Presentation on theme: "Mind and Brain Learning and Memory Chapter 13"— Presentation transcript:
1 Mind and Brain Learning and Memory Chapter 13 Show Brenda Milner video (7:45)Learning and MemoryChapter 13
2 You are responsible for Chapter 13 (text and notes) for you final as well as all other chapters (and notes) covered in class.
3 http://www.youtube.com/watch?v=JliczINA__Y&feature=relat ed
4 Chapter Overview The Nature of Learning Synaptic Plasticity: Long-Term Potentiation and Long-Term DepressionPerceptual LearningClassical ConditioningInstrumental ConditioningRelational Learning
5 The Nature of Learning Introduction Learning refers to the process by which experiences change our nervous system and hence our behavior; we refer to these changes as memoriesExperiences are not stored – they change the way we perceive, perform, think, and planThey do so by physically changing the structure of the nervous system, altering neural circuits that participate in perceiving, performing, thinking and planning.
6 The Nature of Learning Learning can take at least 4 basic forms Perceptual LearningStimulus-Response LearningClassical ConditioningInstrumental ConditioningMotor LearningRelational Learning
7 The Nature of Learning Perceptual Learning Learning to recognize a particular stimulusPrimary function: ability to identify and categorize objects and situationsEach sensory system is capable of perceptual learningAccomplished by changes in the sensory association cortex
8 The Nature of Learning Stimulus-Response Learning Learning to automatically make a particular response in the presence of a particular stimulusInvolves the establishment of connections between circuits involved in perception and those involved in movementClassical conditioningInstrumental conditioning
9 The Nature of Learning Classical Conditioning Unconditional Stimulus (US) – stimulus that produces a defensive or appetitive response.Unconditional Response (UR) – response to the US.Conditional Stimulus (CS) – stimulus, which when paired with the US during training, comes to elicit a learned response.Conditional Response (CR) – response to the presentation of the CS.Classical conditioning is a learning procedure that involves pairing a neutral stimulus with a biologically potent stimulus
10 Figure 13.1 A Simple Neural Model of Classical Conditioning When CC takes place, what kinds of changes occur in the brain? present tone, nothing happens since the synapse connecting the tone-sensitive neuron and the motor neuron is weak….that is, when the AP reaches the terminal the EPSP that is produced in the motor neuron is too weak to make the neuron fire. However, if we present puff of air to the eye, the eye blinks…nature has provided the animal with a strong synapse between these 2 neurons. To produce CC we first present tone followed by puff of air…after several pairings, the tone elicits eyeblink by itself.
11 The Nature of Learning Hebb Rule 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.About 60 years ago Hebb proposed a rule that might explain how neurons are changed by experience in a way that would cause changes in behavior…how would the Hebb rule apply to the circuit we just looked at?
12 Figure 13.1 A Simple Neural Model of Classical Conditioning If Tone is presented first then weak synapse is active. If puff is presented immediately after then strong synapse P becomes active and makes the neuron fire. The act of firing then strengthens any synapse with the motor neuron that has just been active…in our case synapse T. After several pairings of the 2 stimuli, synapse T becomes strong enough to cause the motor neuron to fire….then we can say that learning has occurred.
13 The Nature of LearningInstrumental Conditioning (Operant conditioning)learning procedure whereby the effects of a particular behavior in a particular situation increase (reinforce) or decrease (punish) the probability of the behavior.Reinforcing Stimulus – appetitive stimulus that follows a particular behavior and thus makes the behavior become more frequent.Punishing Stimulus – aversive stimulus that follows a particular behavior and thus makes the behavior become less frequent.CC involves automatic or species-typical responses, but OC involves behaviors that have to be learnedCC involves an association between 2 stimuli, OC involves an association between a response and a stimulus.OC is considered more flexible because it permits an organism to adjust its behavior according to the consequences of that behavior.CC involves automatic or species-typical responses, but OC involves behaviors that have to be learnedCC involves an association between 2 stimuli, OC involves an association between a response and a stimulus.OC is considered more flexible because it permits an organism to adjust its beh according to the consequences of that beh.
14 Figure 13.2 A Simple Neural Model of Instrumental Conditioning Let’s look at case of reinforcement…rat in Skinner box bar-pressing for food. At first, doesn’t press lever but when it eventually does it receives food, this food increases the likelihood that he will bar press again…reinforcement causes the sight of the lever to serve as the stimulus that elicits the barpressing response.
