Download doc Chapter 13 Notes

Chapter 13: Learning and Memory
Notes taken by: Ashley Brown
Contact for mistakes: [email protected]
Tbh these notes might suck (esp. near the end I got way bored), some parts might be
word for word from the book but I felt that since I used like soley the notes from the
other chapters I might as well contribute something. Best of luck to all and hope
these help
The Nature of Learning:
Learning: the process by which experiences change our nervous system and therefore
our behavior
Memory are these changes in our nervous system; alterations in neural circuits that
participate in perceiving, performing, thinking, and planning
Four types of learning
1. Perceptual Learning: learning to recognize a particular stimulus that has been
perceived before
- Primary function: the ability to identify and categorize objects and situations
- Each sensory system is capable of perceptual learning
- Accomplished primarily by changes in the sensory association cortex
2. Stimulus-response learning: learning to automatically make a particular response in
the presence of a particular stimulus
- Involves establishing connections between circuits involved in perception and
in movement
- Can be either an automatic response like a defensive reflex or a complicated
sequence of movements
- Two major categories:
o Classical conditioning: a learning procedure in which an unimportant
stimulus acquires the properties of an important one. This is done by
taking a stimulus that normally has no meaning (this is the
conditioned stimulus - CS) and following it by a stimulus (called the
unconditioned stimulus - US) that has a defensive or reflexive
response (called the unconditioned response – UR). Eventually the
CS will be able to evoke the response too, which is then called the
conditioned response, CR
 Can be explained the Hebb Rule: a hypothesis proposed by
Donald Hebb that the cellular Basis of learning involves
strengthening of a synapse that is repeatedly active when the
postsynaptic neuron fires
 An association between 2 stimuli
o Instrumental conditioning: Also called operant conditioning. It is a
learning procedure whereby the effects of a particular behavior in a
particular situation increase (reinforce) or decrease (punish) the
probability of the behavior
 Involves behaviors that have been learned (as opposed to
automatic like in classical)
 An association between a response and a stimulus
 Strengthens the connections involved in perception and those
involved in movement
 More flexible than classical; makes it so things can adjust its
behavior according to the consequences of that behavior
 When followed by a favorable consequence or a
reinforcing stimulus the behavior will be repeated
more often
 When followed by an unfavorable consequence or a
punishing stimulus it will occur less frequently
3. Motor learning: Learning to make a new response. A component of stimulus response
learning
4. Relational learning: involves learning the relationships among individual stimuli
- Connections between different areas of the association cortex such as
interconnections between different sensory association cortexes
- Spatial learning is a type because you have to recognize objects, the learn the
relative locations with respect to others
- Episodic learning: learning the sequences of events that we witness is another
type of relational learning because we have to keep track of/remember the events
themselves and then recognize the order that they occur in
Synaptic Plasticity: Long-Term Potentiation
Learning involves synaptic plasticity or changes in the structure or biochemistry of
synapses that alter their effects on postsynaptic neurons
Induction of Long-Term Potentiation:
Long-term potentiation (LTP): a long-term increase in the excitability of a neuron to a
particular synaptic input caused by repeated high-frequency activity of that input
- Can cause the long-term strengthening of the synapses between two neurons
as seen in Hebb’s rule
o Associative long-term potentiation: a long-term potentiation in
which concurrent stimulation of weak and strong synapses to a given
neuron strengthens the weak ones
- Inducing LTP:
o place a stimulating electrode among the axons in the perforant path
and a recording electrode near the granule cells of the dentate gyrus
o A pulse of electrical is delivered which produces a population EPSP,
or an evoked potential that represents the EPSPs of a population of
neurons, that is recorded in the dentate gyrus. This is the “before” after
you stimulate the perforant path with high intensity with high
frequency stimulation we induce LTP
Hippocampal formation: a forebrain structure of the temporal lobe, constituting an
important part of the limbic system; includes the hippocampus proper (Ammon’s horn),
dentate gyrus, and subiculum
- Neurons of the dentate gyrus send axons to the CA3 field and then form
synapses with the dendrites of pyramidal cells
o One branch of the axons from the CA3 pyramidal cells travel through
the fornix to reach areas of the basal forebrain
o Another branch synapse with the pyramidal cells of the CA1 field
 These cells provide the main output of the hippocampus to the
subiculum, entorhinal cortex, and basal forebrain
- Granule cells of the dentate gyrus receive info from the entorhinal cortex via
the perforant path. The entorhinal cortex channels all the major neocortical
inputs and outputs
Role of NMDA Receptors:
Experiments showed that synaptic strengthening occurs when molecules of NT bing with
postsynaptic receptors located in a dendritic spine that is already depolarized.
