Hippocampal ablation and passive avoidance.

Six rats with bilateral ablation of the hippocampus and six rats with extensive destruction of the neocortex were trained to enter a small compartment, while hungry, for a food reward. After 35 trials, spread over 4 days of training, the animals were given a shock while they were eating in the goal box. After the shock the rats with cortical lesions would not enter the goal compartment on the remainder of the trials given on the same day and only gradually began to re-enter over the next 2 days. The effect of the shock on the subjects with hippocampal ablation was slight and transient, suggesting that the ability to make passive avoidance responses was impaired.