Abstract

When you see an object, not only do you perceive its physical appearance but also experience a non-physical impression such that distinguishes an old friend from strangers. Perirhinal cortex, the final stage of visual object processing, is essential for perception and memory of visual objects as revealed by lesion studies, but its mechanisms remain unclear. To study the underlying neuronal processing, we recorded neuronal activities in the perirhinal cortex of macaque monkeys and found neurons selectively representing the memories of visual objects. To examine how the perirhinal cortex activity causally influences behaviour, we optimised optogenetic techniques for macaque monkeys, and used those while the monkeys were performing a memory judgement task. Surprisingly, optogenetic activation of the perirhinal cortex neurons caused monkeys to judge any presented object as “seen before” even when the monkeys had not seen that object before. This result suggests that perirhinal cortex neurons output a semantic feature of learned objects i.e., ‘familiarity’ to be used for judgements about objects. To determine the output circuits of the perirhinal cortex and how those circuits guide perceptual and memory judgements, my group has begun to study common marmosets, a small primate species highly suited for optical circuit-interrogation technologies. In the seminar, I will discuss my previous works in macaques and current attempts in marmosets.