Hippocampal lesions and trace conditioning in the rabbit.

Trace conditioning of the nictitating membrane response (NMR) was examined in rabbits with lesions of the dorsal hippocampus and fimbria-fornix. Using a white noise conditional stimulus and an electrical shock unconditional stimulus, the number and amplitude of conditional responses (CRs) was similar in hippocampus-lesioned and control subjects. At some stages of conditioning, the latencies of CRs from hippocampus-lesioned subjects were slightly shorter than those of the controls. We suggest that the hippocampus is not essential for trace conditioning but may exert a modulatory influence on the timing of the CR.