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10/29/15 POVSVisionCore Fall2015 VallabhDas NeuralControlofEye Movements • FoveaiscentralporDon ofreDnawithmaximum densityof photoreceptors • Tobeabletoseean object,itsimagemust fallonthefovea (Zigmond,Bloom,Landis,Roberts,Squire1999) 1 10/29/15 Whycontroleyemovements? Topointthefoveaata staDonaryormovingobject GazeShiYing Tokeepthefoveaonan objectduringself-moDon GazeHolding (AlternaDvesoluDontoagazeshiYing eyemovementistomovetheheadto acquireatargetbut….) TypesofEyeMovements OptokineDcNystagmus-YouTube 2 10/29/15 TypesofEyeMovements GazeShiYing • Saccades • FastVergence GazeHolding • VesDbulo-Ocularreflex • OptokineDcreflex • Pursuit • Slowvergence AnotherClassificaDonScheme Conjugate – Saccades – Smooth-pursuit – VOR – OKN DisjuncDve – Vergence 3 10/29/15 …andanother Voluntary Reflexive – Saccades – Smooth-pursuit – Vergence – VOR – OKR …andanother Fast – Saccades – FastVergence – VOR Slow – OKR – Pursuit – SlowVergence 4 10/29/15 Oculomotorcontrolstrategies:Top-down andboeom-upinfluences • Acommonfeatureofneuralcontrolsystems aretop-downandboeom-upinfluences • Boeom-upcontrolàGatherparametersof thesensorysignaltodevelopthemotor command – Decodingoferrorsignals;forexamplereDnalerror posiDonforsaccades;direcDonandspeedfor pursuit – Influenceofcontrast,luminanceetc Oculomotorcontrolstrategies:Top-down andboeom-upinfluences • Top-DownInfluencesàUsesomepre-defined strategiestoinfluencethemotorcommand – InfluenceofaeenDon – Experience – ExpectaDon – Asanexample,top-downinfluencesallowustochoose fromamongseveraltargets • ThefinaleyemovementisusuallyafuncDonof bothboeom-upandtop-downcontrol. • Inthiscourse,wewillfocusmostlyonboeom-up control. 5 10/29/15 Oculomotorcontrolstrategies– fromSensaDontoAcDon OrganizaDonofOcularMotorSub-Systems ReDnalError PosiDon ReDnalError Velocity(foveal) HeadacceleraDon Headvelocity ReDnalError Velocity(full-field) Saccades Smooth-pursuit VesDbulo-ocularreflex OptokineDcsystem NeuralIntegrator Motornuclei EyePlant 6 10/29/15 EyeMovementDirecDons • Horizontal – AbducDon – AdducDon • VerDcal – ElevaDon – Depression • Torsional – IntorsionorIncyclotorsion – ExtorsionorExcyclotorsion AxesofRotaDon • TheaxisofrotaDonisnotthesameasthe direcDonofmoDon – AxisofrotaDonisperpendiculartomovement direcDon • HorizontalmovementisaboutaverDcalaxis • VerDcalmovementisaboutahorizontalaxes • Torsionalmovementisaboutaxis perpendiculartohorizontalandverDcalaxis 7 10/29/15 Terminology • DucDons–movementofoneeye – AbducDon – AdducDon – SupraducDon – InfraducDon – IncycloducDon – ExcycloducDon Terminology • Versions–conjugatemovementofbotheyes – Dextroversion – Levoversion – Supraversion – Infraversion – Dextrocycloversion – Levocycloversion • Vergence–disjuncDvemovementsoftheeyes – Convergence – Divergence – Cyclovergence – VerDcalvergence 8 10/29/15 Terminology • SignconvenDon – Usuallyrightwardandupwardmovementsare denotedbyposiDvevalues – LeYwardanddownwardmovementsarenegaDve – VergenceisleYeyeminusrighteyeandtherefore convergenceisposiDve • GazedirecDons – Primaryisstraightahead – SecondaryisalongthehorizontalorverDcalmeridians – TerDaryisanyposiDonthatisacombinaDonof horizontalandverDcalposiDons(oblique) EOM • ContracDonandrelaxaDon ofEOMareresponsiblefor eyemovements • MusclesarealwaysacDve • 6pairsofextraocular muscles SideviewofLeYEye – LR,MRmediatehorizontal eyemovements – SR,IO&IR,SOmediate verDcalandtorsionaleye