Lecture Presentation for Chapter 17

Report
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
(continued)
• 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 There Are Several Kinds of Memory and Learning
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., Henry Molaison,
suffered from severe epilepsy.
Because his seizures began in the
temporal lobes, a decision was made
to remove the anterior temporal lobes
on both sides.
H.M.’s surgery removed the amygdala,
the hippocampus, and some cortex.
Figure 17.1 Brain Tissue Removed from Henry Molaison (Patient H.M.)
17 There Are Several Kinds of Memory and Learning
• Retrograde amnesia is the loss of
memories formed before onset of
amnesia and is not uncommon after
brain trauma.
• Anterograde amnesia is the inability
to form memories after onset of
amnesia.
H.M. had normal short-term memory
but had severe anterograde amnesia.
17 There Are Several Kinds of Memory and Learning
Damage to the hippocampus can
produce memory deficits.
H.M. was able to show improvement
with motor skills but could not
remember performing them (i.e. he
could not recall the tasks verbally.).
H.M.’s memory deficit was confined to
describe the tasks he performed.
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. (Things we are aware that
are learned.)
• Nondeclarative (procedural)
memory deals with how—shown by
performance rather than conscious
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 left dorsal
thalamus, bilateral damage to the
mammillary bodies (limbic structures in
the hypothalamus), and probable
damage to the mammillothalamic tract.
Like Henry Molaison, he has short-term
memory but cannot form declarative longterm 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.
Patients often confabulate—fill in a
gap in memory with a falsification
which they accept as true.
Brain damage occurs in mammillary
bodies and dorsomedial thalamus,
similar to N.A., and to the basal
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 and severe
shrinkage of the hippocampus and
parahippocampal cortex; his semantic
memory is good.
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 Memory Has Temporal Stages: Short, Intermediate, and Long
• Iconic memories are the briefest
memories and store sensory
impressions that only last a few
seconds.
• Short-term memories (STMs)
usually last only for up to 30 seconds
or throughout rehearsal.
Short-term memory is also known as
working memory.
Figure 17.6 Stages of Memory Formation
17 Memory Has Temporal Stages: Short, Intermediate, and Long
Working memory can be subdivided
into three components, all supervised
by an executive control module:
• Phonological loop—contains auditory
information
• Visuospatial sketch pad—holds
visual impressions
• Episodic buffer—contains more
integrated, sensory 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 17.7 Serial Position Curves from Immediate-Recall Experiments (Part 1)
Figure 17.7 Serial Position Curves from Immediate-Recall Experiments (Part 2)
17 Memory Has Temporal Stages: Short, Intermediate, and Long
Long-term memory has a large
capacity.
Information can also be forgotten or
recalled inaccurately.
17 Successive Processes Capture, Store, and Retrieve
Information in the Brain
A functional memory system
incorporates three aspects:
• Encoding—sensory information is
passed into short-term memory.
• Consolidation—short-term memory
information is transferred into longterm storage.
• Retrieval—stored information is
used.
Figure 17.8 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
Thus, the prefrontal cortex and
parahippocampal cortex are
important for consolidation.
These mechanisms reflect
hemispheric specializations
(left hemisphere for language and
right hemisphere for spatial ability).
17 Successive Processes Capture, Store, and Retrieve
Information in the Brain
The engram, or memory trace, is the
physical record of a learning
experience and 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
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 17.9 Encoding, Consolidation, and Retrieval of Declarative Memories
17 Successive Processes Capture, Store, and Retrieve
Information in the Brain
In posttraumatic stress disorder (PTSD,
characterized as reliving and being
preoccupied by traumatic events), memories
produce stress hormones that further reinforce
the memory.
GABA, ACh, and opioid transmission can also
enhance memory formation in animal models.
Treatments that can block chemicals acting on
the basolateral amygdala may alter the effect
of emotion on memories.
Box 17.1 The Amygdala and Memory
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
disruption or alteration.
Reconsolidation is the return of a
memory trace to stable long-term
storage after it’s temporarily volatile
during recall.
17 Successive Processes Capture, Store, and Retrieve
Information in the Brain
Reconsolidation can distort memories.
Successive activations can deviate
from original information.
New information during recall can also
influence the memory trace.
17 Successive Processes Capture, Store, and Retrieve
Information in the Brain
Leading questions can lead to
‘remembering’ events that never
happened.
‘Recovered memories’ and ‘guided
imagery’ can have false information
implanted into the recollection.
Figure 17.10 Are “Recovered” Memories Reliable?
17 Different Brain Regions Process Different Aspects of Memory
Testing declarative memories in
monkeys:
• Delayed non-matching-to-sample
task—a test of object recognition
memory, where the subject must
choose the object that was not seen
previously.
Figure 17.11 The Delayed Non-Matching-to-Sample Task
17 Different Brain Regions Process Different Aspects of Memory
Medial temporal lobe damage causes
impairment on the delayed
nonmatching-to-sample task.
