Transcript Memory - Sinauer Associates

17
Learning and Memory
17 Learning and Memory
Functional Perspectives on Memory
• There Are Several Kinds of Memory and
Learning
• Memory Has Temporal Stages: Short,
Intermediate, and Long
• Successive Processes Capture, Store, and
Retrieve Information in the Brain
• Different Brain Regions Process Different
Aspects of Memory
17 Learning and Memory
Neural Mechanisms of Memory
• Memory Storage Requires Neuronal
Remodeling
• Invertebrate Nervous Systems Show
Plasticity
• Synaptic Plasticity Can Be Measured in
Simple Hippocampal Circuits
17 Learning and Memory
Neural Mechanisms of Memory (cont'd)
• Some Simple Learning Relies on Circuits
in the Mammalian Cerebellum
• In the Adult Brain, Newly Born Neurons
May Aid Learning
• Learning and Memory Change as We Age
17 Functional Perspectives on Memory
Learning is the process of acquiring
new information.
Memory is:
• The ability to store and retrieve
information.
• The specific information stored in the
brain.
17 There Are Several Kinds of Memory and Learning
Patient H.M. suffers from amnesia, or
memory impairment.
• Retrograde amnesia is the loss of
memories formed before onset of
amnesia.
• Anterograde amnesia is the inability
to form memories after onset of a
disorder.
17 There Are Several Kinds of Memory and Learning
Damage to the hippocampus can
produce memory deficits.
H.M.’s surgery removed the amygdala,
the hippocampus, and some cortex.
H.M.’s memory deficit was confined to
verbal tasks.
Figure 17.1 Brain Tissue Removed from Henry Molaison (Patient H.M.)
Figure 17.2 Henry’s Performance on a Mirror-Tracing Task
17 There Are Several Kinds of Memory and Learning
Two kinds of memory:
• Declarative memory deals with what
– facts and information acquired
through learning that can be stated or
described.
• Nondeclarative (procedural)
memory deals with how – shown by
performance rather than recollection.
Figure 17.3 Two Main Kinds of Memory: Declarative and Nondeclarative
17 There Are Several Kinds of Memory and Learning
Damage to other areas can also cause
memory loss.
Patient N.A. has amnesia due to
accidental damage to the
dorsomedial thalamus.
Like Henry Molaison, he has shortterm memory but cannot form
declarative long-term memories.
Figure 17.4 The Brain Damage in Patient N.A.
17 There Are Several Kinds of Memory and Learning
Korsakoff’s syndrome is a memory
deficiency caused by lack of thiamine
– seen in chronic alcoholism.
Brain damage occurs in mammillary
bodies and basal frontal lobes.
Patients often confabulate – fill in a
gap in memory with a falsification.
17 There Are Several Kinds of Memory and Learning
Two subtypes of declarative memory:
• Semantic memory – generalized
memory.
• Episodic memory – detailed
autobiographical memory.
Patient K.C. cannot retrieve personal
(episodic) memory due to accidental
damage to the cortex.
17 There Are Several Kinds of Memory and Learning
Three subtypes of nondeclarative memory :
• Skill learning – learning to perform a task
requiring motor coordination.
• Priming – repetition priming – a change in
stimulus processing due to prior exposure
to the stimulus.
• Conditioning – the association of two
stimuli, or of a stimulus and a response.
Figure 17.5 Subtypes of Declarative and Nondeclarative Memory
17 There Are Several Kinds of Memory and Learning
Nonassociative learning involves a single
stimulus presented once or repeated.
Three types of nonassociative learning:
• Habituation – a decreased response to
repeated presentations of a stimulus.
• Dishabituation – restoration of response
amplitude after habituation.
• Sensitization – prior strong stimulation
increases response to most stimuli.
17 There Are Several Kinds of Memory and Learning
Associative learning involves
relations between events.
• In classical conditioning –
Pavlovian conditioning – a neutral
stimulus is paired with another
stimulus that elicits a response.
Eventually the neutral stimulus by itself
will elicit the response.
17 There Are Several Kinds of Memory and Learning
• In instrumental conditioning – or
operant conditioning – an
association is made between:
 Behavior (the instrumental
response).
 The consequences of the behavior
(the reward).
17 Memory Has Temporal Stages: Short, Intermediate, and Long
• Iconic memories are the briefest
and store sensory impressions.
• Short-term memories (STMs)
usually last only for seconds, or
throughout rehearsal.
Short-term memory is also known as
working memory.
17 Memory Has Temporal Stages: Short, Intermediate, and Long
Working memory can be subdivided
into three components, all supervised
by a central executive:
• Phonological loop – contains auditory
information.