- shows the LTP requires (1) activation of synapses and (2) depolarization of
the post synaptic neuron
- Can be explained by the NMDA receptor which is a specialized ionotropic
glutamate receptor that controls a calcium channel that is normally blocked by
Mg2+ ions but when its depolarized its not blocked
o AP5 is a drug that blocks NMDA receptors and therefore blocks the
establishment of LTPs  this shows that the activation of NMDA
receptors is necessary for the first step in the processes of events that
establishes LTP aka entry of calcium into the dendritic spines
o the properties of the NMDA receptor account for both the existence of
LTP and for its associative nature
Dendrites in some types of pyramidal cells can produce action potentials called dendritic
spikes. They have a high threshold of excitement
- these spikes are necessary for LTP
Mechanisms of Synaptic Plasticity
Strengthening of an individual synapse appears to be accomplished by inserting more
AMPA receptors, an ionotropic glutamate receptor that controls a sodium channel and
when open produces EPSPs, into the postsynaptic membrane of the dendritic spine
- After LTP the AMPA receptors of CA1 cells move from the dendritic spine
through the synapse to the membrane of the postsynaptic neuron
o This movement is caused by a calcium dependent enzyme called
CaM-KII (type 2 calcium-calmodulin kinase)
 The enzyme becomes concentrated in the postsynaptic density
(a band inside the postsynaptic membrane that contains
proteins, receptors and all that good stuff)
It has also been suggested that LTP changes the synaptic structure and causes production
of new synapses.
- thin dendritic spines become fatter, mushroom shaped spines
- also new dendrites can grow that then form connections with nearby axons
Some research also indicates that PRESYNATIC changes can occur as well such as an
increase in the amount of glutamate released by the terminal button
- This could be because nitric oxide can communicate messages from one cell
to another. Several studies show that NO could be a retrograde messenger
involved in LTP
Long lasting LTP requires protein synthesis.
Three types of LTP:
- LTP1 involves almost immediate changes in synaptic strength caused by
insertion of AMPA receptors. Last for an hour or 2.
- LTP2 a local protein synthesis that is made possible because dendrites contain
mRNA that can be translated into proteins/enzymes
- LTP3 is the more durable type of LTP that involes production of mRNA in the
nucleus that is then transported to the dendrites where protein synthesis then
takes place. Requires dopamine.
LTP initiates 2 processes:
- the production of plasticity-related proteins through normal synthesis of
mRNA in the nucleus
- the production of a chemical “tag” in the dendritic spines where LTP has
taken place
SUMMARY OF LTP:
Terminal button releases glutamate which binds to the NMDA receptor
Ca2+ enter postsynaptic cell if membrane is depolarised (via NMDA receptors)
CA2+ activate CAM-KII
CAM-KII facilitates the insertion of AMPA receptors into postsynaptic density
LTP causes structural changes (e.g., dendritic growth)
Long lasting LTP requires protein synthesis
Other Forms of Long-Term Potentiation
In field CA3 of the hippocampal formation LTP appears to involve only presynaptic
changes
Perceptual Learning
Learning is what enables us to adapt to our environment and respond to change.
Perceptual ability involves learning to recognize things, not what to do when they’re
there.
- can involve learning to recognize entirely new stimuli
- also involved with recognizing changes or variations in familiar stimuli
Learning to Recognize Stimuli
Visual info pathway:
LGN of thalamus  primary visual cortex (first level of analysis) extrastriate cortex
 (analysis of particular attributes of a visual scene like form, color, movement)  next
level of visual association which is either the ventral (object recognition or “what”)
stream or dorsal (perception of location or “where”) stream
Perceptual learning involves changes in synaptic connections in the visual association
cortex
Perceptual Short-Term Memory
Short-term memory is the memory of a stimulus or an event that last for short while
usually just a few seconds
Recognition of a stimulus is when sensory activates an established set of neural circuits.
Short term memory of a stimulus involves the activity of these circuits that continues
after the stimulus disappears. Like for visual you can see this with continuous activation
of the fusiform face area to remember someone is still there after recognizing them
Delayed matching-to-sample task requires the subject to indicate which of several
stimuli has just been perceived. It is used to experiment with short-term memory.
