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Synaptic self

Synaptic self






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    Synaptic self Synaptic self Presentation Transcript

    • Chapter 1: Highlights• People dont come preassembled, but areglued together by life We all start out withdifferent sets of genes and we havedifferent experiences. Nature and nurtureshape the synaptic organization of thebrain. The particular patterns of synapticconnections in an individuals brain, and theinformation encoded by these connectionsare the keys to who that person is. Thegenetic blueprint begins to unfold in thenewly fertilized egg.
    • Chapter 1: Highlights• Genes actually do two things : 1. They make us allthe same (were humans) 2. They also distinguishus from one another (unique genetic makeup)How do genes affect individual behavior ? They doso by making proteins that shape the way neuronsget wired together Genetic forces, operating onthe synaptic arrangement of the brain, constrain,at least to some extent, the way we act, think andfeel Its important to recognize that genes onlyshape the broad outline of mental and behavioralfunctions Inheritance may bias us in certaindirections, but many other factors dictate howones genes are expressed
    • Chapter 1: Highlights• Nature and nurture function similarly : they aresimply two different ways of making deposits inthe brains synaptic ledgers In life, rodents arereally afraid of cats. If any one of them, uponseeing a cat for the first time, will "freeze" dead inits tracks. Freezing also occurs if a rat, merelyhears a sound that preceded an aversive stimulus(a mild electrical shock) on some prior occasionHow is the connection is formed ? The sound is awarning signal. (prediction) Any rat that survivesan encounter with a cat should store in its brain asmuch about the situation possible.
    • Chapter 1: Highlights• The next time the sounds or sights, or smells thatpreceded the arrival of the cat occur, those stimulican be attended to in order to increase its chancesof staying alive There is only one system in thebrain taking care of species-typical dangers andnovel ones experienced by individuals in theirlives. Amygdala is part of the brain system thatcontrols freezing behavior and other defensiveresponses in "threatening" situations Its synapsesare wired by nature to respond to the cat, and byexperience to respond in the same way to dangersthat are learned about
    • Chapter 1: Highlights• Rather than create a separate system to accommodatelearning about new dangers, just enable the systemthat is already evolutionary wired to detect danger tobe modifiable by experience The brain can deal withnovel dangers by taking advantage of evolutionary fine-tuned ways of responding. All it has to do is create asynaptic substitution whereby the new stimulus canenter the circuits that the prewired ones used Thebasic wiring plan for fear : 1. Synaptic delivery of theinformation about the outside world to the amygdala 2.If the amygdala detects something dangereous via itsinputs, then its outputs are engaged Fear system canlearn and store information about the stimuli that warnof impending bodily harm or other dangers.
    • Chapter 1: Highlights• Learning is not the function that fear systemis originally designed to perform Fearsystem is built instead to accomplish certaintasks. Learning (synaptic plasticity) is just afeature that helps them do their job betterPlasticity in all the brain systems is aninnately determined characteristic. If thesynapses of a particular brain system cannotchange, this system will not have the abilityto be modified by experience and tomaintain the modified state.
    • Chapter 1: Highlights• Learning and its synaptic result memory, playmajor roles gluing a coherent personality togetheras one goes through life without learning andmemory processes, personality would be merelyan empty, impoverished expression of our geneticconstitution. "Life teaches us who we are" Thesystems responsible for much of what we do andhow we do it are shaped by learning Theinformation the brain system encode and storetoday will contribute importantly to how theyfunction tomorrow The brain learns and storesmany things in networks that function outside ofconscious awareness. These learned tendenciesaffect all aspects of mind and behavior.
    • Chapter 1: Highlights• Many of our thoughts , feelings, and actions takeplace automatically, with consciousness onlycoming to know them as they happen, if at all.Many things that the brain does are not availableto consciousness. Unconscious operation of thebrain is the rule rather than the exception We canbe and often are aware of what we are doingwhen these things happen, but much of the timeconsciousness is informed after the fact While youend up consciously knowing what the person said,you dont have conscious access to the processesthat allowed you to comprehend the sentence
    • Chapter 2: Highlights• The brain and the self are not different Until the 19thcentury, psychology was a branch of philosophyWilhelm Wundt, a German physiologist, began doingexperiments to understand the way the mind worksrather than just speculating about it. He and hisfollowers known as introspectionists, took the keysteps to convert required to convert psychology into anexperimental science Their main topic of investigationwas conscious experience and they explored byexamining their own experiences Behaviorism Early inthe twentieth century, some psychologists began toargue that one conscious experience can be knownpersonally, and cannot be verified by others This ideacaught on and eventually and spawned behaviorism
    • Chapter 2: Highlights• Behaviorism : Valid psychology has to focus on observableevents (behavioral responses) rather than internal statesCognitive Psychology Toward the middle of the century, itdawned on some scientists that the operations(computations) performed by computers were not unlikewhat a human does when solving a problem. This notion wasembraced by farsighted psychologists like Jerry Bruner andGeorge miller. Cognitive scientists were studying mentalprocesses rather than the content of consciousness. Theywere more concerned with how colors are detected anddiscriminated than in what it is like actually to experiencethem It is widely recognized that we can have consciousaccess to the outcome of cognitive processes, but we are notusually aware of the processes that were involved ingenerating that content the fact that cognitive processes arenot dependent on consciousness( actually, consciousnessdepends on "unconscious" cognitive processes)
    • Chapter 2: Highlights• The mind as a trilogy Traditionally, the mind has been viewed as a trilogyconsisting of cognition, affect (emotion), conation (motivation). the factthat emotion and motivation are "not" studied by cognitive science Also,cognitive science has not grappled successfully with how various cognitiveprocesses interact to form the mind Considerable progress has beenmade in understanding how perception, memory and thinking work butnot about how they work together And in light of the mind as a trilogy, anunderstanding of self requires how cognitive, emotional and motivationalprocesses interact . A view of the self Carl Rogers description of self : "theorganized, consistent conceptual gestalt composed of perceptions of thecharacteristics of the "I" or "me" Recent research in social psychology hasemphasized that many important aspects of human social behavior,including decision making as well as the way we react to members ofracial and ethnic groups are mediated unconsciously
    • Chapter 2: Highlights• Things we consciously know about who we are make up the"explicit" aspects of the self. These are what we refer by theterm "self aware". The implicit aspects of the self, bycontrast, are all other aspects of who we are that are notimmediately available to consciousness, either because theyare by their nature inaccesible, or because they are accesiblebut not being accessed at the moment. The capacity forconscious self -awareness enables one to have explicit selfImplicit and explicit These terms are borrowed from thestudy of memory, it is now widely recognized that the brainsystem involved in forming explicit, consciously accessiblememories is distinct from a variety of other systems that arecapable of learning and storing information implicitly. to theextent that our lifes experiences contribute to who we are,implicit and explicit memory storage constitute keymechanisms through which the self is formed and maintained
    • Chapter 2: Highlights• To be self aware is to retrieve from long term memoryour understanding of who we are and place it in theforefront of thought In contrast we use implicitinformation about our selves all the time, even thoughwe may not be consciously aware of it. Those aspectsof the self that are learned and stored in implicitsystems make up the implicit aspects of the self Self isa unit. Organisms go to great pains to keep themselvesalive and well. self preservation is a universal motiveindependent of whether the organism is aware that itis working toward this goal Self is not static It is addedto and subtracted from genetic maturation, learning,forgetting stress, aging and disease.
    • Chapter 2: Highlights• This is true of both implicit and explicit aspects ofthe self, which may be influenced similarly ordifferently at any one point. A caveat researchshows that people are not always true to their so-called personality traits One may be shy at work,domineering at home. People DO NOT actconsistently in different situations Behavioral andmental states are not dictated by constitutionalfactors but instead are situationally determinedAbility to predict behavior depend upon knowingabout a persons thoughts, motivations andemotions relative to a particular set ofcircumstances
    • Chapter 2: Highlights• People dont posses stablepersonality traits over time, butstable "if...then" profiles As BobDylan said : "I change during thecourse of a day. I wake and Im oneperson, and when I go to sleep Iknow for certain that Im someoneelse. I dont know who Im most ofthe time. It doesnt even matter tome.
