HM (patient)
A memory impaired patient known as HM (an acronym used to keep his identity confidential) has been widely studied since the late 1950s and has been very important in the development of theories that explain the link between brain function and memory, and in the development of cognitive neuropsychology, a branch of psychology that studies brain injury to infer normal psychological function.
In 1953 HM had parts of his medial temporal lobe removed bilaterally (on both sides) in order to alleviate the effects of intractable epilepsy. He lost two thirds of his hippocampal formation, parahippocampal gyrus, and amygdala.
After the surgery he suffered from severe anterograde amnesia: although his short-term memory was intact, he could not commit new facts or events to long-term memory. He also suffered moderate retrograde amnesia, and could not remember most events in the 3-4 period before surgery, and some events up to 11 years before. He could however learn new motor skills, despite not being able to remember learning them
HM has not only been important for the knowledge he has provided about memory impairment and amnesia, but also because his exact brain surgery has allowed a good understanding of how particular areas of the brain may linked to specific processes hypothesised to occur in memory formation. In this way, he has provided vital information about brain pathology, as well as having helped form theories of normal memory function.
Particularly, the fact that he seems to be able to complete tasks that require recall from short-term memory and procedural memory but not long term memory suggests that recall from these memory systems may be mediated, at least in part, by different areas of the brain. Similarly, the fact that HM cannot create new long term memories, but can recall long term memories that existed well before his surgery suggests that encoding and retreival of long term memory information may also be mediated by distinct systems.
The case was first reported in a paper by Scoville and Milner in 1957. Psychological investigations of this patient were led by psychologist Brenda Milner.
See also
References
Referenced By
Cognitive neuropsychology | Hippocampus | Hippocampus (mythology)
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