The amygdala is not necessary for
declarative memory tasks.
The hippocampus (in conjunction with
the entorhinal, parahippocampal) and
perirhinal cortices, is important for
these tasks.
Figure 17.12 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 17.13 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 spatial
relationships.
Latent learning is when acquisition
has taken place but has not been
demonstrated in performance tasks.
Figure 17.14 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.
Place cells remap when a rodent is
placed in a new environment.
17 Different Brain Regions Process Different Aspects of Memory
Grid cells and border cells are
neurons that fire when animal is at
an intersection and at the perimeter
of an abstract grid map,
respectively.
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 (relative
to the rest of the brain) in mammals
and birds.
In food-storing species of birds, the
hippocampus is larger but only if
used to retrieve stored food.
Figure 6.6 Food Storing in Birds as Related to Hippocampal Size
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 sex
differences in spatial memory,
depending on behavior.
Polygynous male meadow voles travel
further (to find females) and have a
larger hippocampus than female
meadow voles or males of monogamous
pine voles.
Figure 17.15 Sex, Memory, and Hippocampal Size
17 Different Brain Regions Process Different Aspects of Memory
Imaging studies help to understand learning
and nondeclarative memory for different skills:
• Sensorimotor skills, such as mirror-tracing.
• Perceptual skills—learning to read mirrorreversed text.
• Cognitive skills—planning and problem
solving.
All three of these depend on functional basal
ganglia; the motor cortex and cerebellum are
also important for some skills.
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.
Conceptual priming (priming based on
word meaning) is associated with
reduced activation of the left frontal
cortex.
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 17.16 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 17.16 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 17.16 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 17.17 Brain Regions Involved in Different Kinds of Learning and Memory
17 Neural Mechanisms of Memory Storage
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 the
environment.
17 Memory Storage Requires Neuronal Remodeling
Sherrington speculated that alterations in
synapses were the basis for learning.
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 neurotransmitterreceptor interactions.
Figure 17.18 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 17.18 Synaptic Changes That May Store Memories (Part 2)
Figure 17.18 Synaptic Changes That May Store Memories (Part 3)
Figure 17.18 Synaptic Changes That May Store Memories (Part 4)
17 Memory Storage Requires Neuronal Remodeling
Lab animals living in a complex environment
demonstrated biochemical and anatomical
brain changes from those living in simpler
environments.
Three housing conditions:
• Standard condition (SC)
• Impoverished (or isolated) condition (IC)
• Enriched condition (EC)
Figure 17.19 Experimental Environments to Test the Effects of Enrichment on Learning and Brain
Measures
17 Memory Storage Requires Neuronal Remodeling
Animals housed in EC, compared to those
in IC, developed:
• heavier, thicker cortex;
• enhanced cholinergic activity;
• More dendritic branches (especially on
basal dendrites near the cell body), with
more dendritic spines suggesting more
synapses.
Figure 17.20 Measurement of Dendritic Branching (Part 1)
Figure 17.20 Measurement of Dendritic Branching (Part 2)
Figure 17.20 Measurement of Dendritic Branching (Part 3)
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
Invertebrates demonstrate nonassociative
learning which 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 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 17.21 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 17.22 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 17.22 Synaptic Plasticity Underlying Habituation in Aplysia (Part 2)
17 Synaptic Plasticity Can Be Measured in Simple Hippocampal
Circuits
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.
Hebb’s idea was supported when
researchers used tetanus (a brief increase
of electrical stimulation that triggers
thousands of axon potentials) on the
hippocampus.
17 Synaptic Plasticity Can Be Measured in Simple Hippocampal
Circuits
Long-term potentiation (LTP)—a
stable and enduring increase in the
effectiveness of synapses.
A weakening of synaptic efficacy—
termed long-term depression—can
also encode information.
Figure 17.23 Long-Term Potentiation Occurs in the Hippocampus (Part 1)
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 can be generated in conscious
and freely behaving animals, in
anesthetized animals, and in tissue
slices and that LTP is evident in a
variety of invertebrate and vertebrate
species.
LTP can also last for weeks or more.
Superficially, LTP appears to have the
hallmarks of a cellular mechanism of
memory.
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 (also
called subicular complex or
hippocampal gyrus).
The hippocampus has regions called
CA1, CA2, and CA3 (CA=Cornus
Ammon which means Ammon’s
Horn).
Figure 17.23 Long-Term Potentiation Occurs in the Hippocampus (Part 2)
17 Synaptic Plasticity Can Be Measured in Simple Hippocampal
Circuits
The CA1 region has two kinds of
glutamate receptors:
• NMDA receptors (after its selective
ligand, N-methyl-D-aspartate)
• AMPA receptors (which bind the
glutamate agonist AMPA)
17 Synaptic Plasticity Can Be Measured in Simple Hippocampal
Circuits
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 17.24 Roles of the NMDA and AMPA Receptors in the Induction of LTP in the CA1 Region
(Part 1)
Figure 17.24 Roles of the NMDA and AMPA Receptors in the Induction of LTP in the CA1 Region
(Part 2)
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 (calciumcalmodulin kinase II) which 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 AMPA
receptors.
