Generalization and the hippocampus: More than one story?

Memory-based cognition depends on both the ability to remember specific details of individual experiences and the ability to combine information across experiences to generalize and derive new knowledge. A hippocampal role in rapid encoding of specific events is long established. More recent research also demonstrates hippocampal contributions to generalization, but their nature is still debated. The current review provides an overview of hippocampal-based generalization in two lines of research-episodic inference and categorization-and discusses evidence for four candidate mechanisms and representational schemes that may underpin such generalization. We highlight evidence showing that the hippocampus contributes specific memories to generalization decisions, but also forms generalized representations that integrate information across experiences. Multiple views are currently plausible of how such generalized representations form and relate to specific memories. Future research that uses behavioral and neural indices of both generalization and specificity may help resolve between the candidate generalization mechanisms, with the possibility that more than one view of hippocampal-based generalization may be valid. Importantly, all views share the emphasis on the broader role of the hippocampus in cognition that goes beyond remembering the past.