Responses of inferior temporal cortex and hippocampal neurons during delayed matching to sample in monkeys (Macaca fascicularis).

Single-unit activity was recorded from inferior temporal (IT) cortex and the hippocampus in 2 macaques trained on auditory-visual and visual-visual delayed matching-to-sample tasks. The main purpose of the study was to compare the response properties of delay neurons between the 2 areas. The authors noted that (a) IT cortex delay activity was usually selective to a particular stimulus, whereas hippocampal delay activity was usually nonselective; (b) the level of delay activity was generally larger in the hippocampus than in IT cortex; and (c) unlike IT cortex delay activity, hippocampal delay activity tended to increase in magnitude as the delay progressed. The authors also examined the functional significance of delay activity and noted a higher probability of encountering a delay neuron when the monkeys were performing 75%-100% correct as compared with 50%-75% correct. The significance of these findings for visual recognition memory is discussed.