The Case of H.M.

"Everyday is alone by itself" - H.M.

Henry Gustav Molaison, known by the initial H.M., was an American memory disorder patient who was widely studied as he played a vital role in development of theories of link between brain function and memory, and cognitive neuropsychology. He was born on February 26, 1926 and suffered from epilepsy caused by bicycle accident at age of 9. He suffered seizures for several years and finally was sent to Hartford Hospital for treatment. As a result, he lost approximately two-thirds of his hippocampus (two parts of the lower brain), parahippocampal gyrus and amygdale. The surgery was successful in controlling the seizures but H.M suffered severe amnesia; he could not commit new events to long-term memory. He could no longer remember anything for more than few minutes though he could still remember events that happened more than 2 years before the surgery. New experiences were quickly forgotten though he could remember a set of numbers or fact for short while.

The case of H.M. provided about memory impairment and amnesia, and allowed for better understanding of how some areas of brain may be linked to specific processes in memory formation. Problem with H.M wasn’t long-term memory or short-term memory. His personality, IQ and knowledge of the world were intact but the problem was that he lost the ability to convert short-term memories into long-term memories, known as anterograde amnesia (inability to learn new information).

Based on H.M.’s memory loss, scientists formed some hypotheses about memory formation.

1)     Short-term memories are biologically different from long-term memories because they don’t require hippocampus for formation

2)     Long-term memories are stored throughout the brain, but hippocampus is necessary for it to reach long-term storage. Once it is stored, hippocampus sis no longer required. So, hippocampus is not needed for memory maintenance or retrieval after formation.

These hypotheses explain why H.M. could remember events before surgery but not store any new memories after. However, scientists could spot that Henry could perform skill learning by unconscious memory (procedural memory). For H.M., though he couldn’t remember learning such skills, he showed some degree of improvement which means skill learning doesn’t require hippocampus.