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Memory Systems

Memory Systems. Isabelle Rapin Seminar in Developmental Disabilities February 20, 2013 No conflict of interest. Multiple Memory Systems. Short term memory systems Sensory buffers (for each modality + endogenous inputs from memory) Working memory Long term memory systems

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Memory Systems

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  1. Memory Systems Isabelle Rapin Seminar in Developmental Disabilities February 20, 2013 No conflict of interest

  2. Multiple Memory Systems • Short term memory systems • Sensory buffers (for each modality + endogenous inputs from memory) • Working memory • Long term memory systems • Declarative (or explicit) • Non-declarative • Retrieval systems

  3. 1. Schema of STM systems Short Term Memory Sensory buffers Working memory Sensory cortices Prefrontal cortex

  4. Short Term Memory • Components: buffers + working memory • Sensory buffers: in continuous on-line reciprocal contact with working memory circuitry • Working memory: processes only information that reaches awareness, does so in the light of other inputs and priorities* • Duration range: < 1 - few seconds • Requirement: repeated inputs or rehearsal • Fate:erasure or potential storage *Information that does not reach awareness may have non-declarative priming effects

  5. Working Memory Circuitry • Prefrontal cortex: in continuous on-line reciprocal connections with • Sensory cortices for each modality (specific buffers) • Limbic circuits • Arousal circuits • Motor output circuits * * * • Note: Hippocampus circuitry: (data from amnestic patients) • Not critical on-line, • Critical for long term storage

  6. LTM declarative systems Declarative (or explicit) memories Episodic memory (time-bound facts of the individual’s past) Semantic memory (knowledge of the world) Medial temporal cortices + Medial temporal cortices +

  7. Declarative (explicit) Memory1. Episodic (Tulving) • Uniquely human capacity to look back to the past and predict the future • Powerful tool • Retrieve specific facts/events in time/place context (unique, autobiographical) • Late to develop evolutionarily (man only?) and ontogenitically (infant amnesia) • Fragile to degeneration • Critically dependent on (not limited to!) hippocampal/medial temporal cortices

  8. Declarative (explicit) Memory 2. Semantic Memory • Knowledge (as opposed to remembrance of specific facts) • “Picked-up” knowledge from exposure to mostly forgotten past events/experiences • Starts at birth, long before episodic memory • Broad and powerful • Much more resilient than episodic memory

  9. 2 - LTM non-declarative systems Non-declarative (implicit) memories/learning nodes Procedural (skills, habits) Priming Conditioning Non-associative Basal ganglia (putamen), etc. Sensory cortices Emotional: amygdala Motor: cerebellum + Reflex pathways

  10. Hippocampus system • Binds inputs from all sensory modalities with limbic and prefrontal executive inputs • Reciprocally connected with relevant cortical and subcortical circuitry • Required for declarative memory • For fresh and midterm declarative memories • Not for very long term “ “ • Not required for non-declarative memories

  11. Brain molecular/cellular underpinnings of memory(Kandel, etc.) • Molecular – short term manipulation of incoming information to guide on-going behavior • Alteration in strength/effectiveness of already existing synapses • Neurotransmitter release/uptake • Cellular – long term storage • Requires protein synthesis and growth of new • synaptic receptors • dendrites • Brain circuitry – long-term (yrs) consolidation

  12. Retrieval • Long-term explicit memory storage: • mainly in modality-specific relevant neocortical, ± limbic areas • Recognition -- cue, strong, bottom-up • Retrieval of unique item -- top/down, effortful • Long-term implicit memory storage: • mainly in cortical/subcortical circuitry relevant to task/skill performance (e.g., motor cortex, basal ganglia, cerebellum, brainstem, spinal cord)

  13. Amnestic syndrome • Result of bilateral hippocampal damage • Not necessarily irreversible except for peri-lesional time-window • Impairs new explicit learning • Impairs explicit but not implicit memories • Does not impair procedural memory/skills • Does not preclude learning new skills! • Occasional cases in kids, even infants

  14. Evidence for neural circuitry of memory • Lesion studies • Behavioral evidence • Imaging • Autopsy • Electrophysiology • Functional imaging (PET, fMRI…) • Subtraction: task vs. no task (“rest”) • Subtraction: impaired group vs. “typical” group

  15. Problems with functional studies • Smallness of samples • Homogeneity of samples • Failure to replicate • Multiplicity of nodes in widely distributed pathways • Requirement for cooperation • Great difficulty/impossibility of testing young children • Cost • Time required for data analysis • Fancy statistical analyses required

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