Chapter 11 Learning, memory & amnesia

Chapter 11 Learning, memory & amnesia - 1 Chapter 11...

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11.1 Amnesic effects of bilateral medial temporal lobectomy H. M. – an epileptic who had his temporal lobes removed in 1953 His seizures were dramatically reduced – but so was his LTM (for events post- surgery) Retrograde (backward-acting) – unable to remember the past Anterograde (forward-acting) – unable to form new memories While H. M. is unable to form most types of new LTM, his STM is intact Formal assessment of H. M.’s anterograde amnesia H. M. improves with practice on sensorimotor tasks (mirror-drawing test, rotary- o Without recalling previous practice sessions H. M. readily ‘learns’ responses through classical conditioning, but has no memory of conditioning trials Scientific contributions of H. M.’s case Medial temporal lobes are involved in memory o H. M. is unable to move memories from STM to LTM, a problem with memory consolidation Memory may exist but not be recalled – as when H. M. exhibits a skill he doesn’t know he has learned o As when H.M exhibits a skill he doesn’t know he has learned Explicit vs implicit memory Explicit memories – conscious memories Implicit memoryes – unconscious memories, as when H. M. shows benefits of prior experience Repetition priming tests – used to assess implicit memory – o Performance in identifying word fragments is improved when the words have been seen before Medial temporal lobe amnesia Not all patients with this new form of amnesia are unable to form new explicit LTM – as was the case with H. M. Semantic memory (general information) may function normally while episodic memory (events one has experienced) does not o They are able to learn facts but don’t remember doing so (the episode when it occurred) Medial temporal lobe amnesiacs may have trouble imagining future events 1
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R. B. suffered damage to just one part of hippocampus (CA1 pyramidal cell layer) R. B.’s case suggests that hippocampal damage alone can produce amnesia H. M.’s damage – and amnesia – was more severe than R.B.’s 11.2 Amnesia of Korsakoff’s Syndrome Most commonly seen in alcoholics (or others with thiamine deficiency) Typically damage in medial diencephalon – medial thalamus + medial hypothalamus Amnesia comparable to medial temporal lobe amnesia in early stages o Anterograde amnesia for episodic memories Differs in later stages o Severe retrograde amnesia develops Differs in that it’s progressive, complicating its study What damage causes amnesia seen in Korsakoff’s? Hypothalamic mammillary bodies
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Chapter 11 Learning, memory & amnesia - 1 Chapter 11...

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