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Physiology of Behavior

Twelfth Edition

Chapter 13

Learning and Memory

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Chapter Preview

Overview of Learning and Memory

Stimulus-Response Learning

Motor Learning

Perceptual Learning

Relational Learning

Amnesia

Long-term Potentiation

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Learning Objectives (1 of 5)

13.1 Compare characteristics of four types of learning: stimulus-response, motor, perceptual, and relational learning.

13.2 Contrast characteristics of three types of memory: sensory, short-term, and long-term memory.

13.3 Describe the role of the amygdala and AMPA and NMDA receptors in classical Conditioning.

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Learning Objectives (2 of 5)

13.4 Explain the roles of the basal ganglia, mesolimic and mesocortical pathways, and the prefrontal cortex in reinforcement related to operant conditioning.

13.5 List the contributions of various cortical regions to motor learning.

13.6 Explain the role of the basal ganglia in operantly conditioned motor learning.

13.7 Explain the roles of cortical regions in learning to recognize and remembering Stimuli.

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Learning Objectives (3 of 5)

13.8 Contrast the roles of extrastriate and prefrontal cortex in retaining perceptual information in short-term memory.

13.9 Describe the role of the hippocampus in consolidation, reconsolidation, and neurogenesis related to relational learning and episodic memories.

13.10 Describe the role of the cortex in semantic memory.

13.11 Compare the role of the hippocampus in consolidation and retrieval of memories.

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Learning Objectives (4 of 5)

13.12 Describe the stimulus-response learning ability of patients with hippocampal damage.

13.13 Describe the motor learning ability of patients with hippocampal damage.

13.14 Describe the perceptual learning ability of patients with hippocampal damage.

13.15 Describe the role of the hippocampus in relational learning ability citing research from human and animal models.

13.16 Identify the events required for LTP to occur.

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Learning Objectives (5 of 5)

13.17 Compare the relationship between NMDA and AMPA receptors in LTP.

13.18 Describe how AMPA receptors contribute to LTP.

13.19 List the changes in presynaptic neurons, postsynaptic neurons, and protein synthesis that accompany LTP.

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Overview of Learning and Memory

Learning

Acquire new information

Our experiences change our nervous system and behavior

Memory

Long-term changes in the nervous system following learning

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Figure 13.1 The Steps of Learning and Memory

Figure 13.1 page408

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Types of Learning: Stimulus-Response Learning

Motor Learning

Perceptual Learning

Relational Learning

Stimulus-Response Learning: Learning to automatically make particular response in presence of particular stimulus (includes classical and instrumental conditioning)

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Stimulus-Response Learning

Stimulus-Response Learning: ability to learn to perform a particular behavior when a particular stimulus is present

Classical Conditioning

Operant Conditioning

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Classical Conditioning

Unconditional Stimulus (US): Stimulus that produces defensive or appetitive response

Unconditional Response (UR): Response to US

Conditional Stimulus (CS): Stimulus, which when paired with US during training, comes to elicit learned response

Conditional Response (CR): Response to presentation of CS

Automatic reflexes

Association between two stimuli

Classical Conditioning: Learning procedure to form association between two stimuli

Unconditional Stimulus (US): Stimulus that produces defensive or appetitive response

Unconditional Response (UR): Response to US

Conditional Stimulus (CS): Stimulus, which when paired with US during training, comes to elicit learned response

Conditional Response (CR): Response to presentation of CS

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Operant Conditioning

New behaviors that have been learned

Association between stimulus and response

Permits an organism to change a behavior according to consequences

Reinforcer

Punisher

Operant conditioning AKA instrumental learning

A reinforcing or punishing outcome follows a specific behavior in a specific situation

Reinforcer increases the likelihood of the behavior occurring again in the future, while the punisher decreases it

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Figure 13.2 Classical Conditioning

In eye-blink conditioning, a puff of air (US) causes the eye to blink (UR). The puff of air is paired with a tone (CS) for several trials. After pairing, the tone alone elicits a blink (CR).

