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LONG TERM MEMORY
Retrieval and the Brain
Learning Objective Topics
•  Retrieval
•  Neuroscience of Memory
•  LTP
•  Brain areas
•  Consolidation
•  Reconsolidation
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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)
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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
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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 . . .
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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
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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
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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
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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
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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
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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.
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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?
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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
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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
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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
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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)
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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.
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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
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Learning Objective Topics
•  Retrieval
•  Neuroscience of Memory
•  LTP
•  Brain areas
•  Consolidation
•  Reconsolidation
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Reconsolidation
http://www.radiolab.org/2007/jun/07/
Nader, Schafe, & Le Doux, 2000
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Reconsolidation
Nader, Schafe, & Le Doux, 2000
Reconsolidation Experiments
•  Ansiomycin – inhibits protein synthesis
•  Hupbach et al., 2007 – human study
•  Propranolol
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