H.M. (Henry Molaison) was a patient who underwent a surgical procedure in 1953 to treat his severe epilepsy. The surgery involved the removal of parts of his brain, specifically the hippocampus, which resulted in profound memory loss. H.M. could no longer form new long-term memories, a condition known as anterograde amnesia, while his short-term memory remained intact. His case became crucial for understanding memory and the brain. Researchers studied H.M. extensively, revealing that the hippocampus plays a vital role in forming new memories. His experiences contributed significantly to the fields of neuroscience and psychology, influencing theories about memory storage and retrieval.