Studied in humans and rabbits

Puff of air is paired with tone

Consequently tone alone elicits an eye-blink response

Figure 13.2 page 409

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Figure 13.3 A Simple Neural Model of Operant Conditioning

Figure 13.3 page 409

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Types of Learning

Motor Learning

Component of stimulus-response learning

Changes in responses of motor system following a stimulus

Perceptual Learning

Ability to learn to recognize stimuli that have been perceived before

Each sensory system is capable

Relational Learning

Connections between association cortex

Includes spatial learning

Motor learning E.g. interaction with objects such as bicycles, keyboards

Perceptual learning E.g. recognizing people by their shape or their voice

Relational learning E.g. we hear a cat meow in the dark, we imagine what it looks like

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Figure 13.4 An Overview of Perceptual, Stimulus-Response, and Motor Learning

Figure 13.4 page 410

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Types of Memory

Sensory Memory

Short-term Memory

Long-term Memory

Non declarative Memory (implicit)

Declarative Memory (explicit)

Sensory memory is a brief period of time (ranging from fractions of a second to a few seconds) that the initial sensation of environmental stimuli is initially remembered

Short-term memory: This stage is longer than sensory memory, but still limited to seconds or minutes.

Capacity limited to a few items, such as the digits in a phone number or the letters in a name.

The length of short-term memory can be extended through rehearsal or techniques like chunking

Long-term memory.

relatively permanent and can last for minutes, hours, days, or decades.

Information that will be retained from short-term memory is consolidated into long-term memory

Nondeclarative memory, or implicit memory, includes memories that we are not necessarily conscious of (automatic, such as driving a car)

Declarative memory: or explicit memory, is memory of events and facts that we can think and talk about

Episodic

Semantic

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Table 13.1 Examples of Declarative and Non declarative Memory Tasks

Declarative Memory Tasks

Remembering past experiences

Finding way in new environment

Nondeclarative Memory Tasks

Learning to recognize broken

drawings

Learning to recognize

pictures and objects

Learning to recognize faces

Learning to recognize

melodies

Classical conditioning

Operant conditioning

Learning sequence of button presses

Table 13.1 and figure 13.6, page 412

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Figure 13.6 Types of Memory

Table 13.1 and figure 13.6, page 412

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Stimulus-Response Learning: Classical Conditioning

Classical Conditioning:

Rodent model of conditioned emotional response

Role of the amygdala

Lateral nucleus

Refer figure 13.7

Role of Glutamate

Long-term potentiation (LTP)

Refer figure 13.8

Conditioned emotional response: an aversive stimulus (foot shock) paired with neutral stimulus (tone) produces responses such as freezing, increased BP, secretion of adrenal stress hormone, etc.

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Figure 13.7 Conditioned Emotional Responses

The figure shows the probable location of the changes in synaptic strength produced by the classically conditioned emotional response that results from pairing a tone with a foot shock.

Figure 13.7 page 413

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Conditioned Emotional Response

LTP of conditioned emotional response: Occurs in lateral amygdala

Activation of NMDA glutamate receptor

Increasing AMPA glutamate receptors at synapse

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Figure 13.8 Overview of NMDA and AMPA Receptors in LTP Associated with Classical Conditioning

Figure 13.8 page 414

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Stimulus-Response Learning: Operant Conditioning

Role of Basal ganglia:

Circuits begin in sensory association cortex (perception)

End in motor association cortex (movements)

Two pathways

Direct transcortical connections

Connections via basal ganglia and thalamus

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Figure 13.9 Stimulus and Response Pathways

Figure 13.9 page 415

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Stimulus and Response Pathways

Information from transcortical pathways is transferred to the basal ganglia as the behavior becomes automatic. The caudate and putamen receive information from the frontal lobes about movements.

Finally, information goes to the primary motor cortex where the response behavior is initiated.

Information then goes to the premotor and supplementary motor cortex.

Information then goes to the Globus pallidus.