movements 9 10/29/15 AnatomicalorganizaDonofEOM • MedialrecDareparalleltomedialwall • LateralrecDareabout90degapart AnatomicalorganizaDonofEOM • VerDcalrecDare23degtemporalineacheye • Obliquesare51degnasalineacheye 51 TopViewofLeYEye 10 10/29/15 Cyclo-verDcalmuscleacDondependson horizontalposiDonoftheeye • Iftheeyeisturnedouttoward thetemple • Obliqueshavemoretorsional acDon • VerDcalrecDhavemore verDcalacDon. • Iftheeyeisturnedintowardsthe nose • ObliqueshavemoreverDcal acDon. • VerDcalrecDhavemore torsionalacDon • LRareresponsibleforABducDon(temporalwardmovement) • MRareresponsibleforADducDon(nasalwardmovement) • PrimaryacDonofSRandIRisverDcalmovement;secondary acDonistorsion • PrimaryacDonofSOandIOistorsionalmovement;secondary acDonisverDcal 11 10/29/15 Primary,secondaryandterDary acDonsofEOM Muscle Primary Secondary Ter3ary MedialRectus ADducDon - - LateralRectus ABducDon - - InferiorRectus Depression ExcycloducDon AdducDon SuperiorRectus ElevaDon IncycloducDon AdducDon InferiorOblique ExcycloducDon ElevaDon AbducDon SuperiorOblique IncycloducDon Depression AbducDon ComplimentaryPairsofMuscles • EOMineacheyeareorganizedinagonistantagonistpairsthatbehaveinpush-pull manner – LRandMR – SRandIR – SOandIO 12 10/29/15 Descartes-Sherrington’sLaw • ReciprocalinnervaDonofagonist-antagonist musclepairs • AsagonistinnervaDonincreases,antagonist innervaDondecreases. • Examples–RMRandRLR Complimentarypairsofmuscles • Therearealsoyokemusclepairsthathelpwith eyealignmentandbinocularcoordinaDonin horizontalandverDcalplanes • RightLRandLeYMR • LeYLRandRightMR 13 10/29/15 Hering’sLaw • EqualinnervaDonofyokedmusclepairs. • “...oneandthesameimpulseofwilldirects botheyessimultaneouslyasonecandirecta pairofhorseswithsinglereins.” • Example:Forrightwardmovements,RLRand LMRinnervaDonincreasestogether;RMR andLLRinnervaDondecreasetogether YokeMusclepairsinthecyclo-verDcal plane • LeYSR(Elev,Incyclo)andRightIO(Excyclo,Elev) • RightSRandLeYIO • LeYIR(Dep,Excyclo)andRightSO(Dep,Incyclo) • RightIRandLeYSO • Qs:Whyaretheseyokemusclepairsandnot verDcalrecDandobliques? 14 10/29/15 Donder’sandLis3ng’sLawsofTorsion • Donder’sLaw-EachgazedirecDonhasauniquetorsional posture,nomaeerwhatpaththeeyetooktogetthere. • Lis3ng’sLaw–AnyeyeposiDoncanbedescribedby rotaDonoftheeyefromprimaryposiDonaboutasingle axislyinginaspecificfronto-parallelplane(“LisDng’s plane”). • LisDng’sLawusuallyholdstrueforsteadygazeposiDons andwiththeheadsDllandupright,butitisviolatedduring manyeyemovements;Forexample,ifyouweretofreeze theeyerightinthemiddleofasaccadeyoumightfindthat LisDng’slawwasnottrue. • Acurrenthypothesisisthatmechanicalmovementofthe musclepulleysleadstothegeneraDonoftorsional posiDonsrequiredtomaintainDonder’sandLisDng’slaws. OrganizaDonofOcularMotorSub-Systems ReDnalError PosiDon ReDnalError Velocity(foveal) HeadacceleraDon Headvelocity ReDnalError Velocity(full-field) Saccades Smooth-pursuit VesDbulo-ocularreflex OptokineDcsystem NeuralIntegrator Motornuclei EyePlant 15 10/29/15 MechanicalModeloftheOculomotor Plant • Globe,eyemusclesand orbitalDssuetogether makeuptheoculomotor plant. • Elementsofthe oculomotorplantas determinedbytheeyepullexperimentare – Viscousdragdueto connecDveDssue(R) Eyepulledeccentrically andreleased K ExponenDaldecay (returntocenter) R – elasDcrestoringforcedue tomuscle(K) ElasDcity,ViscosityandInerDa Elas3cityofmusclesandconnec3ve3ssues: • describessDffnessofmuscle,it’sstretchability • determinesposiDonofeye • Analogyisaspring Viscosityofmuscleandother3ssues • DescribesinternalfricDonandotherresistancetomovement • Determinesvelocitylimit(howrapidlytheeyecanchangeposiDon) • Analogyisadamperonadoor Iner3aofglobeandmuscles • RelatestomassdistribuDonofglobeandmuscles • DeterminesacceleraDonlimit(howrapidlytheeyecanchangevelocity) • InerDaofglobeisquitesmall 16 10/29/15 Doorwith damper Oculomotor Plant • Neuralcommandsmustcompensatefor sluggishdynamicsoftheeyeplant HowdoyoucompensateforPlantDynamics? ?? Oculomotor Plant • APulse-Stepmodelforaneuralcommandsignal wouldovercomethevisco-elasDcpropertyofthe plant(onceagainconsiderananalogyofadoorwith adamper). 17 Unit Response (spks/s) Motoneuron acDvityreflects pulse-step behavior Unit response (Volts-scaled) 10/29/15 Time(secs) Example:MotoneuronAcDvity (Movie) 18 10/29/15 Backtofirst-ordermodel FR(t-δt)=K*E(t)+R*E’(t)+B • TonicorstepacDvityisproporDonaltoeyeposiDon(E); coefficient‘K’isthereforetheposiDonsensiDvityof themotoneuron. • PhasicorPulseacDvityisproporDonaltoeyevelocity (E’);coefficient‘R’isthereforethevelocitysensiDvity ofamotoneuron. • ‘B’istheresDngfiringrateofthemotoneuronwhen subjectisfixaDngastraight-aheadtarget. • ‘δt’isthemotoneuronallatency. Rate-PosiDonCurves (fromSylvestreandCullen1999) (fromRobinsonandKeller1972) 19 10/29/15 Reviewofpulse-step • Eyeglobe,EOMandorbitalDssuetogethermakeupthe oculomotorplant. • TheplanthasviscoelasDcproperDes;EOMcontributeprimarilyto elasDcityandorbitalDssuecontributetoviscosity. • ViscoelasDcproperDesmaketheplantrespondsluggishlytoa constantforce;neuralcommandsmustcompensateforthese sluggishdynamics. • Apulse-stepinnervaDonoftheEOMcompensatesforplant properDes;motoneuronsinthethreemotornucleishowthese kindofresponses. • EyevelocityisproporDonaltothepulseofinnervaDon;getsthe eyequicklyfrompointAtopointB;primarilynecessaryto overcomeviscosity. • EyeposiDonisproporDonaltostepofinnervaDon;holdstheeye ateccentriclocaDons;primarilynecessarytocounterelasDcity. ThreeCranialNervesinnervatesixmuscles • Midbrainatthelevelof themesencephalic reDcularformaDon • CNIII(oculomotor)– medial,superiorand inferiorrecD;inferior oblique • CNVI(abducens)– lateralrectus • CNIV(trochlear)– superioroblique (Kandel,Schwartz,Jessell4thed) 20 10/29/15 OculomotorNucleussubdivisions • OMNprojectsto ipsilateralMR,IRandIO andcontralateralSR • NeuronsprojecDngto eachmuscleare organizedindisDnct subdivisions • IRsubdivisioninOMNis mostrostralfollowed caudallybyMR,IOand SR TrochlearandAbducensmotornuclei • ThetrochlearnucleusprojectstothecontralateralSO muscleviathetrochlearnerve • Abducensnucleushastwosetsofintermingled neurons – Abducensmotorneurons(AMN)projecttoipsilateralLR viaabducensnerve – Abducensinternuclearneurons(AIN)crossthemidlineat theleveloftheabducensnucleusandprojecttothe contralateraloculomotornucleusviathefiberbundle calledthemediallongitudinalfasciulus(MLF) • TheabducensnucleusissomeDmescalledthecenter ofconjugategazebecauseofitscentralroleinthe binocularcoordinaDonofeyemovements 21 10/29/15 FinalCommonPathforConjugate HorizontalEyeMovements AIN AMN • Theanatomical interconnecDonsbetweenthe abducensandoculomotor nucleiresultsinthe generaDonofcoordinated movementsofthetwoeyes. • FormsthebasisforHering’s lawwhichsaysthatthetwo eyesarecontrolledasone. Legend:MLF-mediallongitudinalfasciculus;AMN-abducensmotor neurons;AIN-abducensinternuclearneurons; RaDonaleforNeuralIntegraDon ReDnalError PosiDon Saccades