Effects of Large and Small Bilateral Hippocampal Lesions on Two Types of Passive-Avoidance Responses

Ten rats with large bilateral hippocampectomies, 10 rats with smaller amounts of damage of the dorsal hippocampus, 10 rats with destruction of postero-lateral neocortex, and 15 normal animals were trained in two types of passive-avoidance situations. One passive-avoidance task required inhibition of drinking while thirsty, the other required an animal to refrain from entering a small compartment after i: had been trained to enter, while hungry, for a food reward. Animals with the largest amounts of hippocampal destruction were impaired in both types of problems. Animals with smaller degrees of hippocampal damage were not different from normal animals in their ability to inhibit licking but were impaired in the other task. Animals with neocortical destruction showed impairment only in the licking situation.