Biological Psychology - Learning and Memory PDF

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Summary

BİOLOGİCAL(PSYCHOLOGY(CH.12(((LEARNING(AND(MEMORY( BThe!second!major!class!of!stimulus–response!learning!is!instrumental! ?Learning'refers'to'the'process'by'which'experiences'change'our'nervous' conditioning!(also!called!operant!conditioning). system'a...

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BİOLOGİCAL(PSYCHOLOGY(CH.12(((LEARNING(AND(MEMORY( ?Learning'refers'to'the'process'by'which'experiences'change'our'nervous' system'and'hence'our'behavior.' ?We'refer'to'these'changes'as'memories.'' ?Experiences'are'not'“stored”;'rather,'they'change'the'way'we'perceive,' perform,'think'and'plan.'' ?They'do'so'by'physically'changing'the'structure'of'the'nervous'system,' altering'the'neural'circuits'that'participate'in'perceiving,'performing,' thinking,'and'planning.'' ?Learning'can'take'at'least'four'basic'forms:'perceptual'learning,' stimulus?response'learning,'motor'learning,'and'relational'learning.''

BThe!second!major!class!of!stimulus–response!learning!is!instrumental! conditioning!(also!called!operant!conditioning). 5. Instrumental(conditioning((operant!conditioning)!A!learning! procedure!whereby!the!effects!of!a!particular!situation!increase! (reinforce)!or!decrease!(punish)!the!probability!of!the!behavior.!( BWhereas!classical!conditioning!involves!automatic,!speciesBtypical! responses,!instrumental!conditioning!involves!behaviors!that!have! been!learned.!Also,!whereas!classical!conditioning!involves!an! association!between!two!stimuli,!instrumental!conditioning!involves!an! association!between!a!response!and!a!stimulus.!! BInstrumental!conditioning!permits!an!organism!to!adjust!its!behavior!according! to!the!consequences!of!that!behavior.!That!is,!when!behavior!is!followed!by! favorable!consequences,!the!behavior!tends!to!occur!more!frequently;!when!it! is!followed!by!unfavorable!consequences,!it!tends!to!occur!less!frequently.! Favorable!consequences!are!referred!as!reinforcing!stimuli;!unfavorable! consequences!are!referred!as!punishing!stimuli.!!

?If'we'want'to'understand'how'sensory'information'from'our'environment'–' whether'it'be'taste,'touch,'or'smell'–'is'decoded'or'interpreted'by'the'brain'and' used'for'laying'down'processes'such'as'learning'and'memory'–'then'we'must' understand'how'patterns'of'action'potentials,'or'nerve'cell?firing,'is'extracted,'and' how'information'is'taken'out'of'those'patterns,'and'laid'down'in'biochemical' mechanisms.''''

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Perceptual(learning(is!the!ability!to!learn!to!recognize!stimuli!that! have!been!perceived!before.!The!primary!function!of!this!type!of! learning!is!the!ability!to!identify!and!categorize!objects!and! situations.!!Unless!we!have!learned!to!recognize!something,!we! cannot!learn!how!we!should!behave!with!respect!to!it;!we!will!not! profit!from!our!experiences!with!it,!and!profiting!from!experience!is! what!learning!is!all!about.!( ?Each'of'our'sensory'systems'is'capable'of'perceptual'learning.'We'can'learn'to' recognize'objects'by'their'visual'appearance,'the'sounds'they'make,'how'they' feel,'or'how'they'smell.'We'can'recognize'people'by'the'shape'of'their'faces,'the' movements'they'make'when'they'walk,'or'the'sound'of'their'voices.'When'we' hear'people'talk,'we'can'recognize'the'words'they'are'saying'and'perhaps'their' emotional'state.'As'we'shall'see,'perceptual'learning'appears'to'be' accomplished'primarily'by'changes'in'the'sensory'association'cortex.'That'is,' learning'to'recognize'complex'visual'stimuli'involves'changes'in'the'visual' association'cortex,'learning'to'recognize'complex'auditory'stimuli'involves' changes'in'the'auditory'association'cortex'etc.''