• Visuospatial sketch pad – holds
visual impressions.
• Episodic buffer – contains more
integrated information.
17 Memory Has Temporal Stages: Short, Intermediate, and Long
• An intermediate-term memory
(ITM) outlasts a STM, but is not
permanent.
• Long-term memories (LTMs) last
for days to years.
17 Memory Has Temporal Stages: Short, Intermediate, and Long
Mechanisms differ for STM and LTM
storage, but are similar across
species.
• The primacy effect is the higher
performance for items at the
beginning of a list (LTM).
• The recency effect shows better
performance for the items at the end
of a list (STM).
Figure 17.6 Serial Position Curves from Immediate-Recall Experiments
17 Memory Has Temporal Stages: Short, Intermediate, and Long
Long-term memory has a large
capacity, but can be altered.
The memory trace, or record of a
learning experience, can be affected
by other events before or after.
Each time a memory trace is activated
and recalled, it is subject to changes.
17 Successive Processes Capture, Store, and Retrieve
Information in the Brain
A functional memory system
incorporates three aspects:
• Encoding – sensory information is
encoded into short-term memory.
• Consolidation – information may be
consolidated into long-term storage.
• Retrieval – stored information is
retrieved.
Figure 17.7 Hypothesized Memory Processes: Encoding, Consolidation, and Retrieval
17 Successive Processes Capture, Store, and Retrieve
Information in the Brain
Multiple brain regions are involved in
encoding, as shown by fMRI.
For recalling pictures, the right
prefrontal cortex and
parahippocampal cortex in both
hemispheres are activated.
For recalling words, the left prefrontal
cortex and the left parahippocampal
cortex are activated.
17 Successive Processes Capture, Store, and Retrieve
Information in the Brain
Consolidation of memory involves the
hippocampus but the hippocampal
system does not store long-term
memory.
LTM storage occurs in the cortex, near
where the memory was first
processed and held in short-term
memory.
Figure 17.8 Encoding, Consolidation, and Retrieval of Declarative Memories
17 Successive Processes Capture, Store, and Retrieve
Information in the Brain
The process of retrieving information
from LTM can cause memories to
become unstable and susceptible to
to disruption or alteration.
Reconsolidation is the return of a
memory trace to stable long-term
storage, after recall.
17 Successive Processes Capture, Store, and Retrieve
Information in the Brain
Strong emotions can enhance memory
formation and retrieval.
Many compounds participate:
acetylcholine, epinephrine,
norepinephrine, vasopressin, the
opioids, and GABA.
Drugs that are agonists or antagonists
of these can be involved.
17 Successive Processes Capture, Store, and Retrieve
Information in the Brain
In posttraumatic stress disorder
(PTSD), memories produce a stress
hormone response that further
reinforces the memory.
Treatments that can block chemicals
acting on the basolateral amygdala
may alter the effect of emotion on
memories.
Box 17.2 The Amygdala and Memory
17 Different Brain Regions Process Different Aspects of Memory
Testing declarative memories in
monkeys:
• Delayed non-matching-to-sample
task – must choose the object that
was not seen previously.
Medial temporal lobe damage causes
impairment on this task.
Figure 17.9 The Delayed Non-Matching-to-Sample Task
Figure 17.10 Memory Performance after Medial Temporal Lobe Lesions
17 Different Brain Regions Process Different Aspects of Memory
Imaging studies confirm the
importance of medial temporal
(hippocampal) and diencephalic
regions in forming long-term
memories.
Both are activated during encoding
and retrieval, but long-term storage
depends on the cortex.
17 Different Brain Regions Process Different Aspects of Memory
Episodic and semantic memories are
processed in different areas.
Episodic (autobiographical) memories
cause greater activation of the right
frontal and temporal lobes.
Figure 17.11 My Story versus Your Story
17 Different Brain Regions Process Different Aspects of Memory
Early research indicated that animals
form a cognitive map – a mental
representation of a spatial
relationship.
Latent learning has taken place but
has not been demonstrated in
performance tasks.
Figure 17.12 Biological Psychologists at Work
17 Different Brain Regions Process Different Aspects of Memory
The hippocampus is also important in
spatial learning.
It contains place cells that become
active when in, or moving toward, a
particular location.
Grid cells and border cells are
neurons that fire when animal is at an
intersection or perimeter of an
abstract grid map.
17 Different Brain Regions Process Different Aspects of Memory
In rats, place cells in the hippocampus
are more active as the animal moves
toward a particular location.
In monkeys, spatial view cells in the
hippocampus respond to what the
animal is looking at.
