Retrograde amnesia following hippocampal lesions in the shock-probe conditioning test

The present experiment examined the role of the hippocampal formation (HPC) in long-term memory of an association between an object and a fear-eliciting event. Rats either received sham or neurotoxic lesions of the HPC 1 or 14 days after learning that contacting a wire-wrapped probe (i.e., object) elicits a shock. After recovery from the surgery, rats were re-exposed to the wire-wrapped probe and burying and avoidance of the probe were assessed and used as memory and fear indices. Regardless of the learning-to-surgery interval, the rats with hippocampal lesions buried and avoided the probe significantly less than sham rats and no more than rats that never experienced shock from the probe. These findings suggest that the lesions caused severe retrograde amnesia and that the HPC has a long-lasting role in memory of a discrete stimulus associated with a fear-eliciting event.