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LONG TERM MEMORY Retrieval and the Brain Learning Objective Topics • Retrieval • Neuroscience of Memory • LTP • Brain areas • Consolidation • Reconsolidation 1 Long-term memory • “How does info become encoded/stored in LTM?” • Rehearsal/practice • Levels of processing • Forming connections or associations • Self-reference effect • Generation effect • Organization of info • Imagery • “How do we retrieve info from LTM?” • Retrieval cues • Encoding specificity / State dependent learning • Transfer appropriate processing Retrieval cues • Tulving & Pearlstone (1966) • Do retrieval cues improve memory? • Is forgetting just a retrieval failure? • Method • Study words (from categories) in random order • Test: free recall, cued-recall (provide categories) • Ex: Say all the birds, say all the professions, etc. • Results • Free recall: 40% • Cued-recall: 75% • Conclusions • YES – retrieval cues improve memory! • Availability vs. accessibility • Tip-of-the-tongue phenomenon (TOT) 2 Learning Objective Topics • Retrieval • Neuroscience of Memory • LTP • Brain areas • Consolidation • Reconsolidation Episodic Memory Encoding: Hebbian learning" “When an axon of Cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth processes or metablic change takes place in one or both cells such that A’s efficiency, as one of the cells firing B, is increased” - Hebb, 1949 A 3 Episodic Memory Encoding: Hebbian learning" “Cells that fire together are wired together” Are you down with LTP? • Long term potentiation • Associative LTP When a weak and a strong input act on a cell at the same time . . . 4 Associative LTP • The weak synapse becomes stronger Rules of Associative LTP • Cooperativity • LTP may be induced by a single pathway to a synapse • OR may be induced by the convergence of many weak stimuli that are active at the same time • Associativity • weak inputs are strengthened when co-occurring with stronger inputs • Input Specificity • There is no spread to other synapses • Input specific • Only the stimulated synapse shows potentiation 5 LTP Synapse level More postsynaptic receptors • What can change during LTP? Dendritic spine Increased release of neurotransmitter • (How does the synapse get stronger?) Sprouting of new terminal button Smaller, thicker neck of dendritic spine 6 Are you down with LTP? • LTP in the hippocampus may be the building block for long term learning • Blocking LTP prevents learning in rats Learning Objective Topics • Retrieval • Neuroscience of Memory • LTP • Brain areas • Consolidation • Reconsolidation 7 Movies and memory (amnesia!) http://socrates.berkeley.edu/~kihlstrm/movies.htm • Bourne Iden<ty (Ma> Damon) • Who Am I? (Jackie Chan) • The Long Kiss Goodnight (Geena Davis) • Memento (Guy Pierce) • The Eternal Sunshine of the Spotless Mind • 50 First Dates (Drew Barrymore) Case studies: Amnesia http://www.liveleak.com/view?i=fd0_1261475829 • What does evidence from H.M. tell us? • What is the medial temporal lobe is necessary for? • What is it not necessary for? 8 Underside of brain Main structures of medial temporal lobe (MTL) Brain areas associated with memory • Explicit memory • Medial temporal lobe • Hippocampus • Perirhinal cortex • Implicit memory • Striatum for procedural skills • Neocortex for priming tasks • Seman<c memory • LeS inferior prefrontal cortex • Neocortex -‐ widely distributed • Episodic memory • Right anterior and dorsolateral prefrontal cortex • Medial temporal lobes 9 Medial temporal lobe • Medial temporal lobe NOT responsible for… • Implicit memory or procedural memory • Not where LTM are stored • STM or WM • Medial temporal lobe IS responsible for… • Conscious LTM forma<on • Consolida<on: Strengthening associa<on • Transfer of info from STM to LTM Learning Objective Topics • Retrieval • Neuroscience of Memory • LTP • Brain areas • Consolidation • Reconsolidation 10 Consolidation • Synaptic consolidation – rapid • Systems consolidation – longer restructuring • Two theories of how consolidation happens in the brain: Standard Model of Consolidation A B C A B C neocortex Event We process multiple types of information at any given time Squire and Zola 11 Standard Model of Consolidation Event A B C A B A B C A B C C MTL Event h1 We process multiple types of information at any given time MTL encodes this information: • ensemble of neurons • act as a pointer to neocortical neurons • represents the attended information. Standard Model of Consolidation Event A A Event B C A B B C A B C C Feature information in neocortex is bound together into an episode (cohesion) A h1 We process multiple types of information at any given time B C h1 MTL encodes this information: • ensemble of neurons • act as a pointer to neocortical neurons • represents the attended information. 12 Standard Model of Consolidation Event A A Event B C A B B C A B C C h1 We process multiple types of information at any given time MTL encodes this information in an ensemble of neurons that act as a pointer to neocortical neurons representing the attended information. Feature information in neocortex is bound together into an episode (cohesion) A B C h1 The neocortex is eventually capable of representing the memory without the aid of MTL structures (consolidation) Standard Model • How would this predict retrograde amnesia after MTL damage? 13 Problem with the Standard Model The hippocampus may be used even for very remote memories. Episodic and semantic memories may be stored in different ways. (Standard model suggests that they are both stored using the same mechanism.) Multiple Trace Theory (Agrees with the Standard Model for this step) A B C A B C neocortex Event We process multiple types of information at any given time 14 Multiple Trace Theory (Agrees with the Standard Model for this step) Event A A Feature information in neocortex is bound together into an episode (cohesion) Event B C A B B C A B C A C h1 We process multiple types of information at any given time B C h1 MTL encodes this information: • ensemble of neurons • act as a pointer to neocortical neurons • represents the attended information. Multiple Trace Theory of Consolidation A B C h1 Nadel and Moscovitch Each reactivation of the memory trace occurs = different context 15 Multiple Trace Theory of Consolidation A B C h1 Reactivation: • activate the hippocampus • now in a new neuronal context Multiple Trace Theory of Consolidation A B C h1 Reactivation: • activate a subset of the feature-traces • now in a new environmental context 16 Multiple Trace Theory of Consolidation A B C h1 h2 Upon reactivation, a new ensemble of MTL neurons is created • multiple, related traces in the hippocampus Multiple Trace Theory of Consolidation A B C h1 h2 Semantic memories = stored separately from the context in which they were learned (episodic memory) 17 Multiple Trace Theory of Consolidation A B C Semantic memories become independent of the MTL (represented only in the neocortex) Multiple Trace Theory of Consolidation A B C h1 h2 Episodic memories remain reliant on the MTL pointer to combine all of the sensory attributes experienced. 18 Multiple Trace Theory of Consolidation Then why do we get the temporal gradient for retrograde amnesia after MTL damage? A B C h1 h2 The temporal gradient arises because memories with multiple traces (typically those established long ago) are less vulnerable to loss than memories with fewer traces (typically those established more recently) Fill in the prediction of each theory 19 Learning Objective Topics • Retrieval • Neuroscience of Memory • LTP • Brain areas • Consolidation • Reconsolidation 41 Reconsolidation http://www.radiolab.org/2007/jun/07/ Nader, Schafe, & Le Doux, 2000 20 42 Reconsolidation Nader, Schafe, & Le Doux, 2000 Reconsolidation Experiments • Ansiomycin – inhibits protein synthesis • Hupbach et al., 2007 – human study • Propranolol 21