    • Chapter 2: Highlights• What is a self ? The self is the totality ofwhat an organism is physically,biologically, psychologically, socially andculturally. Different components of theself reflect the operation of differentbrain systems Self can be understood interms of brain systems involved inlearning and storing information inexplicit and implicit systems, aboutthings that are significant in peopleslives
    • Chapter 2: Highlights• The processing by these systems always occurs ina physical and social context (a situation) And theprocessing is performed by networks that functionthe way they do because of both geneticinheritance and past experiences In order tounderstand self, we need to explain how brainsystems underlying thinking, emotion andmotivation develop under the influence of natureand nurture Also, we need to know how thesesystems make it possible for us to attend to,perceive, learn about and store and retrieveexperiences
    • Chapter 3: Highlights• Every vertebrate brain can be divided into three broadzones : the hindbrain, midbrain and forebrain From thecrude experiments of early years of 20th century , itwas concluded that the hindbrain controls very basicfunctions, those necessary for staying alive Themidbrain is involved in maintaining wakefulness andcoarse, isolated behavioral reactions the forebraincoordinates complex behavioral and mental processesAll three levels are represented in all vertebrates Eventhe evolutionarily advanced forebrain is structuredaccording to a common underlying organizational planthat is applicable to every vertebrate species Differentspecies have been subjected to different evolutionarypressures and their brains reflect their unique histories
    • Chapter 3: Highlights• Changes in cortical size and complexity are superimposed ona basic neocortical plan. In all mammals, process related tosensation (vision, audition, touch) are represented in the rearand processes involved in controlling movement in the frontof the cortex Within a given species, the similarities ofcortical organization are striking The major patterns of ofcortical wrinkles are amazingly consistent from person toperson the basic overall architectural plan of the brain ispretty much the same in any two individuals The key toindividuality is not to be found in overall organization of thebrain To understand the defining qualities of each person weneed to go beyond the superficial organization of the brainDefining qualities are in the microscopic structure andfunction of neural systems and especially in the cells andsynapses that constitute them
    • Chapter 3: Highlights• Neuron doctrine : Brain cells can be called neurons and brainis composed of discrete cells In 1950s, with the invention ofthe electron microscope, scientists could finally examine thebrain in sufficient resolution They saw that tiny fibersextending out of a neuron do not typically make directphysical contact with neighboring cells Indeed, they areseparated by tiny spaces, across which the brain does itsbusiness WHAT MAKES NEURONS SPECIAL Neurons have twomajor parts : The first is cell body Cell body is involved inimportant housekeeping functions, such as storing geneticmaterial and making proteins and other molecules that arenecessary for the cells survival The cell body does much thesame work in neurons as it does in other cells The majorstructural difference between neurons and other cells lies inthe special appendages the neurons have - the nerves
    • Chapter 3: Highlights• Nerve fibers are sort of like telephone wires. Theyallow neurons in one part of the brain to communicatewith neurons in another By way of connections,communities of cells that work together to achieve aparticular goal can be formed across space and time inthe brain There are two varieties of nerve fibers, axonsand dendrites. Axons are output channels, dendritesare input channels An axon carries messages to othercells It can end nearby, allowing communication withits close neuronal neighbors, or it can stretch over verylong distances as much as several feet the end of theaxon, called termial, is the point at which the sendingneuron communicates with receiving neurons
    • Chapter 3: Highlights• Many dendrites have little knobs called spines extendingfrom them Spines are often where axons from other neuronsterminate and form synapses Spines are especially importantas receivers of messages from axons Each axon branchesmany times before it ends allowing a single neuron to spawnmany terminals The result is divergence. The messages sentout from one cell can affect many others At the same time,each neuron can receive inputs from numerous others. This iscalled convergence. the point at which the sending andreceiving elements of neurons meet is the synapse.Presynaptic : information usually flows across the synapsestarting from the axon terminal. Postsynaptic : receiving side,often occupied by a dendritic spine GALVANIZED FROG LEGSNerve conduction : how information is transferred along anerve fiber of a single neuron Synaptic transmission : howinformation is exchanged between neurons across thesynaptic space
    • Chapter 3: Highlights• Nerves do conduct electricity but in a special wayImpulses conducted through a nerves arebiologically propagated, moved along byelectrochemical reactions An action potential :biologically propagated impulse in a nerve Oncetriggered (action potential) it travels like a rollingwave down the axon toward terminal Thepropagation occurs as a kind of neurodominoeffect - an electrical change in one part of theaxon membrane produces a similar change inadjacent parts, all the way down to the terminalSYNAPTIC CHATTER
    • Chapter 3: Highlights• While electric stimulation of a sensory nerve elicited an electricalresponse in the motor nerve, stimulation in the motor nerve did notevoke a response in the sensory nerve Sherrington concluded that thejunction between cells, the synapse, had a valvelike property- it onlytransmitted in one direction, from sensory to motor nerves Researchrevealed that the one-way conduction between neurons is due to the factthat synaptic transmission involves the release of chemicals from storagesites in the presynaptic axon terminal these molecules are released whenaction potentials propagated from the cell body reach the terminal Thereleased chemicals then drift across the liquid filled synaptic space theycome in contact with spines or other portions of post synaptic cellBecause the chemical storage sites usually are present in the presynapticterminal and NOT in the postsynaptic dendrite, transmission only occursin one direction The release of neurotransmitter molecules from thepresynaptic terminal is a means, NOT an end
    • Chapter 3: Highlights• Its goal is to generate an electrical response in the postsynaptic cell. the electrical change produced in the dendritehas to be propagated to the cell body, and then to the axon,before an action potential can occur This is so because theaction potential is generated in the initial part of the axonwhere it connects with the cell body The arrival oftransmitter from single presynaptic cell terminal is typicallyNOT sufficient to produce an action potential in the postsynaptic cell Only if the postsynaptic cell is bombarded withtransmitter molecules from many presynaptic molecules frommany presynaptic terminals at about the same time - withinmilliseconds- will an action potential result A givenpostsynaptic cell is believed to receive relatively few synapticcontacts from any one presynaptic neuron.
