The striatum and beyond: contributions of the hippocampus to decision making

Recent research on the neural bases of decision making has focused on the role of the striatum and dopamine in learning to predict and obtain rewards. These studies have illuminated the processes by which repeated experiences of choice and reward feedback lead to the updating of value representations, allowing an organism to use past experience to improve choices when encountering the same situation. However, in a constantly changing environment, choices may not repeat themselves. Instead, decisions often involve novel contexts and options, requiring flexible generalization of past experience to novel choices. Extensive evidence from studies of the neural bases of learning and memory suggests that flexible use of learned knowledge depends on a “declarative” memory system in the hippocampus. Investigations of the neural bases of decision making and of memory systems have developed largely independently of each other. However, there are a number of important links between them, at both the brain and behavioral levels. Here, we briefly review these two literatures and propose a critical role for the hippocampus in decision making when past experience must be flexibly generalized to new situations. Further, we suggest that dopamine modulates learning in both the striatum and the hippocampus, with these two systems working together to adaptively guide choices. Finally, we present behavioral evidence from a novel paradigm designed to probe the role of hippocampal-dependent memory in decision making. The findings demonstrate that past experience can flexibly guide decision making in novel contexts, indicating a possible cooperation between reinforcement history and declarative memories in guiding decision making.