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Stimulus]response(learning(is!the!ability!to!learn!to!perform!a! particular!behavior!when!a!particular!stimulus!is!present.!Learning!to! automatically!make!a!particular!response!in!the!presence!of!a! particular!stimulus;!includes!classical!and!instrumental!conditioning.!( (

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Classical(conditioning!is!a!form!of!learning!in!which!an!unimportant! stimulus!acquires!the!properties!of!an!important!one.!It!involves!an! association!between!two!stimuli.!For!example,!! If!we!direct!a!brief!puff!of!air!toward!a!rabbit’s!eye,!the!eye!will! automatically!blink.!This!is!unconditional(response!because!it!occurs! unconditionally,!without!any!special!training.!! The!stimulus!that!produces!the!puff!of!air!is!unconditional(stimulus.(( Now!we!begin!the!training.!We!present!a!series!of!brief!1000BHz! tones,!each!followed!500!ms!later!by!a!puff!of!air.!After!several!trials! the!rabbit’s!aye!begins!to!close!even!before!the!puff!of!air!occurs.! This!is!classical!conditioning.!! Conditional(stimulus!is!the!1000BHz!tone!and!! conditional(response!is!the!eye!blink.!(

Reinforcing(stimulus(An!appetitive!stimulus!that!follows!a!particular! behavior!and!thus!makes!the!behavior!become!more!frequent.!! BThe!process!of!reinforcement!strengthens!a!connection!between!neural! circuits!involved!in!perception!(the!sight!of!the!lever)!and!those!involved!in! movement!(the!act!of!lever!pressing).!(

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Punishing(stimulus!An!aversive!stimulus!that!follows!a!particular! behavior!and!thus!makes!the!behavior!become!less!frequent.!(

A!simple!neural!model!of!instrumental!conditioning.!!

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BThe!third!major!category!of!learning,!motor!learning,!is!actually!a! component!of!stimulus–!response!learning. 8. Motor(learning!Learning!to!make!a!new!response.!Learning!how!to! dance,!how!to!swim,!how!to!read,!how!to!climbing.! BMotor!learning!as!the!establishment!of!changes!within!motor! systems,!but,!in!fact,!motor!learning!cannot!occur!without!sensory! guidance!from!the!environment.!! BFor!example,!motor!skilled!movements!involve!interactions!with! objects:!bicycles,!tennis!racquets,!etc.!( BFor!example,!if!we!teach!an!animal!to!make!a!new!response!whenever!we! present!a!stimulus!it!has!never!seen!before,!it!must!learn!to!recognize!the! stimulus!(perceptual!learning),!and!make!the!response!(motor!learning),!and!a! connection!must!be!established!between!these!two!new!memories!(stimulusB response!learning).!!

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Hebb(rule!The!hypothesis!proposed!by!Donald!Hebb!that!the!cellular! basis!of!learning!involves!strengthening!of!synapse!that!is!repeatedly! active!when!the!postsynaptic!neuron!fires.!! BIf!a!synapse!repeatedly!becomes!active!at!about!the!same!time!that! the!postsynaptic!neuron!fires,!changes!will!take!place!in!the!structure! or!chemistry!of!the!synapse!that!will!strengthen.( ( ( A!simple!neural! model!of! classical! conditioning:! When!the!1000B Hz!tone!is! presented!just! before!the!puff! of!air!to!the!eye,! synapse!T!is! strengthened.!!

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An!Overview!of!Perceptual,!Stimulus–Response!(SBR),!and!Motor!Learning!

