Eye Movements

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Eye Movements. 1. The Plant. The Oculomotor Plant Consists Of only 6 muscles in 3 pairs. This Yields 3 degrees of Mechanical Freedom. Donders Law/ Listings Law. Neural Constraints Reduce this to 2 degrees of freedom. 3-D eye movements. Donders Law Relates torsion to eye position - PowerPoint PPT Presentation

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  • Eye Movements

  • 1. The Plant

  • The Oculomotor Plant ConsistsOf only 6 muscles in 3 pairs

  • This Yields 3 degrees ofMechanical Freedom

  • Neural ConstraintsReduce this to2 degrees of freedomDonders Law/ Listings Law

  • 3-D eye movementsDonders Law Relates torsion to eye positionListings lawTorsion results from rotation of eye around perpendicular axisListings planePlane orthogonal to line of sightDoes not apply when head is free

  • Kinematics vs DynamicsIn the Oculomotor SystemRotations about theCenter of Gravity

    No Loads

    No Inertia

    Force = Position

  • Oculomotor muscles and nervesOculomotor nerve (III)Medial rectusSuperior/Inferior rectiInferior obliqueTrochlear nerve (IV)Superior obliqueAbducens nerve (VI)Lateral rectusMedial longitudinal fasciculus

  • 2. The BehaviorsGaze Holding:VOROKN

    Gaze Shifting:SaccadesVergence

    Smooth Pursuit

  • Classes of eye movementsReflexive gaze stabilizationVORStabilize for head movementsOptokineticStabilize for image motionVoluntary gaze shiftingSaccadesAcquire stationary targetSmooth pursuitAcquire moving targetVergenceAcquire target in depth

  • Gaze During Nystagmus

  • Saccades

  • 3-D Gaze TrajectoryVergence

  • 2. The Motor Neurons

  • Force PatternsRobinsons Lollipop ExperimentsStaticsDynamics

  • Oculomotor NeuronsDuring Static Gaze

  • Dynamics and Statics

  • 3. VOR

  • Cupula and otoliths move sensory receptorsCristaeMaculae

  • Angular PositionAngular AccelerationAngular VelocityCupula Deflection

  • Canal afferents code velocitySpontaneous activity allows for bidirectional signaling S-curve is commonDifferent cells have different ranges and different dynamicsPopulation code

  • Canal Output DuringSlow Sinusoidal Rotation

  • VOR With and Without Vision

  • rVOR gain varies with frequencyAlmost perfect > 1HzLow gain for low frequencies (0.1Hz)Sensory mechanisms can compensate (optokinetic reflex)

  • Oculomotor muscles and nervesOculomotor nerve (III)Medial rectusSuperior/Inferior rectiInferior obliqueTrochlear nerve (IV)Superior obliqueAbducens nerve (VI)Lateral rectus

  • The 3-Neuron ArcPrimary Effects of Canals on Eye Muscles Canal Excites Inhibits

    Horizontal Ipsi MR, Contra LR Ipsi LR, Contra MR

    Anterior Ipsi SR, Contra IO Ipsi IR, Contra SO

    Posterior Ipsi SO, Contra IR Ipsi IO, Contra SR

  • Robinsons Model of the VOR

  • Robinson

  • 4. OKN

  • Type I Vestib Neuron

  • Bode Plot of OKN

  • Bode Plot of VOR

  • Bode Plot of OKN

  • 5. Saccades

  • Saccadic system

  • OPN Stimulation

  • Brainstem saccadic controlParamedian pontine reticular formation (PPRF) Burst and omnipause neuronsAim to reduce horizontal motor errorProject to directly to lateral rectus motor neuronsProjects indirectly to contralateral medial rectusMedial longitudinal fasciculusMesencephalic reticular formationAlso influenced by omnipause neuronsVertical motor errorProjects to superior and inferior rectus motor neurons

  • Robinsons Model of the VOR

  • Lee, Rohrer and Sparks

  • Jay and Sparks

  • 5. Pursuit

  • Smooth pursuitTrack movement on part of retinaTwo theoriesMotor (Robinson)Retinal slip only provides velocityDoes not capture pursuit onsetSensory (Lisberger and Krauzlis)Position, velocity and acceleration

  • Smooth pursuit system

  • Smooth pursuit brainstemEye velocity for pursuit medial vestibular nucleus and nucleus prepositus hypoglossiProject to abducens and oculomotor nucleiInput from flocculus of cerebellum encodes velocityPPRF also encodes velocityInput from vermis of cerebellum encodes velocityDorsolateral pontine nucleusRelays inputs from cortex to cerebellum and oculomotor brainstem

  • Smooth pursuit cortexVisual motion areas MT and MSTActive in visual processing for pursuitStimulation influences pursuit speedProjects to DLPN and FEFDoes not initiate pursuitFrontal eye fieldsStimulation initiates pursuitLesions diminish pursuit

  • Jergens

  • Scudder

  • *****************

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