Figure 13.9 page 415

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Operant Conditioning: Pathways

Transcortical Pathways

Acquisition of declarative, episodic memories (with hippocampus)

Basal Ganglia Pathways

As learned behaviors become automatic, they are “transferred” to basal ganglia

Caudate nucleus and putamen

declarative, episodic memories—complex perceptual memories of sequences of events that we experience or that are described to us

Caudate nucleus and putamen - receive sensory information from all regions of the cerebral cortex and frontal lobes about movements that are planned or are actually in progress

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Figure 13.10 Diagram of the Basal Ganglia and Their Connections

Black arrows represent excitatory connections. Red arrows represent

inhibitory connections.

Figure 13.10 page 416

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Neural Circuits Involved in Reinforcement

Ventral Tegmental Area (VTA): Group of dopaminergic neurons in ventral midbrain whose axons form mesolimbic and mesocortical systems and are important in reinforcement

Nucleus Accumbens: Nucleus of basal forebrain near septum; receives dopamine from neurons of VTA and is thought to be involved in reinforcement and attention

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Figure 13.11 The Ventral Tegmental Area and the Nucleus Accumbens

Diagrams of sections through a rat brain show the location of these regions.

Figure 13.11 page 418

(Adapted from Swanson, L. W., Brain maps: Structure of the rat brain, New York: Elsevier, 1992.)

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Figure 13.12 Dopamine and Reinforcement

Release of dopamine in the nucleus accumbens, measured by microdialysis, was produced when a rat pressed a lever that delivered electrical stimulation to the ventral tegmental area. (Based on data from Phillips et al., 1992.)

Figure 13.12 page 418

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Role of Dopamine in Reinforcement

LTP via dopamine in operant conditioning

Function of the Reinforcement System

Detecting reinforcing stimuli: VTA

Role of the PFC

Input to VTA

A reinforcement system must perform two functions: detect the presence of a reinforcing stimulus (that is, recognize that something good has just happened) and strengthen the connections between the neurons that detect the discriminative stimulus (such as the sight of a lever) and the neurons that produce the instrumental response (a lever press). (Refer to Figure 13.12.)

Assuming that this proposed mechanism is correct, several questions remain: What activates the dopaminergic neurons in the midbrain, causing their terminal buttons to release dopamine? What role does the release of dopamine play in strengthening synaptic connections? Where do these synaptic changes take place?

In addition, if a reinforcing stimulus does not occur when it is expected, the activity of dopaminergic neurons suddenly decreases (Day et al., 2007).

A functional-imaging study by Berns et al. (2001) found similar results with humans. Figure 13.22 shows that when a small amount of tasty fruit juice was squirted in people’s mouths unpredictably, the nucleus accumbens was activated, but when the delivery of fruit juice was predictable, no such activity occurred. (See Figure 13.13.)

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Table 13.2 Activity of VTA Neurons in Response to Reinforcers

Event	Expected or Unexpected Reinforcement?	VTA Neurons Active or Inactive?
Walking by a vending machine you accidentally bump into it. A candy bar falls out.	Unexpected	Active
You type your password into an e-mail program and your e-mail account opens.	Expected	Inactive

Table 13.2 page 419

Figure 13.13 page 419

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Figure 13.13 Expected and Unexpected Reinforcers

The functional MRI scans show the effects of expected and unexpected reinforcers (sips of fruit juice) on activity of the nucleus accumbens (arrows) in humans. (Based on Berns, G. S., McClure, S. M., Pagnoni, G., and Montague, P. R. Journal of Neuroscience, 2001, 21, 2793–2798.)

Table 13.2 page 419

Figure 13.13 page 419

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Motor Learning

Motor learning: learning a novel sequence of motor behaviors

Role of the cortex

Supplementary motor area, premotor cortex, ventral premotor area

Role of the basal ganglia

Nondeclarative motor memories

Supplementary motor: performing previously learned, automatic series of behaviors.

