SELECTIVE HIPPOCAMPAL-LESIONS IN RATS DO NOT AFFECT RETRIEVAL-PROCESSES PROMOTED BY PRIOR CUEING WITH THE CONDITIONED-STIMULUS OR THE CONTEXT

Following partial training in an avoidance brightness discrimination t ask in a Y-maze, the retention performance can be enhanced by a pretes t exposure to various training features (prior cuing). The effectivene ss of these cues may vary as a function of the length of the retention interval. These results demonstrate that prior cuing promotes the ret rieval of the memory trace and that the memory trace is submitted to a long-lasting time-dependent reorganization. The present experiments w ere designed to examine the involvement of the hippocampal formation i n retrieval processes promoted by prior cuing. Rats with bilateral ibo tenic acid hippocampal lesions and sham-operated rats were postoperati vely trained in the avoidance brightness discrimination task. Retrieva l processes promoted by prior cuing were not affected by hippocampal l esions: After a 1-day training-to-test interval (TTI), the rats in bot h conditions demonstrated a dramatic improvement of retention performa nce following a pretest exposure to the conditioned stimulus (CS; Expe riment 1). After a 21-day TTI, exposure to the CS was no longer effect ive, and a pretest exposure to the experimental context enhanced perfo rmance (Experiment 2). In contrast, when the lesioned rats were tested in a radial arm maze task, they showed severely impaired performance, demonstrating the effectiveness of the hippocampal lesions on behavio r. These results demonstrated that damage to the hippocampus does not disrupt the promotion of retrieval processes by prior cuing. In partic ular, the lesions did not prevent the rats from being able to relate t he CS and the experimental context to the initial training episode. Th e fact that the hippocampal lesions also did not disrupt time-dependen t changes in the effectiveness of certain retrieval cues suggests that this structure is not involved in the long-term maturation processes evidenced by prior cuing.