The hippocampus, a seahorse-shaped structure in the medial temporal lobe, is perhaps the most important brain structure for memory research. It is essential for the formation of new episodic and semantic memories (declarative memory), spatial navigation, and the contextual binding of disparate elements into coherent memory representations. The profound amnesia of patient H.M. following bilateral hippocampal removal established its central role in memory formation.
Functions
The hippocampus serves as a rapid learning system that binds together the distributed cortical representations of an experience (sights, sounds, emotions, context) into a coherent memory trace. It supports pattern separation (distinguishing similar memories), pattern completion (retrieving a complete memory from a partial cue), and memory consolidation (gradual transfer of memories to neocortical storage). In spatial cognition, place cells fire when the animal is at specific locations, and grid cells in the entorhinal cortex provide a spatial coordinate system.
The hippocampus (specifically the dentate gyrus) is one of the few brain regions where new neurons are produced throughout life — adult neurogenesis. Exercise, environmental enrichment, and learning increase hippocampal neurogenesis, while stress and depression decrease it. Though the functional significance of adult neurogenesis in humans remains debated, it may contribute to the formation of new memories and the separation of similar memory traces.