Paired associate learning in the rat: Role of hippocampus, medial prefrontal cortex, and parietal cortex

Abstract

Rats were tested for their ability to learn a list of four paired associates (foods paired with spatial locations). In this task, rats display increased levels of correct orienting responses as a function of serial position of the paired associate within the list (temporal order function) when short inter-trial intervals are used between paired associates. Furthermore, the rats are more likely to use intramaze rather than extramaze cues. These data suggest that rats utilize a temporal strategy to remember a list of paired associates. After training in this task, new rats received medial prefrontal cortex, hippocampus, parietal cortex, or cortical control lesions and were retested. The data indicate that rats with cortical control lesions continued to display a temporal order function, whereas rats with medial prefrontal cortex lesions showed a reduction in the number of correct orienting responses and failed to demonstrate the temporal order function, suggesting that the medial prefrontal cortex might mediate the selection of temporal strategies. Rats with hippocampal lesions also showed a marked reduction in level of correct orienting responses, but they continue to display a temporal order function, suggesting that these rats can still utilize a temporal strategy, but may have difficulties in remembering the appropriate paired associate items. Rats with parietal lesions did not display any significant changes in their temporal order function.