Effects of medial prefrontal cortex and dorsal striatum lesions on retrieval processes in rats

Exposure to training-related cues is known to reactivate associated memory and improves subsequent retention performance under various circumstances. The present studies investigated the neural basis of retrieval cue effects, by studying in two separate experiments, the involvement of the medial prefrontal cortex and of the dorsal striatum. Rats with lesions to the prelimbic-infralimbic cortex (PL-IL), to the anterior dorsal cingulate (ACd), and to the lateral and medial parts of the dorsal striatum (IDS and mDS) were first trained in a brightness discrimination avoidance task. One day later, rats were tested after being placed in the cueing box with either no training-related cue or with additional exposures to the light discriminative stimulus. None of the lesions affected the acquisition performance. During the retention test, control rats cued with the light in the box exhibited significantly better retention performance than those simply placed in the box, confirming our previous results. While mDS lesions did not modify effects of the retrieval cue, IDS as well as both PL-IL and ACd lesions blocked the facilitative effects of the discriminative stimulus. The present data indicate that ACd, PL-IL and IDS are involved in processes promoted by exposure to training cues, the nature of which are reviewed and discussed. This study in conjunction with previous ones suggests that retrieval cues activate several subcircuits mainly based on an amygdalo-prefrontal-striatum network. Activation of this network results in an improvement of the expression of the associated conditioned response, and may thus be viewed as increasing the efficacy of the retrieval processes. (C) 2004 IBRO. Published by Elsevier Ltd. All rights reserved.