15 The Nature of Learning Motor Learning Learning to make a new response Component of stimulus-response learningPerceptual learning = making changes in the sensory systems of the brainS-R learning – making connections between sensory and motor systems in the brainMotor learning = making changes in the motor systemsBut motor learning can’t occur without sensory input from the environment…most skilled movement involves an interaction with objects
16 Figure 13.3 An Overview of Perceptual, Stimulus-Response (S-R), and Motor Learning. Most learning situations involve all three types of learning described so far…e.g., teach an animal to make a response in the presence of a stimulus it has never seen beforeIt must learn to recognize the stimulus, make the response and then a connection must be made between these 2 new memories. If you teach an animal to make an already learned response in the presence of a new stimulus, then only perceptual and S-R learning will occur.
17 The Nature of Learning Relational Learning More complex form of learningInvolves learning the relationships among individual stimuliIncludes the ability to recognize objects through more than one sensory modalityInvolves learning the relative location of objects in the environment – spatial learningRemembering the sequence in which events occurred during particular episodes – episodic learningHippocampusThe 3 types of learning described so far consist of changes in one sensory system, between one sensory and one motor system, or in the motor system. But learning can be much more complex than that.Relational learning relies heavily on hippocampus
18 Chapter Overview The Nature of Learning Synaptic Plasticity: Long-Term Potentiation and Long-Term DepressionElectrical stimulation of circuits within the hippocampus can lead to long-term synaptic changes that seem to be responsible for learningPerceptual LearningClassical ConditioningInstrumental ConditioningRelational Learning
19 See Figure 13.4 Primary input to the HF comes from the EC Axons of EC neurons pass through the perforant path and synapse with granule cells in the DGFrom these cells, the mossy fibers project to the pyramidal cells in CA3From CA3, Schaffer collaterals project to CA1 cellsThe 3 synapses know as the trisynaptic loopLocation of hippocampus in rats (HF – hippocampal formation; DG – dentate gyrus; EC – entorhinal cortex)Schaffer axons branch …the collateral fibers go the CA1 and the commissural fibers go the contralateral HIP via the CC
20 Induction of LTPA stimulating electrode is placed in the PP and a recording electrode is placed in the DGA single pulse of electrical stimulation is delivered to the PP and the resulting population EPSP is recorded in the DGPopulation EPSP is the evoked potential that represents EPSPs of a population of neurons.LTP can be induced by stimulating the PP axons with a burst of electrical pulses (i.e., 100) within a few secondsTo induce LTP…PP – perforant pathThe size of the first population EPSP tells us the strength of the synaptic connections before LTP is inducedEvidence that LTP has occurred is obtained by periodically delivering a single pulse and then measuring the response in the DG to see if it is bigger than the original response
21 The size of the first population EPSP tells us the strength of the synaptic connections before LTP is inducedEvidence that LTP has occurred is obtained by periodically delivering a single pulse and then measuring the response in the DG to see if it is bigger than the original responseLTPPicture from the original article by Berger (1984)
22 Synaptic Plasticity: LTP and LTD Can be induced in other parts of the HF and in other brain regionsCan last for several monthsCan be induced in slices and in living animalsCan follow the Hebb Rule (in slices)Associative Long-Term Potentiation – long-term potentiation in which concurrent stimulation of weak and strong synapses to a given neuron strengthens the weak ones.Hebb rule in slices…when weak and strong synapses to a single neuron are stimulated at the same time, the weak synapse becomes strengthened…it is produced by the associationa (in time) between the activity of the two sets of synapses.
24 Figure 13.7 The Role of Summation in Long-Term Potentiation Nonassociative LTP requires an additive effectSeries of pulses delivered at high rate will produce LTPSame # of pulses given at slow rate will not (LTD)Rapid rate of stimulation causes EPSPs to summateRapid stimulation depolarizes the postsynaptic membrane more than slow stimulation
25 Figure 13.8 Long-Term Potentiation Experiments have shown that synaptic strengthening occurs when NTS binds with postsynaptic receptors located in a dendrite that is already depolarizedLTP requires 2 eventsActivation of synapsesDepolarization of the postsynaptic membraneThe explanation for this phenomenon lies in the properties of the NMDA receptor….
