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Memory & the Medial Temporal Lobe

Memory & the Medial Temporal Lobe. Lesson 22. Memory. Storage of information perceptions learning personality Information processing approach RAM vs. hard drive Multiple memory stores different characteristics Clive Wearing ~. Multiple Memories. Sensory memory

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Memory & the Medial Temporal Lobe

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  1. Memory & the Medial Temporal Lobe Lesson 22

  2. Memory • Storage of information • perceptions • learning • personality • Information processing approach • RAM vs. hard drive • Multiple memory stores • different characteristics • Clive Wearing ~

  3. Multiple Memories • Sensory memory • capacity: large; sensory receptors • duration: < 1 sec. • Short-term memory (STM) • capacity: 7 ± 2 chunks • duration: < 1 min. • maintenance: rehearsal ~

  4. Multiple Memories • Long-term memory (LTM) • capacity: functionally unlimited • duration: minutes - years • Working memory • intermediate to STM & LTM • information needed longer than 1 min, but not permanent ~

  5. stimuli transfer rehearsal attention Sensory Memory STM LTM retrieval forgetting forgetting forgetting A Model of Memory

  6. Subdivisions of LTM 1. Declarative - Explicit • Episodic: • autobiographical • time-tagged, automatic • Semantic: • generic • not time-tagged, effortful ~

  7. Subdivisions of LTM 2. Procedural – Implicit • non-declarative, unconscious • Motor learning • Nonassociative Learning • modulation of reflexes • Associative Learning • Classical & Operant Conditioning ~

  8. Neural Mechanism of STM • Donald Hebb • Change in neural activity • not structural • temporary • Reverberatory Circuits • cortical loops of activity • activity persists for short period of time ~

  9. Reverberating loops • Maintains neural activity for a period

  10. Neural Mechanism of LTM • LTM relatively permanent • structural change required • Hebbian Synapse • use strengthens synaptic efficiency • requires simultaneous activity • pre- and postsynaptic neurons • Long-term potentiation (LTP) ~

  11. Where are memories stored? • Engram • physical change representing learning and memory • Lashley • Mass Action & Equipotentiality • Classical Conditioning: Eye-blink • lateral interpositus nucleus of cerebellum • Memories stored locally • in different parts of brain ~

  12. H.M. • Greatest contribution to study of memory • can’t remember any of it • similar to Clive Wearing • Bilateral medial temporal lobectomy • to control seizures • hippocampus (HC) ~

  13. Hippocampus Mid-sagittal View

  14. Spared some memory • Personality • Intelligence • LTM • Verbal STM memory OK • Motor skills

  15. Trauma time Memory Deficits • Some retrograde amnesia • but many old memories intact • Severe anterograde amnesia • unable to form new memories ~ Retrograde Anterograde

  16. Evidence of deficits • Digit Span + 1 • Block tapping memory span • Delayed-matching-to-sample • verbal OK - rehearsal • nonverbal impaired – ellipses ~

  17. Evidence of Spared Abilities • Performance improved with practice • Procedural memory • but no conscious memory of it • Mirror Drawing • Tower of Hanoi ~

  18. Conclusions: Role of Hippocampus • Removal of HC  deficits • Memory Storage? • STM not in HC • LTM not in HC • HC transfers info STM  LTM? • Declarative memories: YES • Procedural: NO • H. M. anterograde amnesia for declarative memories ~

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