Introductionbrainandcognitionpart2

Introductionbrainandcognitionpart2

Hoorcollege1:Action

●Motorcontrolishierarchical(p.327–331&336–339) ●Functionalneuroanatomyofcorticalmotorregions(p.331–335) ●Neuralcodinginmotorregions(p.339–342,p.356–357,notp.343–344) ●Goalselectionandactionplanning(p.345–349)

●Linksbetweenactionandperception:Mirrorneurons(p.350–352)

●Movementinitiationandthebasalganglia(p.359–363)•Motorlearning:Forward

modelsandexpertise(p.369–375) Motorhierarchy

Top:Corticalassociation,

premotor,and supplementarymotorareas translatingintentionsand goalsintoactionplansand movementpatterns

Middle:Primarymotor

cortex,brainstem structures,basalganglia andcerebellumconverting movementpatternsinto commandstothemuscles

Bottom:Spinalmotor

neuronsinnervating muscles,togetherwith spinalsensoryneurons capableofproducingsimple reflexes 1.Motorcontrolishierarchical

Bottom:

Muscleinnervation ●Musclesconsistoffibersattachedtotheskeleton

●Comeinantagonistpairs:flexorandextensor(ifoneisflexed/contracted,theotheris

extended/relaxed) ●Musclecontractionthroughacetylcholinereleasedbyfiringofalphamotorneurons ●Firingfrequencyofalphamotorneurons(andnumberofmusclefibers)determines forcegeneratedbymuscle 1 / 4

●Alphamotorneuronsoriginateinspinalcord,exitthroughventralroot ●Gammamotorneuronsadjustmusclespindles(importantforsensingthestretchof themuscle) ●Sensoryneuronsenteringthespinalcordthroughdorsalrootsendinputfrommuscle spindlestoalphamotorneuronsviaspinalinterneurons Spinalreflexes ●Alphamotorneuronsoriginatein spinalcord,exitthroughventral root ●Gammamotorneuronsadjust musclespindles(importantfor sensingthestretchofthemuscle) ●Sensoryneuronsenteringthe spinalcordthroughdorsalroot sendinputfrommusclespindlesto alphamotorneuronsviaspinal interneurons ●Ifstretchisunexpected,alpha

neuronactivation:stretchreflex

●Reflexesserveposturalstability andprotectivefunctionswithout anyhelpfromthecortex ●Flexor/extensorcoordinationin stretchreflexviainhibitoryinterneuron Centralpatterngenerators ●Catwalkingonatreadmillinvolvingswing(flexion)andstance(extension)evenwith transectedspinalcord(noconnectiontothebrain) ●Spinalcordalone(withoutthebrain)iscapableofproducingrhythmicmovements suchaswalking ●Indicatesthatthebraindoesnotneedtospecifypatternsofmuscleactivitybutcan simplyactivatespinalpatterngenerators ●Catscanwalkwithoutaconnectionfromthespinalcordtothebrain,humanscannot

Middle:

Brainstemstructures ●12cranialnervesforcriticalreflexesinvolvedinbreathing,eating,eyemovements, facialexpressionsoriginateinbrainstem

●Keystructures:vestibularnuclei,reticularformationnuclei,substantianigra

●Projectionstospinalcordcalledextrapyramidaltracts(notpartofthepyramidaltract frommotorcortex) ●Extrapyramidaltractscontrolposture,muscletone,andmovementspeed Cerebellumandbasalganglia cerebellum -contains75%ofallneuronsofthehumancentralnervoussystem -keyroleinerrorcorrection(forwardmodels) 2 / 4

-damageresultsinataxia:difficultymaintainingbalanceandcoordinatedmovements

basalganglia -5nucleiwithoutputstocortexviathalamus -keyroleinmovementselectionandinitiation (gatingfunction) -Damagecanresultinparkinson’sor huntington’sdisease 2.Functionalneuroanatomyofcorticalmotor regions Corticalmotorregions primarymotorcortex -keyareaformotorinitiation,activationoflower levels

-mainoutput:pyramidal(corticospinal)tract

secondarymotorareas -keyareasformovementplanningandcontrol -premotorcortex(lateralpartofBA6) -supplementarymotorarea(medialpartofBA6) Additionalkeycorticalregions -broca’sarea(BA44/45) -Inferior(BA39/40)andsuperiorparietallobule

(BA5/7)

-Medialprefrontalcortexinclusieffrontaleye field(BA8) Primarymotorcortex(M1) Keyareaformotorinitiation(boekbekijken) -controlofmovementonoppositesideofthe bodyviacorticospinaltract(similarformost othertracts) -HemiplegiaafterM1lesion(stroke)lossofvoluntarymovementsoncontralateralside ofthebody Corticospinal(pyramidaltract) -eithertospinalinterneurons -ordirectlywiththelongestaxoninthebody(>1m)monosynapticallytoalphamotor neurons(corticomotorneurons)to controlfingersandhands(toolue) Somatotopicorganization -differentM1regionsrepresent differentbodyparts 3 / 4

-butorganizationiscoarserthaninsomatosensorycortex(S1)i.enotsuchclear homunculus -representationsofeffectorscorrespondtotheirimportanceformovementandlevelof control -overrepresentationofhandsandlips -canbemappedwithTMSandfMRI -representationoffingerscorrespondtohowoftentheyareusedtogether Secondarymotorareas -coarsesomatotopicorganizationsimilartoM1 -keyforplanningandcontrolmovement premotorcortex(PM,lateralpartBA6)

-connectionswithparietalcortex:informationaboutbodyandhowitispositionedin

space -importantforsensory-guidedmovementsequences(e.g.grabbingacup,hittinga ball) supplementarymotorarea(SMA,medialBA6)

-connectionswithmedialfrontalcortex:informationaboutpreferencesandgoals

-importantfordecidingwhichobjecttochoose(coffeeorsoda)andfor memory-guidedmovementsequences(playingthepiano) Twodorsalstreamstopremotorcortex(PM) Dorsal-dorsalstreamtodorsalPM

-fromsuperiorparietallobule:reaching

-Opticataxiawhenlesioned:inabilityto

reachforobjectsdespiteintactrecognition Ventro-dorsalstreamtoventralPM

-frominferiorparietallobule:transitive

(manipulationofobjects)andintransitive (signifyanintention)gestures

-apraxiawhenlesioned:inabilityto

coherentlyuseobjects(e.g.useacomb) andtolinkgesturesintomeaningful actions(wavegoodbye)despiteintact objectknowledge 3.neuralcodinginmotorregions CodingofmovementdirectioninM1 Whatdomiddle/toplevelsofthehierarchycode -concretemuscleactivity(force)orabstractproperties(movementdirectionorfinal location)

-central-outtask:movelevertoaspecifictargetlocation(aap)

activityofM1neuronscodemovementdirection -Exampleneuronfiringfordownwardsmovementindependentofstartingandtarget location -manyM1neuronsshowsuchdirectionaltuning(‘preferreddirection’)→tuning profiles

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