    • Chapter 3: Highlights• As a result, much of the convergence that drives apostsynaptic cell toward action potentials comes from theconvergence of different presynaptic cells onto thepostsynaptic neuron That is near simultaneous arrival ofneurotransmitter from different presynaptic neurons In orderfor the inputs to arrive in the post synaptic cell body at thesame time, action potentials have to have been triggered inthe various presynaptice cells at about same time The longerthe axon, the longer it takes for the action to travel it downOnce the post synpatic cell generates an action potential, itsrole shifts from that of a receiver to sender It now becomes apresynaptic neuron that helps fire action potentials in othercells Much of what the brain does involves electrical-to-chemical-to-electrical coding of experience A circuit is agroup of neurons that are linked together by synapticconnections
    • Chapter 3: Highlights• A system is a complex circuit that performs a specific function, like seeing,hearing or detecting and responding to danger seeing, for example,involves the detection of light by circuits in the retina then by way of theoptic nerve, to the visual thalamus (the main switchboard) then theoutput is relayed to visual cortex to create visual perception The visualsystem can thus be thought of as a series of hierarchically arrangedcircuits linked together by synaptic connections to perform some functionSynaptic interactions between 2 types of neurons, called projectionneurons and interneurons, are key to understanding how circuits andsystems function Projection neurons have relatively long axons thatextend out of the area in which their cell bodies are located. In ahierarchical circuit, their main job is to turn on the next projection cell inthe hierarchy Projection cells tend to activate or excite postsynapti cellsInterneurons, also called local circuit cells, send their short axons tonearby neurons, and are involved in information processing within a givenlevel of a hierarchical circuit
    • Chapter 3: Highlights• One of their main job is to REGULATE the flow of synaptic traffic by controlling theactivity of projection neurons Inhibitory interneurons release a transmitter from theirterminals that decreases the likelihood that the postsynaptic cell will fire an actionpotential. these neurons play an important role in counterbalancing the excitatoryactivity of projection cells Projection cells tend to be idle in the absence of inputsfrom other projection cells. Inhibitory interneurons, though, are often tonicallyactive,which means they are firing all the time Part of the reason why projection cellsare inactive when not being stimulated is that they receive tonic inhibition frominterneurons. As a result, when excitatory inputs try to turn on a projection cell,preexisting inhibiton of the projection cell has to be overcome. The balance betweenexcitatory and inhibitory inputs to a neuron determines whether it will fire A B + +Excitatory connection from A to B A B I + + - +/- Feed forward inhibition Nowsuppose, that the interneuron I is constantly inhibiting the projection cell B. It isgoing to be much harder for the input A to trigger the projection cell If we put moreexcitatory neurons in with A to drive B, and time arrival just so, the tonic inhibitioncan be overcome The cell can now be continuously activated but being stuck in fastforward is not good for neurons, which can be damaged or even destroyed byunchecked excittion
    • Chapter 3: Highlights• Each burst of excitation should be countered with another round ofinhibition When projection cells in one area of a hierarchical circuit sendenough convergent inputs at about the same time to activate projectioncells in the next area, the level of inhibition in the second area usuallygoes up as well. This happens because the excitatory inputs to an areaoften activate interneurons as well as projection neurons. The momentaryincrease in excitatory inputs to interneurons leads to a momentaryincrease in inhibitory behavior which in turn produces a momentaryinhibition of the projection neurons When an excitatory surge overcomestonic inhibition, elicited inhibition can rein in the excitation, resetting thecircuit, preparing it for new inputs Only if the excitatory inputs arrivesimultaneously, can they overcome the inhibition and elicit activity. Somelocal circuits are excitatory. They can be thought of amplifiers. Imagine acircuit consisting of neurons A and B connected in series. As before, B isassociated with an interneuron, but in this case its an excitatory neuron(E) The axon of A branches and contacts both B and E When A turns on B,the interneuron E is also activated Output of E causes further excitation ofB As a result, the output of B is amplified by an excitatory interneuron thejob of a projection neuron is to turn on the next projection cell in thecircuit What does this mean ?
    • Chapter 3: Highlights• Action potentials in the axons of projection cells have to trigger therelease of chemicals that cross the synapse Chemicals will contribute tothe firing of an action potential in the post synaptic cell The chemicalneurotransmitter first must be able to act quickly at post synaptic sites Itmust also be able to change the electrical state of the post synaptic cell insuch a way that the occurrence of an action potential is more likely tooccur Both speed and excitation are fulfilled by the amino acidneurotransmitter glutamate, which is the main transmitter in projectionneurons throughout the brain In contrast, inhibitory neurons often releasethe amino acid GABA In contrast to glutamate, this inhibitory transmitterreduces the likelihood of an action potential being generated in the postsynaptic cell By sending axons to nearby projection neurons, GABAinterneurons thereby regulate the flow of traffic through a given areaGlutamate and GABA are together responsible for much of the neuro-transmission business in the brain These molecules work by attaching tomolecules called receptors on the post synaptic cell. Receptors selectivelyrecognize and bind transmitter molecules Glutamate receptors recognizeand bind glutamate, but ignore GABA.
    • Chapter 3: Highlights• GABA receptors are just as selective At rest, when the cell isnot being influenced by inputs, the chemical composition ofthe inside of the cell is more negatively charged than the fluidoutside In general, the inside of a neuron that is not beingstimulated is about 60 milivolts more negative than theoutside This is the resting potential of the cell When a neuronis stimulated by excitatory neurons, the membrane potentialbecomes more positive How glutamate works Glutamatereceptor molecules span the cell membrane, with part facinginside the cell and part facing outside When glutamate bindsto the outside part of a post synaptic receptor, a passageopens up through the receptor This allows positively chargedions in the extracellular fluid to move inside the cell whichchanges the chemical balance between outside and inside Ifenough glutamate receptors are occupied on the postsynaptic cell at about the same time, the voltage insidebecomes sufficiently positive, then an action potential occurs
    • Chapter 3: Highlights• How GABA works when GABA receptors are occupied, the inside of thecell becomes more negative due to the influx of negative ions This makesit hard for glutamate to change the concentration of the positive ions inthe post synaptic cell sufficiently to trigger an action potential thelikelihood of firing at any one moment depends on the net balancebetween excitation and inhibition across all of the inputs at that particulartime Glutamate receptors tend to be located out on the dendrites,especially in the spines GABA receptors tend to be found on the cell body,or on the part of dendrites close to the cell body In order for glutamatemediated excitation to reach the cell body to help trigger an actionpotential, it has to get past the GABA guard without GABA inhibition,neurons would send out action potentials continuously under theinfluence of glutamate, and would eventually literally fire themselves todeath MOD SQUADS Modulators : Whether the post synaptic cell firesdepends not only on the counterbalancing force of GABA inhibition butalso on other chemicals that are present at the time.
    • Chapter 3: Highlights• The way a modulator is distinguished from a transmitter isdifferent for different kinds of modulators One importantdifference is related to their speed Modulators have slowerand longer-lasting effects. Glutamate and GABA are fastacting. 3 classes of modulators 1. Peptides 2. Amines 3.Hormones Peptides are larger molecules and slow to affectthe post synaptic site Peptides are often present in the sameaxon terminal as glutamate and GABA (but in their ownseparate compartments) They are released with the fasttransmitter when an action potential comes down the axonBut peptides bind to distinct post synaptic receptors and canas a result augment or reduce the effect of the fasttransmitter with which they are released Peptides effects arelong lasting and tend to have more of an effect onsubsequent squirts of fast transmitter. Peptides can affectdramatically the ability of a cell to be fired by other inputsbut cannot do so with precise timing
    • Chapter 3: Highlights• Best known of neuroactive peptides are theopiates -endorphin ! Endorphins and enkephalinsare triggered by pain and stress and bind to theirspecial receptors, altering pain sensations andmood "Joggers high" is said to be an opiate effectThe monoamines monoamines include substanceslike serotonin, dopamine, epinephrine andnorepinephrine The cells that producemonoamines are found in only a few areas, mostlyin the brain stem but the axons of these cellsextend to widespread areas throughout the brainMonoamines achieve their effects by facilitating orinhibiting the actions of glutamate or GABA (andthe peptides that are released with them)
    • Chapter 3: Highlights• Monoamines are NOT involved in preciserepresentation of stimuli in specific circuitsMonoamines produce global state changes inmany brain areas simultaneously Such as the highdegree of arousal when we encounter a suddendanger Prozac, for example, prevents the removalof serotonin from the synaptic space Bypreventing the removal of serotonin, allowingmore to stay around longer, Prozac amplifiesserotonins effects LSD acts on serotonin receptorsas well hormones Hormones are typically releasedfrom bodily organs into the bloodstream wherethey travel to brain
    • Chapter 3: Highlights• There they can alter the efficacy of glutamate orGABA transmission by binding to specificreceptors on cells Because hormones reach thebrain through the bloodstream, they can influencemany regions simultaneously however, since onlycertain areas, possess the relevant receptors,considerable specificity can be achieved byhormonal modulation circuits in action whatmakes a sound different from sight, a feardifferent form desire, a memory different fromperception is NOT so much the chemistry involvedbut instead, the specific circuits in which thechemicals act
    • Chapter 3: Highlights• The amygdala detects danger in a system which can be described in termsof a three level excitatory chain of cells that release glutumate In short,projection cells in sensory systems activate projection cells in theamygdala which activate projection cells in motor control areas Amygdalacells receive inputs from the sensory world constantly but they ignore themajority of them when the right kind of stimulus is present- one signifiesdanger or some other biologically significant event What keeps aprojection cell in the amygdala from firing in response to meaninglessstimuli ? The answer is GABA In the amygdala,resting potential of somecells can be as negative as -80mV This is due to sustained or tonicinhibition by GABA This means it takes "extra" excitation to turn theamygdala on With GABA receptors on amygdala projection cells occupiedand passing chloride, the inside of the cells becomes more negativeStimuli that are inherently dangerous or unpleasant are able to overcomethe tonic inhibition As are stimuli that have emotional resonance acquiredthrough past learning thus, an otherwise meaningless sound of modestintensity that previously occurred in association with pain has the sameeffect as a natural (innate) form of danger
    • Chapter 3: Highlights• Both innate and learned danger signals cause amygdala cellsto fire rapidly for a sustained period, are thus able toovercome the GABA guard Even after fear arousing stimuliget past tonic inhibition and cause amygdala cells to fire, theyare still subject to GABA control The inputs to the amygdalaactivate GABA cells as well as projection neurons As a result,as the inputs become more active, the elicited inhbition inthe amygdala builds up, which in turn begins to shut downthe activity of amygdala cells The amygdala also receivesmodulatory inputs of various types. Serotonin fibersterminate there and when the amount of serotonin rises inthe amygdala the activity of excitatory projection cells isinhibited Serotonin excites GABA cells, and thus increases thedegree to which they inhibit projection neurons
    • Chapter 4: Highlights• emotions are bioregulatory reactions that aim atpromoting, directly or indirectly the sort ofphysiological states that secure survival and well-being the term ‘‘emotion’’ is not well defined inmost publications. Perhaps this is not surprisingsince there is little consensus about what emotionis, and how it differs from other aspects of mindand behavior Introspections from personalsubjective experiences tell us that some mentalstates have a certain ‘‘feeling’’ associated withthem and others do not Those states that humansassociate with feelings are often called emotions
    • Chapter 4: Highlights• The terms ‘‘emotion’’ and ‘‘feeling’’ are, infact, often used interchangeably. in Englishwe have words like fear, anger, love,sadness, jealousy, and so on, for thesefeeling states, and when scientists studyemotions in humans they typically use these‘‘feeling words’’ as guideposts to explorethe terrain of emotion. the phenomena ofinterest responses that occur when anorganism detects and responds tosignificant events in the course of survivingand/or maintaining well-being
    • Chapter 4: Highlights• The focus is on circuits that instantiatefunctions that allow organisms to surviveand thrive by detecting and responding tochallenges and opportunities. Included, at aminimum, are circuits involved in defense,maintenance of energy and nutritionalsupplies, fluid balance, thermoregulation,and reproduction. Emotion, motivation,reinforcement, and arousal are closelyrelated topics and often appear together inproposals about emotion.