Premotor cortex is involved in motor learning and memory that is guided by sensory information.

Ventral premotor cortex is home to mirror neurons that facilitate motor learning when observing another individual

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Learning to Recognize Things

Perceptual Learning: learning to recognize things

New stimuli

Changes in familiar stimuli

Role of the Cortex

Learning: Extrastriate

Two streams (next slide)

Memory: MT/MST of extrastriate

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Learning to Recognize Stimuli

Ventral Stream

WHAT Pathway

Dorsal Stream

WHERE Pathway

Ventral Stream: Pathway of information from primary visual cortex to temporal lobe, which is involved in object recognition (WHAT pathway)

Dorsal Stream: Pathway of information from primary visual cortex to parietal lobe, which is involved with perception of location of objects (WHERE pathway)

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Figure 13.14 Role of the Extrastriate Cortex in Perceptual Learning

Activation of neural circuits in the sensory association cortex constitutes the “readout” of perceptual memory. Seeing a specific visual stimulus results in a unique pattern of neural activity in the extrastriate cortex. The same visual stimulus, if seen again later, will stimulate the same neural activity in the extrastriate cortex.

Figure 13.14 page 422

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Figure 13.15 Evidence of Retrieval of Visual Memories of Movement

The bars represent the level of activation, measured by fMRI, of MT/MST, a region of the visual association cortex that responds to movement. Participants looked at photographs of static scenes or scenes that implied motion similar to the ones shown here.

(Based on data from Kourtzi and Kanwisher, 2000.)

Figure 13.15 page 422

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Perceptual Learning

Retaining perceptual information in short-term memory

Role of extrastriate cortex

Fusiform face area and parahippocampal place area

Role of prefrontal cortex

“Manipulate and organize to-be-remembered information, devise strategies for retrieval, and also monitor the outcome” (Miyashita, 2004)

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Relational Learning And Role of Hippocampus

Relational Learning: Establishment and retrieval of memories of events, episodes, and places.

Role of the hippocampus

Regions (see figure 13.16)

Limbic cortex of medial temporal lobe: perirhinal cortex and parahippocampal cortex

Subcortical connections

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Figure 13.16 Cortical Connections of the Hippocampal Formation

(a) A view of the base of a monkey’s brain. (b) Connections with the cerebral cortex.

Figure 13.16 page 425

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Figure 13.17 The Major Subcortical Connections of the Hippocampal Formation

A midsagittal view of a rat brain shows these connections. MMB=Mammillary bodies.

Figure 13.17 page 426

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Role of Hippocampal Formation in Consolidation of Declarative Memories

Hippocampal formation plays role in formation of declarative memories

Hippocampus is involved in modifying memories as they are being formed

But the hippocampal formation clearly plays a role in the process through which declarative memories are formed.

Most researchers believe that the process works something like this: The hippocampus receives information about what is going on from sensory and motor association cortex and from some subcortical regions, such as the basal ganglia and amygdala.

It processes this information and then, through its efferent 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 among the elements of the memories.

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Episodic and Semantic Memories

Episodic Memory: Memory of a collection of perceptions of events organized in time and identified by a particular context

Semantic Memory: Memory of facts and general information

Semantic Dementia: Loss of semantic memories caused by progressive degeneration of neocortex of lateral temporal lobes

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Role of the Hippocampus

Dopamine, noradrenergic, serotonin, acetylcholine connection

Consolidation of memories

Semantic dementia

Reconsolidation of memories

Hippocampal Neurogenesis

Adult neurogenesis

Morris Water Maze

Reconsolidation: Process of consolidation of memory that occurs subsequent to original consolidation that can be triggered by reminder of original stimulus

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Figure 13.18 Adult Neurogenesis

Stem cells in the subgranular zone of the hippocampus divide and give rise to granule cells, which migrate into the dentate gyrus.