ReDnalError Velocity HeadacceleraDon Headvelocity Smooth-pursuit VesDbulo-ocularreflex ReDnalError Velocity OptokineDcsystem Velocity Command ???? Motornuclei Position & Velocity Command EyePlant 22 10/29/15 MathemaDcalintegraDonofvelocityinformaDonis requiredtogenerateposiDoninformaDon (FromLeighandZee1999) SchemaDcforNeuralIntegraDon 23 10/29/15 NIFuncDon • NIfuncDonisusuallyevaluatedbythe‘DmeconstantofneuralintegraDon’asmeasuredin darkness. • TheDmeconstantistheDmetakenforthe eyetodriYback63%fromaneccentric posiDon. • AperfectNIhasaninfiniteDme-constant. • Areal(normal)NIinhumanshasaDme constantofabout20-70sec. NeuralIntegraDon(cont) • NucleusPrepositus Hypoglossiandadjacent medialvesDbular nucleusfuncDonsasthe horizontalneural integrator. • IntersDDalNucleusof CajalfuncDonsasthe verDcalandtorsional neuralintegrator. 24 10/29/15 NeuralIntegraDon(cont) • Floccularlobeinthecerebellumisalso importantforneuralintegraDon. CBM + + NI • GeneDcdisordersofcertaincalciumchannels specifictothecerebellumresultsinmicewith deficientneuralintegraDon WhathappensifyoulesiontheNI? • A–NodriY • Postlesiondata indicatesgaze-evoked nystagmus • AYerbilaterallesion, neuralintegrator funcDonislost FromCannonandRobinson1987 25 10/29/15 LeakyneuralintegratorinapaDentresults ingaze-evokednystagmus OrganizaDonofOcularMotorSub-Systems ReDnalError PosiDon ReDnalError Velocity(foveal) HeadacceleraDon Headvelocity ReDnalError Velocity(full-field) Saccades Smooth-pursuit VesDbulo-ocularreflex OptokineDcsystem NeuralIntegrator Motornuclei EyePlant 26 10/29/15 Whydowemakesaccadiceye movements? Yarbus1967 TheSaccadeWaveform 7 6 1 2 1 2 3 4 4 5 6 7 SaccadeAmplitude TargetAmplitude SaccadePeakVelocity SaccadeLatency SaccadeDuraDon Catch-upSaccade InterSaccadeInterval 3 SaccadeGain= 1 2 5 27 10/29/15 Saccades–SalientFeatures • GeneratedinresponsetoposiDonalreDnalerror • Extremelyfast-Upto800deg/sec; • Accurate-Gain~0.9 • DuraDon-~30-50msec • Latencyis~200msec • Conjugateeyemovement SaccadicMainSequenceRelaDonships • Well-definedrelaDonshipsbetweensaccademetric parameters. • Usefultosummarizesaccadicbehaviorand quanDtaDvelydifferenDatebetweennormaland abnormalsaccadicbehavior. Amplitude-DuraDon 0.12 1000 0.10 Saccade Duration (s) Saccade Peak Velocity (deg/sec) Amplitude-PeakVelocity 1200 800 600 400 200 0 0 5 10 15 20 25 Saccade Amplitude (deg) PV=PVmax*(1-e-Amp/C) 30 0.08 0.06 0.04 0.02 0.00 0 5 10 15 20 25 30 Saccade Amplitude (deg) Dur=D0+D1*Amp 28 10/29/15 SaccadeLatency 70 100 60 80 Count Count 50 60 40 40 30 20 20 0 0.10 10 0 0.15 0.20 0.25 Saccade Latency (msec) 0.30 3 4 5 6 7 8 9 10 Inverse of Saccade Latency (1/msec) • LatencyistheDmetakenbetweentheappearanceofatargetandtheeye movementtothetarget • Averagesaccadelatencyisaround200msec;slightlyfasterinamonkey • CorDcalandsub-corDcalprocessingrelatedtovisualprocessing,target selecDonandmotorprogrammingcontributestolatency • UndercertaincondiDonssaccadescanbeofultra-shortlatency(~80ms) andtheseareexpresssaccades SaccadicControl-Brainstem • Networkofneuronsin brainstemcontrolsaccade metrics(velocity,amplitude duraDon) • ExcitatoryBurstNeurons(EBN) intheParamedianPonDne ReDcularFormaDondrive horizontalsaccades • EBNinrostralintersDDalmedial longitudinalfasciculus(riMLF) driveverDcalsaccades • Lesionsintheseareawillabolish saccadesinaparDcularplane (Kandel,Schwartz,Jessell4thed) 29 10/29/15 SaccadicControl-Brainstem • Networkofneuronsin brainstemcontrolsaccade