    • Chapter 4: Highlights• Focusing on survival functions and circuits allows phenomena related to emotion,motivation, reinforcement, and arousal to be treated as components of a unifiedprocess that unfolds when an organism faces a challenge or opportunity. feelings aremental representations of the physiological changes that occur during an emotion. Inthe broadest sense, feeling is the perception of an emotional state neuro- scientistshave long assumed that specific emotional/motivational circuits are innately wiredinto the brain by evolution, and that these mediate functions that contribute tosurvival and well-being of the organism emotions, as defined in the context ofhuman basic emotions theory, may not be the best way to conceive of the relevantinnate circuits. Enter survival circuits. the body is a highly integrated systemconsisting of multiple subsystems that work in concert to sustain life both on amoment to moment basis and over long time scales survival circuits A major functionof the brain is to coordinate the activity of these various body systems. An importantcategory of life-sustaining brain functions are those that are achieved throughbehavioral interac- tions with the environment. Basic emotion circuits are meant asan explanation of the feelings for which each circuit is said to be responsible. theirfunction is to negotiate behavioral interactions in situations in which challenges andopportunities exist, not to create feelings. Survival circuits help organisms surviveand thrive by orga- nizing brain functions.
    • Chapter 4: Highlights• When activated, specific kinds of responses rise in priority, other activitiesare inhibited, the brain and body are aroused, attention is focused onrelevant environ- mental and internal stimuli, motivational systems areengaged, learning occurs, and memories are formed Survival circuits aretuned to detect information relevant to particular kinds of environmentalchal- lenges and opportunities they use this information to controlbehavioral responses and internal physiological adjustment that helpbring closure to the situation Nature and Nurture in Survival CircuitsSurvival circuits detect key trigger stimuli on the basis of innateprogramming or past experience. innate programming geneticallyspecified synaptic arrangements Innate evaluative networks makepossible species-wide stimulus-response connections that alloworganisms to respond to specific stimulus patterns in tried and true ways(i.e., with hard-wired/innate reactions) that have been honed by naturalselection.
    • Chapter 4: Highlights• Conditions under which associations are formed between novel stimuliand biologically innately significant events, typically innate triggers Pastexperience These experience-dependent associations allow meaninglessstimuli that occur in conjunction with significant events to acquire theability to activate the innate response patterns that are genetically wiredto innate trigger stimuli. Survival circuits interact to meet challenges andopportunities. Indeed, survival functions are closely intertwined In thepresence of a threat to survival or well-being, the brain’s resources aremonopolized by the task of coping with the threat. Other activities, suchas eating, drinking, and sex, are actively suppressed In satisfyingnutritional/energy demands, behavioral responses are guided by thesensory properties of potential food sources and by cues associated withfood. auditory or visual cues that occur in connection with food items canmodu- late the energy/nutritional circuitry Specifically, areas of theamygdala (LA, BA, ABA) process these learned cues associated with foodand relay them to the LH. Such cues, if sufficiently potent, can stimulateeating in animals that are sated. Feeding does not occur in a vacuum. Asnoted above, when threat levels rise, feeding is suppressed
    • Chapter 4: Highlights• While threat processing normally trumps feeding, at some point the risk ofencountering harm is balanced against the risk of starvation. Circuit Functions versusBehavioral Responses the responses used by survival circuits to achieve survival goalscan be species-specific even though the circuit is largely species-general By focusingon the evolved function of a circuit (defense, repro- duction, energy and nutritionmaintenance, fluid balance, ther- moregulation), rather than on the actual responsescontrolled by the circuit, a species-independent set of criteria emerge InformationProcessing by Survival Circuits: Computation of Stimulus Significance relatively simplesensory processing by subcortical areas can provide the requi- site inputs tostructures such as the amygdala, bypassing or short-circuiting cortical areas humanscan recognize certain emotions by the eyes alone and do not need to process theface as a whole (e.g., Whalen et al., 2004), and evidence exists that this can behandled subcortically ( Multiple Roles of Innate and Learned Stimuli unconditionedand conditioned emotional stimuli can be thought of in other terms, asunconditioned and conditioned survival circuit triggers. they can also be described asincentives—stimuli that motivate instrumental behavior. The same stimuliadditionally function as reinforcers—stimuli that strengthen the probability that aninstrumental response will be learned and later performed. Motivation andreinforcement are obviously closely aligned with the topic of emotion Consider atone that is paired with food. The tone in other words is an appetitive Pavlovian CSthat elicits innate approach behavior. it is also a survival circuit trigger, as it canstimulate eating, even in satiated rats, by acti- vating hypothalamic circuits involvedin energy management
    • Chapter 4: Highlights• The same CS will also function as aconditioned incentive that canmodulate instrumental behaviors incontrast to the ability of a CS to elicitPavlovian innate (uncon- ditionedapproach) behaviors. Thus, a CSassociated with food will facilitateperformance of an instrumentalresponse that is also maintained byfood
    • Chapter 4: Highlights• This is called Pavlovain-to-instrumental transfer sincethe value of the Pavlovian CS is transferred to (altersperformance of) the instrumental response. a hungryrat will learn to press a bar simply to receive the toneCS. In this case the tone is considered a reinforcer, asecond-order or conditioned reinforcer (a first order orprimary reinforcer would be something like food itselfrather than a stimulus associated with food). Althoughwe’ve focused on multiple roles of CSs a similarargument can be made for USs. These are simplystimuli that innately activate survival circuits, promotethe performance of consummatory responses (food iseaten, sex is consummated) in their presence, orsupport Pavlovian associative conditioning orinstrumental conditioning.
