Velocity storage in the vestibulo-ocular reflex arc (VOR)

Vestibular and optokinetic nystagmus (OKN) of monkeys were induced by platform and visual surround rotation. Vision prolonged per-rotatory nystagmus and cancelled or reduced post-rotatory nystagmus recorded in darkness. Presumably, activity stored during OKN summed with activity arising in the semicircular canals. The limit of summation was about 120 degrees/s, the level of saturation of optokinetic after-nystagmus (OKAN). OKN and vestibular nystagmus, induced in the same or in opposite directions diminished or enhanced post-rotatory nystagmus up to 120 degrees/s. We postulate that a common storage mechanism is used for producing vestibular nystagmus, OKN, and OKAN. Evidence for this is the similar time course of vestibular nystagmus and OKAN and their summation. In addition, stored activity is lost in a similar way by viewing a stationary surround during either OKAN or vestibular nystagmus (fixation suppression). These responses were modelled using direct pathways and a non-ideal integrator coupled to the visual and peripheral vestibular systems. The direct pathways are responsible for rapid changes in eye velocity while the integrator stores activity and mediates slower changes. The integrator stabilizes eye velocity during whole field rotation and extends the time over which the vestibulo-ocular reflex can compensate for head movement.