Why do some scientists think the hippocampus remains necessary for recalling episodic 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.

Some scientists argue that the hippocampus remains necessary for recalling episodic memories based on the multiple trace theory.1

While the standard model of systems consolidation suggests that long-term memories eventually become independent of the hippocampus as the cortex takes over, the multiple trace theory posits that the hippocampus is continuously required for the retrieval of context-rich, episodic memories. In contrast, this theory suggests that the hippocampus is not necessary for the recall of semantic or gist-based memories, which may become independent of the structure over time.1

Additionally, some research indicates that the hippocampus plays a specific role in conscious recollection—the experience of "mental time travel"—which is a hallmark of episodic memory. Other perspectives suggest the hippocampus acts as an index that binds together the various elements of an experience, maintaining these connections to support the retrieval of unified, context-heavy memories.1