Dorsal, but not ventral, hippocampal inactivation alters deliberation in rats

When facing a choice at a decision point in a maze, rats often display hesitations, pauses and reorientations. Such "vicarious trial and error" (VTE) behavior is thought to reflect decision making about which choice option is best, and thus a deliberation process. Although deliberation relies on a wide neural network, the dorsal hippocampus appears to play a prominent role through both its neural activity and its dynamic interplay with other brain areas. In contrast, the involvement of the ventral hippocampus in deliberation is unexplored. Here, we compared directly the effects of dorsal (dHPC) and ventral intermediate (vHPC) hippocampal inactivations induced by intracerebral muscimol injections on VTE behavior as a model of deliberation. To this aim, we analyzed VTE events as rats were required to switch strategy to a new unlearned reward rule. We used a protocol in which task performance in muscimol-injected animals was minimally altered so as to evidence specific effects on VTE behavior. Our results show subtle alterations in VTE behavior following dHPC, but not vHPC, inactivations, therefore suggesting a specific contribution of the dorsal hippocampus to deliberation through its role in prospective evaluation of future actions.