26 Synaptic Plasticity: LTP and LTD Role of NMDA ReceptorsNMDA Receptor – specialized ionotropic glutamate receptor that controls a calcium channel that is normally blocked by Mg2+ ions.Calcium ions enter the cells through channels controlled by NMDA receptors only when glutamate is present and the postsynaptic membrane is depolarizedNTS- and voltage dependent ion channelFound in HIP, esp CA1
28 Synaptic Plasticity: LTP and LTD Role of NMDA ReceptorsAP5 – 2-amino-5-phosphonopentanoate, a drug that blocks NMDA receptors.Blocks the establishment of LTPCa entry is essential step in LTP…AP5 blocks LTP
29 Synaptic Plasticity: LTP and LTD Need glutamate & depolarization….but how do dendrites become depolarized if only axons can produce action potential?Dendritic Spike – action potential that occurs in the dendrite of some types of pyramidal cells.Threshold for activation is very highOnly occurs when action potential is triggered in the axonBackwash of depolarization across cell body triggers dendritic spikeWhenever the axon of a pyramidal cell fires, all of its dendritic spines become depolarized for a brief time.
30 Synaptic Plasticity: LTP and LTD Simultaneous occurrence of synaptic activation and a dendritic spike strengthens the active synapse.Magee and Johnston (1997) injected individual CA1 pyramidal cells in hippocampal slices with a fluorescent dye that permitted them to see the influx of calciumWhen individual synapses became active at the same time that a dendritic spike had been triggered, Ca “hot spots” occurred near the activated synapsesSize of EPSPs produced by these activated synapses became larger – synapse became strengthenedTTX (blocks Na current) injected near dendrite – prevented dendritic spikes, no LTP!
31 Synaptic Plasticity: LTP and LTD Role of NMDA receptors in Associative LTPIf weak synapses are active by themselves, nothing happens (NMDA receptors don’t open)However, if the activity of strong synapses located elsewhere on the postsynaptic cell has caused the cell to fire, then a dendritic spike will depolarize the postsynaptic membrane enough to eject Mg ions from the Ca channels (of NMDA receptor)If some synapses then become active, Ca will enter the dendritic spines and cause the synapses to become strengthened
32 Synaptic Plasticity: LTP and LTD What is responsible for the increase in synaptic strength that occurs during LTP?Dendrites on CA1 neurons contain 2 types of glutamate receptors: NMDA and AMPA
33 Synaptic Plasticity: LTP and LTD Mechanisms of Synaptic PlasticityAMPA Receptors – ionotropic glutamate receptor that controls a sodium channel; when open it produces EPSPs.Strengthening of individual synapses is accomplished by the insertion of more AMPA receptors into the postsynaptic membrane of the dendritic spineCaM-KII – type of calcium-calmodulin kinase, an enzyme that must be activated by calcium; may play a role in the establishment of LTP.Nitric Oxide Synthase – enzyme responsible for the production of nitric oxide.Drugs that block this enzyme prevent the establishment of LTP in CA1More AMPA receptors means bigger EPSP when stimulated by glutamate; CaM-KII involved in moving AMPA receptors..CaM-KII located in postsynaptic density after LTP inducedLTP might also involve presynaptic changes…NO is a soluble gas that could diffuse back to terminal button from the dendritic spine (retrograde messenger)
34 Figure 13.16 Chemistry of LTP Activation of terminal button releases glutamate, which binds with NMDA receptors in the postsynaptic membrane of the dendritic spineIf the membrane was depolarized by a dendritic spike, then calcium ions enter and activate CAM-KIICAM-KII travels to the postsynaptic density and causes the insertion of AMPA receptorsLTP also initiates changes in synaptic structure and production of new synapses
35 Figure 13.16 Chemistry of LTP The entry of calcium also activates NO synthaseThis produces NO which diffuses out of the dendritic spine and back to the terminal buttonThe NO may then trigger chemical reactions that increase the release of glutamateLong-lasting LTP also requires the synthesis of new proteins and the presence of dopamine
36 Synaptic Plasticity: LTP and LTD Low-frequency stimulation of the synaptic inputs to a cell can decrease their strengthLong-Term Depression (LTD) also plays a role in learning…some synapses are strengthened and others weakenedlong-term decrease in the excitability of a neuron to a particular synaptic input caused by stimulation of the terminal button while the postsynaptic membrane is hyperpolarized or only slightly depolarized.Like LTP, requires activation of NMDA receptorsLTD involves a decrease in AMPA receptors
