What is the difference between episodic memories and semantic memories?

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Patient H.M. and short-term memory loss explained — hippocampus Learn about Henry Molaison (better known as “patient H.M.”), whose short-term memory loss following a lobotomy helped researchers to understand how brain structures are related to brain function.

The hippocampus is a critical region of the brain involved in the formation and storage of long-term, declarative memories—those related to facts and events. Within the study of memory, researchers distinguish between two primary types of declarative information:

Episodic memories: These are context-rich experiences. They involve the ability to consciously recollect specific events, often described as a form of "mental time travel" during recall. According to the multiple trace theory, the hippocampus remains essential for the long-term retrieval of these detailed, context-dependent memories.1
Semantic memories: These are often referred to as "gist" memories, consisting of general facts or knowledge that are not necessarily tied to a specific time or place. Unlike episodic memories, the multiple trace theory suggests that the hippocampus is not required for the long-term recall of these types of memories.1

While there is broad consensus that the hippocampus is vital for memory, the exact mechanisms—such as whether it acts as an index for distributed information or binds contexts into unified experiences—remain a subject of ongoing scientific debate.1