Perceptual short-term memories often involve other brain regions than just the sensory
association cortexes.
- prefrontal cortex: plays a role to manipulate and organize to-be-remembered
information, devise strategies for retrieval, and also to monitor the outcome
- dorsolateral prefrontal cortex involved when reordering words, and later
people were more likely to remember from reordering than rehearsing
Classical Conditioning
The amygdala is involved in classically conditioned emotional responses.
- More firing in the lateral nucleus of amygdala corresponded with a larger
magnitude of a conditioned emotional response
- Involves LTP  LTP in the lateral amygdala, mediated by NMDA receptors,
plays a critical role in the establishment of conditioned emotional responses
Instrumental Conditioning
Basal Ganglia
Instrumental conditioning entails the strengthening of connections between neural
circuits that detect a particular stimulus and neural circuits that produce a response so
they begin in regions of sensory association cortexes and end in the motor association
cortex of the frontal lobe
Two major pathways between the sensory association cortex and motor association
cortex:
- Direct transcortical connections: connections from one area of the cerebral
cortex to another
o Together with the hippocampal formation, theses are involved in the
acquisition of episodic memories (complex perceptual memories of
sequences of events)
o Involved in the acquisition of complex behaviors that involve
deliberation or instruction
- Connections via the basal ganglia and thalamus
As behaviors become automatic and routine they are “transferred” to the basal ganglia
Reinforcement
When good things happen reinforcement mechanisms in the brain become active and the
establishment of synaptic changes is facilitated.
Neural Circuits Involved in Reinforcement:
Axons of dopaminergic cells project to areas of the brain through three major pathways
- Nigrostriatal pathway connects substantia nigra with the striatum: involved in
movement
- Mesocortical pathway connects the ventral tegmental area (VTA) (which is
a group of dopaminergic neurons in the ventral midbrain that plays a critical
role in reinforcement) to the cerebral cortex: its involved in cognition,
motivation, and emotion
- Mesolimbic pathway connects the VTA to the nucleus accumbens (NAC)
which is a nucleus of the basal forebrain near the septum and is involved in
reward and desire also in attention and reinforcement
o Neurons in the NAC project to the ventral part of the basal ganglia
The bundle of axons that carry the information from the VTA to the NAC is called the
medial forebrain bundle (MFB)
Also shown that dopaminergic neurons projecting to the NAC might also be involved in
stress
Functions of the Reinforcement System: must serve to (1) detect the presence of a
reinforcing stimulus and (2) strengthening the connections between the neurons that
detect the discriminative stimulus and the neurons that produce the instrumental response
- Detecting: the reinforcement depends on both the stimulus and the state of the
animal i.e. a hungry animal will get reinforcement with food present.
o Activated by unexpected reinforcing stimuli
o Sometimes novelty in itself can activate dopaminergic neurons and
facilitate LTP and learning
o Anticipation also can increase activation of the VTA when it is
activated
 Prefrontal cortex involved: it could turn on the reinforcement
mechanism when it determines that the ongoing behavior is
bringing the organism near its goal aka that its strategy is
working. Also thinking and planning can bring reinforcement
too.
 The prefrontal cortex is also a target of dopamine neurons as
well a source of their control.
- Strengthening: Instrumental conditioning involves a discriminative stimulus, a
response, and a reinforcing stimulus. The discriminative stimulus activates
weak synapses on motor neurons responsible for movement, then the response
activates strong synapse and then the reinforcing stimulus if present triggers
the stimulation of a NT or neuromodulator throughout the region in which the
synaptic change takes place and this is what is needed to strengthen the weak
synapses of the discriminative stimulus and that’s what you need dopamine
for LTP
Relational Learning
More complex learning, also more common because involves memories related to other
memories. Like seeing a photograph of a friend makes you remember their name, times
you’ve had together, where they’re from, etc.
Relational learning includes the establishment and retrieval of memories of events,
episodes, and places.
Human Anterograde Amnesia
At first glance appears to be the inability to learn new information following an event.
-
later see that basic abilities of perceptual learning, stimulus-response learning,
and motor learning are still intact but not relational learning.
