Chapter 13 – The Biology Of Learning And Memory

Question 1

Type of conditioning produced by the pairing of two stimuli, one of which evokes an automatic response

Answer 1

Classical conditioning

Question 2

A stimulus that initially elicits no response of note

Stimulus that evokes a particular response only after it has been paired with an unconditioned stimulus

Answer 2

Conditioned stimulus CS

Question 3

Stimulus that automatically evokes an unconditional response

Answer 3

Unconditioned stimulus UCS

Question 4

Response automatically evoked by an unconditioned stimulus

Answer 4

Unconditioned response UCR

Question 5

Response evoked by a conditioned stimulus after it has been paired with an unconditioned stimulus

Answer 5

Conditioned response CR

Question 6

A type of condition in which reinforcement or punishment changes the future probabilities of a given behaviour

Answer 6

Instrumental conditioning or operant conditioning

Question 7

Any event that increases the future probability of the preceding response

Answer 7

Reinforcer

Question 8

An event that suppresses the frequency of the preceding response

Answer 8

Punishment

Question 9

Physical representation of what has been learned

An example would be a connection between two brain areas

Answer 9

Engram

Question 10

Describe Karl Lashley’s search for the engram

Answer 10

Lashley reasoned that if learning depends on new or strengthened connections between two brain areas, a knife cut somewhere in the brain should interrupt that connection and abolish the learned response.

He trained rats on mazes and a brightness discrimination task and then made deep cuts in varying locations in their cerebral cortices.

No knife cut significantly impaired the rats performances. Evidently, the types of learning that he studied did not depend on connections across the cortex.

Also tested whether any portion of the cerebral cortex is more important than others for learning by training rats on mazes before or after removing large portions of the cortex.
The lesions impaired performance, but the deficit depended more on the amount of brain damage than on its location. Learning and memory apparently did not rely on a single cortical area. Proposed two principles about the nervous system: equipotentiality and mass action

Question 11

Concept that all parts of the cortex contribute equally to complex behaviors; any part of the cortex can substitute for any other

Answer 11

Equipotentiality

Proposed by Karl Lashley after finding that removing large portions of the cortex impaired performance depending on the amount of brain damage rather than on its location

Question 12

Concept that the cortex works as a whole and the more cortex, the better

Answer 12

Mass action

Proposed by Karl Lashley after finding that removing large portions of the cortex impaired performance depending on the amount of brain damage rather than on its location

Question 13

Karl Lashley’s conclusions about equipotentiality and mass action rested on two unnecessary assumptions:

Answer 13

1. That the cerebral cortex is the best or only place to search for and engram
2. That all kinds of memory are physiologically the same

Question 14

Describe how and why Richard Thompson arrived at a different conclusion than Karl Lashley

Answer 14

Sought the engram of memory not in the cerebral cortex like Lashley, but in the cerebellum.

Studied classical conditioning of eyelid responses in rabbits by presenting first a tone (CS) and then a puff of air (UCS) to the cornea of the rabbits eye which made the rabbit blink in response to the air puff. After repeated pairings, classical conditioning occurred and rabbits blink at the tone also.

If learning is like a sequence occurring in several areas, learning occurring in one area will prevent learning by blocking the input to another area or the output from another area.

Thompson identified one nucleus of the cerebellum, the lateral interpositus nucleus LIP, as essential for learning because the cells showed little response to the tone at the beginning of training, but as learning proceeded, their responses increased. Also, when investigators temporarily suppressed that nucleus in an untrained rabbit and then presented the CS and UCS, the rabbit show no responses during the training. After waiting for the rabbit to recover, The rabbit begin to learn with continued training, but it learned at the same speed as animals that have received no previous training.
To find out if learning actually occurred in the LIP and did not just relay information to a later area where learning occurs, investigators suppressed activity in the red nucleus, a midbrain motor area that receives input from the cerebellum. When the red nucleus was depressed, the rabbits again showed no responses during training. However, as soon as the red nucleus had recovered from the suppression, the rabbit showed strong learned responses to the tone – suppressing the red nucleus temporarily prevented the response but did not prevent learning. Evidently, learning did not require activity in the red nucleus or any area after it. Learning seems to have occurred in the LIP.

