Psychology › Brain & biology › Hippocampus: forming new memories
Patient H.M. (Henry Molaison)
Surgery 1953; studied to 2008· Finding or experiment
Well replicatedStrong, repeated evidence.
Henry Molaison lost the ability to form new lasting memories after epilepsy surgery in 1953, becoming neuroscience's most studied patient.
See it on the Psychology map →What it says
To stop severe seizures, surgeon William Scoville removed much of the hippocampus and nearby tissue on both sides of the 27-year-old's brain. The seizures eased, but he could no longer form new memories of facts or events; he met psychologist Brenda Milner for decades as if for the first time. Yet he could hold a number in mind briefly, kept his intelligence, and improved daily at a mirror-drawing task without remembering practicing it. He died in 2008, aged 82.
Why it matters
He showed memory is not one thing: short-term memory and skill learning survived, while forming new long-term memories needed the hippocampal region. Surgeons stopped removing both sides.
The evidence
Status: well replicated. Scoville and Milner's 1957 paper, decades of tests by Suzanne Corkin's MIT team, and his brain, cut after death into 2,401 thin slices, now a public digital atlas.
Open questions
Exactly which damaged structures caused which losses is still argued, and a 2016 book by Luke Dittrich raised questions about consent and the handling of his case.
Connections (2)
▸Patient H.M. (Henry Molaison) revealed the role of Hippocampus: forming new memoriesWell replicated
The connection
Before Henry Molaison, many scientists thought memory was spread across the whole cortex. His surgery removed the hippocampus and nearby tissue on both sides, and he lost the ability to form new long-term memories while keeping intelligence, language and older memories. That pointed to the hippocampal region as the gateway for storing new memories.
Who showed it and when
Hartford Hospital, Connecticut, 1953, surgery by William Scoville; studied by Brenda Milner of the Montreal Neurological Institute, then by Suzanne Corkin at MIT until 2008.
The evidence
Scoville and Milner's 1957 paper compared ten patients: memory loss tracked how much hippocampal tissue was removed. Later patients with damage limited to the hippocampus confirmed it.
Open questions
His lesion also included the amygdala and entorhinal cortex, so the hippocampus's own share was clarified only by later cases and animal studies.
▸Patient H.M. (Henry Molaison) revealed separate Memory systems: short-term, long-term, episodic, proceduralWell replicated
The connection
After surgery removed much of Henry Molaison's hippocampus in 1953, he could no longer form new memories of facts or events. Yet his short-term memory was normal, and he steadily improved at a mirror-drawing task he could not remember practicing. This showed memory is several systems in different brain areas.
Who showed it and when
Hartford, Connecticut, 1953 surgery by William Scoville; studied from the mid-1950s by Brenda Milner of Montreal, later by Suzanne Corkin at MIT until his death in 2008.
The evidence
Scoville and Milner's 1957 paper, decades of tests, and the 2009 slicing of his brain that mapped the damage; other amnesia patients show the same pattern.
Open questions
His damage extended beyond the hippocampus, so exactly which structures cause which memory losses is still being refined.