17 Different Brain Regions Process Different Aspects of Memory
Comparisons of behaviors and brain
anatomy show that increased
demand for spatial memory results in
increased hippocampal size in
mammals and birds.
In food-storing species of birds, the
hippocampus is larger but only if
used to retrieve stored food.
17 Different Brain Regions Process Different Aspects of Memory
Spatial memory and hippocampal size
can change within the life span.
In some species, there can be be sex
differences in spatial memory,
depending on behavior.
Polygynous male meadow voles travel
further and have a larger
hippocampus than females or
monogamous pine vole males.
Figure 17.13 Sex, Memory, and Hippocampal Size
17 Different Brain Regions Process Different Aspects of Memory
Imaging studies help to understand learning
and memory for different skills:
• Sensorimotor skills, such as mirror-tracing.
• Perceptual skills – learning to read mirrorreversed text.
• Cognitive skills – planning and problem
solving.
17 Different Brain Regions Process Different Aspects of Memory
Imaging studies of repetition priming
show reduced bilateral activity in the
occipitotemporal cortex, related to
perceptual priming.
Perceptual priming reflects prior
processing of the form of the
stimulus.
17 Different Brain Regions Process Different Aspects of Memory
During conceptual priming, there is
reduced activity compared to
baseline in only the left frontal cortex.
Conceptual priming reflects the
meaning of the stimulus.
17 Different Brain Regions Process Different Aspects of Memory
Imaging of conditioned responses can show
changes in activity.
PET scans made during eye-blink tests
show increased activity in several brain
regions, but not all may be essential.
Patients with unilateral cerebellar damage
can acquire the conditioned eye-blink
response only on the intact side.
17 Different Brain Regions Process Different Aspects of Memory
Different brain regions are involved
with different attributes of working
memories such as space, time, or
sensory perception.
Memory tasks assess the contributions
of each brain region.
17 Different Brain Regions Process Different Aspects of Memory
The eight-arm radial maze is used to
test spatial location memory.
Rats must recognize and enter an arm
that they have entered recently to
receive a reward.
Only lesions of the hippocampus
produce a deficit in this
predominantly spatial task.
Figure 17.14 Tests of Specific Attributes of Memory (Part 1)
17 Different Brain Regions Process Different Aspects of Memory
In a memory test of motor behavior the
animal must remember whether it
made a left or right turn previously.
If it turns the same way as before it
receives a reward.
Only animals with lesions to the
caudate nucleus showed deficits.
Figure 17.14 Tests of Specific Attributes of Memory (Part 2)
17 Different Brain Regions Process Different Aspects of Memory
Sensory perception can be measured
by the object recognition task.
Rats must identify which stimulus in a
pair is novel.
This task depends on the extrastriate
cortex.
Figure 17.14 Tests of Specific Attributes of Memory (Part 3)
17 Different Brain Regions Process Different Aspects of Memory
Interim summary of brain regions
involved in learning and memory:
• Many brain regions are involved.
• Different forms of memory are
mediated by at least partly different
mechanisms and brain structures.
• The same brain structure may be
involved in many forms of learning.
Figure 17.15 Brain Regions Involved in Different Kinds of Learning and Memory
17 Neural Mechanisms of Memory
Molecular, synaptic, and cellular events
store information in the nervous system
New learning and memory formation can
involve new neurons, new synapses, or
changes in synapses in response to
biochemical signals.
Neuroplasticity (or neural plasticity) is the
ability of neurons and neural circuits to be
remodeled by experience or environment.
17 Memory Storage Requires Neuronal Remodeling
Sherrington speculated that alterations in
synapses were the basis for learning.
Hebb proposed that when two neurons are
repeatedly activated together, their
synaptic connection will become stronger.
Cell assemblies - ensembles of neurons linked via Hebbian synapses could store
memory traces.
17 Memory Storage Requires Neuronal Remodeling
Physiological changes at synapses
may store information.
Changes can be presynaptic, or
postsynaptic, or both.
Changes can include increased
neurotransmitter release, or
effectiveness of receptors.
17 Memory Storage Requires Neuronal Remodeling
Synaptic changes can be measured
physiologically, and may be
presynaptic, postsynaptic, or both.
Changes include increased
neurotransmitter release and/or a
greater effect due to changes in
receptors.
Figure 17.16 Synaptic Changes That May Store Memories (Part 1)
17 Memory Storage Requires Neuronal Remodeling
Changes in the rate of inactivation of
transmitter would also increase
effects.
Inputs from other neurons might
increase or decrease
neurotransmitter release.
