Backward spreading of memory-retrieval signal in the primate temporal cortex

Bidirectional signaling between neocortex and Limbic cortex has been hypoth esized to contribute to the retrieval of Long-term memory. We tested this h ypothesis by comparing the time courses of perceptual and memory-retrieval signals in two neighboring areas in temporal cortex, area TE (TE) and perir hinal cortex (PRh), while monkeys were performing a visual pair-association task. Perceptual signal reached TE before PRh, confirming its forward prop agation. In contrast, memory-retrieval signal appeared earlier in PRh, and TE neurons were then gradually recruited to represent the sought target. A reasonable interpretation of this finding is that the rich backward fiber p rojections from PRh to TE may underlie the activation of TE neurons that re present a visual object retrieved from Long-term memory.