37 Synaptic Plasticity: LTP and LTD Other Forms of LTPSome forms of LTP do not involve NMDA receptors and are not blocked by AP5 (CA3).For example, mossy fiber input from dentate gyrus to CA3Presynaptic changes only – no alterations in structure of dendritic spines
38 Chapter Overview The Nature of Learning Synaptic Plasticity: Long-Term Potentiation and Long-Term DepressionPerceptual LearningClassical ConditioningInstrumental ConditioningRelational Learning
39 Figure 13.18 The Major Divisions of the Visual Cortex of the Rhesus Monkey Primary visual cortex receives information from the lateral geniculate nucleus of the thalamusVentral Stream – pathway of information from the primary visual cortex to the temporal lobe, which is involved in object recognition (‘what’ pathway).Dorsal Stream – pathway of information from the primary visual cortex to the parietal lobe, which is involved with perception of the location of objects (‘where’ pathway).Primary visual cortex = striate cortex; then sent to extrastriate cortex (analyze form, color and movement)Lesions to the inferior temporal cortex disrupt object discriminationOther areas important for perception of movement (MT/MST..part of extrastriate cortex)
40 Chapter Overview The Nature of Learning Synaptic Plasticity: Long-Term Potentiation and Long-Term DepressionPerceptual LearningClassical ConditioningInstrumental ConditioningRelational Learning
41 Figure 13.21 Conditioned Emotional Responses Information about the CS & US converge in the LA so synaptic changes responsible for learning could take place in this areaHebb rule - weak synapses (from tone) are strengthened when US activates neurons in the LA….LA neurons fire and activate CN …which evokes the response (Ch 11)
42 Classical Conditioning Evidence for the involvement of lateral nucleus of the amygdala in CERChanges in the LA responsible for CER learning involve LTP…and is accomplished through activation of the NMDA receptorLTPInjection of drugs that block LTP into the amygdala prevents the establishment of conditioned emotional responsesCER training (tone-shock pairings) causes AMPA receptors to be driven into dendritic spines of synapses between LA neurons and axons that provide auditory inputCER training causes AMPA insertion
43 Classical Conditioning Rumpel et al., (2005) used a virus to insert a gene for a fluorescent dye coupled to a subunit of the AMPA receptor into the LA of rats…learning caused AMPA insertionThey also inserted a gene for a dye coupled to a defective subunit of the AMPA receptor…the defective subunit prevented AMPA insertion and conditioning did not take place
44 Classical Conditioning Infusion of many drugs into the LA that prevent LTP disrupt acquisition of a CERConclusion:LTP in the amygdala, mediated by NMDA receptors, plays a critical role in the establishment of CER
45 Chapter Overview The Nature of Learning Synaptic Plasticity: Long-Term Potentiation and Long-Term DepressionPerceptual LearningClassical ConditioningInstrumental ConditioningRelational Learning
46 Instrumental Conditioning Instrumental conditioning involves a connection between a particular stimulus and a particular response2 major pathways between sensory association cortex and motor association cortexDirect transcortical connectionsInvolved in episodic memory (along with HIP)Connections via the basal ganglia and thalamus2 pathways play different rolesCircuits must involve sensory association cortex and motor association cortex
47 Basal GangliaLearned behaviors become automatic and routine, they are transferred to the basal gangliaLeaving the transcortical circuits free to learn new tasks
48 Figure 13.23 The Basal Ganglia and Their Connections Neostriatum (caudate nucleus & putamen) receives sensory input from all regions of the cerebral cortex. Also receives information from frontal lobes about movement (planned or in progress).Outputs are sent to GP which sends information back to frontal cortex to premotor cortex (where plans for movement are made) and motor cortex (where movement is executed)
49 Instrumental Conditioning Basal GangliaStudies of laboratory animals have indicated that:lesions of the basal ganglia disrupt instrumental conditioning without affecting other forms of learning.Fernadez-Ruiz et al., (2001) destroyed portions of the caudate and putamen that receive visual information from the ventral streamLesions did not disrupt visual perceptual learningImpaired the monkeys’ ability to learn to make a visually guided operant responseWilliams and Eskandar (2006): as monkeys learned a operant response, the rate of firing of single neurons in the caudate nucleus increasedThe activity of caudate neurons is correlated with rate of learningBlocking NMDA receptors in the basal ganglia with an injection of AP5 disrupts learning guided by a simple visual cueMany of these studies involve learning to make a particular response in the presence of a particular visual cue
