Learning objectives
- Reproduce the impact of the medial temporal lobe lesion in patient H.M. on various cognitive aspects (i.e. What forms of learning were affected and which were unaffected?
- Reproduce how the delayed-nonmatching to sample task works and what brain regions it requires.
- Repr...
Notes
H.M.
Henri Gustav Molaison was an H.M. patient. Dr. William Skoville removed a part of his limbic
system, including the hippocampus. This had good and bad results:
- Good results
o No more seizures
o No changes in personality
o I.Q. improved
- Bad results
o Loss of memories from two years before surgery (retrograde)
o Unable to form new memories (anterograde) “once he stopped thinking about a new
experience the memory would be lost for ever.”
How is a memory formed? Three stages of a memory
Memory consolidation is the conversions of memory acquisition to memory storage. Memory
retrieval is trying to pull stored information back.
Digit span: in the case of H.M. he could repeat digits, provided that the time between learning and
recall is within the duration of STM.
Block-tapping memory-span test: in the case of H.M. the test demonstrated that H.M.’s amnesia was
global, and not limited to one sensory modality.
Mirror drawing task: “up is down, down is up and left is left, right is right” in the case of patient H.M.
in time he got better during the days so he did store the information, however, he had no conscious
recollection of having performed it before.
So patient H.M. improved with sensorimotor task and on non-sensorimotor tasks. And readily
learned responses through classical conditioning. However, there was no recollection of the training,
or the doctors or hospital etc.
, Explicit vs. Implicit memories
Explicit memories are conscious memories, remembering facts.
Implicit memories are unconscious memories, as when H.M. showed the the benefits of prior
experience in the mirror drawing task.
Example of explicit memory: where did you lock your bike today?
Example of implicit memory: “how to ride a bike.”
Repetition priming tests are used to assess implicit memory; performance in identifying word
fragments or picture fragments is improved when the words/drawings have been seen before.
Major scientific contributions of H.M.’s case
- Medial temporal lobes are critical for memory
- STM, LTM and remote memory
- H.M. had severe memory consolidation problem for certain forms of memory
- Memories may exist but could not be recalled
Patient R.B.
Patient R.B. is another example of a patient with damage to area CA1 of the hippocampus. The
hippocampus consists of areas CA1, CA2, CA3 and CA4.
Hippocampal damage alone can produce amnesia particularly in explicit forms of memory.
Clive Wearing, the man with no memory
Pay close attention to what he can do and what he cannot…
- Damage to his hippocampi strongly affected his explicit memories
- Memory for facts could be as short as a few seconds
- Does not recall ever seeing a doctor or receiving treatment
- Does remember his wife (the only one) (due to emotional bond)
- Can read music and play the piano very well
- Knows that a ring of the doorbell means that there is someone at the door
Korsakoff’s syndrome
Korsafkoff’s syndrome is a nervous system disorder:
- Commonly seen in severe alcoholics
- Lack of vitamin B (thiamine)
- Characterised by amnesia, confusion, personality
changes, and physical problems
- Early stages: anterograde amnesia for episodic
memories (related to what, where and when)
- Later stages: severe retrograde amnesia develops
- Progressively stronger impact with time
What damage causes the amnesia in Korsakoff?
Hypothalamic mammillary bodies are not the cause because Korsakoff is seen in cases without such
damage. Damage in the thalami mediodorsal nuclei is a probable cause because damage is seen
here when there is no mammillary body damage. However, the cause is likely to be causes by the
damaging of multiple diencephalic structures.
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