Henry Molaison, better known as Patient H.M. is the most famous case of a patient with severe memory loss. After a procedure to remove part of his hippocampus to stop epilepsy, Molaison remembered nothing from his 11 prior years and nothing going forward in his life. Research on him during his life and since his death has been groundbreaking.
From these trials Milner was able to conclude that this form of memory, called motor learning, must be distinct from the system of memory that records new facts, faces and experiences. Furthermore, it must be located in a different part of the brain, one unaffected by Henry's operation. Milner's discovery that we have multiple memory systems and that they are located in different parts of the brain was a huge step forward in neuroscience.
Henry was always supportive of the research that he enabled and said he was glad that he could be of help to others. In 1992 he gave his consent for his brain to be used in further research after his death, and this led to the establishment of 'Project HM'.
There are other dissociations discovered on H. M., most notably the experiments on motor and skill learning. In a 1962 experiment Milner trained H. M. on a mirror-drawing task. This task involves tracing some figure on the paper by only seeing the mirror image of the drawing. Normal people are initially pretty bad at this task, but they can get better with training. H. M. had a normal learning curve for this task.
There have been dozens of experiments on H. M.'s memory impairment. In his post-operative years since 1953, his symptoms have been very stable. The major findings show that he is impaired at virtually any kind of learning task in which there is a delay between presentation and recall, particularly if interfering material is presented in between. The learning materials used in tests include photographs of people, verbal material, sequences of digits, complex geometric designs or nonsense patterns.
Henry gave science the ultimate gift; his memory. Thousands of people who have suffered brain damage, whether through accident, disease or a genetic quirk, have given similar gifts to science by agreeing to participate in psychological, neuropsychological, psychiatric and medical studies and experiments, and in some cases by gifting their brains to science after their deaths. Our knowledge of brain disease and how the normal mind works would be greatly diminished if it were not for the generosity of these people and their families (who are frequently also involved in interviews, as well as transporting the "patient" back and forth to the psychology laboratory). After Henry's death his brain was dissected into 2000 slices and digitized as a three-dimensional brain map that could be searched by zooming in from the whole brain to individual neurons. Thus his tragically unique brain has been preserved for posterity.
Henry's memory loss was far from simple. Not only could he make no new conscious memories after his operation, he also suffered a retrograde memory loss (a loss of memories prior to brain damage) for an eleven year period before his surgery. It is not clear why this is so, although it is thought this is not because of his loss of the hippocampi on both sides of his brain.
H.M.’s memory impairment has generally been taken as reflecting a failure to convert transient, immediate memory into stable long-term memory. A key insight about the organization of memory, and medial temporal lobe function, came with a consideration of his capacity to remember information that he had acquired before his surgery.
H.M. not only motivated the development of an animal model of human memory impairment and the subsequent delineation of the medial temporal lobe memory system. As described next, the study of H.M. also led to fundamental insights into the function of the medial temporal lobe and the larger matter of how memory is organized in the brain.
And for those five decades, he was recognized as the most important patient in the history of brain science. As a participant in hundreds of studies, he helped scientists understand the biology of learning, memory and physical dexterity, as well as the fragile nature of human identity.
In 1953, he underwent an experimental brain operation in Hartford to correct a seizure disorder, only to emerge from it fundamentally and irreparably changed. He developed a syndrome neurologists call profound amnesia. He had lost the ability to form new memories.
For the next 55 years, each time he met a friend, each time he ate a meal, each time he walked in the woods, it was as if for the first time.