ADAPTIVE GAIN CONTROL OF THE VESTIBULO-OCULAR REFLEX IN GOLDFISH
SCHAIRER, JOHN OTTO
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The vestibulo-ocular reflex helps to stabilize the direction of gaze during head rotation. A perfectly adjusted vestibulo-ocular (VO) reflex produces eye movements which compensate exactly for head rotation. The VO gain, defined as eye velocity divided by head velocity in the opposite direction, equals one when the eye movements compensate exactly for head movement. A process of adjustment of the VO gain takes place when retinal slip indicates that the eye movement does not exactly compensate for head rotation. This has been demonstrated previously in several mammals including man. This thesis reports some properties of VO gain adjustment in goldfish.;Goldfish were restrained inside a vertically striped drum and their eye position monitored. By sinusoidal rotation of the fish and the drum together slip was generated which could only be eliminated by a VO gain of zero. Over a six hour training period the VO gain of 12 fish decreased to 0.15 ('(+OR-)) 0.07. By combined sinusoidal rotation of the fish and drum in opposite directions the VO gain was trained towards a gain of two. Six hours of training towards two produced a mean VO gain of 1.41 ('(+OR-)) 0.23 in nine fish. Frequency responses obtained before and after training demonstrated broad spectrum increases in gain with training towards two but narrow frequency decreases in gain about the training frequency after training towards zero. No significant phase shifts were observed after training towards two. Fifty degree phase lags occurred at and below the training frequency after training towards zero.;Multiple daily training sessions showed that the gain returned to near its original value between 5 hour training sessions, but a small consistent reduction in gain was measured at the start of each training session. More rapid gain reductions were seen during the second day of training than during the first.;Rotation of the striped drum at twice the amplitude of the goldfish, induced changes of VO gain towards -1, simulating the effects of reversing prisms used in many mammalian experiments. Training towards -1 produced a wide variation in gain and phase among goldfish. A spontaneous oscillating sinusoidal slow phase eye movement in the dark was generated which appeared to contribute to maintaining visual fixation on the moving striped drum when the lights were on.;Sinusoidal rotation of the striped drum about stationary goldfish for three hours produced modest gain increases and spontaneous oscillatory eye movements similar to those produced after training towards -1.;Removal of the corpus cerebellum resulted in a broader ange of initial VO gains and blocked reductions in gain during training towards zero. Cerebellectomy did not affect the response to optokinetic stimuli.;These data demonstrate the adaptive changes of the VO gain in a lower vertebrate. More rapid and complete gain changes occur in goldfish than have been reported in mammals. This work lays the conceptual and experimental groundwork for localizing and investigating the cellular events which underlie this physiological change in neural properties.