Vestibulo-ocular and optokinetic reactions to rotation and their interaction in the rabbit

Abstract

1. Compensatory eye movements due to sinusoidal yaw movements on a torsion swing were measured in alert rabbits. A range of combinations of frequencies (0.048-1.8 Hz) and amplitudes (1-25 degrees ) were used. Gain (cumulative slow phase eye movement amplitude/swing amplitude) and phase (eye position vs. swing position - 180 degrees ) were calculated from averaged records.2. Eyes were either closed (canal-ocular reactions only), open in earth-fixed visual surroundings (natural interaction of vestibular and optokinetic reactions), or looking at platform-fixed surroundings, which rotated with the animal (conflict situation). In some rabbits, the same stimulus programme was applied a month after bilateral destruction of the labyrinths (optokinetic reactions only).3. For canal-ocular reactions, no true threshold was found. Yet the system showed a small but systematic non-linearity which is tentatively explained by an acceleration-dependence of gain. For the higher frequencies (0.40-1.8 Hz) used, gain was 0.55-0.75, with a decrease at the lower frequencies, down to 0.16-0.33 at 0.048 Hz. The response showed a phase-lead of about 45 degrees at 0.048 Hz and was nearly in phase at 1-1.8 Hz. The long time constant of the cupula-endolymph system was estimated at about 3.3 sec.4. With earth-fixed visual surroundings a frequency-independent gain (range 0.55-0.82) with negligible phase error was found for the entire stimulus range tested. This natural combination of canal-ocular and optokinetic systems appears to function very efficiently, with mutual correction of the defects of the systems apart.5. With platform-fixed visual surroundings the canal-ocular system was severely inhibited and its non-linearities were markedly enhanced by the optokinetic system, especially when the torsion swing moved slowly.6. The general shape of input-output relations of optokinetic reactions after labyrinthectomy were similar to those found earlier in normal animals, but gain was subnormal for the entire stimulus range tested.