HM (patient)

Henry Molaison (February 26, 1926 – December 2, 2008), known widely by the pseudonym HM, was an American memory disorder patient who had a significant impact on the development of theories that explain the link between brain function and memory. After undergoing a bilateral medial temporal lobe resection to treat intractable epilepsy, HM developed profound anterograde amnesia, unable to form new long-term memories, though his working memory and procedural memory remained intact. His case played a pivotal role in the understanding of the organization of human memory and the functions of the hippocampus.

Early Life and Surgery

Henry Molaison was born in Manchester, Connecticut. At the age of 27, after suffering from severe epilepsy that was not controlled by medication, he underwent an experimental surgical procedure performed by neurosurgeon William Scoville. The surgery involved the removal of two-thirds of the hippocampus, uncus, and amygdala from both hemispheres of his brain. Although the surgery was successful in reducing his epileptic episodes, it left him with extensive memory deficits.

Memory Deficits

HM's case was unique in that his intellectual abilities and perceptual skills remained largely intact, but he could not commit new events to long-term memory. He also exhibited partial retrograde amnesia, forgetting events that occurred in the years leading up to his surgery. This condition made him one of the most studied cases in medical and psychological history. Brenda Milner, a neuropsychologist, was among the first to study HM extensively, revealing the distinction between declarative and procedural memory.

Impact on Neuroscience

HM's case had a profound impact on the field of neuroscience and psychology, particularly in the areas of memory and learning. It provided concrete evidence that the hippocampus plays a crucial role in converting short-term memories to long-term memories and suggested that different types of memory are mediated by distinct parts of the brain. His case also contributed to the understanding of memory consolidation processes.

Later Life and Legacy

Throughout his life, HM was studied by numerous psychologists and neuroscientists. He lived in a care institution in Windsor Locks, Connecticut, where he continued to participate in research until his death in 2008. Following his death, his brain was donated to science, and in 2014, it was sliced into 2401 sections and digitized for further study.

Conclusion

Henry Molaison (HM) remains one of the most important figures in the study of memory and neuroscience. His case has provided invaluable insights into the workings of the human brain and has influenced the treatment and understanding of memory disorders. The study of his brain continues to contribute to the field, making HM's legacy an enduring one in the history of neuroscience.

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