Learning and memory
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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

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Learning and memory

Learning and Memory


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 memory1

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 memory2

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

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 learning1

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

Figure 17.1 Brain Tissue Removed from Henry Molaison (Patient H.M.)


17 there are several kinds of memory and learning2

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 learning3

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

Figure 17.2 Henry’s Performance on a Mirror-Tracing Task


17 there are several kinds of memory and learning4

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

Figure 17.3 Two Main Kinds of Memory: Declarative and Nondeclarative


17 there are several kinds of memory and learning5

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 mammillothalamictract.

Like Henry Molaison, he has short-term memory but cannot form declarative long-term memories.


Figure 17 4 the brain damage in patient n a

Figure 17.4 The Brain Damage in Patient N.A.


17 there are several kinds of memory and learning6

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 frontal cortex.


17 there are several kinds of memory and learning7

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 learning8

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

Figure 17.5 Subtypes of Declarative and Nondeclarative Memory


17 memory has temporal stages short intermediate and long

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

Figure 17.6 Stages of Memory Formation


17 memory has temporal stages short intermediate and long1

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 long2

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 long3

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 1)


Figure 17 7 serial position curves from immediate recall experiments part 2

Figure 17.7 Serial Position Curves from Immediate-Recall Experiments (Part 2)


17 memory has temporal stages short intermediate and long4

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

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 long-term storage.

  • Retrieval—stored information is used.


Figure 17 8 hypothesized memory processes encoding consolidation and retrieval

Figure 17.8 Hypothesized Memory Processes: Encoding, Consolidation, and Retrieval


17 successive processes capture store and retrieve information in the brain1

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 brain2

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 brain3

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 brain4

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

Figure 17.9 Encoding, Consolidation, and Retrieval of Declarative Memories


17 successive processes capture store and retrieve information in the brain5

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

Box 17.1 The Amygdala and Memory


17 successive processes capture store and retrieve information in the brain6

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 brain7

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 brain8

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

Figure 17.10 Are “Recovered” Memories Reliable?


17 different brain regions process different aspects of memory

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

Figure 17.11 The Delayed Non-Matching-to-Sample Task


17 different brain regions process different aspects of memory1

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

Figure 17.12 Memory Performance after Medial Temporal Lobe Lesions


17 different brain regions process different aspects of memory2

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 memory3

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

Figure 17.13 My Story versus Your Story


17 different brain regions process different aspects of memory4

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

Figure 17.14 Biological Psychologists at Work


17 different brain regions process different aspects of memory5

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 memory6

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 memory7

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 memory8

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

Figure 6.6 Food Storing in Birds as Related to Hippocampal Size


17 different brain regions process different aspects of memory9

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

Figure 17.15 Sex, Memory, and Hippocampal Size


17 different brain regions process different aspects of memory10

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 mirror-reversed 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 memory11

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 memory12

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 memory13

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 memory14

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

Figure 17.16 Tests of Specific Attributes of Memory (Part 1)


17 different brain regions process different aspects of memory15

17 Different Brain Regions Process Different Aspects of Memory

In a memorytest 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

Figure 17.16 Tests of Specific Attributes of Memory (Part 2)


17 different brain regions process different aspects of memory16

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

Figure 17.16 Tests of Specific Attributes of Memory (Part 3)


17 different brain regions process different aspects of memory17

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

Figure 17.17 Brain Regions Involved in Different Kinds of Learning and Memory


17 neural mechanisms of memory storage

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

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 neurotransmitter-receptor interactions.


Figure 17 18 synaptic changes that may store memories part 1

Figure 17.18 Synaptic Changes That May Store Memories (Part 1)


17 memory storage requires neuronal remodeling1

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 remodeling2

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 2)


Figure 17 18 synaptic changes that may store memories part 3

Figure 17.18 Synaptic Changes That May Store Memories (Part 3)


Figure 17 18 synaptic changes that may store memories part 4

Figure 17.18 Synaptic Changes That May Store Memories (Part 4)


17 memory storage requires neuronal remodeling3

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)


Learning and memory

Figure 17.19 Experimental Environments to Test the Effects of Enrichment on Learning and Brain Measures


17 memory storage requires neuronal remodeling4

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 1)


Figure 17 20 measurement of dendritic branching part 2

Figure 17.20 Measurement of Dendritic Branching (Part 2)


Figure 17 20 measurement of dendritic branching part 3

Figure 17.20 Measurement of Dendritic Branching (Part 3)


17 invertebrate nervous systems show plasticity

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 plasticity1

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 plasticity2

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

Figure 17.21 The Sea Slug Aplysia


17 invertebrate nervous systems show plasticity3

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

Figure 17.22 Synaptic Plasticity Underlying Habituation in Aplysia (Part 1)


17 invertebrate nervous systems show plasticity4

17 Invertebrate Nervous Systems Show Plasticity

Over several days, the animal habituates faster, representing long-term 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

Figure 17.22 Synaptic Plasticity Underlying Habituation in Aplysia (Part 2)


17 synaptic plasticity can be measured in simple hippocampal circuits

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 circuits1

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

Figure 17.23 Long-Term Potentiation Occurs in the Hippocampus (Part 1)


17 synaptic plasticity can be measured in simple hippocampal circuits2

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 circuits3

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 circuits4

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

Figure 17.23 Long-Term Potentiation Occurs in the Hippocampus (Part 2)


17 synaptic plasticity can be measured in simple hippocampal circuits5

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 circuits6

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 circuits7

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 1)


Figure 17 24 roles of the nmda and ampa receptors in the induction of ltp in the ca1 region part 2

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 circuits8

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 (calcium-calmodulin 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 circuits9

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

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 circuits10

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 circuits11

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

Figure 17.25 Steps in the Neurochemical Cascade during the Induction of LTP


17 synaptic plasticity can be measured in simple hippocampal circuits12

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 circuits13

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 circuits14

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

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

Figure 17.26 Two Types of Conditioning (Part 1)


17 some simple learning relies on circuits in the mammalian cerebellum1

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

Figure 17.26 Two Types of Conditioning (Part 2)


17 some simple learning relies on circuits in the mammalian cerebellum2

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 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 2)


Figure 17 27 functioning of the neural circuit for conditioning of the eye blink reflex part 3

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 cerebellum3

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 cerebellum4

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

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

Figure 17.28 Neurogenesis in the Dentate Gyrus


17 in the adult brain newly born neurons may aid learning1

17 In the Adult Brain, Newly Born Neurons May Aid Learning

In some studies, neurogenesis has been implicated in hippocampus-dependent 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 learning2

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 learning3

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

17 Learning and Memory Change as We Age

With age, we tend to show some memory impairment in tasks of conscious recollection that:

  • require effort, and

  • 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 age1

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

Figure 17.29 Active Brain Regions during Encoding and Retrieval Tasks in Young and Old People


17 learning and memory change as we age2

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 age3

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 age4

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 age5

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

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 engram1

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

Figure 17.31 Artificial Activation of an Engram (Part 1)


17 the cutting edge artificial activation of an engram2

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

Figure 17.31 Artificial Activation of an Engram (Part 2)


17 the cutting edge artificial activation of an engram3

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 3)


Figure 17 31 artificial activation of an engram part 4

Figure 17.31 Artificial Activation of an Engram (Part 4)


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