The negative potential at 10 msec (called n10) of the ocular vestibular-evoked myogenic potential (oVEMP) recorded beneath the eyes in response to bone-conducted vibration (BCV) delivered to the skull at the midline in the hairline (Fz) is a new indicator of otolithic, and in particular utricular, function. Our aim is to find the optimum combination of frequency and rise-time for BCV stimulation, to improve the sensitivity of oVEMP testing in the clinic.
We tested 10 healthy subjects with 6 msec tone bursts of BCV at three stimulus frequencies, 250, 500, and 750 Hz, at rise-times ranging between 0 and 2 msec. The BCV was delivered at Fz.
The n10 response was significantly larger at the shorter rise-times, being largest at zero rise-time. In addition, we examined the effect of stimulus frequency in these same subjects by delivering 6 msec tone bursts at zero rise-time at a range of frequencies from 50 to 1200 Hz. The main effect of rise-time was significant with shorter rise-times leading to larger n10 responses and the Rise-Time × Frequency interaction was significant so that at low frequencies (100 Hz) shorter rise-times had a modest effect on n10 whereas at high frequencies (750 Hz) shorter rise-times increased n10 amplitude substantially. The main effect of frequency was also significant: The n10 response tended to be larger at lower frequency, being largest between 250 and 500 Hz.
In summary, in this sample of healthy subjects, the most effective stimulus for eliciting oVEMP n10 to BCV at Fz was found to be a tone burst with a rise-time of 0 msec at low stimulus frequency (250 or 500 Hz).
A recent test of otolith function comprised delivering short tone bursts of bone-conducted vibration to the skull at the midline forehead at the hairline, and measuring the early negative potential in the ocular vestibularevoked myogenic potential response at a latency of around 10 msec (n10) component of the ocular vestibular-evoked myogenic potential. To improve effectiveness of this test in the clinic, the authors examined the effect of varying the rise-time and frequency of the stimulus tone bursts in healthy subjects, and found that stimuli with short rise-times produced larger n10 responses, as did stimuli of low frequency. A rise-time of 0 msec and frequencies between 250 and 500 Hz gave optimum n10 responses.
1Vestibular Research Laboratory, School of Psychology, The University of Sydney, Sydney, New South Wales, Australia; 2MSA ENT Academy Center, Cassino, Frosinone, Italy; and 3Department of Neurology, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia.
ACKNOWLEDGMENTS: The authors are grateful for the support of National Health and Medical Research Council of Australia and of the Garnett Passe and Rodney Williams Memorial Foundation. The authors acknowledge the help of colleagues at the University of Sydney and Royal Prince Alfred Hospital.
Ian Curthoys and Ann M. Burgess are currently receiving project grant APP1046826, and previously received project grant 632746 from the National Health and Medical Research Council of Australia. Ian Curthoys and Hamish MacDougall are currently receiving grants from the Garnett Passe and Rodney Williams Memorial Foundation; one of these grants helps to fund Ann Burgess’ salary. Hamish MacDougall, Leigh McGarvie, and Ian Curthoys are unpaid consultants to GN Otometrics, Taastrup, Denmark.
Address for correspondence: Ann M. Burgess, Vestibular Research Laboratory, University of Sydney, School of Psychology, Sydney, NSW 2006, Australia. E-mail: email@example.com