Every twenty minutes or so, the same nurse would walk back into Henry's room and introduce herself for the first time. While she stood there, Henry knew her name and her job. Then the few seconds ran out and he reset, and the whole introduction began again.
Olga Ivashkina, a neurobiologist, calls Henry Molaison the best-studied person in the neuroscience of memory. He was born around 1926 and had epilepsy that the drugs of the day could not control. In 1953 American neurosurgery was in a mood to operate on almost anything, and surgeons were cutting "with a steady hand", as Ivashkina puts it, for schizophrenia, for hysteria, for whatever came in. For Henry the surgeon removed most of the hippocampus on both sides, along with the cortex beside it and structures such as the amygdala. The seizures eased, though they did not vanish. He could no longer form new memories of his own life. He also lost a large part of the years before the operation, about fifteen of them, Ivashkina thinks.
The surprise is what stayed. Henry could still learn how to do things, and that matters to anyone who has ever ridden a bike. Learning a skill and remembering the day you learned it turn out to be stored in different places.
You know this from the inside. Nobody recites "right foot up, left foot down" while cycling. Ivashkina has her own example. She learned to drive a manual car and passed the exam, but the skill never sank in. Even now, when she drives one, she has to think: this gear, clutch down. Her husband changes gears without a thought. Both of them can do it. Only one of them has it in the hands.
Henry's skills were tested by Brenda Milner, a Canadian psychologist and neurobiologist. She had him draw while looking only at a mirror, which means steering the hand the wrong way, over and over, against every habit. He did it well. In 1953 no one could have predicted that. Today it looks obvious, Ivashkina says, but it was not obvious then.
The reason is that a skill is built from the same material as any other memory, networks of neurons, and kept in other rooms. The networks for how to wash your hands, play the piano or run with a ball sit in the motor regions of the cortex, the basal ganglia and the cerebellum. The hippocampus is the great hub for life events. For skills there is no such hub. Henry's surgeon had taken the hub and left the rooms.
So Ivashkina can answer the question a host once asked her: could a person with amnesia learn the guitar?
He may not learn to sing songs … but he can learn to run through chords, if the amnesia comes from damage to the hippocampus and the systems around it.
Он может не научиться петь песни, … но может научиться перебирать аккорды, если эта амнезия связана с повреждениями гиппокампа и окологипокампальных систем.
— Olga Ivashkina, Osnova, 32:29
Songs fail because words and meanings live in the other kind of memory. The chords get through. And the answer depends on where the damage is. If it sits in the cortex instead, Ivashkina says, other losses are possible, depending on the spot.
Here the story turns, and she is careful with it. A skill can form without the hippocampus "as a rule", and the rule is not a law. A study in Nature Communications in 2025 recorded from epilepsy patients who had electrodes in their brains while they learned a sequence of finger movements. During the short rest breaks, their hippocampus fired more of the brief bursts called ripples, and the more ripples a person had, the more their speed improved after the break.
The hippocampus is not the keeper of skills, then. It may still sit in the practice room, quietly, while the player rests.