The!fourth!form!of!learning,!relational!learning,!involves!learning!the! relationships!among!individual!stimuli.! 9. Relational(learning!Learning!the!relationships!among!individual! stimuli.!! BFor!example,!consider!what!we!must!learn!to!became!familiar!with! the!contents!of!a!room.!! BFirst,!we!must!learn!to!recognize!each!of!objects.!! BIn!addition,!we!must!learn!the!relative!locations!of!the!objects!with! respect!to!each!other.!! Other!type!of!relational!learning:!Episodic!learning!is!remembering!sequences! of!events!(episodes)!that!we!witness!–requires!us!to!keep!track!of!and! remember!not!only!individual!events!but!also!the!order!in!which!they!occur.!(

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SUMMARY( ! Learning!procedures!changes!in!the!way!we!perceive,!act,! think,!and!feel.!It!does!so!by!producing!changes!in!the!nervous!system! in!the!circuits!responsible!for!perception,!in!those!responsible!for!the! control!of!movement,!and!in!connections!between!the!two.!! ! Perceptual!learning!consists!primarily!of!changes!in! perceptual!systems!that!make!it!possible!for!us!to!recognize!stimuli!so! that!we!can!respond!to!them!appropriately.! ! StimulusBresponse!learning!consists!of!connections!between! perceptual!and!motor!systems.!The!most!important!forms!are!classical! and!instrumental!conditioning.!! Classical!conditioning!occurs!when!a!neutral!stimulus!is! ! followed!by!an!unconditional!stimulus!that!naturally!elicits!an! unconditional!response.!After!this!pairing,!the!neutral!stimulus! becomes!a!conditional!stimulus;!it!now!elicits!the!response!by!itself,! which!we!refer!to!as!the!conditional!response.!! ! Instrumental!conditioning!occurs!when!a!response!is! followed!by!a!reinforcing!stimulus,!such!as!a!drink!of!water!for!a!thirsty! animal.!The!reinforcing!stimulus!increases!the!likelihood!that!the!other! stimuli!that!were!present!when!the!response!was!made!will!evoke!the! response.!Both!forms!of!stimulusBresponse!learning!may!occur!as!a! result!of!strengthened!synaptic!conditions,!as!described!by!the!Hebb! rule.!! ! Motor!learning,!although!it!may!primarily!involve!changes! within!neural!circuits!that!control!movement,!is!guided!by!sensory! stimuli;!thus,!it!is!actually!a!form!of!stimulusBresponse!learning.!! Relational!learning,!the!most!complex!form!of!learning,! ! includes!the!abilities!to!recognize!objects!through!more!than!one! sensory!modality,!to!recognize!the!relative!location!of!objects!in!the! environment,!and!to!remember!the!sequence!in!which!events!occurred! during!particular!episodes.!! ( Induction(of(Long]term(Potentiation(( BElectrical!stimulation!of!circuits!within!the!hippocampal!formation!can!lead!to! longBterm!synaptic!changes!that!seem!to!be!among!those!responsible!for! learning.!! BLomo!discovered!that!intense!electrical!stimulation!of!axons!leading!from!the! entorhinal!cortex!to!the!dentate!gyrus!caused!a!longBterm!increase!in!the! magnitude!of!excitatory!postBsynaptic!potentials!in!the!postBsynaptic!neurons;! this!increase!has!come!to!be!called!long]term(potentiation.(!

10. Long]term(potentiation((LTP)(A!longBterm!increase!in!the!excitability! of!a!neuron!to!a!particular!synaptic!input!caused!by!repeated!high! frequency!activity!of!that!input.!(potentiate!means!“to!strengthen,!to! make!more!potent”)!! BEvidence!that!longBterm!potentiation!has!occurred!is!obtained!by! periodically!delivering!single!pulses!to!the!perforant!path!and! recording!the!response!in!the!dentate!gyrus.! BIf!the!response!is!greater!than!it!was!before!the!burst!of!pulses!was! delivered,!longBterm!potentiation!has!occurred.(

