Hippocampal conditioned responses in the absence of entorhinal input.

Hippocampal unit responses to conditioned stimuli were analyzed in intact rats and in rats deprived of the input from the entorhinal cortex to the hippocampus. Cells in normal rats responded more intensely to a conditioned stimulus when it was applied within 1 min from a previous one. The rats with lesions had smaller conditioned hippocampal responses and, in addition, there were no differences between responses to stimuli applied after short or long intertrial intervals. No effects on gross conditioned behavior were noticed.