Question 15

A nucleus of the cerebellum that is essential for learning

Answer 15

Lateral interpositus nucleus LIP

Question 16

Thompson found a localized engram whereas Lashley did not. What key differences in procedures or assumptions were probably responsible for their different results?

Answer 16

Thompson studied a different, simpler type of learning. Also, he looked in the cerebellum instead of the cerebral cortex

Question 17

What evidence indicates that the red nucleus is necessary for performance of a conditioned response but not for learning the response?

Answer 17

If the red nucleus is inactivated during training, the animal makes no conditioned responses during the training, so the red nucleus is necessary for the response. However, as soon as the red nucleus recovers, the animal can show conditioned responses at once, without any further training, so learning occurred while the red nucleus was inactivated

Question 18

Memory of events that have just occurred

Answer 18

Short-term memory

Question 19

Memory of events that occurred further back in time

Answer 19

Long-term memory

Question 20

Describe three characteristics or evidence that support the idea of short-term memory and long-term memory

Answer 20

1. Short-term memory and long-term memory differ in their capacity. If you hear a series of numbers or letters, you can probably repeat no more than about seven of them, and with other kinds of material, your maximum is even less. Long-term memory has a vast, difficult to estimate capacity
2. Short term memory depends on rehearsal. You can recall long-term memories that you haven’t thought about in years.
3. With short-term memory, once you have forgotten something, it is lost. With long-term memory, a hint might help you reconstruct something you thought you had forgotten

Question 21

To strengthen a memory and make it more long-lasting

Answer 21

Consolidate

Question 22

Restrengthening of a memory by a similar later experience

Answer 22

Reconsolidation

Question 23

Describe the changing views of consolidation of memories

Answer 23

Researchers had proposed that all information initially entered a short term storage, where it stayed until the brain had time to consolidate it into long-term memory. If anything interrupted the rehearsal before consolidation took place, the information was simply lost.

Problems:
1. Many short-term memories are not simply temporary stores on their way to being long term memories. Example – You may remember a hockey score until it changes, and rehearsing it for an hour doesn’t turn it into a long-term memory.
2. Understanding of consolidation changed – original idea was that the brain held onto something in short-term memory for whatever time is needed to do what it had to do in order to establish a long-term memory, mainly synthesize new proteins. And once formed, the long-term memory was supposed to be permanent.
Problems – first, the time needed for consolidation varies enormously. Example, more likely to remember a significant or emotional memory.
Secondly, a consolidated memory is not solid forever

Question 24

How do epinephrin and cortisol enhance memory storage?

Answer 24

Epinephrin and cortisol both enhance emotional memories by stimulating the amygdala and hippocampus

Question 25

The way we store information while we are working with it

Answer 25

Working memory

Question 26

Assignment in which an animal must respond on the basis of a signal that it remembers but that is no longer present

A common test of working memory- requires responding to something that you saw or heard a short while ago

Answer 26

Delayed response task

Example: having to stare at a central fixation point, and a light flashes briefly at some point toward the periphery in any direction. You have to continue staring at the central point for a few seconds until you hear a beep, and then look toward the place where you remember seeing the light.
During the delay, certain cells in the prefrontal cortex as well as the parietal cortex increase their activity. The increase in activity does not necessarily take the form of repeated action potentials; another possibility is that still sore extra calcium, increasing their readiness to respond to new signals when the time comes.

Question 27

What is the primary brain location for working memory, and what is one hypothesis for how it stores temporary information?

Answer 27

The prefrontal cortex is the primary location. According to one hypothesis, it stores temporary information by elevated calcium levels, which potentiate later responses

Question 28

Memory loss

Answer 28

Amnesia

Even in severe cases, no one loses all kinds of memory equally.