17 Memory Storage Requires Neuronal Remodeling
Structural changes at the synapse may
provide long-term storage.
New synapses could form or some
could be eliminated with training.
Training might also lead to synaptic
reorganization.
Figure 17.16 Synaptic Changes That May Store Memories (Part 2)
17 Memory Storage Requires Neuronal Remodeling
Lab animals living in a complex environment
demonstrated biochemical and anatomical
brain changes.
Three housing conditions:
• Standard condition (SC)
• Impoverished (or isolated) condition (IC)
• Enriched condition (EC)
Figure 17.17 Experimental Environments to Test the Effects of Enrichment on Learning and Brain
Measures
17 Memory Storage Requires Neuronal Remodeling
Animals housed in EC developed:
• Heavier, thicker cortex.
• Enhanced cholinergic activity.
• Larger cortical synapses.
• Altered gene expression.
• Enhanced recovery from brain damage.
17 Memory Storage Requires Neuronal Remodeling
EC also increases growth in dendrites:
• More dendritic spines suggesting
more synapses.
• Increased dendritic branching,
especially on basal dendrites, nearer
the cell body.
Figure 17.18 Measurement of Dendritic Branching (Part 1)
Figure 17.18 Measurement of Dendritic Branching (Part 2)
17 Invertebrate Nervous Systems Show Plasticity
Aplysia is used to study plastic
synaptic changes in neural circuits.
The advantages of Aplysia:
• Has fewer nerve cells.
• Can create detailed circuit maps for
particular behaviors – little variation
between individuals.
17 Invertebrate Nervous Systems Show Plasticity
Habituation is studied in Aplysia.
Squirts of water on its siphon causes it
to retract its gill.
After repeated squirts, the animal
retracts the gills less – it has learned
that the water poses no danger.
Figure 17.19 The Sea Slug Aplysia
17 Invertebrate Nervous Systems Show Plasticity
The habituation is caused by synaptic
changes between the sensory cell in
the siphon and the motoneuron that
retracts the gill.
Less transmitter released in the
synapse results in less retraction.
Figure 17.20 Synaptic Plasticity Underlying Habituation in Aplysia (Part 1)
17 Invertebrate Nervous Systems Show Plasticity
Over several days the animal
habituates faster, representing longterm habituation.
The number of synapses between the
sensory cell and the motoneuron is
reduced.
Figure 17.20 Synaptic Plasticity Underlying Habituation in Aplysia (Part 2)
17 Synaptic Plasticity Can Be Measured in Simple Hippocampal
Circuits
Long-term potentiation (LTP) – a
stable and enduring increase in the
effectiveness of synapses.
Tetanus – a brief increase of electrical
stimulation that triggers thousands of
axon potentials.
17 Synaptic Plasticity Can Be Measured in Simple Hippocampal
Circuits
Synapses in LTP behave like Hebbian
synapses:
• Tetanus drives repeated firing.
• Postsynaptic targets fire repeatedly
due to the stimulation.
• Synapses are stronger than before.
17 Synaptic Plasticity Can Be Measured in Simple Hippocampal
Circuits
LTP occurs at several sites in the
hippocampal formation – formed by
the hippocampus, the dentate
gyrus and the subiculum.
Regions CA1 and CA3 are most often
studied.
Figure 17.21 Long-Term Potentiation Occurs in the Hippocampus (Part 1)
Figure 17.21 Long-Term Potentiation Occurs in the Hippocampus (Part 2)
Figure 17.21 Long-Term Potentiation Occurs in the Hippocampus (Part 3)
17 Synaptic Plasticity Can Be Measured in Simple Hippocampal
Circuits
The CA1 region has both NMDA and
AMPA receptors.
Glutamate first activates AMPA
receptors.
NMDA receptors do not respond until
enough AMPA receptors are
stimulated and the neuron is partially
depolarized.
17 Synaptic Plasticity Can Be Measured in Simple Hippocampal
Circuits
NMDA receptors at rest have a
magnesium ion (Mg2+) block on their
calcium (Ca2+) channels.
After partial depolarization, the block is
removed and the NMDA receptor
allows Ca2+ to enter in response to
glutamate.
Figure 17.22 Roles of NMDA and AMPA Receptors in the Induction of LTP in CA1 Region (Part 1)
Figure 17.22 Roles of NMDA and AMPA Receptors in the Induction of LTP in CA1 Region (Part 2)
Figure 17.22 Roles of NMDA and AMPA Receptors in the Induction of LTP in CA1 Region (Part 3)
17 Synaptic Plasticity Can Be Measured in Simple Hippocampal
Circuits
The large Ca2+ influx activates certain
protein kinases – enzymes that add
phosphate groups to protein molecules.
