Contribution of dorsal versus ventral hippocampus to the hierarchical modulation of goal-directed action
Adaptive behavior often necessitates that animals learn about events in a manner that is specific to a particular context or environment. These hierarchical organizations allow the animal to decide which action is the most appropriate when faced with ambiguous or conflicting possibilities. This study examined the role of hippocampus in enabling animals to use the context to guide action selection. We used a hierarchical instrumental outcome devaluation task in which male rats learn that the context provides information about the unique action-outcome relations that are in effect. We first confirmed that rats encode and use hierarchical context-(action-outcome) relations. We then show that chemogenetic inhibition of ventral hippocampus (vHPC) impairs both the encoding and retrieval of these associations, while inhibition of dorsal hippocampus (dHPC) impairs only the retrieval. Importantly, neither dHPC or vHPC were required for goal-directed behavior per se as these impairments only emerged when rats were forced to use the context to identify the current action-outcome relationships. These findings are discussed with respect to the role of the hippocampus and its broader circuitry in the contextual modulation of goal-directed behavior and the importance of hierarchical associations in flexible behavior.