# Proof Narrative: Hippocampal damage leads to anterograde amnesia for new episodic memories and does not impair skill learning or retrograde memories from early life.

## Verdict

**Verdict: PROVED (with unverified citations)**

One of the most replicated findings in neuroscience holds up: hippocampal damage breaks the ability to form new memories while leaving older memories and learned skills intact.

## What was claimed?

The claim is that damage to the hippocampus — a small, seahorse-shaped structure deep in the brain — produces a very specific pattern of memory loss. A person with such damage would be unable to remember new experiences after the injury, yet would still be able to learn new physical skills, and would retain memories from childhood and early life. This matters because it tells us something fundamental about how memory works: not all memory is the same, and not all of it depends on the hippocampus.

## What did we find?

The story of this claim is largely the story of one man: Henry Molaison, known for decades simply as "H.M." In 1953, surgeons removed large portions of his hippocampus on both sides of his brain to treat severe epilepsy. What followed transformed neuroscience.

After surgery, H.M. could hold a thought for a moment, but new experiences simply did not stick. He forgot daily events nearly as fast as they occurred. Every morning was, in a sense, his first morning after the operation. He could have a conversation, leave the room, and return minutes later with no memory of ever speaking to the person before him. This is anterograde amnesia — the inability to form new long-term memories — and it was present in H.M. in its most severe form.

Yet something surprising emerged. When researchers had H.M. practice a task called mirror tracing — drawing a shape while only able to see his hand's reflection — he got better day after day. His error rate declined across sessions just as it would for anyone learning a new skill. The remarkable part: each time he sat down to practice, he had no memory of having done it before. His hands knew what his mind did not. This demonstrated that skill learning — the kind of procedural, motor memory involved in riding a bike or playing piano — is stored and retrieved through circuits that do not depend on the hippocampus.

His past, too, was largely intact. Memories from his childhood, from early life before the surgery, were preserved. He could recall people, places, and events from decades earlier. The damage had not reached back to erase what was already stored. This pattern — where older memories survive while new ones cannot be formed — is exactly what you would predict if the hippocampus is required to encode new memories but not to store consolidated ones.

Two independent sources confirm each of these three findings. Wikipedia's article on Henry Molaison states directly that he "developed severe anterograde amnesia: although his working memory and procedural memory were intact." The Society for Neuroscience's BrainFacts.org confirms he "retained the ability to form non-declarative memories, which took the form of improvement in motor skills." For his preserved childhood memories, Wikipedia's article on anterograde amnesia is unambiguous: "He could remember anything from his childhood."

## What should you keep in mind?

Two of the five citations used in this proof could not be URL-verified — meaning the quoted text could not be confirmed at the live webpage. However, each unverified source supports a finding that is independently confirmed by at least one fully verified source, so no conclusion rests on unverified material alone.

The claim concerns classic motor skill learning, and the evidence is strong for that domain. Some research suggests the hippocampus may play a role in more complex forms of procedural learning — particularly tasks involving probabilistic sequences — so the finding does not extend to every possible meaning of "skill learning."

On early-life memories: the preserved-childhood-memories finding applies to autobiographical, episodic memories. Spatial navigation memory may be a separate case — there is evidence that hippocampal damage can impair remote spatial memories even when acquired early in life. The claim as stated holds for autobiographical memories but should not be read as a blanket guarantee for all memory types from early life.

Finally, H.M.'s surgery removed tissue beyond just the hippocampus, including parts of the amygdala. Later research on patients with more selective hippocampal damage confirmed the hippocampus-specific role, but it is worth knowing that H.M.'s case is not a surgically clean isolation.

## How was this verified?

This claim was evaluated as a compound statement requiring three independent sub-claims to each be confirmed by at least two independent sources, with adversarial searches conducted to look for evidence that could break any part of the proof. You can read [the structured proof report](proof.md) for the full evidence summary and reasoning, review [the full verification audit](proof_audit.md) for citation verification details and adversarial check records, or [re-run the proof yourself](proof.py) to reproduce the results from scratch.