A comparison of normal old rats and young adult rats with lesions to the hippocampus or prefrontal cortex on a test of matching-to-sample.

Rats with lesions to the dorsal hippocampus (HPC) or prefrontal cortex (PFC), normal old rats, and young adult controls were compared on a test of matching-to-sample. Subjects were presented with two lights in succession and were trained to press a lever when the lights were the same brightness and withhold a lever-press when they were different. The PFC and aged groups, but not the HPC group, were impaired when the comparison stimulus was presented immediately after the sample stimulus. When delays of 5 and 15 sec were introduced between the stimuli, the HPC and aged groups' performance deteriorated to chance levels. The PFC group's performance was not differentially affected by the delays. The results were consistent with previous findings that implicated the HPC in episodic memory and the PFC in working memory. The aged group was impaired on both types of memory, revealing signs of HPC and PFC dysfunction.