The contribution of the lateral semicircular canal to the short latency vestibular evoked potentials in cat

Short latency vestibular evoked potentials (VsEPs) to angular acceleration impulses (maximal intensity 20,000°/sec², rise time 1.5-3 msec) were recorded by skin electrodes in cats before and after various surgical procedures. Under general anesthesia, the animals underwent unilateral labyrinthectomy and the VsEPs in response to stimulation of the remaining inner ear in the plane of the lateral semicircular canal (SCC) with the head flexed 20°-25° were recorded as a baseline. The lateral SCC was then selectively obliterated near its ampulla. This induced major changes in the VsEPs recorded in response to stimulation of the remaining inner ear in this plane: the first 2 VsEP waves were absent, and only longer latency, smaller amplitude waves were present in response to both clockwise and counterclockwise stimulation. On the other hand, obliteration of the anterior and posterior SCCs and, in addition, destruction of both maculae were without major effects on the first 2 VsEP waves in response to excitatory stimulation. The results confirm that when the head is flexed 20°-25° and stimulated with angular acceleration impulses in the horizontal plane, the major site of initiation of the VsEPs in cats and probably in man is the crista ampullaris of the lateral SCC.