    • Chapter 4: Highlights• These are innate or learned stimuli that activate survival circuits andtrigger the expression of the innate responses controlled by these circuits,that modulate the performance of learned (previously reinforced)instrumental behaviors, and that lead to the reinforcement of newinstrumental behaviors Motivation in the Survival Circuit Scheme Emotionand motivation were traditionally treated as separate topics. Emotion wasviewed as a reaction (e.g., a fearful, angry, disgusted, joyful, or sademotional reaction) to some environmental situation, and motivation as adrive from within (e.g., hunger, thirst, or sexual drive) Bindra (1969), forexample, argued that emotion, like motivation, is influenced by internalfactors (e.g., hormones) and motivation, like emotion, is impacted byexternal stimuli (incentives). Motivation, as assessed behaviorally,involves approach toward desired outcomes and avoidance of undesiredoutcomes So-called approach/avoidance motivation often occurs in twostages: 1. an anticipatory/exploratory/search for goal objects 2. and theperformance and consummatory responses (innate responses controlledby surivial circuits) once goal objects are in reach Theanticipatory/exploratory/search phase is guided by incentives Incentives,as noted, are essentially innate or conditioned emotional stimuli; in otherwords, stimuli with the potential to activate survival circuits.
    • Chapter 4: Highlights• One of the key discoveries that led to the rise of incentiveviews was that stimuli that lacked the ability to satisfy needsand reduce drives (for example, the nonnutritive sugarsubstitute saccharin) were nevertheless motivating A majorconsequence was that the connection between motivationand specific functional circuits (what we are calling survivalcircuits) began to be deemphasized. Motivation became asomewhat generic process by which behavior was invigoratedand guided toward goals by incentives. The nucleusaccumbens emerged as a key focal point of this generalmotivational system Behavioral invigoration or energizationwas said to be a func- tion of dopamine release in theaccumbens and incentive pro- cessing by the accumbens wasthought to guide behavior toward goals.
    • Chapter 4: Highlights• While there may indeed be generic aspects ofmotivation (e.g., behavioral invigoration), evidence alsosupports motivationally specific information processingas well. motivation is tied to specific survival functions.Once incentives have guided the organism to goalobjects, innate consummatory responses, which arespecific to the particular survival circuit and function,are initiated. Their termi- nation essentially ends thesurvival (emotional) episode—food is eaten, liquid isdrunk, sex is consummated, safety is reached. suchbehaviors, when repeatedly performed in recurringsituations, can become habitual and divorced from theactual attainment of the goal. In such cases of stimulus-response habit formation, the neural control switchesfrom the ventral to the dorsal striatum
    • Chapter 4: Highlights• The idea proposed here is that conscious feelings resultwhen global organismic states are represented in thecognitive workspace. The basic ingredients of theglobal organismic state would include 1. informationabout the stimulus and other aspects of the social andphysical environment, 2. the survival circuit thestimulus activates, 3. CNS arousal initiated by thesurvival circuit, 4. feedback from survival responsesthat are expressed in the body, 5. and long-termmemories (episodic and semantic) about the stimulus6. and long term memories about the resulting stateThus, in the presence of a survival circuit trigger (a.k.a.an emotional stimulus), the various ingredients wouldbe integrated, and the resulting state categorized bymatching the state with long-term memory stores.
    • Chapter 4: Highlights• When this occurs, a conscious feeling of the globalorganismic state begins to exist. Such a state,having been categorized on the basis of memoriesof similar states, could be dimensional in nature(just based on arousal and valence) or could takeon specific qualities (could be more like what onefelt when previously in danger than whenfrustrated or when enjoying a tasty meal).Labeling of the state with emotion words addsadditional specificity to the experience, creatingspecific feelings (fear, pleasure, disgust, etc).Survival circuits are not posited to have any directrelation (causal role) in feelings. They indirectlyinfluence feelings.
    • Chapter 5: Highlights• the Working Memory Educational Implications ThePrefrontal Cortex As teachers, we should be awareof the implications of the Cognitive Load Theory.Cognitive neuroscience is the study of thestructure and workings of the physical brain,rather than the mind, as studied by cognitivescientists (Bruning et al, 2011). The concept ofworking memory proposes that a dedicatedsystem processes and stores information in theshort term, and that this system underlies humanthought processes (Baddeley, 2003).
    • Chapter 5: Highlights• Neuroscience & So, first we must ask,does neuroscientific research supportthe cognitively oriented models andexplanations of working memory? Yes,overwhelmingly so. (Bruning et al., 2011)The answer is yes, overwhelmingly so.The particularly highly developed rostralend (near the nose and mouth) of thefrontal lobe, of which the function isrelatively poorly understood.
    • Chapter 5: Highlights• The difference of prefrontal cortex developmentbetween primates (especially humans) and othermammals leads to the assumption that it isinvolved with the characteristics that distinguishus from other mammals, such as the capacity forcomplex planning & problem solving. Human brainimaging experiments suggest that numerous areasin the prefrontal cortex are involved in workingmemory. In these lateral and medial views, sixareas in the frontal lobe show sustained activitycorrelated with working memory when presentedwith facial, auditory and spatial stimuli. The BasalGanglia
    • Chapter 5: Highlights• A group of structures linked to the thalamus andinvolved with action selection, ie. the decision ofwhich of several possible behaviors to execute at agiven time (a function of working memory). Astudy by McNab & Klingberg (2008) identififiedthe basal ganglia as being responsible for allowingonly relevant information into working memory.This study therefore reveals a specifific neuralmechanism by which an individual’s ability toexert control over the encoding of newinformation is linked to their working memorycapacity, measured in the absence of overtdistraction.
    • Chapter 5: Highlights• So the activity in the prefrontal cortex when presentedwith this stimuli follows the aforementioned suggestionthat it is involved with such things as complex planningand problem solving. So, raise your hand if you havefound yourself able to speak to a friend even in acrowded bar or busy street. This is basically theconcept that if we overload the working memory upwith too much information, it decreases learningefficiency. Therefore if we take the basal gangliasfunction, of filtering out irrelevant information, this isjust another thing for the working memory to do, andso we should attempt to avoid irrelevant information inorder to maximize efficient learning.
    • Chapter 6: Highlights• Alterations in synaptic connectivity underlielearning Brain is a device for recording changes -for forming memories through learning memory isthe stabilization and maintenance of changes overtime Hebbs Magic in order for two stimuli to bebound together in the mind, to becomeassociated, the neural representations of the twoevents have to meet up in the brain This meansthere has to be some neuron (or a set of neurons)that receives information about both stimuli then,and only then, can stimuli be linked together andan association be formed between them In 1894,
    • Chapter 6: Highlights• Cajal proposed that "the ability of neurons to grow in anadult and their power to create new connections can explainlearning" William James wrote in his famous 1890 textbook"when two brain processes have been active together, one ofthem, on reoccuring, tends to propagate its excitement intothe other" Hebbs notion is that "when an axon of cell A isnear enough to excite cell B or repeatedly and consistentlytakes part in firing it, some growth process or metabolicchanges take place in one or both cells such as As efficiency,as one of the cells firing B, is increased" A S A respondsstrongly to S before pairing when weak and strong inputs to acell are active at the same time, the weak pathway isstrengthened by way of its association with the strongpathway A W A responds weakly to W before pairing A Wpairing S A A responds strongly to W after pairing W Today,
    • Chapter 6: Highlights• Hebbian learning is used to describe changes inthe connection strength between two neuronscaused by the fact the postsynaptic cell was activewhen presynaptic inputs arrived Searching forSynapses by the early 1950s, a number of studieshad succesfully shown that repeated delivery of abrief electrical stimulus to a nerve pathway couldalter synaptic transmission in that pathway SirJohn Eccles found that repetitive stimulation ofnerves going to the spinal cord led to an increasein the size of the electrical response elicited inpostsynaptic neurons in the spinal cord in 1966,
    • Chapter 6: Highlights• Thompson and Spencer studied habituation of thelimb withdrawal reflex in cats Habituation is aform of learning in which repeated presentation ofa stimulus leads to a weakening of a response -you jump the first time you hear a loud noise, butif it is repeated over and over, you jump lessThompson and Spencer ruled out changes in theability of the input and output nerves to transmitsignals, and concluded that the plastic changesmust have crucially involved interneurons.Practical Magic In the mid 1960s Terje Lomomade a chance observation.