Studies on amnesia help clarify the distinctions among different kinds of memory and enable us to explore the mechanisms of memory

Question 29

Inability to form memories for events that happened after brain damage

Answer 29

Anterograde amnesia

Question 30

Loss of memory for events that occurred before brain damage

Answer 30

Retrograde amnesia

Question 31

Memories of single personal events

Answer 31

Episodic memory

Question 32

Deliberate recall of information that one recognizes as a memory

Answer 32

Explicit memory

Question 33

An influence of experience on behavior, even if the influence is not recognized in memory

Answer 33

Implicit memory

Question 34

Deliberate recall of information that one recognizes as a memory

Answer 34

Declarative memory

Question 35

The development of motor skills and habits; a special kind of implicit memory

Answer 35

Procedural memory

Question 36

Describe the general pattern of people with amnesia, including HM (5)

Note: a surgeon removed HM’s hippocampus and some nearby structures from both hemispheres to relieve his epileptic seizures

Answer 36

1. Normal working memory
2. Severe anterograde amnesia for declarative memory – that is, difficulty forming new declarative memories, especially episodic memories
   Example: HM, for several years after his operation, said he was the same age for several years and then began guessing wildly afterwards
3. Some degree of retrograde amnesia – that is, loss of old memories – mainly limited to episodic memories
   Example: although HM could describe facts he learned before his operation, he could relate few personal experiences
4. Better implicit than explicit memory
   Example: a patient with amnesia chose the picture of the hospital worker that was a friendly person instead of the unfriendly person, although they did not remember her
5. Nearly intact procedural memory– The development of motor skills and habits
   Example: people with amnesia slowly get better at Tetris, although they cannot describe the game and say they don’t remember playing it

Question 37

What is the difference between anterograde and retrograde amnesia?

Answer 37

Retrograde amnesia is forgetting events before brain damage; anterograde amnesia is failing to store memories of events after brain damage

Question 38

Which types of memory are least impaired in people with amnesia?

Answer 38

People with amnesia are generally least impaired on working memory, implicit memory, and procedural memory

Question 39

Task in which an animal sees a sample object and then after a delay must choose an object that matches the sample

Answer 39

Delayed matching-to-sample task

Question 40

Task in which an animal sees an object and then after a delay must choose an object that does not match the sample

Answer 40

Delayed nonmatching-to-sample task

Question 41

An apparatus used to test spatial memory in nonhumans.
A maze that has several arms – typically eight – some or all of which have a bit of food at the end. A rats best strategy is to explore each arm once and only once, remembering where it has already gone.

Answer 41

Radial maze

Question 42

A procedure used to test for spatial memory in nonhumans.

A rat swims through murky water to find a rest platform that is just under the surface

Answer 42

Morris water maze

Question 43

Several theories about the hippocampus focus on its role in these three kinds of memories:

Answer 43

Declarative memory, spatial memory, and memory for details and context

Question 44

Describe the theory of the function of the hippocampus in declarative memory

Answer 44

Theory: patients with hippocampal damage acquire new skills, but have enormous trouble learning new facts – propose that the hippocampus is critical for declarative memory, especially episodic memory

Example: in delayed matching-to-sample tasks, and delayed nonmatching-to-sample tasks, animals must remember which object was present on this occasion, thereby showing what we might call a declarative memory, and perhaps an episodic memory. Hippocampal damage strongly impairs performance in most cases

Question 45

Describe the theory of the function of the hippocampus in spatial memory

Answer 45

Theory: electrical recordings indicate that many neurons in a rats hippocampus are tuned to particular spatial locations, responding best when an animal is in a particular place or looking in a particular direction. When people perform spatial tasks, such as imagining the best route between one house in another, fMRI results show enhanced activity in the hippocampus.

Further evidence: PET scans of the brains of London taxi drivers while answering route questions activated their hippocampus much more than did answering non spatial questions, and MRI scans revealed that they had larger than average posterior hippocampus, especially drivers that had been taxi drivers for longer

Rats and radial maze: rats with damage to the hippocampus gradually learn not to enter the never-correct arms, but even after much training they often enter a correct arm twice – they forget which arms they have already tried.
Rats and the morris water maze: rats with hippocampal damage slowly learn to find the platform if it is always started from the same place and the rest platform is always in the same place – however, if it has to start from a different location or if the rest platform occasionally moves, the rat is disoriented.

