BILATERAL ENTORHINAL CORTEX LESIONS IMPAIR DRL PERFORMANCE IN RATS

The entorhinal cortex participates in a variety of spatial and locomot or behaviors that are thought to be mediated by the hippocampal format ion. The present study examined the possibility that the entorhinal ar ea contributes to the maintenance of an operant behavior in which the hippocampus is also implicated-differential reinforcement of low-rate responding (DRL). Rats with bilateral entorhinal cortex lesions or sha m operations were tested for retention of a preoperatively learned DRL (10-sec delay) task. Rats with entorhinal lesions were impaired on me asures of response rate, temporal discrimination, and response efficie ncy for 2 to 3 weeks after surgery. Histological analyses indicated th at all the rats sustained complete entorhinal lesions. The entorhinal cortex may be an important component of the hippocampal formation cont ributing to the performance of DRL tasks.