Transcript HM Case Study

HM Case Study
Aim/Method:
• To study the role of the hippocampus in memory.
Background
• 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.
Surgical outcome
• The surgery was successful in controlling the seizures but H.M suffered
severe amnesia; he could not commit new events to long-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).
• 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.
Case Study Procedure
• HM was told to perform several sensorimotor tasks such as
mirror-reading, playing video games, and solving puzzles
Results:
• HM could not recall ever doing those tasks and claimed he
did not know how to do them but after training, he could
perform them perfectly.
Conclusion:
• The hippocampus is a crucial structure for the transfer of
new knowledge from STM to LTM, though not procedural
memories, which depend on the basal ganglia and
cerebellum.
Conclusion (cont’d)
• 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.
Evaluation:
• Positive
• The atypical shows us about the typical.
• It has showed us that the hippocampus is the key structure involved
in the transfer of new declarative data from STM to LTM.
• Negative
• The fact that he's atypical makes the results hard to generalize to
the wider population.
• Researcher bias may be present.