Clarks nutcrackers, which berry seeds in thousands of locations and then take them up to survive the winter, have the largest hippocampus and perform best on tests of spatial memory, whereas closely related species that brewery last food and depend on it less to survive the winter have smaller hippocampus’ comparatively

Question 46

Describe the theory of the function of the hippocampus in contextual memory

Answer 46

Recent narratives about an event yesterday or today probably include more detail than describing something from long ago which has less detail, usually just the highlights or the gist of the event. A recent memory, which generally depends on the hippocampus, includes much detail. As time passes, memory becomes less detailed, less dependent on the hippocampus, and more dependent on the cerebral cortex.

When rats are trained to do something, and then tested again after a short delay, they remember the response best if they are tested in the same location – their memory depends on the context. Rats with damage to the hippocampus, if they learn something at all, show no difference between testing in the familiar place and some other place – their memory doesn’t depend on context

In humans, recalling a recent memory (which usually includes details and context) activates the hippocampus. Recalling an old factual memory may or may not activate the hippocampus, but episodic memories, because they necessarily include some context to details, do activate the hippocampus. This hypothesis is well-suited to dealing with the observation that people with hippocampal damage have particular trouble with episodic memories

Question 47

Suppose a rat is in a radial maze in which six arms have food once per day, and two other arms never have food. What kind of mistake does a rat with hippocampal damage make?

Answer 47

Although it learns not to enter the arms that are never correct, it seems to forget which arms it has entered today, and it enters a single arm repeatedly

Question 48

According to the context hypothesis, why does hippocampal damage impair episodic memory?

Answer 48

The hippocampus is especially important for remembering context, and episodic memory necessarily includes some context and detail. People with hippocampal damage have particular trouble with episodic memories

Question 49

Describe the role of the basal ganglia in memory

Answer 49

Gradual learning depends on the basal ganglia- implicit learning or habit learning.

Example: when normal participants are given pictures with information that enables a partly accurate prediction, but together a highly accurate prediction, people gradually start doing better, eventually approaching 100% correct, without necessarily being able to say what strategy they are following. Gradually the basal ganglia learned the pattern and established a habit.
People with Parkinson’s disease who have impairments of the basal ganglia perform about the same as normal people at first, because they have an intact hippocampus, but after many trials continue basing their answers on one picture and do not show gradual improvement.
People with hippocampal damage perform randomly for many trials, because they form no declarative memories and they cannot remember that any particular symbol is usually a signal for one type of prediction or the other, but if they continue long enough, they show gradual improvement based on habits supported by the basal ganglia

Question 50

If you learn a skill, such as predicting the weather, as a procedural habit instead of learning the same skill as a declarative memory, how will the outcome differ?

Answer 50

If you learn it as a procedural habit, based on the basal ganglia, you will learn more slowly and probably be unable to describe what you have learned. However, if the task requires simultaneous attention to a variety of cues, you might reach a higher level of accurate performance than someone learning a declarative memory

Question 51

Brain damage caused by prolonged thiamine deficiency

Answer 51

Korsakoff’s syndrome

Severe thiamine deficiency occurs mostly in chronic alcoholics who go for weeks at a time on a diet of nothing but alcoholic beverages, lacking in vitamins. The brain needs thiamine, vitamin B1, to metabolize glucose, its primary fuel. Prolonged thiamine deficiency leads to a loss or shrinkage of neurons throughout the brain.
Symptoms are similar to those of people with damage to the prefrontal cortex, including apathy, confusion, and memory loss, as well as similarity to hippocampal damage, such as major impairment of episodic memory and sparing of implicit memory. Distinctive symptom is confabulation, filling in memory gaps with guesses, especially questions about episodic memory

Question 52

A distinctive symptom of Korsakoff’s syndrome in which patients fill-in memory gaps with guesses

Answer 52

Confabulation

Question 53

On what kind of question is someone with Korsakoff’s syndrome most likely to confabulate?