( 11. Hippocampal(formation!! A!forebrain! structure!of!the! temporal!lobe,! constituting!an! important!part!of! the!limbic! system;!includes! the!hippocampus! proper!(Ammon’s! horn),!dentate! gyrus,!and! subiculum.!( ( ?The'primary'input'to'the'hippocampal'formation'comes'from'the' entorhinal'cortex.'The'axons'of'neurons'in'the'entorhinal'cortex'pass' through'the'preforant'path'and'form'synapses'with'the'granule'cells'of' the'dentate'gyrus.' '

' Population(EPSP(is!an!extracellular!measurement!of!the!excitatory! postsynaptic!potentials!(EPSP)!produced!by!the!synapses!of!the! preforant!path!axons!with!the!dentate!granule!cells.!! BPopulation!EPSP!is!an!evoked!potential!that!represents!the!EPSPs!of!a! population!of!neurons.!! BThe!size!of!the!first!population!EPSP!indicates!the!strength!of!the!synaptic! connections!before!longBterm!potentiation!has!taken!place.!LongBterm! potentiation!can!be!induced!by!stimulation!the!axons!in!the!perforant!path!with! a!burst!of!approximately!100!pulses!of!electrical!stimulation,!delivered!within!a! few!second.!Evidence!that!longBterm!potentiation!has!occurred!is!obtained!by! periodically!delivering!single!pulses!to!the!perforant!path!and!recording!the! response!in!the!dentate!gyrus.!If!the!response!is!greater!than!it!was!before!the! burst!of!pulses!was!delivered,!longBterm!potentiation!has!occurred.!!

12. Associative(long]term(potentiation!A!longBterm!potentiation!in! which!concurrent!stimulation!of!weak!and!strong!synapses!to!a!given! neuron!strengthens!the!weak!ones.!! BWhen!weak!and!strong!synapses!to!a!single!neuron!are!stimulated!at! approximately!the!same!time,!the!weak!synapse!becomes! strengthened.!This!phenomenon!is!called!associative!longBterm! potentiation!because!it!is!produced!by!the!association!(in!time)! between!the!activities!of!the!two!sets!of!synapses.!( ( Role(of(NMDA(Receptors(( BLongBterm!potentiation!requires!two!events:!activation!of!synapses! and!depolarization!of!the!postsynaptic!neuron.!! BThe!explanation!for!this!phenomenon,!at!least! 13. NMDA(receptor(A!specialized!ionotropic!glutamate!receptor!that! 2+ controls!a!calcium!channel!that!is!normally!blocked!Mg !ions;! involved!in!longBterm!potentiation.! ?NMDA'receptors'are'found'in'hippocampal'formation,'especially'in' field'CA1.'(It'gets'its'name'from'a'drug'that'specifically'activates'it:'N?methyl?D? Aspartate)'' ?The'NMDA'receptor'controls'a'calcium'ion'channel.'However,'this' 2+ channel'is'normally'blocked'by'a'magnesium'ion'(Mg ),'which' prevents'calcium'ions'from'entering'the'cell'even'when'the'receptor'is' stimulated'by'glutamate.'' 2+' ?However,'if'the'postsynaptic'membrane'is'depolarized,'the'Mg is' 2+ ejected'from'the'ion'channel,'and'the'channel'is'free'to'admit'Ca ' ions.'' ?Thus,'calcium'ions'enter'the'cells'through'the'channels'controlled'by' NMDA'receptors'only'when'glutamate'is'present'and'when'the' postsynaptic'membrane'is'depolarized.'' ?This'means'that'the'ion'channel'controlled'by'the'NMDA'receptor'is' a'neurotransmitter'and'voltage?dependent'ion'channel.'' ?These'channels'to'open,'the'postsynaptic'membrane'must'first' 2+' depolarize'and'displace'the'Mg ions'that'normally'block'them.( ( ?Cell'biologists'have'discovered'that'the'calcium'ions'are'used'by'many' cells'as'a'second'messenger'that'activates'various'enzymes'and'triggers' biochemical'processes.'The'entry'of'calcium'ions'through'the'ion' channels'controlled'by'NMDA'receptors'in'an'essential'step'in'long? ( term'potentiation.''

