Seven subjects were stimulated at the inferior (IVN) and superior (SVN) vestibular nerve. The EMG signals of the SCM were recorded. These recordings were compared to air- and bone-conduction evoked VEMPs with respect to latency and shape.
All subjects showed normal VEMPs upon acoustic stimulation with a latency of 12.8 ± 1.4 ms for P13, and 22.7 ± 2.0 ms for the N23 pre-operatively. Upon direct electrical stimulation of the IVN, the mean latency of the positive peak was 9.1 ± 2.2 and 13.2 ± 2.3 ms for the negative one. No contralateral SCM response was found. Electrical stimulation of the SVN did not result in any EMG response of the SCM.
The study shows experimental evidence of the vestibulocollic reflex by direct electrical stimulation of the human IVN for the first time. The method can be utilized to map VIIIth nerve subdivisions and to intraoperatively monitor IVN integrity in a real-time mode.