Recognition Memory for Objects, Place, and Temporal Order: A Disconnection Analysis of the Role of the Medial Prefrontal Cortex and Perirhinal Cortex

TLDR

Recognition memory relies on judging prior stimulus occurrence by relative familiarity of individual objects, integrating object–location information, or using recency cues. The study examined how the medial prefrontal cortex and perirhinal cortex contribute to these distinct recognition processes through novel‑object preference, object‑in‑place, and temporal‑order tasks. Using a disconnection procedure, male DA rats received bilateral lesions in PRH or mPFC, unilateral lesions in both cortices ipsi‑ or contralaterally, and a sham group to test integrated system function. PRH, mPFC, and contralateral PRH–mPFC disconnection groups were impaired in object‑in‑place and temporal‑order tasks, only the PRH group was impaired in novel‑object preference, showing that mPFC and PRH are essential for associational and recency discriminations while only PRH is needed for novel‑object discrimination, supporting an integrated recognition‑memory network.

Abstract

Recognition memory requires judgments of the previous occurrence of stimuli made on the basis of the relative familiarity of individual objects, or by integrating information concerning objects and location, or by using recency information. The present study examined the role of the medial prefrontal cortex (mPFC) and perirhinal cortex (PRH) in these distinct recognition memory processes using a series of behavioral tests: a novel object preference task, an object-in-place task, and a temporal order memory task. Also, a disconnection procedure was used to test whether these regions form components of an integrated system for recognition memory. Male DA rats received bilateral lesions in the PRH or mPFC or unilateral lesions placed in both cortices in either the same (PRH–mPFC IPSI) or contralateral (PRH–mPFC CONTRA) hemispheres. A fifth group underwent sham surgery (SHAM). In the object-in-place and temporal order memory tasks, the PRH, mPFC, and PRH–mPFC CONTRA groups were significantly impaired. However, performance in the novel object preference task was only impaired in the PRH group. No group was impaired in the object location task. These results demonstrate that the mPFC and PRH are crucial for object-in-place associational and recency discriminations, whereas the PRH but not the mPFC is important for the discrimination of novel and familiar individual objects. Importantly, these results provide direct support for the hypothesis that to make discriminations based on associational or recency information, both cortical regions operate within an integrated neural network for recognition memory.