Download Eagleman Ch 9. Memory

9: Memory
Cognitive Neuroscience
David Eagleman
Jonathan Downar
Chapter Outline
The Many Kinds of Memory
 Travels in Space and Time
 Remembering the Future
 The Confabulation of Reality
 The Mechanisms of Memory
 Beyond Synaptic Plasticity
 The Mysteries of Memory

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The Many Kinds of Memory
Working and Long-Term Memory
 Implicit Memory
 Explicit Memory
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Working and Long-Term Memory
Working memory uses information to
address a particular problem.
 It only lasts for a short period of time and
has a limited capacity of about seven
items.
 Working memory includes the
phonological loop and the visuospatial
sketchpad.
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Working and Long-Term Memory
Long-term memory stores large quantities
of information for long periods of time.
 There are two subdivisions of long-term
memory

 Implicit
memory encodes information that is
not easy to recall or describe consciously.
 Explicit memory can be consciously recalled.
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Working and Long-Term Memory
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Implicit Memory
Procedural memory refers to the
knowledge of how to do something.
 Priming describes how past experiences
increase the response to a given sensory
stimulus.

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Implicit Memory
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Implicit Memory
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Implicit Memory
In classical conditioning, an unconditioned
stimulus naturally brings about an
unconditioned response.
 A conditioned stimulus is paired with the
unconditioned stimulus, so that it now
brings about the response.
 The response to the conditioned stimulus
is known as the conditioned response.
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Implicit Memory
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Implicit Memory
In operant conditioning, rewards
encourage the animal to repeat a behavior
and punishment discourages the behavior.
 Nonassociative learning refers to longterm changes in reflex pathways.
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Explicit Memory
Episodic memories are autobiographical
memories of specific events.
 The medial temporal lobe, particularly the
hippocampus, are important for storing
and recalling episodic memories.
 Semantic memories are memories of
facts, without details of when or where you
learned the fact.

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Explicit Memory
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Travels in Space and Time: The
Hippocampus and Temporal Lobe
A Map of the Medial Temporal Lobe
 Episodic Memory
 Spatial Memory
 Theories of Hippocampal Function
 Unifying the Functions of the
Hippocampus
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A Map of the Medial Temporal
Lobe
The anterior hippocampus is important for
object recognition memory.
 The posterior parts are important for
spatial memory.
 The amygdala is important for emotional
memories.
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A Map of the Medial Temporal
Lobe
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Episodic Memory

The exact roles of the hippocampus in
episodic memory is still being studied.
 Some
research suggests it is necessary for
encoding new memories, but not for recalling
memories.
 Other research suggests it is necessary for
both encoding and recalling memories.
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Episodic Memory
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Spatial Memory
Place cells and grid cells in the posterior
hippocampus and the adjacent entorhinal
cortex build spatial cognitive maps.
 The Morris water maze and radial arm
maze are experimental procedures that
test spatial maps in rodents.

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Spatial Memory
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Spatial Memory
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Theories of Hippocampal
Function

Several theories attempt to describe the
function of the hippocampus.
 Declarative
theory: The hippocampus is
crucial for new declarative memories.
 Multiple-trace theory: The hippocampus is
crucial for new and old declarative memories.
 Dual-process theory: The hippocampus is
crucial for recalling the context of an event.
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Theories of Hippocampal
Function

Several theories attempt to describe the
function of the hippocampus.
 Relational
theory: The hippocampus stores
the relations between events.
 Cognitive map theory: The hippocampus
originally stored maps of space.
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Remembering the Future:
Prospection and Imagination
How We Imagine Future Experiences
 The Circuitry of Prospection and
Recollection
 Prospection in Other Species
 Models of Prospection
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How We Imagine Future
Experiences
Prospection refers to how we imagine
future events.
 Lesions of the hippocampus impair both
recollection and prospection.
 The medial temporal lobes, medial parietal
and prefrontal areas, and lateral temporal
and parietal lobes are important for both
recollection and prospection.
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How We Imagine Future
Experiences
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The Circuitry of Prospection and
Recollection
The medial prefrontal cortex connects to
the temporal lobes and amygdala.
 It is important for tracking the value of a
stimulus and for establishing long-term
goals.
 The medial parietal lobe connects to
medial temporal areas and is important for
mapping.
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The Circuitry of Prospection and
Recollection
The retrosplenial cortex interacts with the
posterior hippocampus and is important for
navigation.
 The temporoparietal junction and the
superior temporal sulcus integrate
information from various senses.
 The hippocampus may integrate activity in
these different areas.
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The Circuitry of Prospection and
Recollection
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Prospection in Other Species