50 Instrumental Conditioning - Reinforcement Neural circuits involved in reinforcement discovered by Olds & Milner, 1954.ReinforcementNeural Circuits Involved in ReinforcementVentral Tegmental Area (VTA) – group of dopaminergic neurons in the ventral midbrain whose axons form the mesolimbic and mesocortical systems and are important in reinforcement.Nucleus Accumbens – nucleus of the basal forebrain near the septum; receives dopamine from neurons of the VTA and is thought to be involved in reinforcement and attention.See Figure 13.24Neural circuits involved in reinforcement discovered by Olds & Milner, 1954.The activity of the dopaminergic pathway (see chapter 4) very important in reinforcement.Mesolimbic DA pathway begins in the VTA and projects to forebrain regions including AMG, HIP and NA…NA project to BG
51 Figure 4.13 Dopaminergic Pathways in a Rat Brain Mesolimbic = VTA to limbic system including NA, AMYG, & HIP (NA impt for rewarding effects of stimuli including drugs of abuse)Mesocortical = VTA to prefrontal cortex also plays a role in reinforcement)
52 Instrumental Conditioning ReinforcementMicrodialysis studies have revealed that release of DA in the NA is caused by:reinforcing electrical stimulation of the medial forebrain bundle (connects VTA to NA) or the VTAadministration of cocaine or amphetaminepresence of natural reinforcers such as water, food, sex partnerfMRI indicates activity in NA during reinforcing events
53 Instrumental Conditioning Functions of the Reinforcement System:To detect reinforcing stimuli.To strengthen the connections between the neurons that detect the discriminative stimulus (i.e., sight of lever) and the neurons that produce the instrumental response (i.e., lever press).
54 Instrumental Conditioning Reinforcement occurs when neural circuits detect a reinforcing stimulus and cause the activation of dopaminergic neurons in the VTAA stimulus that serves as a reinforcer on one occasion may fail to do so on anotherReinforcement system is not automatically activated when particular stimuli are present; activation also depends on the state of the animal
55 Instrumental Conditioning Detecting reinforcing stimuliReinforcement system appears to be activated by unexpected reinforcing stimuliFirst – DA in VTA responded rapidly when the reinforcing stimuli was presentOnce the animals learn the task, VTA neurons are activated to the “learned” stimuliIf a reinforcing stimulus does not occur when expected, the activity of dopaminergic neurons decreasesBerns et al., (2001): increased activity in NA (fMRI) when tasty drink was given unpredictably, no increase if predictableActivity of these neurons sends a signal that there is something to be learnedReinforcement occurs when neural circuits detect a reinforcing stimulus and cause activation of DAergic neurons in the VTAPFC axons secrete glut which causes VTA neurons to fire in a bursting pattern which increases DA to NA
56 Instrumental Conditioning Prefrontal cortex provides input to VTAPFC involved in devising strategies, making plans, evaluating progress toward a goal.May turn on reinforcement mechanism when it determines that ongoing behavior is close to goal
58 Chapter Overview The Nature of Learning Synaptic Plasticity: Long-Term Potentiation and Long-Term DepressionPerceptual LearningClassical ConditioningInstrumental ConditioningRelational Learning
59 Relational LearningIncludes the establishment and retrieval of memories of events, episodes and placesMore complex type of learning
60 Relational Learning Human Anterograde Amnesia Anterograde Amnesia – amnesia for events that occur after some disturbance to the brain.Retrograde Amnesia – amnesia for events that happened before some disturbance to the brain.Anterograde amnesia is basically an inability to learn new information…BUT some learning is usually spared (perceptual learning, S-R, motor learning)Pure anterograde amnesia is rare; brain damage usually involves some retrograde amnesia as well
61 Figure 13.27 A Schematic Definition of Retrograde Amnesia and Anterograde Amnesia
62 Relational Learning Human Anterograde Amnesia Korsakoff’s Syndrome – permanent anterograde amnesia caused by brain damage from chronic alcoholism or malnutrition.Medial temporal lobe damage – also produces anterograde amnesia (i.e., H.M.)Based on extensive work with H.M., Milner & colleagues concluded:The hippocampus is not the location of LT memories; nor is it necessary for the retrieval of LT memoriesThe hippocampus is not the site of immediate (ST) memoriesThe hippocampus is important for converting ST memories into LT memoriesSergei Korsakoff 1889—first described a severe memory impairmentScoville & Milner 1957 – reported that bilateral removal of the MTL produced a memory impairment similar to that seen in Korsakoff’s syndrome
