Characteristics of tone burst-evoked myogenic potentials in the sternocleidomastoid muscles.
OBJECTIVE
Optimum stimulus parameters for tone burst-evoked myogenic responses can be defined. These optimized responses will be similar to those evoked by clicks in the same subjects.


BACKGROUND
Loud tones give rise to myogenic responses in the anterior neck muscles, similar to click-evoked potentials, and are likely to be saccular in origin.


METHODS
Tone burst-evoked and click-evoked myogenic potentials were measured from the sternocleidomastoid muscles of 12 normal subjects (6 men, 6 women) during tonic activation. The effects of tone burst frequency and duration were systematically investigated. Thresholds were measured and compared with click thresholds for the same subjects. Patients with specific lesions were studied using both stimuli.


RESULTS
Tone burst-evoked responses showed frequency tuning, with the largest reflex amplitudes at either 500 Hz or 1 kHz. As the stimulus duration was increased, using a constant repetition rate, there was an increase in the reflex amplitudes followed by a decline. The overall optimum stimulus duration was 7 milliseconds. The mean tone burst threshold was 114.4-dB sound pressure level. Stimulus thresholds for click-evoked and tone burst-evoked responses were significantly correlated. Tone burst-evoked and click-evoked responses were present after stimulation of the affected ears of subjects with profound sensorineural hearing loss. Four subjects who had previously undergone vestibular neurectomy had an absence of click and tone burst-evoked responses on the side of the lesion, confirming their vestibular dependence.


CONCLUSIONS
Tone burst-evoked myogenic responses are similar to click-evoked responses but require lower absolute stimulus intensities. To be certain of an optimum response, a stimulus duration of 7 milliseconds, an adequate intensity, and frequencies of both 500 Hz and 1 kHz should be used.
Welgampola
M S
MS
Institute of Neurological Sciences, Prince of Wales Hospital and Clinical School, Randwick, Sydney, New South Wales 2031, Australia.
Colebatch
J G
JG
D000161:Acoustic Stimulation / Q000379:methods; D000328:Adult; D001301:Audiometry, Pure-Tone; D001309:Auditory Threshold / Q000502:physiology; D004576:Electromyography / Q000379:methods; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D006319:Hearing Loss, Sensorineural / Q000175:diagnosis / Q000503:physiopathology; D006801:Humans; D008297:Male; D008416:Mastoid / Q000294:innervation*; D008575:Meniere Disease / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery; D018482:Muscle, Skeletal / Q000294:innervation*; D013249:Sternum / Q000294:innervation*; D014725:Vestibular Nerve / Q000503:physiopathology / Q000601:surgery