Other species appear to use prospection.
 Jays
 Rats

It is difficult to design and interpret studies
of prospection in other species.
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Prospection in Other Species
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Models of Prospection
The BBB model proposes that the place
cells in the hippocampus are important for
all mental imagery.
 These cells reactivate maps of the
environment and objects within the
environment.
 Such maps allow the animal to use past
experiences to meet current needs.

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Models of Prospection
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The Confabulation of Reality
Confabulation in the Injured Brain
 The Anatomy of Spontaneous
Confabulation
 Confabulation in the Normal Brain
 The Anatomy of a False Memory
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Confabulation in the Injured
Brain
Confabulation is creating an alternate
version of the past and acting as if it is
completely true.
 Provoked confabulations occur when a
person is prompted for more details than
they can remember.
 Spontaneous confabulations occur without
external cues.
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Confabulation in the Injured
Brain
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The Anatomy of Spontaneous
Confabulation
In confabulation, the person fails to inhibit
currently irrelevant memories.
 Spontaneous confabulations occur
following damage to the medial
orbitofrontal and prefrontal cortex.
 The dorsomedial thalamus or
hypothalamus are sometimes damaged in
patients who confabulate.
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The Anatomy of Spontaneous
Confabulation
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The Anatomy of Spontaneous
Confabulation
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Confabulation in the Normal
Brain
Memory errors are common, even in
uninjured brains.
 Schacter’s Sins of Memory

 Misattribution:
When we attribute a memory to
the wrong source.
 Suggestibility: False memories are implanted
by information we hear after the event.
 Bias: Our current knowledge distorts what we
recall about the past.
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The Anatomy of a False Memory
There are difference in the patterns of
brain activity associated with true versus
false memories.
 These areas include the hippocampus,
parahippocampal cortex, and medial and
lateral prefrontal cortex.
 There was a failure to inhibit the
misinforming memory.
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The Anatomy of a False Memory
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The Mechanisms of Memory
General Mechanisms of Learning and
Memory
 Memory as Synaptic Change
 Long-Term Potentiation and Depression of
Synaptic Connections
 The NMDA Receptor
 Consolidation and Reconsolidation
 Associative Neural Networks
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General Mechanisms of Learning
and Memory
Memory involves widespread activity in the
brain.
 There are general principles of plasticity
that apply to all regions,
 All models of memory include changing
the strength of the synaptic connection
based on previous activity.
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Memory as Synaptic Change
Donald Hebb hypothesized about
experience-dependent plasticity.
 If cell A repeatedly stimulates cell B, then
the connection between A and B is
strengthened.
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Memory as Synaptic Change
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Long-Term Potentiation and
Depression
Long-term potentiation (LTP) was the first
demonstration of the experiencedependent plasticity proposed by Hebb.
 LTP was first described in 1973, about 25
years after it was proposed by Hebb.
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Long-Term Potentiation and
Depression
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The NMDA Receptor
This type of ionotropic glutamate receptor
is important for early stages of LTP.
 This receptor is not active under normal
conditions, because the channel is
blocked by a magnesium ion.
 If the cell is repeatedly depolarized, the
change in membrane voltage causes the
magnesium ion leave the channel.
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The NMDA Receptor
The NMDA receptor allows cations,
including calcium, to enter the cell.
 The calcium activates secondarymessenger systems, promoting learningrelated changes within the cell.
 This receptor acts as a coincidence
detector.
 LTP is specific to a particular synapse.
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The NMDA Receptor
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The NMDA Receptor
Long-term depression occurs when there
is no response of the post-synaptic cell to
repeated input.
 Short-term potentiation and depression
also occur.