Can be caused by damage to the temporal lobes  Scoville and Milner
showed that bilateral removal of the medial temporal lobe produced a memory
impairment in humans that was identical to that of Korsakoff’s syndrome
o Conclusions of study of H.M. : (1) the hippocampus is not the location
of long-term memories, nor is it necessary for the retrieval of long
term memories. (2) the hippocampus is not the location of immediate
(short-term) memories. (3) the hippocampus is involved in converting
immediate (short-term) memories into long-term memories
Retrograde amnesia: the inability to remember events that happened before the brain
damage occurred. Often people with anterograde amnesia also have a small aspect of
retrograde amnesia too.
Korsakoff’s syndrome: permanent anterograde amnesia caused by brain damage
resulting from chronic alcoholism or malnutrition
- can remember old memories, can’t form new ones
- can converse normally and remember events that happened long before their
brain damage but not after
Consolidation: the process by which short-term memories are converted to long-term
memories
- short-term memories: limited amount of storing of information temporarily
- long-term memories: unlimited amount of information permanently
Spared Learning Abilities
People with memory deficits can perform the other three types of learning.
- patients were able to perform better and better on a recognition test even
though they don’t remember ever doing the test before
- patients can acquire stimulus-response learning too, like a classically
conditioned eye blink response without memory of the learning itself
- can also learn motor learning but not know what they’re doing even while
they’re doing it
Declarative and Nondeclarative Memories
Amnesic patients lack declarative memories aka they can not say they have memory of
things but still have Nondeclarative memories
Declarative memories can be verbally expressed, such as a memory for events in a
person’s past
- amnesic patients seem unable to form this type
- involve facts and experiences
Nondeclarative memories have formation that does not depend on the hippocampal
formation. It is a collective term for perceptual, stimulus-response, and motor memory
- appear to operate automatically aka they don’t require deliberate attempts on
the learner to memorize something
- don’t involve facts or experiences
- they are implicit memories
- involve basal ganglia
Anatomy of Anterograde Amnesia
One clear fact: damage to the hippocampal formation (dentate gyrus, CA fields,
hippocampus itself, and the subiculum + subregions) or to regions of brain that supply its
input/receive its outputs causes anterograde amnesia
Most important input to hippocampal formation is the entorhinal cortex
- receives its input from amygdala, various regions of the limbic cortex, and all
association regions of the neocortex either directly or via two adjacent regions
of the limbic cortex: the perirhinal cortex and the parahippocampal cortex
o Perirhinal cortex receives information from the ventral stream and
the parahippocampal from the dorsal stream
o collectively these 3 regions constitute the limbic cortex of the medial
temporal lobe
Also receives input from the subcortical regions via the fornix
- these select and modulate the functions of the hippocampal formation
- fornix carries dopaminergic axons from the VTA, noradrenergic axons from
the locus coeruleus, serotonergic axons from the raphe nuclei, and
acetylcholinergic axons from the medial septum
- also fornix connects hippocampal formation with the mammillary bodies
o Most prominent brain damage in Korsakoff’s syndrome and
presumably the cause of the anterograde amnesia is degeneration of
the mammillary bodies
Primary outcome from hippocampal system comes mainly from field CA1 and the
subiculum
- this is often relayed back through the entorhinal, perirhinal, and the
parahippocampal cortex to the same regions of the association cortex that
provides inputs
Periods of anoxia can cause damage to the CA1 field and this causes anterograde
amnesia.
- these cells are more vulnerable to anoxia because they have a lot of NMDA
receptors
o lack of oxygen, seizures, metabolic disturbances, or hypoglycemia
causes glutamatergic terminal buttons to release glutamate at
abnormally high levels which then stimulate the receptors which
permit lots of calcium into the cell and then the calcium starts
destroying neurons
Role of the Hippocampal Formation in Consolidation of Declarative Memories
So it goes like this
- hippocampus receives information about whats going on from sensory and
motor association cortex and some subcortical regions like basal ganglia and
amygdala
- processes this information
- through its efferent (out of ) connections with these regions, modifies the
memories that are being consolidated there, linking them together in ways that
will permit us to remember the relationships amount the elements of the
memories
This means declarative memories should activate the hippocampal formation, and they
do.
- pictorial or spatial information activates the right hippocampal formation
- activation of the left hippocampal formation is related to a person’s ability to
remember a list of words
In anterograde amnesia the accompanying retrograde amnesia duration is related to the
amount of damage tot eh medial temporal lobe
- damage to limited to the hippocampus results in retrograde amnesia lasting a
few years
- additional damage to the entorhinal cortex produces a retrograde amnesia of
one to two decades
- with hippocampus and much of the medial temporal lobe damage results in
retrograde amnesia that spares only memory acquired in early life such as
those acquired in childhood
In a recognition study at first the hippocampal formation was active with memory but as
the task went on the prefrontal cortex started showing activation with the memory. So
they were transferred.
