Motor output to lateral rectus in cats during the vestibulo-ocular reflex in three-dimensional space

The motor output to the lateral rectus eye muscle was studied in decerebrate cats with electromyographic recordings and in alert cats with multi-unit and single neuron recordings from abducens nucleus. The axis of rotation that produced maximal excitation of the lateral rectus was calculated from responses to rotations in many different stimulus orientations, and was found to lie near the axis of the horizontal semicircular canals, but pitched slightly nose down from the canal axis (4.6 degrees). The results from decerebrate and alert cats were in agreement. The dynamics of lateral rectus activation were quite similar in all planes. Responses at high frequencies were in phase with rotation velocity and responses lagged toward position phase as frequency and velocity were decreased. Differences in decerebrate cat low frequency responses to rotations with and without a sinusoidal gravitational stimulus implicated an otolith input to lateral rectus.