Heterogeneous representations in the hippocampus

•CA1 pyramidal cells represent both space and context.•During encoding, distinct subsets of CA1 neurons are allocated to contextual indexing and spatial mapping.•The hippocampal role in memory might not be unitary rather heterogeneous. The hippocampus is essential for some types of memory, but its specific role remains conjectural. While studies on place cells have supported the hypothesis that the hippocampus provides a spatial substrate for episodic memory, recent engram studies have shown that optogenetic activation of a subset of hippocampal neurons that lack a temporal structure of the spike sequences can also induce memory-associated behavior. In this short review, I discuss the various lines of research that have led to different views of the role of the hippocampus in memory and propose a plausible interpretation of the findings that incorporates two influential theories.