63 Relational LearningHuman Anterograde AmnesiaConsolidation – process by which short-term memories are converted to long-term memories.Figure A Simple Model of the Learning ProcessMany psychologists believe that learning consists of 2 stages; STM and LTMSTM – stores a limited amount of info temporarilyLTM – stores unlimited info permanentlySimplest model of memory says sensory info enters STM and rehearsal keeps it there and eventually it is stored in LTM
64 Relational Learning Spared Learning Abilities Not a total failure in learning abilityPerceptual LearningVisual recognition of incomplete objects (Figure 13.29)Face RecognitionStimulus-Response LearningHM could learn a classically conditioned eyeblink responseInstrumental conditioning task – visual discrimination task in which pennies were given for correct responsesMotor LearningSerial reaction time taskWhile HM’s memory deficit is profound, can perform well on many tasks
65 Figure 13.30 The Serial Reaction Time Task Press button below asterisk…if same 10 item sequence is repeated, reaction time decreases…suggests they learn the pattern…change pattern and reaction time increases.
66 Relational LearningSo, even though amnesics can perform some tasks they have no memory of having ever learned them…led to the notion that the brain has multiple memory systemsDeclarative and Nondeclarative MemoriesDeclarative (explicit) Memory – memory that can be verbally expressed.Nondeclarative (implicit) Memory – memory whose formation does not depend on the hippocampal formation; a collective term for perceptual, stimulus-response, and motor memory.Appear to be automatic, do not require deliberate attempts to memorizeAcquisition of specific behaviors and skillsDo not need to be able to describe these activities in order to do them
67 Table 13.1 Declarative Memory Tasks Nondeclarative Memory Tasks Remembering past experiencesFinding one’s way in new environmentNondeclarative Memory TasksLearning to recognize broken drawingsLearning to recognize pictures and objectsLearning to recognize facesLearning to recognize melodiesClassical conditioningInstrumental conditioningLearning sequence of button presses
68 Relational Learning Anatomy of Anterograde Amnesia Damage to the hippocampus or to regions of the brain that supply its inputs and receive its outputs causes anterograde amnesiaHIP formation = CA fields, DG and SUB; major input is from ECOutputs of Hip (from CA1 and SUB) also go back to EC, and PC and parahip cortexPerirhinal Cortex – region of limbic cortex adjacent to the hippocampal formation that relays information between entorhinal cortex and other regions of the brain.Parahippocampal cortex – region of the limbic cortex adjacent to the hippocampal formation that shares the same general role as the perirhinal cortex.Damage to hippocampus and surrounding cortical tissue seems to cause anterograde amnesia
69 Cortical Connections of the Hippocampal Formation Figure 13.31Monkey brain
70 Figure 13.32 The Major Subcortical Connections of the Hippocampal Formation Hip also receives subcortical input via the fornixFornix carries dopaminergic input from VTAFornix also connects the HIP with the mammillary bodies (located in post. Hypo.)MMB degenerate in Korsakoff’s syndrome
71 Relational LearningRole of the Hippocampal Formation in Consolidation of Declarative MemoriesHIP not really important for STM or LTM but seems to be important for declarative memory formationHIP receives input from sensory and motor cortex and from subcortical regions (BG and AMG), it then processes this information and sends projections back to these same regions and somehow modifies the memories being stored thereHippocampus is involved in modifying memories as they are being formed.The order in which events occurredContextual informationRelationships among elements
72 Rational Learning Hippocampus Time-limited role Anterograde amnesia is usually accompanied by retrograde amnesiaThe duration of the retrograde amnesia related to the amount of damage to the MTLDamage limited to hipp – retrograde amnesia lasting ~ few yearsDamage to hipp + entrorhinal cortex – retrograde amnesia ~ 1-2 decadesDamage to MTL – spared memories from early lifeGradual process controlled by hipp transforms memories located elsewhereBefore transformation is complete, hipp is required for retrieval of memoriesLater, retrieval of memories can occur if hipp has been damaged