Episodic and Semantic Memories
Distinct forms of declarative memories
- episodic memories involve context and they include information about when
and under what conditions a particular episode occurred and the order in
which the episode took place. Specific to a particular time and place because a
given episode only occurs once
o must be learned all at once
- semantic memories involve facts but don’t include information about the
context the facts were learned. Aka they are less specific.
o Acquired gradually over time
Acquisition of both types require the participation of the hippocampus
Episodic memories which are an integrated sequence of perceptual memories are located
in the sensory association cortex because that’s were perceptual memories are located.
Semantic dementia is a degenerative neurological disorder in which loss of semantic
memories occur from progressive degeneration of the neocortex of the lateral temporal
lobes
- episodic memory retained
- difficulty naming pictures of objects, understanding the meaning of words, but
have no problem such as naming 6 digit numbers and matching large numbers
according to their approximate size
Spatial Memory
Bilateral medial temporal lobe lesions produce the most profound impairment in spatial
memory but significant deficits can be produced by damage that is limited to the right
hemisphere.
Right hippocampal formation becomes active when a person is remembering a
navigational task
Taxi drivers have larger right posterior hippocampi
The dorsal hippocampus of rats contains place cells which are neurons that are directly
involved in navigation of space.
Hippocampus used in spatial strategy and caudate nucleus used in response strategy.
Relational Learning in Laboratory Animals
Spatial perception and learning  used Morris water maze
- requires relational learning because they need to navigate around the maze by
getting their bearing from relative locations of stimuli located outside the
maze (windows, doors, etc).
- can also be used for nonrelational stimulus response learning because if they
are released at the same place each time they learn swimming a certain
direction leads them to safety
- rats with hippocampal lesions can learn the stimulus response method but
can’t find the platform if they are released in different spots because they
can’t read spatial clues
Place Cells in the Hippocampal Formation
When animals move around the environment, they have these pyramidal cells that
fire/become active when the animal is in particular places in an environment called
spatial receptive fields. These cells are called place cells and they are most typically
found in the hippocampal formation.
- spatial receptive fields are not encoding to a particular location but rather the
information is represented by particular patterns of activity in circuits of large
numbers of neurons within the hippocampal formation
- firing of place cells represent where an animal “thinks” it is
Hippocampus receives its spatial information from the parietal lobes through the
entorhinal cortex. Neurons in entorhinal cortex also have spatial receptor fields they just
aren’t as clear cut as those of the hippocampal pyramidal cells
Pyramidal cells in CA1 encode both the current location and the intended direction
Role of the Hippocampal Formation in Memory Consolidation
Confirmed that the hippocampus is involved in consolidation of spatial memories for a
limited time and the result of this activity is to help establish the memories in the cerebral
cortex
Slow wave sleep facilitates the consolidation of declarative memories in human subjects
while REM sleep facilitates the consolidation of Nondeclarative memories
Reconsolidation of Memories
The modification of long-term memories involves reconsolidation which is a process of
consolidation of memory that occurs subsequent to the original consolidation that can be
triggered by a reminder of the original stimulus.
- involves LTP  all the stuff about Anisomycin we learned in the revision
conference led to the conclusion that when synaptic plasticity is prevented,
reconsolidation cannot occur so it requires LTP
- when reconsolidating a memory it can be altered or attached new information
and can even be erased or be made inaccessible if there is something that
interferes with reconsolidation
Role of Long-Term Potentiation in Memory
Experiment shows that the participation in hippocampal formation in learning involves
LTP
Role of Hippocampal Neurogenesis in Consolidation
New neurons form connections with other neurons in the dentate gyrus and with neurons
in field CA3 (??? I don’t think I grasp this section [p. 482 – 483] much I recommend
reading it. Or b.s.ing if a question is actually asked…)
Training rats with stimulus-response learning had no response to neurogenesis but ones
that involve relational learning saw an increase in fos protein in newly formed dentate
gyrus neurons that shows that those neurons had been activated by the experience
It was found that it was easier to establish associative LTP in newly formed neurons than
in older neurons.
- Neurogenesis could be a mechanism that facilitates synaptic plasticity by
providing an available pool of neurons that can make new memories
This all takes a long time so enhanced neurogenesis is only a benefit for long-term basis.