Sound-evoked neurogenic responses with short latency of vestibular origin.

OBJECTIVE: In ABR recording, a large negative deflection with a latency of 3 ms (N3) has been recorded in patients with peripheral profound deafness. It has been suggested that N3 might be of vestibular origin. So far, N3 has been recorded only in patients with peripheral profound deafness. If we can record N3 potentials in subjects with preserved hearing, recording N3 potentials might be a new clinical test of the vestibular system. To record neurogenic potentials (N3) of vestibular origin in healthy volunteers and patients with vestibular disorders.

METHODS: Twelve healthy volunteers (10 men and two women, aged 23-37 years) and 12 patients with vestibular disorders (6 men and 6 women, aged 29-71 years) were enrolled in this study. To record responses, surface electrodes were placed on the ipsilateral mastoid and the vertex. An electrode on the nasion served as the ground. Recording was performed using an auditory evoked potential recording system with a mini-mixer and a stereo-amplifier. Signals at the vertex to the ispilateral mastoid were amplified and bandpass filtered (100-3000 Hz). One thousand-hertz short tone bursts (1 kHz STB; rise/fall time=0.5 ms, plateau time=1 ms) were presented to either ear through a headphone with or without white noise (WN) ipsilateral to the stimulated ear. The stimulation rate was 10 Hz, and the analysis time was 10 ms. The responses to 500 stimuli were averaged twice.

RESULTS: When 1 kHz STB (95 dBnHL, equivalent to 130 dBSPL) were presented with 100 dBSPL WN (ipsilateral to the stimulated ear), a negative peak with 3-4 ms latency (N3) was observed in 23 of the 24 ears (95.8%) with reproducibility in healthy subjects. Without WN, N3 was observed in 17 of the 24 ears (70.8%). The threshold of N3 was 90.2 dBnHL on the average. The presence of N3 in the patients was in agreement with the presence of the VEMP, which were also recorded.

CONCLUSIONS: Using techniques of WN exposure ipsilateral to the stimulated ear, we recorded N3 in healthy subjects and in vestibular disorder patients with preserved hearing. This negative peak is likely to be of vestibular origin.

SIGNIFICANCE: N3 may be measured from subjects who cannot contract neck muscles due to their ages, mental states, or consciousness disorders. In other words, N3 may be measured from subjects from whom VEMP cannot be recorded. In combination with VEMP, N3 may be useful for the detection of lesion sites.