    • Chapter 6: Highlights• . He noticed that a brief burst of electrical stimulidelivered to fibers headed for the hippocampus ina rabbit led to a dramatic and long-lasting increasein transmisson (a bigger electrical response toa test stimulus after, as compared to before, theburst) at synapses in hippocampus In Bliss andLomos experiment, a stimulating electrode wasput in the fiber pathway going into thehippocampus and a recording electrode in thehippocampus itself They, then delivered a singleelectrical stimulus to the pathway, and recordedthe electrical response of the postsynapticneurons This served as the baseline
    • Chapter 6: Highlights• Next, they gave the potentiating stimulusa brief burst of many rapidly repeatedpulses Then they started testing againwith a single pulse, and continuedtesting periodically for several hours Thekey finding was that, following thepotentiating pulses, the synapticresponse got bigger, relative to thebaseline response, and remained biggerfor hours
    • Chapter 7: Highlights• basic information about circuits and theirplastic properties to explore broaderaspects of mental function, that is, tobegin to assemble a neurobiological viewof the self. In doing this, we will considereach component of the mental trilogy, aswell as interactions among them.Thinking is the subject of this chapter,and emotion and motivation thefollowing two.
    • Chapter 7: Highlights• Specialized systems come in two flavors. Verbal systems, likesystems involved in speech comprehension, are mainlypresent in the human brain, whereas nonverbal systems arepresent in all brains. Nonverbal specialized systems areepitomized by sensory systems. Each is involved in processingunique kinds of stimuli (sights, sounds, smells, and so on). Aspart of their operation, the verbal and nonverbal specializedsystems are able to retain what they’ve just processed forbrief amounts of time (seconds). This capacity aids inperception, allowing the system to compare what it is seeingor hearing now to what it saw or heard a moment ago. Forexample, when listening to a lecture, you have to hold thesubject of each sentence in your mind until the verb appears,and sometimes you have to refer back to your memory ofearlier sentences to figure out the referent of a pronoun.
    • Chapter 7: Highlights• The information in your working memoryis what you are currently thinking aboutor paying attention to. And becauseworking memory is temporary, itscontents have to be constantly updated.But working memory is not a pureproduct of the here and now. It alsodepends on what we know and whatkinds of experiences we’ve had in thepast. In other words, it depends on long-term memory.
    • Chapter 7: Highlights• The concept of working memorysubsumes what used to be calledshortterm memory. But as the termworkspace implies, working memory ismore than just an area for temporarystorage. It underlies mental work. AsMinsky noted, thinking involves jugglingof mental items—comparing,contrasting, judging, predicting. It is thejob of the executive functions of workingory to do the juggling.
    • Chapter 7: Highlights• The executive represents a powerful mentalcapacity, but is not all-powerful. Like theworkspace, it has its limits. It basically can do oneor at most a few things at a time. This is why youforget a phone number if you are distracted whiledialing. With practice and training, we can learn todivide our attention between two mental taskssimultaneously, but only with difficulty. In thissense, the executive is more like an old-fashionedDOS operating system that can only run oneprogram at a time than like a multitaskingWindows operating system that can concurrentlyrun word processing, spreadsheet, e-mail,calendar, and other programs
    • Chapter 7: Highlights• The maintenance of visual information in working memorythus appears to depend crucially on information transfer oversynaptic pathways between specialized areas of the visualcortex and the prefrontal region. The pathways from thespecialized visual areas tell the prefrontal cortex “what” isout there and “where” it is located. Moreover, these are two-way streets: the prefrontal cortex, by way of synapticpathways back to the visual areas, instructs the visual areasto attend to and stay focused on those objects and spatiallocations that are being processed in working memory.Recent studies by GoldmanRakic and Liz Romanski havefound that auditory working memory involves similarrelations between auditory processing streams and prefrontalareas, suggesting that this scheme involving linkages betweenspecialized sensory processing systems and prefrontal cortexmay be generally applicable across many systems.
    • Chapter 7: Highlights• studies have begun to provide evidence for the operation of executive-likefunctions in the monkey brain. For example, John Reynolds and BobDesimone trained the monkeys to focus their attention on the location ona screen where a dot appears. This is, in essence, the training of anexecutive function, attention. Then they presented a picture in that samearea (that is, within the field of attention). Cells in the early stages of thevisual cortex responded to the picture. When a second stimulus waspresented on the screen with the first, though, the cells did not respond.Executive functions continued to focus cellular activity on the first picture,and the new information about the second picture was ignored. Thiswork, like the studies described above, suggests that attentional signalsare involved in directing traffic in the “what” pathway, controlling whichstimuli are processed. In related work, Leslie Ungerleider and colleagueshad human subjects perform similar tasks while functional brain activitywas measured. They reached a very similar conclusion: that top-downactivity regulates lower visual areas.
    • Chapter 7: Highlights• The importance of top-down signals from the prefrontalcortex in selecting neural activity in lower processors• was also demonstrated in an elegant study by YasushiMiyashita’s team in Japan. They made lesions in the brains of• monkeys in such a way that allowed them to present visualstimuli so that the “where” area in the temporal cortex• received information either bottom-up (from the lower areasof the visual system) or top-down (from the prefrontal• cortex), but not both. They found that top-down informationfrom the prefrontal area was sufficient to selectively• activate cells in the “where” pathway.
    • Chapter 7: Highlights• the special qualities of human consciousness,especially those made possible by language. (Theremay be other ways that the human brain differs as well,but language is a particularly important difference.)This does not imply that we are conscious in English orChinese or Swahili, nor does it suggest that personswho are deaf and mute should be consideredcognitively impaired. My point, rather, is about the waythe human brain is wired. That is, the emergence of thecognitive capacities underlying language changed theway the brain works, making it possible for humanbrains to think and experience events in ways thatother brains cannot. The addition of language into thehuman brain involved a revolution rather than anevolution of function.
    • Chapter 7: Highlights• Other than size, which in this case is significant, the humanprefrontal cortex has another important advantage over theprefrontal cortex of nonhuman primates: it has access to aprocessing module specialized for language use. Increasedsize adds power, but the presence of language does morethan just soup up the cortex. (I’m referring here to the kind ofgrammatical natural language that characterizes essentiallyevery human brain, rather than the other communicativecapacities that can occur in other kinds of animals, likechimps and even parrots.) Language radically alters thebrain’s ability to compare, contrast, discriminate, andassociate on-line, in real time, and to use such information toguide thinking and problem-solving. The difference betweenhaving only nonverbal working memory and having bothverbal and nonverbal working memory is enormous for howthe cognitive system works.
    • Chapter 8: Highlights• The problem is only compounded when we examinethe relation of behavior to feelings in different species.Just because two creatures act the same does notmean they have the same experiences when theyperform those actions. A beetle that finds itself underthe approaching footstep of a human does what ahuman would do—it tries to escape before the footlands. A robot can be programmed to do what a humanwould do if an object is sent flying toward his or herhead—raise an arm to deflect the object. Do the beetleand robot feel fear, or do they simply express adefensive response? The fact that we have feelingswhen we act emotional does not mean that every actthat looks emotional is accompanied by feelings.
    • Chapter 8: Highlights• The simplest way to illustrate the independence ofemotional processing from consciousness in the controlof emotional behavior is to describe an example inwhich consciousness is not a factor. At some point inyour life, you’ve probably jumped out of the way ofsomething rapidly approaching and only afterwardnoticed what it was—a ball thrown at you or a busflying by, for example—and also only afterward noticedyour heart pumping strongly. The feeling of fear cameafter you jumped and after your heart was alreadypumping—the feeling itself did not cause the jumpingor the pumping. While an anecdote like this doesn’tprove anything, there is also quite a lot of scientificevidence for this kind of reaction. The heroin addictstudy described above is one example. Let’s consideranother.
    • Chapter 8: Highlights• A processing approach may also be confused with theso-called cognitive approach to emotions, which treatsemotions as appraisals—that is, as thoughts about agiven situation. While some appraisal theorists allowfor unconscious appraisals (which is consistent with aprocessing approach), most emphasize appraisals asconscious thoughts and use verbal self-report tounderstand the nature of the appraisal process. Thisapproach, obviously, takes us right back to thecredibility problem. Conscious appraisals may indeedoccur during an emotional state, but there are other,more fundamental processes at work as well. Anunderstanding of these more fundamental processes isthe goal of the processing approach.