Figure 13.18 page 427

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Relational Learning in Laboratory Animals

Morris Water Maze

Hippocampal Place Cells

If rats with hippocampal lesions are always released from the same place, they learn this nonrelational, stimulus-response task about as well as normal rats do

However, if they are released from a new position on each trial, they swim in what appears to be an aimless fashion until they finally encounter the platform (See Figure 13.19)

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Figure 13.19 The Morris Water Maze

(a) Environmental cues present in the room provide information that permits the animals to orient themselves in space. (b) According to the task, start positions are variable or fixed. Normally, rats are released from a different position on each trial. If they are released from the same position every time, the rats can learn to find the hidden platform through stimulus-response learning. (c) The graphs show the performance of normal rats and rats with hippocampal lesions using variable or fixed start positions. Hippocampal lesions impair acquisition of the relational task. (d) Representative samples show the paths followed by normal rats and rats with hippocampal lesions on the relational task (variable start positions). (Adapted from Eichenbaum, H., A cortical–hippocampal system for declarative memory, Nature Reviews: Neuroscience, 2000, 1, 41–50. Data from Eichenbaum et al., 1990.)

Figure 13.19 page 428

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Amnesia

Anterograde amnesia

Difficulty in learning new information

Deficit in complex relational memory

Damage to temporal lobes, patient H. M.

Reterograde amnesia

Inability to remember events before the brain damage occurred

Korsakoff’s syndrome

Severe anterograde amnesia

May be caused by alcoholism

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Figure 13.20 Retrograde Amnesia and Anterograde Amnesia

Figure 13.20 page 430

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Retrograde Amnesia and Effects

Amnesia for events that preceded some disturbance to the brain

Korsakoff’s Syndrome; Permanent anterograde amnesia; Brain damage resulting from chronic alcoholism or malnutrition

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Patient H. M.

Received surgery to alleviate severe epilepsy

Bilateral medial temporal lobectomy

Revealed critical area was hippocampus

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Role of Hippocampus

The hippocampus is involved in converting short-term memories into long-term memories.

The hippocampus is not the location of long-term memories nor crucial for their retrieval.

The hippocampus is not the location of short-term memories.

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Anterograde Amnesia

Consolidation

CA1 of hippocampus

Rich in NMDA receptors

Anatomy of Anterograde Amnesia

Perirhinal Cortex: Region of limbic cortex adjacent to hippocampal formation that relays information between entorhinal cortex and other regions of brain

Parahippocampal Cortex: Region of limbic cortex adjacent to hippocampal formation that shares same general role as perirhinal cortex

Anatomy of Anterograde Amnesia

Perirhinal Cortex: Region of limbic cortex adjacent to hippocampal formation that relays information between entorhinal cortex and other regions of brain

Parahippocampal Cortex: Region of limbic cortex adjacent to hippocampal formation that shares same general role as perirhinal cortex

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Retrograde Amnesia

Retrieval

Differential role of hippocampal formation

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Figure 13.21 Retrograde Amnesia in Patients with Hippocampal Damage

Hippocampal damage appears to disrupt the gradual storage of long-term memories. Memories older than approximately 15 years are relatively intact even in people with retrograde amnesia, which suggest that the storage process requires between 10 and 15 years to be completed. (Data from Bayley et al., 2006.)

Figure 13.21 page 432

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Amnesia in Patients with Hippocampal Damage

Stimulus-Response Learning

Demonstrated in H. M. and other patients

Motor Learning

Demonstrated in patients with anterograde amnesia

Perceptual Learning

Improvement in broken drawing task (Figure 13.23)

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Figure 13.23 Examples of Broken Drawings

(Reprinted with permission of author and publisher from Gollin, E. S.,

Developmental studies of visual recognition of incomplete objects, Perceptual

and Motor Skills, 1960, 11, 289–298.)

Figure 13.23 page 433

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Figure 13.24 Bilateral Amygdala Damage in Patient H. M.(a)

Note the lesions in H. M.’s temporal lobe and hippocampus that differ from a typical brain.