Answer 53

Patients with Korsakoff syndrome confabulate on questions for which they would expect to know the answer, such as questions about themselves. Their confabulations are usually statements that were true at one time

Question 54

Condition characterized by memory loss, confusion, depression, restlessness, hallucinations, delusions, sleeplessness, and loss of appetite

Answer 54

Alzheimer’s disease

Have better procedural then declarative memory – learn new skills but are surprised with their good performance.
Memory and alertness vary substantially from time to time, suggesting that many of their problems result from malfunctioning neurons, rather than the death of neurons.
Increased arousal improves memory.

Question 55

What was the first major clue to the causes of Alzheimer’s?

Answer 55

The fact that people with down syndrome almost invariably get Alzheimer’s disease if they survive into middle-age. People with down syndrome have three copies of chromosome 21 rather than the usual two, investigators examined chromosome 21 and found a gene linked to many causes of early-onset Alzheimer’s disease.

Later researchers found two more genes linked to early-onset Alzheimer’s. For cases with onset of symptoms after age 60 to 65, which are vastly more common, one gene has a significant influence, and several other genes appear to be related in one population or another. However, the genes linked to the late-onset variety increase the risk only slightly, as opposed to the genes for early onset that increase it strongly.

Question 56

The genes controlling early-onset Alzheimer’s disease cause a protein called ______-_ to accumulate both inside and outside neurons. The net effect is to damaged dendritic spines, decrease synaptic input, and decrease plasticity. The damaged structures cluster into structures called _____, which accumulate and cause the cerebral cortex, hippocampus, and other areas to atrophy or waste away.
In addition, a second problem relates to the ____ ______ in the intracellular support structure of axons. High levels of amyloid-B cause more phosphate groups to attach to these, causing them to not be able to bind to their usual targets within axons, and start spreading into the cell body and dendrites. Principally responsible for ______, structures formed from degeneration within neurons.

Answer 56

Amyloid-B; plaques; tau protein; tangles

Question 57

How does amyloid-B relate to tau?

Answer 57

The protein amyloid-B accumulates both inside and outside neurons. Within neurons, it increases phosphate attachment to tau proteins. The altered tau proteins no longer attached to their usual sites, and therefore they spread to cell bodies and dendrites, where they add to the damage that amyloid-B caused

Question 58

A loss of semantic memory

Answer 58

Semantic dementia

Question 59

Describe the other brain areas that contribute to various aspects of memory

Answer 59

Parietal lobe: spontaneous elaboration of episodic memories

Anterior and inferior regions of the temporal lobe: semantic memory
Example: a patient with damage here asked what sheep on the road were- problem wasn’t that he couldn’t remember the word sheep, it was as if he had never seen a sheep before.
People with damage to the temporal cortex in just one hemisphere perform approximately normally – serious deficits in semantic memory occur only after bilateral damage.

Parts of the prefrontal cortex: important for learning about rewards and punishment. Respond more quickly, based on the most recent events compared to the basal ganglia.

• cells in the ventromedial prefrontal cortex respond based on the reward to be expected, based on past experience.
• cells in the orbitofrontal cortex respond based on how that reward compares to other possible choices. Cells here are also important for “self control”

Basal ganglia: also learn the reward values of various actions, but they learn slowly, based on the average reward over a long period of time.

Question 60

Which brain area records the expected gains and losses associated with possible actions?

Answer 60

The prefrontal cortex

Question 61

A synapse that increases in effectiveness because of simultaneous activity in the presynaptic and postsynaptic neurons

Answer 61

Hebbian synapse

Question 62

How can a Hebbian synapse account for the basic phenomenon of classical conditioning?

Answer 62

In a Hebbian synapse, pairing the activity of a weaker (CS) axon with a stronger (UCS) axon produces an action potential and in the process strengthens the response of the cell to the CS axon. On later trials, it will produce a bigger depolarization of the postsynaptic cell, which we can regard as a conditioned response

Question 63

A marine invertebrate related to the common slug that is a popular animal for studies of the physiology of learning.

Answer 63

Aplysia

Compared to vertebrates, it has fewer neurons, many which are large and easy to study, and the neurons in these invertebrates are virtually identical from one individual to another.