These effects all increase the synaptic
sensitivity to glutamate.
Figure 17.24 Roles of the NMDA and AMPA Receptors in the Induction of LTP in the CA1 Region
(Part 3)
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 17.25 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, often a diffusible gas
like carbon monoxide (CO) or nitric
oxide (NO) or 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
LTP can occur without NMDA receptor
activation.
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—
training an animal in a memory task
can induce LTP.
17 Some Simple Learning Relies on Circuits in the Mammalian
Cerebellum
Associative learning involves
relations between events.
• In instrumental conditioning—or
operant conditioning—an
association is made between:
Behavior (the instrumental
response).
 The consequences of the behavior
(the reward).
Figure 17.26 Two Types of Conditioning (Part 1)
17 Some Simple Learning Relies on Circuits in the Mammalian
Cerebellum
• 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.
Figure 17.26 Two Types of Conditioning (Part 2)
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 17.27 Functioning of the Neural Circuit for Conditioning of the Eye-Blink Reflex (Part 1)
Figure 17.27 Functioning of the Neural Circuit for Conditioning of the Eye-Blink Reflex (Part 2)
Figure 17.27 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
The trigeminal (V) pathway that carries
information about the corneal
stimulation (the US) to the cranial
motor nuclei also sends axons to the
brainstem (specifically a structure
called the inferior olive).
These brainstem neurons, in turn, send
axons called climbing fibers to synapse
on cerebellar neurons in a region
called the interpositus nucleus .
17 Some Simple Learning Relies on Circuits in the Mammalian
Cerebellum
Blocking GABA in interpositus nucleus
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.
Figure 17.28 Neurogenesis in the Dentate Gyrus
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 selectively turned off in
specific tissues in adults, showed
impaired spatial learning but were
otherwise normal.
17 In the Adult Brain, Newly Born Neurons May Aid Learning
Genetic manipulations can increase
the survival of newly generated
neurons in the dentate, resulting in
improved performance.
These animals showed enhanced
hippocampal LTP, which was
expected since younger neurons
display greater synaptic plasticity.
17 In the Adult Brain, Newly Born Neurons May Aid Learning
Adult neurogenesis is also seen in the
olfactory bulb.
Activation of newly generated neurons
in the olfactory bulb enhances
olfactory learning and memory.
17 Learning and Memory Change as We Age
With age, we tend to show some
memory impairment in tasks of
conscious recollection that:
1. require effort, and
2. rely primarily on internal generation
of the memory rather than on
external cues.
We also experience some decreases
in spatial memory and navigational
skills.
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 17.29 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 and cortex.
Cholinergic pathways to the cortex are
lost in Alzheimer’s disease.
Enhancing cholinergic transmission
helps with memory tasks.
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, which act via glutamate
receptors, work to improve LTP in the
hippocampus.
17 Learning and Memory Change as We Age
One particular protein kinase—PKMζ
(ζ is zeta)—is needed for long-term
maintenance of both hippocampal
LTP and cortical memory traces.
Highly selective memory enhancing
drugs could be developed in the near
future.
17 Learning and Memory Change as We Age
Lifestyle factors can help reduce
cognitive decline:
• Living in a favorable environment
• Involvement in complex and
intellectually stimulating activities
• Having a partner of high cognitive
status
17 The Cutting Edge: Artificial Activation of an Engram
Mice were placed in two contexts:
• Context A—placed in a box with a
white plastic floor in a dimly lit room
with black walls and a faint smell of
almonds; these mice explored the
chamber and showed no signs of
being afraid.
• Context B—classically conditioned to
a tone with electrical shock; these
mice learned to freeze to the tone.
17 The Cutting Edge: Artificial Activation of an Engram
These mice had also been genetically
modified so that whenever neurons in
the dentate gyrus (DG) of the
hippocampus were active, they would
start producing channelrhodopsin, a
protein that would excite those cells,
and only those cells, when exposed
to blue light.
Figure 17.31 Artificial Activation of an Engram (Part 1)
17 The Cutting Edge: Artificial Activation of an Engram
Activity of the subset of DG neurons
with channelrhodopsin was
responsible for the mice finding
context B frightening.
Reactivating those neurons caused the
mice to freeze in fear, even when
they were in a completely different
context.
Figure 17.31 Artificial Activation of an Engram (Part 2)
17 The Cutting Edge: Artificial Activation of an Engram
Turning the light off again caused the
animals to resume activity, indicating
that they remained unafraid of context A.
It wasn’t just that light-induced activation
of any random set of DG neurons
induced fear, because when blue light
reactivated DG neurons that had been
active in a third (nonfearful) context, C,
the animals did not freeze.
Figure 17.31 Artificial Activation of an Engram (Part 3)
Figure 17.31 Artificial Activation of an Engram (Part 4)

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