The hippocampus, collateral behavior, and timing.

Rats with hippocampal lesions (HC), cortical control lesions, or sham operations were trained to lever press on a differential reinforcement of low rates (DRL) schedule requiring 12 sec between responses. In four experiments, factors affecting performance efficiency in this paradigm were manipulated. Providing extra opportunities for collateral mediating behavior (Experiment 1) aided all groups nondifferentially. Adding a limited hold (Experiment 2) or administering chlordiazepoxide HCl (Experiment 3) reduced DRL efficiency in all groups nondifferentially. However, adding an auditory stimulus marking the halfway point in the DRL requirement (Experiment 4) differentially aided the HC group. The implications of these findings for different theories of hippocampal function are discussed.