The dynamic characteristics of the mouse horizontal vestibule-ocular and optokinetic response

In the present study the optokinetic reflex, vestibulo-ocular reflex and th eir interaction were investigated in the mouse, using a modified subconjunc tival search coil technique. Gain of the ocular response to sinusoidal opto kinetic stimulation was relatively constant for peak velocities lower than 8 degrees /s, ranging from 0.7 to 0.8. Gain decreased proportionally to vel ocity for faster stimuli. The vestibule-ocular reflex acted to produce a si nusoidal compensatory eye movement in response to sinusoidal stimuli. The p hase of the eye movement with respect to head movement advanced as stimulus frequency decreased, the familiar signature of the torsion pendulum behavi or of the semicircular canals. The first-order time constant of the vestibu le-ocular reflex, as measured from the eye velocity decay after a vestibula r velocity step, was 660 ms. The response of the vestibule-ocular reflex ch anged with stimulus amplitude, having a higher gain and smaller phase lead when stimulus amplitude was increased. As a result of this nonlinear behavi or, reflex gain correlated strongly with stimulus acceleration over the 0.1 -1.6 Hz frequency range. When whole body rotation was performed in the ligh t the optokinetic and vestibular system combined to generate nearly constan t response gain (approximately 0.8) and phase (approximately 0 degrees) ove r the tested frequency range of 0.1-1.6 Hz. We conclude that the compensato ry eye movements of the mouse are similar to those found in other afoveate mammals, but there are also significant differences, namely shorter apparen t time constants of the angular VOR and stronger nonlinearities. (C) 2001 E lsevier Science B.V. All rights reserved.