One protein kinase is CaMKII – it affects
AMPA receptors in several ways:
• Causes more AMPA receptors to be
produced and inserted in the postsynaptic
membrane.
17 Synaptic Plasticity Can Be Measured in Simple Hippocampal
Circuits
CaMKII :
• Moves existing nearby AMPA
receptors into the active synapse.
• Increases conductance of Na+ and K+
ions in membrane-bound receptors.
These effects all increase the synaptic
sensitivity to glutamate.
17 Synaptic Plasticity Can Be Measured in Simple Hippocampal
Circuits
The activated protein kinases also
trigger protein synthesis.
Kinases activate CREB – cAMP
responsive element-binding
protein.
17 Synaptic Plasticity Can Be Measured in Simple Hippocampal
Circuits
CREB binds to cAMP responsive
elements in DNA promoter regions.
CREB changes the transcription rate
of genes.
The regulated genes then produce
proteins that affect synaptic function
and contribute to LTP.
Figure 17.23 Steps in the Neurochemical Cascade during the Induction of LTP
17 Synaptic Plasticity Can Be Measured in Simple Hippocampal
Circuits
Strong stimulation of a postsynaptic
cell releases a retrograde
messenger that travels across the
synapse and alters function in the
presynaptic neuron.
More glutamate is released and the
synapse is strengthened.
17 Synaptic Plasticity Can Be Measured in Simple Hippocampal
Circuits
There is evidence that LTP may be
one part of learning and memory
formation:
• Correlational observations – time
course of LTP is similar to that of
memory formation.
17 Synaptic Plasticity Can Be Measured in Simple Hippocampal
Circuits
• Somatic intervention experiments –
pharmacological treatments that
block LTP impair learning.
• Behavioral intervention experiments
– show that training an animal in a
memory task can induce LTP.
17 Some Simple Learning Relies on Circuits in the Mammalian
Cerebellum
Researchers use the eye-blink reflex
to study neural circuits in mammals.
An air puff is preceded by an acoustic
tone – conditioned animals will blink
when just the tone is heard.
A circuit in the cerebellum is necessary
for this reflex.
Figure 17.24 Functioning of the Neural Circuit for Conditioning of the Eye-Blink Reflex (Part 1)
Figure 17.24 Functioning of the Neural Circuit for Conditioning of the Eye-Blink Reflex (Part 2)
Figure 17.24 Functioning of the Neural Circuit for Conditioning of the Eye-Blink Reflex (Part 3)
17 Some Simple Learning Relies on Circuits in the Mammalian
Cerebellum
Neurons converge in the interpositus
nucleus of the cerebellum.
Blocking GABA in this area stops the
behavioral response.
The cerebellum is also important in
conditioning of emotions and
cognitive learning, as shown by
humans with cerebellar damage.
17 In the Adult Brain, Newly Born Neurons May Aid Learning
Neurogenesis, or birth of new neurons,
occurs mainly in the dentate gyrus in adult
mammals.
Neurogenesis and neuronal survival can be
enhanced by exercise, environmental
enrichment, and memory tasks.
Reproductive hormones and experience are
also an influence.
17 In the Adult Brain, Newly Born Neurons May Aid Learning
In some studies, neurogenesis has
been implicated in hippocampusdependent learning.
Conditional knockout mice, with
neurogenesis turned off in adults,
showed impaired spatial learning but
were otherwise normal.
Figure 17.25 Neurogenesis in the Dentate Gyrus
17 Learning and Memory Change as We Age
Some causes of memory problems in
old age:
• Impairments of coding and retrieval –
less cortical activation in some tasks.
• Loss of neurons and/or neural
connections – some parts of the brain
lose a larger proportion of volume.
Figure 17.26 Active Brain Regions during Encoding and Retrieval Tasks in Young and Old People
17 Learning and Memory Change as We Age
• Deterioration of cholinergic pathways - the
septal complex and the nucleus basalis of
Meynert (NBM) provide cholinergic input to
the hippocampus.
These pathways seem to be involved in
Alzheimer’s disease.
• Impaired coding by place cells – neurons
encode less spatial information.
17 Learning and Memory Change as We Age
Nootropics are a class of drugs that
enhance cognitive function.
Cholinesterase inhibitors result can
have a positive effect on memory and
cognition.
Ampakines work to improve LTP in the
hippocampus.
17 Learning and Memory Change as We Age
Lifestyle factors can help reduce
cognitive decline:
• Living in a favorable environment.
• Involvement in enriching activities.
• Having a partner of high cognitive
status.