The n10 component of the ocular vestibular-evoked myogenic potential (oVEMP) is distinct from the R1 component of the blink reflex

Y E Smulders, M S Welgampola, A M Burgess, L A McGarvie, G M Halmagyi, I S Curthoys
Clinical Neurophysiology: Official Journal of the International Federation of Clinical Neurophysiology 2009, 120 (8): 1567-76

OBJECTIVE: Bone-conducted vibration (BCV) in the midline at the hairline (Fz), results in short latency potentials recorded by surface electrodes beneath the eyes - the ocular vestibular-evoked myogenic potential (oVEMP). The early negative component of the oVEMP, n10, is due to vestibular stimulation, however it is similar to the early R1 component of the blink reflex. Here we seek to dissociate n10 from R1.

METHODS: Surface potentials were recorded from the infraorbital electromyogram of 10 healthy subjects, 6 patients with bilateral vestibular loss, 2 with unilateral vestibular loss, 4 with facial palsy and 3 with facial and vestibular nerve lesions on the same side. BCV was delivered at Fz, the inion, the glabella or the supraorbital ridge using a tendon hammer or a bone-conduction vibrator.

RESULTS: Onset latencies of the n10 evoked by taps at Fz or inion were significantly shorter than the R1 components of blink responses to supraorbital and glabellar stimuli. Upward gaze increased the amplitude of n10 but not R1. The n10 was absent bilaterally in patients with bilateral vestibular loss and beneath the contralesional eye in patients with unilateral vestibular loss, but in both these groups of patients R1 was preserved. In severe facial palsy the R1 component was absent or delayed and attenuated ipsilesionally, but n10 was preserved bilaterally. In subjects with unilateral facial and vestibular nerve lesions (Herpes Zoster of the facial and vestibulocochlear nerves) the dissociation was complete - the ipsilesional R1 was absent or attenuated whereas the ipsilesional n10 was preserved.

CONCLUSIONS: n10 is distinguished from R1 by its earlier onset, laterality, modulation by gaze position and dissociation in patient groups.

SIGNIFICANCE: The n10 component evoked by BCV at Fz is not the R1 component of the blink reflex.

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