The hippocampus is the human brain structure shaped roughly like a seahorse and named from the Greek word for seahorse.
The name combines hippos, meaning horse, and kampos, a sea monster or seahorse. Each cerebral hemisphere contains a hippocampus in the medial temporal lobe. The structure is part of a larger formation involved in learning and memory, spatial navigation, and the organization of experiences.
The hippocampus became especially prominent in neuroscience after studies of patient Henry Molaison, long known by his initials H.M. Surgery in 1953 removed much of both hippocampi to treat severe epilepsy. H.M. developed profound difficulty forming many new long-term memories, demonstrating that memory is not a single, unified ability.
The hippocampus is not a permanent storage site for every memory. Current research describes it as especially important for forming and retrieving episodic memories and for binding details such as place, time, and context. Other cortical systems help support long-term storage and recall.