metrics(velocity,amplitude duraDon) • ExcitatoryBurstNeurons(EBN) intheParamedianPonDne ReDcularFormaDondrive horizontalsaccades • EBNinrostralintersDDalmedial longitudinalfasciculus(riMLF) driveverDcalsaccades • Lesionsintheseareawillabolish saccadesinaparDcularplane (Kandel,Schwartz,Jessell4thed) SaccadicControl-Brainstem • Inhibitoryandexcitatoryburst neuronsinPPRF • EBNfiringcorrelatedwith saccadevelocity • IBNfiringinhibitsthe contralateralabducensnucleus • Omnipauseneurons(OPN)keep burstneuronssilentunDla saccadeisgenerated • Long-leadburstneurons(LLBN) projecttoEBNandOPNand couldprovideatriggersignal (Kandel,Schwartz,Jessell4thed) 30 10/29/15 Example:SaccadeBurstNeuron (Movie) Time 31 10/29/15 Saccades-CorDcal&CerebellarAreas • AnumberofcorDcaland cerebellarareascontrolother aspectsofsaccadiceye movementssuchas – – – – – – SensorimotorTransformaDon TargetselecDon AeenDon/IntenDon AdaptaDon Sequences/Planning etc (Kandel,Schwartz,Jessell4thed) SuperiorColliculus S I D • • • • • Dorsalmesencephalon PartofreDno-geniculo-corDcalpathway&reDno-tectalpathway Layeredstructure Superficiallayers–topographicallyorganizedvisualmap Intermediateanddeeperlayers–topographicmotormap 32 10/29/15 SuperiorColliculus(cont.) • VisualandMotormapsintheSCareinregisterandencode contralateralvisualspaceandcontralateralsaccades • FuncDonsoftheSuperiorColliculus – – – – ControlsLLBN RostralzoneoftheSCpromotesfixaDon ProvidesinformaDonontargetgoal InvolvedintargetselecDon Saccades-CorDcal&CerebellarAreas • FEF – Rostralbankofarcuate sulcus – ExcitesSCdirectly – ReleasesSCfromBasal GangliainhibiDon – Projectsdirectlyto reDcularformaDon – LesionsofSCandFEF abolishessaccade generaDon (Kandel,Schwartz,Jessell4thed) 33 10/29/15 Saccades-CorDcal&CerebellarAreas • BasalGanglia – InhibitsSC • PPC–AeenDon/IntenDon;prioritymap • SEF – Learnedsequences • VermisandFasDgialNucleiinCBM – Acceleratescontralateralsaccades – Providesalatebraketoipsilateral saccades – SaccadeadaptaDon (Kandel,Schwartz,Jessell4thed) EffectoflesionofFasDgialNucleusina monkey 34 10/29/15 Smooth-Pursuit:Trackingasmoothlymoving object • GeneratedinresponsetoreDnalimagemoDon • Matcheyevelocitytotargetvelocity;targetvelociDescanbeupto 90deg/sec • Latencyabout130msec(comparethistoVORandsaccades) • AccuracyofSPisdeterminedbyitsgain;SPGainàEyeVelocity/ TargetVelocity • UnlikeVORandOKN,SPisnotareflexiveeyemovement • Unlikesaccades,SPisnotanopen-loopresponse FrequencyResponse–Smooth-PursuitBode plot • Qualityofthesmoothpursuitresponsedecreases (Lowgainandincreasing phaseshiY)withincreasing frequencyoftargetmoDon • PhaseshiYssuggestthat thebrainisunableto compensateforlatencyat higherfrequencies (Dasetal1998) 35 10/29/15 PursuitDrivers • Targetvelocity – Mostimportant.Goalistomatcheyevelocityto targetvelocity.Thestep-rampsDmulusis evidencefortheimportanceoftargetvelocity ReconstructedtargetmoDon Efferencecopyloop r_v T_v(reconstr) SPSystem E_v ReDnalErrorVelocity=Targetvelocity–Eyevelocity ReDnalErrorVelocity+EfferencecopyofEyeVelocity=ReconstructedTargetVelocity Inputtothesmooth-pursuitsystemisReconstructedTargetVelocity 36 10/29/15 Smooth-PursuitCorDcoPontoCerebellar Pathway-Cortex • MoDonsensiDveareaMT decodesparametersofreDnal moDonsuchasspeedand direcDon • MSTcontainsreDnalandextrareDnalinformaDonandmight encodereconstructedtarget moDoninspace • MSTisfurtherdividedintotwo – MSTdcellshavelargerecepDve fieldsandlikelyimportantfor encodingvisualmoDonduringselfmovement – MSTlcellsarelikelyforfovealSP (Kandel,Schwartz,Jessell4thed) Smooth-PursuitCorDcoPontoCerebellar Pathway-Pons • TheDorsolateralPonDneNucleus (DLPN)andtheNucleus ReDcularisTegmenDPonDs (NRTP)aremajorponDnerelay nucleithatchannelcorDcal smooth-pursuitrelated informaDontothecerebellum (Kandel,Schwartz,Jessell4thed) 37 10/29/15 Smooth-PursuitCorDcoPontoCerebellar Pathway-Cerebellum • DLPNandNRTPprojects contralaterallytoFloccularand VermalComplexincerebellum • FlocculusandVentral Paraflocculusarelikelyinvolved inadaptaDonofpursuitsignals • VermisandfasDgialnucleuslikely involvedinacceleraDng/ deceleraDngtheeyeduringan ongoingpursuitmovement (Kandel,Schwartz,Jessell4thed) The aVOR • Gaze holding mechanism that generates eye movements to compensate for head motion • Gaze or line of sight is maintained on a stationary target Leigh and Zee 2006 38 10/29/15 Bode plot of VOR performance • During locomotion head frequency is 1-5 Hz and head velocity is <150 deg/sec • VOR performance is optimal for these stimuli Bony and Membranous Labyrinth • Inner ear contains the structures responsible for the VOR • Inner ear is called the labyrinth because of the complexity of its shape • Outer part is called the Bony Labyrinth – Series of cavities inside the petrous portion of the temporal bone – Contains perilymph which is similar to cerebrospinal fluid – The temporal bone of the bony labyrinth is one of the hardest bones of the human body • Inside the bony labyrinth is the membranous labyrinth – Takes the same shape as the bony labyrinth – Separated from bony labyrinth by perilymph 39 10/29/15 • Membranous Labyrinth – Cochlea – Otoliths • Utricle • Saccule – Semicircular canals • Horizontal • Anterior • Posterior Semicircular canals sense angular head acceleration • Thin tubes that contain fluid called endolymph • At the base of each canal is a enlarged region called the ampulla • Inside the ampulla is the crista. Cristae of each canal contains hair cells. 40 10/29/15 Mechano-electric transduction by Hair Cells • Processes of hair cells are embedded in the cupula which lies in the ampullae • Cupula is gelatinous membrane that prevents the free flow of endolymph 41 10/29/15 How do the SCC sense head motion? • Acceleration of the head results in movement of fluid in the SCC. • As the head rotates in one direction, inertia of the fluid causes it to lag, and hence generate relative motion of the endolymph in the SCC. • Motion of the endolymph results in the bending of the cupula and therefore also bending of the stereocilia of the hair cells. • Bending of the stereocilia results in depolarization or hyperpolarization that is a function of the head motion. Vestibular Nystagmus (VN) • Sustained head rotation results in VN • Vestibular imbalance can cause VN • Reducing a signal from one canal is responded to as if the opposing canal were being stimulated • Eyes drift toward side with lesion. 