    • Chapter 8: Highlights• In spite of these difficulties, the limbic systemcontinues to survive, both as an anatomical conceptand as an explanation of emotions, in textbooks,research articles, and scientific lectures. This is in partattributable to the fact that both the anatomicalfoundation and the emotional function it was supposedto mediate were defined so vaguely as to beirrefutable. For example, in most discussions of howthe limbic system mediates emotion, the meaning ofthe term emotion is not defined. Reading between thelines, it seems that the authors are often referring tosomething akin to the common English-language use ofthe term, which is to say feelings. However, as we’veseen, a conception of emotion in terms of feelings isproblematic.
    • Chapter 8: Highlights• Clearly, much has been learned about therole of amygdala circuits in fearconditioning. With this information in hand,we can now begin to ask how processing inthe amygdala relates to processing incortical circuits involved in cognitiveprocessing. We start with a consideration ofthe connections between the hippocampusand the amygdala, and their contribution tothe contextualization of fear—that is, theregulation of fear on the basis of ourassessment of the situation we are in.
    • • In such studies, rats or other animals learn to do things that avoid thedelivery of a shock. Once they learn how to avoid the shock, they performthe response habitually. Given that the hallmark of fear or anxietydisorders is habitual avoidance of situations that might lead to harm oranxiety, this approach seemed to offer the opportunity to understand theneural basis of a clinically relevant kind of learning. However, asmentioned previously, studies of avoidance conditioning failed to lead to aclear understanding of the neural basis of fear. Little effort was made todistinguish the contribution of neural systems to the two kinds of learningthat take place in these tasks— initially, the subject undergoes classicalfear conditioning, where cues in the apparatus come to be associatedwith the shock, then an instrumental avoidance habit is learned on thebasis of its ability to remove the animal from the situation in which shockis likely.” The notion of multiple memory systems had not yet emerged,and it wasn’t fully appreciated that different kinds of learning involvedifferent brain systems. Once researchers started focusing on fearconditioning on its own, stripped out of the context of avoidanceconditioning, progress was swift. And as the popularity of fearconditioning increased, the more complex avoidance-conditioningprocedures, which were more difficult to relate to brain mechanisms, fellout of favor.Chapter 9: Highlights
    • • Dopamine has long been believed to be a critical factor in rewardprocesses. Although there are rewarding conditions that do not dependon dopamine,” much of what we know about rewards centers around therole of dopamine. For example, treating rats with drugs that block theeffects of dopamine at its receptors in the brain eliminates the rewardingeffects of brain stimulation— that is, rats are much less inclined to pressto get the brain jolts under such treatment. Further, if hungry rats aregiven food in one compartment of a two-chambered apparatus, or ifsatiated rats are given rewarding brain stimulation in one of thecompartments, they will later spend more time in that compartment. Thisis called a place preference. Treatment of rats with drugs that block theaction of dopamine prevents the formation of the place preference. Aplace preference can also be established by giving rats a shot ofamphetamine or cocaine, both of which mimic the action of dopamine atits receptors. It’s no accident that these widely abused drugs work likerewards in learning situations, and the relation of dopamine to drugaddiction was important in sustaining interest in reward and motivationduring the years of cognitive domination in neuroscience.Chapter 9: Highlights
    • • In the presence of an emotionally arousing stimulus, thebrain is placed in a state, sometimes called a motive state,that leads to coordinated information processing within andacross regions, and results in the invigoration and guidance ofbehavior toward positive goals and away from aversive. Mostof what we know about how incentives are learned andreacted to comes from studies of aversive conditioning, butmost of what we know about how conditioned incentives areused to invigorate and guide behavior comes from studies ofpositive motivation. I’m therefore going to apply to negativemotivation what is known about the role of the accumbens inpositive motivation in an effort to move forward from ourunderstanding of aversive conditioning into motivationcircuits (the details may therefore need to be revised aftermore research is performed on the role of the accumbens innegative motivation).Chapter 9: Highlights
    • • Decision-making compresses trial-and-error learningexperiences into an instantaneous mental evaluation aboutwhat the consequence of a particular action will be for agiven situation. It requires the on-line integration ofinformation from diverse sources: perceptual informationabout the stimulus and situation, relevant facts andexperiences stored in memory, feedback from emotionalsystems and the physiological consequences of emotionalarousal, expectations about the consequences of differentcourses of action, and the like. This sort of integrativeprocessing, as we’ve seen, is the business of working memorycircuits in the prefrontal cortex. In chapters 7 and 8, wediscussed the role of the prefrontal cortex in workingmemory and considered the contribution of the lateral andmedial prefrontal cortex. Here, we will focus on two of thesubareas of the medial prefrontal cortex in light of theirrelation to the motive circuits outlined above.Chapter 9: Highlights
    • • So how do we reconcile the two views of humanmotivation? McClelland’s theory emphasizes nonverbalmotivational systems, some of which are biologicallyorganized. These work implicitly and function more orless similarly in humans and other mammals, thougheach species can have its own specialized motivesystems as well. McClelland’s views fit well with thedrivel incentive/reinforcement tradition. But thisapproach does not cover the full range of humanmotivation, as McClelland himself has noted.Consciously accessible, verbally encoded, explicitmotives acquired through the use of language are alsoan important part of human mental life, especially insocial situations. The self-consciousness view ofmotivation thus complements rather than contradictsthe implicit view.Chapter 9: Highlights
    • • Self-knowledge is certainly a significantaspect of human motivation, but evenanimals that are not selfaware, or at leastnot robustly aware of who they are the waya human is, are motivated to do things—they seek food and shelter and avoidpredators and injury. Much of what wehumans do is also influenced by processesthat percolate along outside of awareness.Consciousness is important, but so are theunderlying cognitive, emotional, andmotivational processes that workunconsciously.Chapter 9: Highlights
    • Chapter 10: Highlights• In spite of Shakespeare’s insight that mental problems are“troubles of the brain,” hundreds of years later, proponentsof a physical basis for mental illness still had little evidencewith which to make their case. By the late nineteenthcentury, it was widely accepted that actual destruction ofthe brain (the result of diseases like syphilis) could changemental function drastically,’ but the alterations of mood andthought that had come to be known as neuroses andpsychoses were still resistant to physical explanation. YoungSigmund Freud sought a neurological account of mentalillness, but realizing that such a goal was unattainable in hislifetime, turned to psychological explanations andpsychological treatments instead. There was no “sweetoblivious antidote,” to use Shakespeare’s phrase, forhysteria, melancholia, or anxiety.
    • Chapter 10: Highlights• Biological psychiatrists do realize that circuits are significant, and it’s notout of ignorance that they adhere to the soup model. They would loveto have smart drugs, akin to smart missiles, that, when taken orally,would go straight for the circuits that underlie a particular disorder andavoid all others. With this sort of drug, dreaded side effects would beeliminated. But achieving such precision would require that the exactcircuits altered in particular mental disorders be known, and that drugsbe available to adjust selectively the chemistry of the relevant circuits.Although not all of the pieces of the puzzle are in place today, researchefforts are under way to obtain the information that would make thispossible. As Steve Hyman, director of the National Institute of MentalHealth, has noted, psychiatry, arm in arm with neuroscience, is poisedto answer many of its central questions. Hyman, in fact, refers to thetime ahead as “the millennium of mind, brain and behavior.” To facilitatethe achievement of his goal, the National Institute of Mental Healthrecently has established several Research Centers for the Neuroscienceof Mental Disorders (I serve as the director of one of these, the Centerfor the Neuroscience of Fear and Anxiety, which I’ll describe later in thechapter).