Figure 13.24 page 435

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Figure 13.24 Bilateral Amygdala Damage in Patient H. M.(b)

Figure 13.24 page 435

Patient H. M. – continued from previous slide

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Relational Learning

Declarative and nondeclarative memories

Spatial memory

Research with humans

Right hippocampal formation and navigational tasks (Place cells)

Research with animals

Grid cells, head direction cells, border cells

Wood et al. (2000): C1

Declarative affected by medial temporal lobe damage

posterior hippocampus contains place cells—neurons that are directly involved in navigation in space

Spatial strategy (hippocampus), response strategy (caudate nucleus)

Wood et al. (2000): CA1 - see figure 13.27 (upcoming) - different cells fired when the rat was in different parts of the maze.

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Figure 13.25 Spatial and Response Strategies

The figure shows the relation between volume of gray matter of the hippocampus (right) and caudate nucleus (left) and errors made on test trials in a virtual maze that could only be performed by using a response strategy. Increased density of the caudate nucleus was associated with better performance, and increased density of the hippocampus was associated with poorer performance.

Figure 13.25 page 437

(From Bohbot, V. D., Lerch, J., Thorndycraft, B., et al., Gray matter differences correlate with spontaneous strategies in a human virtual navigation task, Journal of Neuroscience, 2007, 27, 10078–10083. Reprinted with permission.)

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Place Cells in the Hippocampal Formation

Place Cell

Neuron that becomes active when animal is in particular location in environment; most typically found in hippocampal formation

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Figure 13.26 Activity of a Hippocampal Border Cell

The firing rate of this cell is indicated by color; “hottest” colors represent the highest rate of firing. As you can see, the cell fired preferentially when the animal was located along the right border of the rectangular enclosure, regardless of the dimensions of the Enclosure. (From Solstad, T., Boccara, C. N., Kropff, E., et al., Representation of geometric borders in the entorhinal cortex, Science, 2008, 322, 1865–1868. Reprinted with permission.)

Figure 13.26 page 437

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Figure 13.27 Apparatus Used by Wood et al.

The rats were trained to turn right and turn left at the end of the stem of the T-maze on alternate trials. The firing patterns of hippocampal place cells with spatial receptive fields in the stem of the maze were different on trials during which the animals turned left or right.

Figure 13.27 page 437

(Adapted from Wood, E. R., Dudchenko, P. A., Robitsek, R. J., and Eichenbaum, H., Hippocampal neurons encode information about different types of memory

episodes occurring in the same location, Neuron, 2000, 27, 623–633.)

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Induction of Long-Term Potentiation (1 of 3)

LTP: Long-term increase in excitability of neuron caused by repeated high-frequency activity of that input

Hippocampal Formation: Forebrain structure of temporal lobe, constituting important part of limbic system

Population EPSP: extracellular measurement of the EPSPs by the perforant path axons with the dentate granule cells

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Induction of Long-Term Potentiation (2 of 3)

Hebb Rule

Hypothesis proposed by Donald Hebb

Cellular basis of learning involves strengthening of synapse that is repeatedly active when postsynaptic neuron fires

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Induction of Long-Term Potentiation (3 of 3)

Role of NMDA Receptor

LTP requires:

1. Activation of the synapses

2. Depolarization of the postsynaptic neuron

NMDA receptor:

neurotransmitter AND voltage-dependent ion channel

See figures

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Figure 13.28 A Simple Neural Model of Classical Conditioning

When the 1,000-Hz tone is presented just before the puff of air to the eye, synapse T is strengthened.

Figure 13.28 page 439

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Figure 13.29 The Hippocampal Formation and Long- Term Potentiation (1 of 2)

(a) This schematic diagram shows the connections of the components of the hippocampal formation and the procedure for producing long-term potentiation.

Figure 13.29 page 440

(From Berger, T. W., Long-term potentiation of hippocampal synaptic transmission

by the American Association for the Advancement of Science. Reprinted with

permission.)