The!NMDA!Receptor!The!NMDA!receptor!is!a!neurotransmitterB!and!voltageB 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.! !

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14. AP5!(2BaminoB5Bphosponopentanote)!is!a!drug!that!blocks!NMDA! receptors,!prevents!calcium!ions!from!entering!the!dendritic!spines! and!thus!blocks!the!establishment!of!LTP.!( ?These'results'indicate'that'the'activation'of'NMDA'receptors'is' necessary'for'the'first'step'in'the'process'events'that'establishes'LTP:' the'entry'of'calcium'ions'into'dendritic'spine.'' 15. Dendritic(spike!An!action!potential!that!occurs!in!the!dendrite!of! some!types!of!pyramidal!cells.!( (

16. AMPA(receptor!An!ionotropic!glutamate!receptor!that!controls!a! sodium!channel;!when!open,!it!produces!EPSPs.!( 17. CAM]KII!Type!II!calciumBcalmodulin!kinase,!an!enzyme!that!must!be! activated!by!calcium;!may!play!a!role!in!establishment!of!longBterm! potentiation.!! CaMBKII!is!an!enzyme!found!in!dendritic!spines.!! CaMBKII!is!a!calciumBdependent!enzyme.!(

( Role!of!AMPA!Receptors!in!LongBTerm!Potentiation.!TwoBphoton!laser!scanning! microscopy!of!the!CA1!region!of!living!hippocampal!slices!shows!delivery!of! AMPA!receptors!into!dendritic!spines!after!longBterm!potentiation.!The!AMPA! receptors!were!tagged!with!a!fluorescent!dye!molecule.!The!two!photographs!at! the!bottom!are!higher!magnifications!of!the!ones!above.!The!arrows!labeled!a! and!b!point!to!dendritic!spines!that!became!filled!with!AMPA!receptors!after!the! induction!of!longBterm!potentiation.!

( Mechanisms(of(Synaptic(Plasticity((

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BIn!neuroscience,!synaptic( plasticity!is!the!ability!of! synapses!to!strengthen!or! weaken!over!time,!in! response!to!increases!or! decreases!in!their!activity.!! BPlastic!change!also!results! from!the!alteration!of!the! number!of!receptors!located! on!a!synapse.!! BThere!are!several!underlying! mechanisms!that!cooperate! to!achieve!synaptic!plasticity,! ' including!changes!in!the! quantity!of!neurotransmitters! released!into!a!synapse!and! changes!in!how!effectively! cells!respond!to!those! neurotransmitters.!! BSynaptic!plasticity!in!both! excitatory!and!inhibitory! synapses!has!been!found!to! be!dependent!upon! postsynaptic!calcium!release.!! BSince!memories!are!postulated!to!be!represented!by!vastly!interconnected! networks!of!synapses!in!the!brain,!synaptic!plasticity!is!one!of!the!important! neurochemical!foundations!of!learning!and!memory.! BTwo!molecular!mechanisms!for!synaptic!plasticity!involve!the!NMDA!and!AMPA! glutamate!receptors.!! BOpening!of!NMDA!channels!(which!relates!to!the!level!of!cellular! 2+ depolarization)!leads!to!a!rise!in!postBsynaptic!Ca !concentration!and!this!has! been!linked!to!longBterm!potentiation,!LTP!(as!well!as!to!protein!kinase! activation);!strong!depolarization!of!the!postBsynaptic!cell!completely!displaces! the!magnesium!ions!that!block!NMDA!ion!channels!and!allows!calcium!ions!to! enter!a!cell!–!probably!causing!LTP,!while!weaker!depolarization!only!partially! 2+ 2+ displaces!the!Mg !ions,!resulting!in!less!Ca !entering!the!postBsynaptic!neuron! 2+ and!lower!intracellular!Ca !concentrations!(which!activate!protein! phosphatases!and!induce!longBterm!depression,!LTD).!