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Consolidation and
Reconsolidation
Consolidation is moving memories from
short-term to long-term storage.
 Consolidation occurs in the hippocampus.
 Once they have been recalled, memories
need to be reconsolidated into long-term
memory.
 Memories are vulnerable to editing or loss
during reconsolidation.
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Consolidation and
Reconsolidation
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Associative Neural Networks
Learning can be simulated on artificial
neural networks.
 Small changes in how the network is
connected result in changes to the output
of the network.

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Associative Neural Networks
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Beyond Synaptic Plasticity: The
Frontiers of Memory Mechanisms
Whole Neurons as a Substrate for
Memory?
 New Neurons for New Memories
 Spines: Another Structural Basis for
Memory?
 Looking inside the Cell: Memory in
Chemical Reactions
 Epigenetics: Making a Single Genome
Play Different Tunes
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Whole Neurons as a Substrate
for Memory?
Although research has focused on
synaptic changes, memory could use a
different process within the cell.
 The birth of new neurons (neurogenesis)
in the hippocampus could be important for
storing information.
 Thousands of new neurons are formed in
the hippocampus every day.
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Whole Neurons as a Substrate
for Memory?
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New Neurons for New Memories
Younger neurons have greater plasticity,
so may be important for forming new
connections.
 New cells may provide a framework for
establishing connections among existing
neurons.
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Spines: Another Structural Basis
for Memory?
Dendritic spines grow and change shape
in a matter of hours in young animals.
 These spines become less plastic and
more stabile in adults.
 The spines may be important for memory
storage.
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Spines: Another Structural Basis
for Memory?
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Looking inside the Cell: Memory
in Chemical Reactions
Chemical reactions within the cell may
store memories.
 This may involve some biochemical
process, such as activating an enzyme.
 CaMKII and CPEB are proteins thought to
be important for memory and learning.
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Looking inside the Cell: Memory
in Chemical Reactions
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Looking inside the Cell: Memory
in Chemical Reactions
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Epigenetics: Making a Single
Genome Play Different Tunes
Epigenetics describe changes to the
structure (not nucleotide sequence) of
DNA and the nuclear proteins.
 Adding methyl groups to DNA can block
transcription.
 Adding acetyl groups to histone proteins
can facilitate transcription.
 Epigenetic modifications are heritable.

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Epigenetics: Making a Single
Genome Play Different Tunes
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The Mysteries of Memory
Are the Roles of LTP and LTD
Overstated?
 The Timing of Spikes
 The Limitations of Neural Networks
 Neural Networks: Solving the Wrong
Problem?
 Remembering Relationships, Not Features
 The Future of Memory Research
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Are the Roles of LTP and LTD
Overstated?
Research supports that LTP and LTD are
necessary for memory formation.
 Research does not support that these
processes provide the full explanation.
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The Timing of Spikes
The roles of the timing of action potentials
has not been addressed by current models
of memory.
 The order of activity (pre-synaptic activity,
then post-synaptic activity) matters greatly
in memory formation.

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The Timing of Spikes
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The Limitations of Neural
Networks
Information must be relevant to be
learned, but artificial neural networks
cannot distinguish relevant from irrelevant.
 Relevance may be encoded by using
neuromodulators to turn plasticity at the
synapse on or off.
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The Limitations of Neural
Networks
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Neural Networks: Solving the
Wrong Problem?
Neural networks can extract the identity of
the object without seeing the whole thing.
 Brains encode information differently,
encoding the relation between different
stimuli.
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Remembering Relationships, Not
Features
Human memory shows invariance,
meaning the details of size, lighting,
position, etc. do not matter.
 This supports the idea that we learn the
relations between things, not just learn
them on a pixel-by-pixel basis.
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Remembering Relationships, Not
Features
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