action as well as the availability of reward after correct completion of the trial. Eighty object images were divided into four groups, each of which was assigned to one of four motor-reward conditions. The monkeys either had to release a lever (go response) or keep pressing it (no-go response), depending on the cue. Each of the go and no-go trials could be either a rewarded or unrewarded trial. A liquid reward was provided after correct responses in rewarded trials, whereas correct responses were acknowledged only by audiovisual feedback in unrewarded trials. Several measures of the monkeys' behavior indicated that the monkeys correctly anticipated the reward availability in each trial. The dependence of neuronal activity on the reward condition was examined by comparing mean discharges to each of the 40 rewarded stimuli with those to each of the 40 unrewarded stimuli. Many cells in both areas showed significant reward dependence in their responses to the visual cues, and this was not likely attributable to differences in behavior across conditions because the variations in neuronal activity were not correlated with trial-by-trial variations in latency of go responses or anticipatory sucking strength. These results suggest the involvement of PRh and TE in associating visual stimuli with reward outcomes.