The man who couldn't make new memories taught us how memory works.
In 1953 a surgeon removed parts of Henry Molaison's brain to stop his seizures. The seizures eased, but he could no longer form new long-term memories. For the next five decades, known only as 'H.M.', he helped scientists discover that memory is not one thing but several.
Molaison, born in Connecticut in 1926, had epilepsy from childhood, and by 27 his seizures were so severe, despite heavy medication, that he could not work. The neurosurgeon William Beecher Scoville traced them to the medial temporal lobes and, on 1 September 1953, removed tissue from both sides of the brain, including much of the hippocampi and amygdalae. At the time, nobody understood how central the hippocampus is to memory.
The result was profound amnesia for anything new. Molaison could hold a conversation and keep information in mind for a short while, but once his attention moved on, it was gone; new people and events never stuck. He also lost many memories from the years just before surgery, while his childhood memories stayed largely intact, and he scored normally on tests of intelligence. Scoville and the psychologist Brenda Milner reported the case in 1957, and he was studied until his death in 2008, his name kept private until then.
One of the most striking findings came from a mirror-drawing task in the early 1960s. Milner asked him to trace a star while seeing only its reflection. Over three days his errors fell steadily, just as a healthy person's would, yet each time he had no recollection of ever having tried it. Learning a skill, it turned out, relies on different brain systems from remembering facts and events. His case helped show that short-term memory, skill learning and long-term memory for experiences can be separated, and that the medial temporal lobes are needed to form new memories of the last kind.
The story has kept evolving. After his death his brain was cut into 2,401 thin slices and digitally reconstructed. Researchers were surprised to find that about half of his hippocampal tissue had survived the surgery, along with an unexpected lesion in the prefrontal cortex, which complicates his image as a 'pure' case. Questions have also been raised about how his research records were handled. Researchers told him many times how important he was to science; he was never able to hold on to the fact.
Source: Wikipedia — Henry Molaison · Text summarised from Wikipedia (CC BY-SA 4.0)
