Unidirectional habituation of vestibulo-ocular responses by repeated rotational or optokinetic stimulations in the cat.

Abstract

1. Unilateral habituation of the vestibulo-ocular reflex was produced in adult cats stimulated by repeated unidirectional velocity steps (vestibular training) or by a continuously moving visual surround (optokinetic training). -- 2. Unidirectional vestibular training produced a strong asymmetry of vestibulo-ocular responses (VOR). Responses to velocity steps applied to the "trained" labyrinth were decreased both in gain and in time-constant. This effect generalized to responses to sinusoidal oscillations (0.03 Hz to 0.1 Hz), i.e. to a stimulus not used during training. -- No spontaneous nystagmus was ever observed in spite of the dynamic VOR asymmetry. -- 3. Unilateral vestibular habituation produced by vestibular training appeared to be a long-lasting phenomenon. It was still present 10 days after the end of training. -- 4. Optokinetic responses were not affected by vestibular training. -- 5. Unidirectional optokinetic training produced an increase in the slow phase velocity of optokinetic nystagmus (OKN) by about 25% in both directions. This effect did not persist for more than a few minutes. A marked spontaneous nystagmus was recorded in the dark after each session of optokinetic training, with a slow phase in the direction opposite to the previous OKN. -- 6. VOR in response to velocity steps and to sinusoidal oscillations were decreased unilaterally after optokinetic training. This effect was of short duration, however, and disappeared within the interval between training sessions. This lack of retention contrasted with the prolonged effect of vestibular training.