42 10/29/15 Canal Planes • Canals work in push-pull – Advantage of push-pull is that in case of disease that destroys one labyrinth, the other side can take over (e.g., ear infection) • Left AC is parallel to Right PC • Push-pull pairs – RLC & LLC – RAC & LPC – RPC & LAC 3-neuronarc • LatencyofVORisshortbecausethereareonly 3neuronsbetweeninputandoutput – Neuron1:Canals->VesDbularNucleus – Neuron2:VesDbularNucleus->Abducens Nucleus – Neuron3:AbducensNucleus->Oculomotor nucleus • 4VesDbularnuclei–Medial,Lateral,Superior andInferior 43 10/29/15 Vision and the VOR • In resting state VOR gain is about 0.8-0.9 • In the presence of a visual target, gain goes upto 0.95-1.00 • This visual enhancement is believed to be due to the SP/OKN system • This is called the visually enhanced VOR (Vis-VOR) Otoliths transduce linear head motion and gravity • Utricles and Saccules • Utricles primarily sense tilt (gravity) and horizontal linear acceleration • Saccules primarily sense vertical linear acceleration • Saccule is parasaggital; Utricle is horizontal © Timothy C. Hain, Northwestern University 44 10/29/15 • Macula are the equivalent of the cristae and contain hair cells • Hair cells in the macula are oriented in various directions • Processes are embedded in otolithic membrane • Calcite crystals called otoconia are strewn on otolithic membrane • Saccule – lateral SVN; Utricle – laterodorsal MVN and ventrolateral SVN WhatistheOKR? • TheoptokineDcreflex(OKR)isavisuallydriveneye movementthathelpstostabilizethereDnalimage duringlarge-fieldmoDon. • Thisreflexgeneratesanystagmus-likeeyemovement inresponsetoaunidirecDonalmoDonofthevisual worldcalledoptokineDcnystagmus(OKN). • OptokineDcNystagmus-YouTube • OKNslowphaseisindirecDonofthemoDonofthe sDmulusandthequickrese~ngphaseisinthe oppositedirecDon • TheOKRcomplementstheVORatlowfrequenciesof headrotaDon 45 10/29/15 ComponentsofOKN (Cohenetal1976) • IniDalrapidriseinOKNslowphasevelocityfollowedbygradual increasetosteadystate • GainofOKNdefinedastheraDoofsteadystateeyevelocitytosDmulus velocityiscloseto1.0forsDmulusvelociDesupto90deg/sec OptokineDcaYer-nystagmus(OKAN) • OKANreferstothepersistence ofnystagmusaYertheOKN sDmulusisremovedandthe subjectisplacedindarkness. • ThereisainiDalrapiddropin eyevelocityfollowedbya moregradualdecayofeye velocity • SomeDmesthereisareversal ofthenystagmusaYerOKAN andthisiscalledOKAAN(rare). (Cohenetal1976) 46 10/29/15 VesDbular-OptokineDcinteracDon • ThusduringsustainedrotaDoninthelight,OKANcancelsPRN Exampleofvergenceeyemovement (vanLeeuwenetal1998) VergenceposiDon=LEposiDon–REposiDon Therefore,convergenceisposiDveanddivergenceisnegaDve 47 10/29/15 NearTriad • Convergenceisaccompaniedbyincreasein accommodaDonandpupillaryconstricDon • AccommodaDonisnecessaryforchangingfocus onviewinganearobject – Broughtaboutbychangesinlensshape • PupillaryconstricDonhelpstoincreasedepthof fieldtherebyreducingtheamountof accommodaDonneeded • Cross-couplingbetweenvergenceand accommodaDoncontrolsystems SDmulustoVergence–ReDnalDisparity • IfreDnaldisparityisnon-zero, itmeansthattheimageis fallingonnon-corresponding reDnalareas. • Acrosseddisparitygivesriseto percepDonof‘near’andisthe sDmulustoconvergence. • Anuncrosseddisparitygives risetopercepDonof‘far’andis thesDmulusfordivergence. • Thus,reDnaldisparitydrivesa formofvergencecalled fusionalvergenceordisparity vergence. (Adler’sPhysiologyoftheEye) 48 10/29/15 SDmulustoVergence–ReDnalBlur • Whenanobjectisbroughtclosertothesubject,it appearsblurredbecausethesubjectisfocused behindtheobject. • ThesubjectmustengageaccommodaDon mechanismstoclearblur. • DuetothelinkagebetweenaccommodaDonand vergencesystems,thisalsoinducesavergenceeye movement. • Thusblurdrivesaformofvergencecalled accommodaLve-vergenceorblurvergence. VergenceandAccommodaDonCrosscouplingmodels (Schor2009) • AblursDmuluscandrivevergenceviaanaccommodaDon-vergencecrosslink;The strengthofthiscrosslinkisdefinedbytheAC/AraDo • AdisparitysDmuluscandriveaccommodaDonviaaconvergence-accommodaDoncrosslink;ThestrengthofthiscrosslinkisdefinedbytheCA/CraDo 49 10/29/15 AccommodaDve-Vergencehasdifferent dynamicsthanFusional-Vergence MonocularViewing BinocularViewing AccommodaDon (diopters) Vergence (MA) (CummingandJudge1986) DynamicproperDesofvergenceeyemovements –MainSequence (Maxwell,Tong,Schor2010) • Convergencemaybefasterthandivergence • DivergencespeeddependsoniniDalvergenceposiDon 50 10/29/15 Howdoesthebraingenerateeye movementsindepth(3-D)? • InaframeworkproposedbyHering,vergenceisan independenteyemovementsubsystemandis controlledseparatelyfromconjugateeye movementssuchassaccades. • AneyemovementmadeinresponsetoasDmulus thatbothchangesindepthandconjugateposiDon isasimplesumofseparatelygeneratedvergence andconjugatemovements. Howdoesthebraingenerateeye movementsindepth(3-D)? • Ifthecompositemovementisthesumofvergence andconjugatecomponents,thenmovementsof eacheyeisasfollows – RE=Conjugate-Vergence/2; – LE=Conjugate+Vergence/2 • InanalternaDveframeworkproposedby Helmholtz,eacheyeiscontrolledindependently. • ThereisevidencesupporDngeitherframework. • HowevertheHeringframeworkismoreuseful clinically. 51 10/29/15 Howareeyemovementsindepthcontrolled– Hering’sframework • Separate conjugateand vergence componentsof eyemovements aresummedat thelevelof motoneurons SOA VergenceSignalsintheBrain–MedialRectus Motoneurons GamlinandMays,1992 52 10/29/15 VergenceSignalsintheBrain– Supraoculomotorarea(SOA) • Midbrainnearresponsecellsinthe supraoculomotorarea(SOA) • 1-2mmdorsolateraltooculomotornucleus • MonosynapDcconnecDonstomedialrectus motoneurons LGN CGMB SOA OMN VergenceSignalsintheBrain– SupraoculomotorArea(SOA) Mays,J.Neurophys1984 53 10/29/15 SupportforHering’sHypothesis–Internuclear Ophthalmoplegia (MoviefromLeigh&Zee(1999)3rdediDon) Vergenceinotherpartsofthebrain- cortex • Disparityencoding(sensory) – V1 – MT/MST – LIP • Vergenceeyemovements(motor) – FEF • Vergenceneuronsareadjacenttothesaccadeneurons intheFEF – SEF • PerhapsimportantforpredicDvevergenceeye movements 54 10/29/15 Vergenceinotherpartsofthebrain- cerebellum • Dorsalvermis – LesionsherecauseesodeviaDon,variaDonofalignmentwith orbitalposiDon,disconjugacyofsaccadesandproblemsin phoriaadaptaDon • FasDgialNucleusandPosteriorInterposedNucleus – ReceiveprojecDonsfromthevermis – ProjecttotheSOA – FNhasneuronsrelatedtoconvergence – PINhasneuronsrelatedtodivergence • Cerebellarflocculus – Alsohasneuronsrelatedtovergencebutismostlikely importantforchangingVORgainwithvergenceangle Neuralcontrolofvergence-newevidence • Itappearsthattheframeworkmaynotbeas Heringproposed • Pre-motordriveismonocular(Helmholtz) – NeuralrecordingsinthePPRFduringasymmetric vergencesuggeststhatthesecellsencode movementsofasingleeyeratherthana conjugatesignal 55 10/29/15 Anamalgamatedframeworkfor binocularcontrol • ‘Fast’and‘slow’vergencesystems • Fastvergenceusesmostlymonocularcircuits (Helmholtz-like) • Slowvergencenecessaryofvergencepursuit, finetuningofbinocularposiDonaYerfast componentandstaDcalignmentismostly binocular(Hering-like) Summary • Whystudytheneuralcontrolofeyemovements? – Visionandeyemovementsareawindowintothebrain • FromsensaDontoacDon – Simpleandelegantmodelforneuralcontrolofmovement • Nostretchreflex;Unchangingmechanicalload • Movementsrestrictedtothreeplanes – IndependentsubsystemsclassifieddependingonfuncDon – Clinically,manyabnormaliDesareassociatedwithclear pathophysiology 56