BDendritic!spines!on!CA1!pyramidal!cells!contain!two!types!of! glutamate!receptors:!NMDA!receptors!and!AMPA!receptors.!! BStrengthening!of!an!individual!synapse!appears!to!be!accomplished!by! insertion!of!additional!AMPA!receptors!into!the!postsynaptic! membrane!of!the!dendritic!spine.!! BAMPA!receptors!control!sodium!channels;!thus,!when!they!are! activated!by!glutamate,!they!produce!EPSPs!in!the!membrane!of!the! dendritic!spine.!! BTherefore,!with!more!AMPA!receptors!present,!the!release!of! glutamate!by!the!terminal!button!causes!a!larger!excitatory! postsynaptic!potential.!In!other!words,!the!synapse!becomes!stronger.!! !

18. Ritric(oxide((NO)(synthase(An!enzyme!responsible!for!the! production!of!nitric!oxide.!! Several!studies!has!shown!that!drugs!that!block!nitric!oxide! synthase!prevent!the!establishment!of!LTP!in!field!CA1.!! BNitric!oxide!is!a!soluble!gas!produced!from!the!amino!acid! arginine!by!the!activity!of!an!enzyme!known!as!nitric!oxide!(NO)! synthase.!BOnce!produced,!NO!lasts!only!a!short!time!before!it!is! destroyed.( ( ?The'establishment'of'LTP'includes'changes'in'the'size'and'shape'of' dendritic'spines.'LTP'causes'the'enlargement'of'thin'spines'into'fatter,' mushroom?shaped'spines.'The'establishment'of'LTP'caused'the'growth' of'now'dendritic'spines.'After'about'15'to'19'hours,'the'new'spines' formed'synaptic'connection'with'terminals'of'nearby'axons.'' ?Activation'of'a'terminal'button'releases'glutamate,'which'binds'with'NMDA' receptors'in'the'postsynaptic'membrane'of'the'dendritic'spine.' 'If'this'membrane'was'depolarized'by'a'dendritic'spike,'then'calcium'ions'will' enter'through'channels'controlled'by'the'NMDA'receptors'and'activate'CaM?KII,' a'calcium?dependent'protein'kinase.'' Activated'CaM?KII'travels'to'the'postsynaptic'density'of'dendritic'spines,'where'it' causes'the'insertion'of'AMPA'receptors'into'the'postsynaptic'density.'' In'addition,'LTP'initiates'rapid'changes'in'the'synaptic'structure'and'the' production'of'new'synapses.'' The'entry'of'calcium'also'activates'a'calcium?dependent'NO'synthase,'and'the' newly'produced'NO'then'presumably'diffuses'out'of'the'dendritic'spine,'back'to' the'terminal'button.'' There,'it'may'trigger'unknown'chemical'reactions'that'increase'the'release'of' glutamate.'' Finally,'long?lasting'LTP'(LTP2'and'LTP3)'requires'the'presence'of'dopamine'and' local'and'remote'synthesis'of'new'proteins'that'stabilize'the'changes'made'in' the'structure'of'the'potentiated'synapse.''

( To!sum!up..! 1.!Rapid,!intense!stimulation!of!CA1!neurons!in!the!hippocampus! depolarizes!them.! 2.!Binding!of!Glu!and!DBserine!to!their!NMDA(receptors!opens!them.! 2+ 3.!Ca !ions!flow!into!the!cell!through!the!NMDA!receptors!and!bind!to! calmodulin.! 4.!This!activates!calciumBcalmodulinBdependent!kinase!II!(CaMKII).! !!!!!!a.!CaMKII!phosphorylates!AMPA!receptors!making!them!more! + permeable!to!the!inflow!of!Na !ions!and!thus!increasing!the!sensitivity!of! the!cell!to!depolarization.! !!!!!!!b.!In!time!CaMKII!also!increases!the!number!of!AMPA!receptors!at! the!synapse.! 5.!Increased!gene!expression!(i.e.,!protein!synthesis!—!perhaps!of!AMPA! receptors)!also!occurs!d...