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Figure 13.29 The Hippocampal Formation and Long- Term Potentiation (2 of 2)

(b) Population EPSPs were recorded from the dentate gyrus before and after electrical stimulation that led to long-term potentiation

Figure 13.29 page 440

(From Berger, T. W., Long-term potentiation of hippocampal synaptic transmission

by the American Association for the Advancement of Science. Reprinted with

permission.)

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Figure 13.30 The Role of Summation in Long-Term Potentiation

If axons are stimulated rapidly, the EPSPs produced by the terminal buttons will summate, and the postsynaptic membrane will depolarize enough for long-term potentiation to occur. If axons are stimulated slowly, the EPSPs will not summate, and long-term potentiation will not occur.

Figure 13.30 page 440

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Figure 13.31 LTP Occurs When the Pre- and Postsynaptic Cells Are Depolarized at the Same Time

Synaptic strengthening occurs when synapses are active while the membrane of the postsynaptic cell is depolarized

Figure 13.31 page 440

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Figure 13.32 The NMDA Receptor

The NMDA receptor is a neurotransmitter- and voltage-dependent ion channel. (a) When the postsynaptic

membrane is at the resting potential, Mg2+ blocks the ion channel, preventing Ca2+ from entering. (b) When

the membrane is depolarized, the magnesium ion is evicted. Thus, the attachment of glutamate to the binding site causes the ion channel to open, allowing calcium ions to enter the dendritic spine.

Figure 13.32 page 441

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Role of NMDA Receptors

AP5

Dendritic spike

Role of NMDA Receptors

NMDA receptor

Specialized ionotropic glutamate receptor that controls calcium channel that is normally blocked by Mg2+ ions; involved in long-term potentiation

AP5

2-Amino-5-phosphonopentanoate, a drug that blocks NMDA receptors

Dendritic spike

Action potential that occurs in dendrite of some types of pyramidal cells

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Associative Long-Term Potentiation

Long-term potentiation in which concurrent stimulation of weak and strong synapses to given neuron strengthens weak ones

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Figure 13.33 Associative Long-Term Potentiation

If the activity of strong synapses is sufficient to trigger an action potential in the neuron, the dendritic spike will depolarize the membrane of dendritic spines, priming NMDA receptors so that any weak synapses active at that time will become strengthened.

Figure 13.33 page 442

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Role of AMPA receptors

Glutamate receptors on dendritic spine of CA1 pyramidal cell

Synaptic strengthening in LTP (figure 13.34)

Enzyme: CaM-KII

Many studies have shown that CaM-KII plays a critical role in long-term potentiation.

Silva et al., (1992) found that LTP could not be established in mouse hippocampal tissue with a targeted mutation that prevented the production of CaM-KII

Shen and Meyer (1999) found that after LTP was established in hippocampal neurons, CaM_KII molecules accumulated in the postsynaptic densities of dendritic spines

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Figure 13.34 Synaptic Strengthening (1 of 3)

(a) When the conditions for long-term potentiation are met, Ca2+ ions enter the dendritic spine through NMDA receptors. The calcium ions activate enzymes in the spine.

Figure 13.34 page 443

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Figure 13.34 Synaptic Strengthening (2 of 3)

(b) The activated enzymes cause AMPA receptors to move into the spine.

Figure 13.34 page 443

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Figure 13.34 Synaptic Strengthening (3 of 3)

Figure 13.34 page 443

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Role of Synaptic Changes

Postsynaptic Changes: size and shape of dendritic spines

Presynaptic Changes:

Increase in amount of glutamate released

Nitric oxide synthase

Protein synthesis

Early LTP

Long-lasting LTP: PKM-Zeta enzyme

nitric oxide (NO) is a soluble gas produced from the amino acid arginine by the activity of an enzyme known as nitric oxide synthase.

NO lasts only a short time before it is destroyed. Thus, if produced in dendritic spines in the hippocampal formation, it

could diffuse only as far as the nearby terminal buttons, where it might produce changes related to the induction of LTP.

Discussion lead

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