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Ch 11: Learning, Memory & Amnesia

Ch 11: Learning, Memory & Amnesia. Learning & Memory. Neuroplastic processes related to the ability of the brain to change its functioning in response to experience Learning How experience changes the brain Memory How the changes are stored & later activated. H.M.

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Ch 11: Learning, Memory & Amnesia

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  1. Ch 11: Learning, Memory & Amnesia

  2. Learning & Memory • Neuroplastic processes related to the ability of the brain to change its functioning in response to experience • Learning • How experience changes the brain • Memory • How the changes are stored & later activated

  3. H.M. • A patient that had a bilateral medial temporal lobectomy as a treatment for his epilepsy • Removal of the medial portions of both temporal lobes; including most of the hippocampus, amygdala & nearby cortex • Alleviated most of his seizures, but had a significant impact on his memory • Much of our understanding of memory comes from study of this man & the changes to his memory • No one since has had this procedure

  4. Amnesia • Any pathological loss of memory • Retrograde amnesia • Inability to remember information from the past • Anterograde amnesia • Inability to remember new information; can’t form new memories • Short term memory (STM) • Storage of new info for a brief time while a person attends to it • Long term memory (LTM) • Storage of new info once the person stops attending to it

  5. H.M.’s Amnesia • Most of his memory from before the surgery was intact • With the exception of the 2 years prior to the surgery • His short term memory was normal • But it was virtually impossible for him to form new long term memories • As soon as he stopped focusing on new information, he forgot it • He was effectively frozen in time • Global amnesia • Amnesia for memory presented in all sensory modalities

  6. Assessment of H.M.’s Anterograde Amnesia • 7 tests of his long term memory • Digit Span + 1 Test • Block-Tapping Memory-Span Test • Mirror-Drawing Test • Rotary-Pursuit Test • Incomplete-Pictures Test • Pavlovian Conditioning • ???

  7. Digit Span + 1 Test • Asked to repeat 5 digits that were read to him, then those 5 + a new digit, etc. • Normal: 15 digits; HM: failure by 8 • Block-Tapping Memory-Span Test • Asked to tap a series of blocks on a table in the same order the experimenter did • Correct at 5 blocks, incapable of 6

  8. Mirror-Drawing Test • Trace a star shape while looking at your hand in a mirror; errors measured • Repeated many times over a few days • His performance improved over time, even though he had no memory of having done the task before

  9. Rotary-Pursuit Test • Maintain contact between a stylus and a target on a rotating disc • Again, improvement without him remembering the task • Incomplete-Pictures Test • Patient must identify the object in a drawing, with it drawn to different levels of completeness • Again, improvement without him remembering the task • PavlovianConditioning • Eye-blink task • Tone plays before a puff of air in the eye; eventually the tone alone causes a blink • HM able to learn this, although it took longer than normal

  10. H.M. Summary • Mild retrograde amnesia • Only 2 years before surgery • Extreme anterograde amnesia • Short term memory was fine • But long term memory was severely impaired • However, tests showed that while he could not consciously remember having done these tasks before, his improved performance on them indicates some type of memory was being formed

  11. Conclusions from H.M.’s Amensia • Memory functions seem to be highly dependent on the structures of the medial temporal lobe • His differential ability to remember things showed that there were distinctly different types of memory storage • His specific problem seemed to be with memoryconsolidation, the translation of STM to LTM • Because his performance improved but he couldn’t remember the task, it was determined there are 2 categories of LTM

  12. 2 Types of LTM • Explicit memories • Things you consciously remember • 2 types • Semantic • Memories of general facts or information • Episodic • Memories of events in your life (aka autobiographical memories) • Implicit memories • Memories that are formed without conscious awareness of them • Indicated by increased performance over time in tasks such as mirror drawing

  13. Amnesia of Korsakoff’s Syndrome • Korsakoff’s syndrome is a memory disorder common in chronic alcoholics • Brain damage results from thiamine deficiency • Late stages involve sensory & motor problems, extreme confusion, personality changes & potential organ failure • Amnesia similar to that of medial temporal lobe amnesia • Early on, anterograde amnesia for explicit episodic memories is most prominent symptom • Later, severe retrograde amnesia sets in

  14. Amnesia of Alzheimer’s Disease • First symptom of Alzheimer’s is the deterioration of memory • Major anterograde & retrograde deficits in explicit memory • Often have deficits in STM & some types of implicit memory (verbal & perceptual, not sensorimotor) • Acetylcholine depletion may be the cause of amnesia in Alzheimer’s

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