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the vestibular organ and the vestibulo ocular reflex n.
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The vestibular organ and the vestibulo-ocular reflex

The vestibular organ and the vestibulo-ocular reflex

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The vestibular organ and the vestibulo-ocular reflex

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  1. The vestibular organ and the vestibulo-ocular reflex Bijan Pesaran 29 April, 2008

  2. Vestibular organ

  3. Bony and membranous labyrinth

  4. Cupula and otoliths move sensory receptors Cristae Maculae

  5. Dynamics of semicircular canals • Torsion-pendulum model • MD2Θ(in) = MD2Θ(out) +rD Θ(out)+k Θ(out) • System is over-damped • For frequencies up to 20 Hz, cupula motion reflects velocity of head motion

  6. Hair cell orientation varies across the maculae

  7. Hair cells respond to cupula motion

  8. Canal afferents in vestibular nerve code velocity • S-curve is common • Can be excitatory and inhibitory • Different cells have different ranges • Population code

  9. The oculomotor muscles

  10. Rotational degrees of freedom

  11. Static VOR • Stabilize eyes due to tilt of head • In humans weak, dominated by dynamic VOR and vision • Easily demonstrated in rabbits • Complicated by stimulation of proprioceptors in neck (COR) • Move head with body • In humans, torsional counter-roll due to tilt

  12. A neural integrator model can maintain eye position

  13. Nystagmus has two phases

  14. Quick phase • Not due to eye position • No effect of removing eyes • Not at consistent eye position • Related to eye velocity • Periodic phase intervals • Unimodal at low head speeds • Multimodal with 0.5s interval at higher speeds

  15. rVOR gain varies with frequency • Almost perfect > 1Hz • Low gain for low frequencies (0.1Hz) • Sensory mechanisms can compensate (optokinetic reflex)

  16. rVOR plasticity • Motor plasticity is necessary to compensate for changes in muscle properties • Adaptation to magnifying lens takes days • Depends on cerebellum to learn • Doesn’t depend on cerebellum to maintain • Cerebellum provides error signal

  17. Translation VOR • Compensates for linear motion as opposed to rotational motion • Only studied in primates – rudimentary in lateral-eyed species • Only stabilizes one point – fovea • Consider optic flow during motion

  18. tVOR depends on viewing distance Rightward Leftward Short latency of 10-12 ms but longer than rVOR 5-7 ms

  19. Motion velocity Motion direction Viewing distance Eye position • tVOR depends on viewing angle

  20. Gaze shifts require eye and head movements • Need to move eye and head to new position with stable vision • Keep eye velocity equal and opposite to head movement • During saccade itself, turn off VOR • At this time, see no compensation for changes in head position