Intense brief sound evokes short-latency myogenic potentials around the eyes in humans. These potentials are named ocular vestibular-evoked myogenic potentials (OVEMP), but the origin and pathway of these responses remain unclear. To establish an animal model for OVEMP, we recorded sound-evoked potentials around the eyes using awake monkeys. Two macaque monkeys were used in the research. A pair of electrodes was attached under an eye, and each animal was made to gaze at the monitor with their eyes in a fixed position while sitting in a primate chair. When a 135-dB SPL air-conducted 500-Hz tone burst was applied, the peak latencies of the first negative and second positive waves were 10.4 msec and 13.7 msec. The peak latency of the first negative wave did not change when the frequency was changed. The threshold of the myogenic potentials at a frequency of 500 Hz was lowest among the 4 tested frequencies (500Hz, 1kHz, 2kHz and 4kHz). The contralateral amplitude to the sound stimulation was greater than the ipsilateral amplitude. Furthermore, the amplitude for an upward-gazing position was greater than that for a downward-gazing position. The characteristics of these potentials were similar to those of OVEMP in humans, suggesting that the sound-evoked myogenic potentials around the eyes in monkeys may be utilized as an animal model of OVEMP.
