The memories left by a patient who could not remember — H.M. and the hippocampus

The name that appears most often in neuroscience textbooks belongs not to a famous scientist but to a patient: Henry Molaison (1926–2008), known in research papers for decades only by the initials H.M.

The 1953 operation

Molaison had suffered severe epileptic seizures since childhood. In 1953, at 27, Molaison underwent surgery by neurosurgeon William Scoville to remove the inner part of both temporal lobes. The tissue removed included much of the hippocampus.

The seizures eased, but something unexpected happened: Molaison could no longer remember new things. A person met minutes earlier was a stranger on the next meeting, and what had just happened was quickly forgotten.

What remained

Psychologist Brenda Milner met Molaison over many years and checked, one by one, what had been lost and what remained. The 1957 report by Scoville and Milner can be summarized like this:

• Much of the memory from before the operation remained.
• The ability to hold digits for a few seconds, working memory, was intact.
• The ability to move new events and facts into long-term memory was almost gone.

The hands remembered

An even more surprising finding followed. Milner had Molaison trace a star while watching only its reflection in a mirror, a difficult task, over several days. Molaison’s performance improved day after day, yet each time Molaison said the task was new.

Skills learned by the hands could be acquired without the hippocampus. That observation led to the idea that remembering what you did and learning how to do something rely on different systems in the brain. In a 2009 essay, Larry Squire credited the work with H.M. as the starting point of modern research that divides memory into multiple systems.

The research continues

Molaison died in 2008, and only then was the name made public. With consent given in life, the brain was donated, cut into more than 2,000 thin sections and reconstructed digitally, with results published in 2014. One person’s life became a reference point for memory research for more than half a century.

#hippocampus #memory #patient H.M. #Brenda Milner #history of neuroscience

Sources

1. Loss of recent memory after bilateral hippocampal lesions. Scoville WB, Milner B. Journal of Neurology, Neurosurgery & Psychiatry 20, 11–21 (1957)
2. The legacy of patient H.M. for neuroscience. Squire LR. Neuron 61, 6–9 (2009)
3. Postmortem examination of patient H.M.'s brain based on histological sectioning and digital 3D reconstruction. Annese J et al. Nature Communications 5, 3122 (2014)