One commonly studied behaviour is the withdrawl response: if someone touches the siphon, mantle, or gill of the animal, it vigourously withdraws the irritated structure

Question 64

A decrease in response to a stimulus that is presented repeatedly and accompanied by no change in other stimuli

Answer 64

Habituation

Question 65

An increase in response to mild stimuli as a result of exposure to more intense stimuli

Answer 65

Sensitization

Question 66

Describe habituation in Aplysia

Answer 66

If an Aplysia’s gills are repeatedly stimulated with a brief jet of seawater, it withdraws at first, but after many repetitions, it stops responding. The decline in response is not due to muscle fatigue because, even after habituation has occurred, direct stimulation of the motor neuron produces a full-size muscle contraction. Also not due to changes in the sensory neuron because the sensory neuron still gives a full, normal response to stimulation; it merely fails to excite the motor neuron as much as before.
Therefore, habituation in Aplysia depends on a change in the synapse between the sensory neuron and the motor neuron

Question 67

Describe sensitization in Aplysia

Answer 67

A strong stimulus almost anywhere on Aplysia’s skin intensifies a later withdrawal response to a touch.

Strong stimulation on the skin excites a facilitating interneuron that releases serotonin onto the presynaptic terminals of many sensory neurons. Serotonin blocks potassium channels in these membranes. The result is that after later action potentials, the membrane takes longer than usual to repolarize because potassium is slow to flow out of the cell. Therefore, the presynaptic neuron continues releasing its neurotransmitter for longer than usual. Repeating this process causes a sensory neuron to synthesize new proteins that produce long term sensitization

Question 68

When serotonin blocks potassium channels on the presynaptic terminal, what is the effect on transmission?

Answer 68

Blocking potassium channels prolongs the action potential and therefore prolongs the release of neurotransmitters, producing an increased response

Question 69

Phenomenon that when one or more axons connected to a dendrite bombard it with a rapid series of stimuli, some of the synapses become more responsive to new input of the same type for minutes, days, or weeks

Answer 69

Long-term potentiation LTP

The first evidence for a similar process to what was found in Aplysia among vertebrates came from studies of neurons in the rat hippocampus, leading to the phenomenon LTP

Question 70

LTP shows three properties that make it an attractive candidate for a cellular basis of learning and memory:

Answer 70

1. Specificity – if some of the synapses onto a cell have been highly active and others have not, only the active ones become strengthened
2. Cooperativity – nearly simultaneous stimulation by two or more axons produces LTP much more strongly than does repeated stimulation by just one axon
3. Associativity – pairing a weak input with a strong input enhances later responses to the weak input. In this regard, LTP matches what we would expect of Hebbian synapses

Question 71

Property that highly active synapses become strengthened and less active synapses do not

Answer 71

Specificity

Question 72

Tendency for nearly simultaneous stimulation by two or more axons to produce long-term potentiation much more effectively than stimulation by just one

Answer 72

Cooperativity

Question 73

Property that a weak input paired with a stronger input enhances its later response

Answer 73

Associativity

Question 74

A prolonged decrease in response at a synapse where the axons have been less active than certain other axons afferent to that neuron

Answer 74

Long-term depression LTD

You can think of this as a compensatory process. As one synapse strengthens, another weakens

Question 75

A glutamate receptor that can respond to amino-3-hydrozy-5-methyl-4-isoxazoleproprionic acid, AMPA

Answer 75

AMPA receptor

Question 76

A glutamate receptor that can respond to the drug N-methyl-D-aspartate, NMDA

Answer 76

NMDA receptor

Question 77

Describe the roles of AMPA and NMDA receptors in LTP

Answer 77

Both are ionotropic receptors – when they are stimulated, they open a channel to let ions enter the postsynaptic cell.

The AMPA receptor is a typical ionotropic receptor that opens sodium channels. The NMDA receptor, however, is different – its response to the transmitter glutamate depends on the degree of polarization across the membrane. When glutamate attaches to an NMDA receptor while the membrane is at its resting potential, the ion channel is usually blocked by magnesium ions, which are positively charged and are attracted to the negative charge inside the cells but do not fit through the NMDA channel. The NMDA channel opens only if the magnesium leaves, and the surest way to detach the magnesium is to depolarize the membrane, decreasing the negative charge that attracts it.

