Perirhinal and postrhinal, but not lateral entorhinal, cortices are essential for acquisition of trace eyeblink conditioning.

The acquisition of temporal associative tasks such as trace eyeblink conditioning is hippocampus-dependent, while consolidated performance is not. The parahippocampal region mediates much of the input and output of the hippocampus, and perirhinal (PER) and entorhinal (EC) cortices support persistent spiking, a possible mediator of temporal bridging between stimuli. Here we show that lesions of the perirhinal or postrhinal cortex severely impair the acquisition of trace eyeblink conditioning, while lateral EC lesions do not. Our findings suggest that direct projections from the PER to the hippocampus are functionally important in trace acquisition, and support a role for PER persistent spiking in time-bridging associations.