Henry Molaison

A unique case in the study of amnesia

Henry Molaison, who has died aged 82, was a mild-mannered American who would not have become famous had he not hit his head, developed intractable epilepsy, undergone surgery and lost the capacity to remember new things, thus becoming uniquely useful to neuroscience.

An only child, Molaison was born in Hartford, Connecticut. When he was nine he was run over by a cyclist and hit his head. He developed epilepsy soon afterwards, although it is unclear whether the accident triggered it. His fits became more frequent and eventually, despite dangerously high doses of medication, he had to give up his job as an assembler in a motor factory.

Finally, he was referred to Henry Scoville at a nearby hospital. Brain surgery to cure or relieve epilepsy had already been pioneered by Wilder Penfield at the Montreal Neurological Institute and, after lengthy discussion with Molaison and his parents, Scoville removed both temporal lobes of his cerebral cortex, and a seahorse-shaped structure called the hippocampus. It was 1953, and Molaison was 27. It was an experimental procedure, given that such surgery in those days involved a certain amount of guesswork.

The operation largely cured the epilepsy - Molaison averaged one fit a year thereafter - but removed his capacity to form new memories. He could remember things from his childhood, and had incomplete memories for the months before the operation. He remembered Scoville because of their lengthy pre-op discussions, and he could do everyday things such as making his bed.

Meanwhile, Penfield had been joined in Montreal by Brenda Milner, whose research interest was memory loss in patients who had undergone temporal-lobe surgery, usually for epilepsy. She tested them before surgery and at intervals afterwards. Milner reported two cases similar to Molaison's at a conference in Chicago in 1955. Scoville read the abstract and phoned Penfield. Milner was invited to Hartford to study Molaison, whom she called HM in research papers.

For the next 50 years Milner travelled to Hartford, staying a few days at a time, to study Molaison, who was always keen to help science. She discovered that he could remember short-term things and had a capacity for sustained attention. He could remember the number 584 for 15 minutes by continual rehearsal and an elaborate mnemonic scheme - provided he was not distracted. Milner's graduate student Lilli Prisco showed that he could receive perceptual stimuli normally, but they became unavailable to him within 30-40 seconds. Later, she discovered that verbal rehearsal was essential to this process. He could recognise increasingly fragmented drawings of objects and animals, which is presumably mediated by the visual cortex at the back of the head.

Molaison was looked after by his parents and then by another relative until 1980, when, aged 54, he moved into the care home where he spent the rest of his life. In 1997 Suzanne Corkin of Massachusetts Institute of Technology examined a magnetic-resonance image of his brain and showed that the surgical lesion was symmetrical and included most of the amygdala, about 5cm of the hippocampus and most of the medio-temporal lobes, where short-term memory is converted to long-term. Recent research elsewhere suggests that it was the hippocampal lesion that caused the severity of his memory loss.

"Henry had a strong desire to do something for science," said Milner, now 79. "I feel I have lost a friend. You could say it was a lopsided friendship as he never remembered me." Molaison regretted that his memory prevented him from making friends, as he could not remember anyone. Scoville never performed the operation again, and campaigned against it.

• Henry Gustav Molaison, amnesia patient, born 26 February 1926; died 2 December 2008

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