When an axon release is glutamate repeatedly, so many sodium ions enter through the AMPA channels that the dendrite become strongly depolarized. The depolarization displaces the magnesium molecules, enabling glutamate to open the NMDA channel. At that point, both sodium and calcium enter through the NMDA channel.

The entry of calcium is the key to maintaining LTP. When calcium enters through the NMDA channel, it activates a protein called CaMKII which sets in motion a series of reactions leading to the release of a protein called CREB. CREB goes to the nucleus of the cell and regulates the expression of several genes. In some cases, the altered gene expression lasts for months or years, long enough to account for long-term memory.

The effects of CaMKII and CREB are magnified by BDNF – brain-derived neurotrophic factor, a neurotrophin similar to nerve growth factor. Persisting activity at synapses leads to action potentials that start in axons but back-propagate into the dendrites, which then release BDNF. The formation and maintenance of LTP depends on all these chemicals.

Question 78

When neurons are repeatedly activated, only those with the greatest production of these chemicals (such as CaMKII, CREB, and BDNF) will undergo LTP. Describe possible final outcomes: (4)

Answer 78

1. The dendrite builds more AMPA receptors or moves old ones into better positions
2. The dendrite may make more branches and spines, thus forming additional synapses with the same axon
3. Phosphate groups attach to certain AMPA receptors to make them more responsive than before
4. In some cases, the neuron makes more NMDA receptors

Question 79

Ones LTP has been established, it no longer depends on NMDA synapses. Drugs that block NMDA synapses prevent the ________ of LTP, but they do not interfere with the ________ of LTP that was already established. In other words, once LTP occurs, the AMPA receptors stay potentiated, regardless of what happens to the NMDAs

Answer 79

Establishment; maintenance

Question 80

A transmitter released by a postsynaptic cell that travels back to the presynaptic cell to modify it

Answer 80

Retrograde transmitter

Question 81

Describe changes in the presynaptic neuron regarding LTP

Answer 81

In many cases, LTP depends on changes in the presynaptic neuron instead or in addition to changes in the postsynaptic neuron.

Extensive stimulation of a postsynaptic cell causes it to release a retrograde transmitter that travels back to the presynaptic cell to modify it. In many cases, that retrograde transmitter is nitric oxide. As a result, a presynaptic neuron decreases its threshold for producing action potentials, increases its release of neurotransmitter, expands its axon, and releases its transmitter from additional sites along its axon

In short, LTP reflects increased activity by the presynaptic neuron as well as increased responsiveness by the postsynaptic neuron

Question 82

Before LTP: in the normal state, what is the effect of glutamate at the AMPA receptors? At the NMDA receptors?

Answer 82

Before LTP, glutamate stimulates AMPA receptors but usually has little effect at the NMDA receptors because magnesium blocks them

Question 83

During the formation of LTP: when a burst of intense stimulation releases much more glutamate than usual at two or more incoming axons, what is the effect of the glutamate at the AMPA receptors? At the NMDA receptor’s? Which ions enter at the NMDA receptor’s?

Answer 83

During the formation of LTP, the massive glutamate input strongly stimulates the AMPA receptors, thus depolarizing the dendrite. This depolarization enables glutamate to excite the NMDA receptors also. Both calcium and sodium enter there.

Question 84

After the neuron has gone through LTP: what is now the effect of glutamate at the AMPA receptors? At the NMDA receptors?

Answer 84

After LTP has been established, glutamate stimulates the AMPA receptors more than before, mainly because of an increased number of AMPA receptors. At the NMDA receptors, it is again usually ineffective

Question 85

Long-term potentiation in the hippocampus is important for certain types of learning, but as time passes and learning proceeds, the memory becomes less dependent on the hippocampus and more dependent on the:

Answer 85

Cerebral cortex

Question 86

At this point, what type of drug or chemical is most clearly shown to improve memory without unacceptable side effects?

Answer 86

Caffeine and other stimulants produce benefits. Other drugs may become helpful, but the evidence does not support their use at this time