    • Chapter 10: Highlights• This conclusion was supported and refined by the near-simultaneous discovery of the beneficial effects ofchlorpromazine, a phenothiazine drug marketed asThorazine. This drug was isolated because its chemicalstructure was similar to that of antihistamines. A Frenchsurgeon tried administering chlorpromazine to some of hispatients to test whether it might be more effective thanother antihistamines in sedating patients and reducingrespiratory complications in surgery. The drug tUrned out tohave a powerful calming or tranquilizing effect, which ledthe surgeon to propose using it with psychotics. Two Frenchpsychiatrists, Jean Delay and Pierre Deniker, triedadministering chlorpromazine to a few schizophrenicpatients who were resistant to all other forms of treatment.Not only were they tranquilized, their psychotic symptoms(paranoia and hallucinations) were also reduced.
    • Chapter 10: Highlights• Recent efforts to explain schizophrenia and other mentaldisorders have turned to more complex conceptions thatfocus on alterations of function in specific brain regions andcircuits rather than global changes in the level ofmonoamines. For example, a number of studies havedemonstrated structural differences between the brains ofschizophrenics and normal control subjects. Included arechanges in size or volume of certain brain regions, and thenumber of cells and their shape and arrangement indifferent regions. Some of the key areas in which structuralchanges have been discovered include the prefrontal cortexand medial temporal lobe (hippocampus and amygdala).Changes in the number of dopamine receptors have alsobeen found in the prefrontal cortex and basal ganglia. Theprefrontal cortex, hippocampus, and amygdala also exhibitfunctional anomalies in blood flow and/or neural activity, asdetermined by PET and functional MRI scanningtechniques]
    • Chapter 10: Highlights• The revised version of the dopamine theory thusproposes that schizophrenia involves overactivityof the D2 class of receptors in the basal gangliaand underactivity of Di receptors in theprefrontal cortex. The hyperactivity of D2receptors in the basal ganglia accounts forpositive symptoms, and the underactivity of Direceptors in the prefrontal cortex accounts fornegative symptoms. This explains why drugs thatblock D2 receptors only treat positive symptoms,but leaves open the question of how atypicalantipsychotic drugs, which mainly targetserotonin or norepinephrine systems, treatnegative symptoms.
    • Chapter 10: Highlights• In general, there is a growing interest in the idea that alterations insynaptic connectivity in neural circuits, rather than just levels ofneurotransmitters or receptors, are important. Neurotransmitters andreceptors still figure prominently in this approach, but in the context ofconnections within and between areas. For example, Francjne Benes,noting that the number of GABA cells is decreased in the hippocampusof schizophrenics, has proposed that the disorder involves a shift ofdopamine connections from excitatory glutamate cells to GABA cells inthe hippocampus to compensate for a loss of inhibitory cells, and DavidLewis has proposed that a specific class of GABA cells located in aspecific layer of the prefrontal cortex plays a critical role in cognitiveregulation and is altered in schizophrenia. In imaging studies,researchers such as David Silbersweig and Emily Stern are beginning toexamine changes in neural activity in networks involvinginterconnections of the prefrontal cortex with other cortical andsubcortical areas.
    • Chapter 10: Highlights• Once a disorder exists, and the brain has changed, the changes have tobe dealt with in some way in order for a patient to recover. Drugs caninduce adaptive changes in neural circuits, or put neural circuits in astate where adaptation and learning are promoted. But there’s noguarantee that, left to its own devices, the brain will learn the rightthings. Patients, in other words, are likely to benefit most from drugtherapy when the drug-induced adaptivity of their brains is directed in ameaningful way. This is probably best achieved by traveling down thepharmacological road to recovery with some one who understands notjust the drug or the person, but the drug, the per son, and the lifesituation the person is experiencing. HMOs may not like it, but the drug,therapist, and patient are partners in the synaptic adjustment processcalled therapy, with drugs attacking the problem from the bottom up,the therapist from the outside in, and with the patient reaching up anddown from his or her own synaptic self.
    • Chapter 11: Highlights• Connection machines can, like brains, be divided up in sucha way that different groups of processors are responsible forparticular tasks. Although each task is then performed lessefficiently than it would be if all the processors weredevoted to it, overall this can be a more efficient use of themachine since multiple tasks can be worked on at the sametime. Reversing the logic, if we had fewer neural systemsusing up the same overall computing power in our brainsthe systems would each be more powerful. However,because we have to do lots of different things each day tostay alive and well (eat, sleep, walk, avoid danger and pain,hear, see, smell, taste, talk, and think, to name some), withfewer brain systems we would almost certainly be lesscapable, even if the remaining systems were each moreproficient at their particular tasks.
    • Chapter 11: Highlights• We’ve met a number of the brain’sneural systems throughout this book.Included are networks involved insensory function, motor control,emotion, motivation, arousal, visceralregulation, and thinking, reasoning, anddecisionmaking. What is remarkable isthat synapses in all of these systems arecapable of being modified byexperience. Consider a few examples.
    • Chapter 11: Highlights• Before we examine what holds the self together, let’sconsider how fragile a patch job it is. The bottom lineis simple: Functions depend on connections; breakthe connections, and you lose the functions. This istrue of the function of a single system (a lesion of thevisual thalamus, for example, will prevent informationfrom the eyes from reaching the cortex, and thus willprevent the cortex from being able to perceive thevisual world) as well as of interactions betweensystems (a lesion in a certain part of the temporallobe will prevent information about visual objectsfrom reaching the prefrontal cortex and thus willprevent that stimulus from being held in workingmemory, and hence from being used as the basis forthinking and decision-making).
    • Chapter 11: Highlights• Another example involves conduction aphasia.Patients who suffer from this condition can speakwithout trouble and can understand spoken words(for example, they can point to the picture of anobject named by someone else), but cannot, uponhearing a spoken word or sentence, repeat it, oranswer a question posed to them. The reason for this,according to the late Norman Geschwjnd, one of thegreat neurologists of the twentieth century; is thatthe neural pathway that transmits informationbetween the areas of the brain responsible for thecomprehension and production of speech is cut.Conduction between the brain areas is thusdisrupted.
    • Chapter 11: Highlights• The various systems of your brain share the sameexperiences. They encode them differently, butthey encode the same external events. They willnot always focus on the same details, and eachmay not always participate in every experience.But to the extent that a neural system encodesan experience, it is likely that some othersystems of the brain are encoding the sameexperience. As a result of parallel encoding by,and parallel plasticity within, neural systems, ashared culture develops and persists among thesystems, even if they never communicatedirectly.
    • Chapter 11: Highlights• Parallel processing in different brainsystems is further coordinated bymodulators. As we’ve seen, these arereleased throughout the brain in thepresence of significant stimuli, includingnovel, unexpected, or painful stimuli, orstimuli that otherwise signal emotionalarousal. In the last chapter, we examinedthe role of one class of modulators, themonoamlnes, in mental disorders. Here weexamine their role in normal brainfunction. These are two sides of the samecoin
    • Chapter 11: Highlights• All that is required to induce plasticity at a synapse is theright kind of synaptic activity. If cells processing sensoryevents can undergo plasticity as a result of the kind ofactivity those events trigger in sensory systems, then whycan’t cells processing a thought change the connections ofthe cells with which they communicate? Obviously, they do;we simply need to learn more about precisely how thishappens. The downward mobility of thought provides apowerful means by which parallel plasticity in neuralsystems is coordinated. The more elaborate theconvergence zones present in a species, the more elaboratewill be the cognitive capacity of the species and the moresophisticated will be the ability of information convergenceto coordinate plasticity in that species. With thoughtsempowered this way, we can begin to see how the way wethink about ourselves can have powerful influences on theway we are, and who we become. One’s self-image is self-perpetuating.
    • Chapter 11: Highlights• Synaptic connections hold the self together in most of usmost of the time. Sometimes, though, thoughts, emotions,and motivations come uncoupled. If the mental trilogybreaks down, the self is likely to begin to disintegrate andmental health to deteriorate. When thoughts are radicallydissociated from emotions and motivations, as inschizophrenia, personality can, in fact, change drastically.When emotions run wild, as in anxiety disorders ordepression, a person is no longer the person he or she oncewas. And when motivations are subjugated by drugaddiction, the emotional and intellectual aspects of lifesuffer. That the self is synaptic can be a curse—it doesn’ttake much to break it apart. But it is also a blessing, as thereare always new connections waiting to be made. You areyour synapses. They are who you are.