73 Relational Learning Declarative Memory Episodic and Semantic Memories Episodic Memory – memory of a collection of perceptions of events organized in time and identified by a particular context.Specific to a particular time and placeSemantic Memory – memory of facts and general information.Do not include information about the context in which the facts were learnedEpisodic memory – must be learned all at onceSemantic Memory - can be acquired graduallyRequires the hippocampusRemember earlier breakdown of memory systems….declarative memory actually 2 different kinds of memories
74 Semantic Dementia – loss of semantic memories caused by progressive degeneration of the neocortex of the lateral temporal lobes.Difficulty naming objectsDifficulty understanding the meaning of words
75 Relational Learning Spatial Memory Memory for spatial information used to move around one’s environment and get from one place to another.Role of Hippocampus in Spatial MemoryDamage to (right) HIP causes spatial memory impairmentsLondon taxi drivers have bigger HIP than control subjectslonger an taxi driver had spent in this occupation, the larger the volume of rt hippPlace Cells – special neurons in the hippocampus that are directly involved in navigation in space (rats).Virtual-reality townsSpatial Strategy – maze learning strategy based on spatial cues; activation of HIP (fMRI).Response Strategy – maze learning strategy based on a series of responses (turns); activation of caudate nucleus.People who tend to use spatial strategies – larger hippPeople who tend to follow response strategies – larger caudatePatients like HM have difficulty finding their way aroundDamage to HIP causes spatial impairment in people; London taxi drivers have bigger HIP than control subjects
76 Relational Learning Relational Learning in Laboratory Animals Spatial Perception and LearningMorris Water MazeStarting with HM, people became interested in idea of MMS and developing animal models of memory…what role does the hip play in animals, can we develop animal models of declarative and episodic memory, what is a relational task in animals???Deficit in spatial learning is the most consistent effect of HIP damage in rodents (fixed start vs variable start)
78 Spatial LearningDamage to the hippocampus – animals swim in what appears to be an aimless fashion until they finally encounter the platformHippocampal lesions disrupt navigation in homing pigeonsHippocampus of birds and rodents that store seeds in hidden caches and later retrieve them is larger than that of animals that don’t
79 Relational Learning Relational Learning in Laboratory Animals Hippocampal Place CellsFound in dorsal hippocampus in rats (corresponds to the posterior hippocampus in humans)“fire” at a high rate when the animal is in a particular location, called the cell’s place field“fire” at a low rate when the animal is in a different locationFirst discovered by O’Keefe & Dostrovsky
81 Relational Learning Relational Learning in Laboratory Animals Role of Hippocampal Formation in Memory ConsolidationTime limited role in memoryMice trained in water maze; inactivate HIP with lidocaine 1 day later or 30 days later (Figure 13.40)Memory ReconsolidationA process of consolidation of a memory that occurs subsequent to the original consolidation that can be triggered by a reminder of the original stimulus.Mice expt…inactivate hippocampus with lidocaine or inactivate areas of cortex…see opposite patternReconsolidation involves a modification of LT memories
82 Phases of Memory Reconsolidation Acquisition - the pairing of the context/cue to the aversive stimuli24 hoursConsolidation—blocked by protein synthesis inhibitors (anisomycin)3-4 hoursReconsolidation—blocked by protein synthesis inhibitors (anisomycin)TrainReactivateTestEvidence suggests that reactivation of a memory can return it to a labile state requiring reconsolidation via protein synthesis
83 Figure 13.41 A Schematic Description of the Experiment by Misanin, Miller, and Lewis (1968) Eyewitness testimonyPTSD
84 Reconsolidation of Memories Reconsolidation requires LTPInjection of anisomycin (blocks protein synthesis and prevents memory consolidation), blocks reconsolidation
85 Relational Learning Relational Learning in Laboratory Animals Role of LTP in memoryWhen rats learn mazes, strength of population EPSP in CA3 increasesMutations targeted at NMDA receptors in CA1Prevented establishment of LTPPoor spatial learning on Morris water mazeHippocampal NeurogenesisNew neurons can be produced in the hippocampus of the adult brain (DG)Training on relational tasks increases neurogenesisEasier to establish LTP with these ‘new’ neuronsWhen animals learn tasks that require HIP, the learning induces the same type of changes produced by LTP