[The effect of high-rate electrical stimulation on excitability of auditory nerve in Guinea pigs].
OBJECTIVE
To assess the effect of high-rate electrical stimulation on excitability of the auditory nerve by recording the change of amplitude of the electrically evoked auditory brainstem responses (EABR).


METHODS
After guinea pigs were in the anesthetic state, both bullae were exposed and the round window membranes incised. A standard electrode array was carefully inserted a distance of approximately 4 mm into the scala tympani of the both experimental cochlea and the control cochlea. The most apical electrodes were used as stimulating electrodes. The round window was then sealed with crushed temporal muscle. The electrode arrays were maintained in the same position throughout the experiment. While the stimulus intensities were kept constantly in the normal clinical level (6 dB above EABR threshold), four stimulus rates of 200 (n=14), 400 (n=10), 1000 (n=11), 2000 (n=10) pulses/s(PPS) were each delivered to bipolar electrodes in scala tympani of 45 guinea pigs for 2 h of acute electrical stimulation. Thresholds and wave I amplitudes of EABR were recorded for periods of 3 h following 2 h of acute stimulation. By comparing the pre-stimulus amplitudes of wave I in EABR with the post-stimulus ones(t test), the effect of high-rate electrical stimulation on excitability of the auditory nerve was assessed.


RESULTS
While the acute stimulus intensity was kept constantly in the normal clinical level (6 dB above EABR threshold), with comparison of pre-stimulus response with post-stimulus response of wave I, the latter increased by 20%, 30%, 9%, 7% at each of the four different stimulus rates of 200, 2000, 400, 1000 PPS.


CONCLUSIONS
Within the 3 h post-stimulus monitoring period after 2 h acute stimulation, no reduction but increase in EABR amplitude was observed using stimulus intensity of 6 dB above EABR threshold at four stimulus rates (200, 400, 1000, 2000 PPS). Electrical stimulation presented at high rates of 1000 to approximately 2000 PPS with clinical intensity (6 dB above EABR threshold) did not result in the reduction of excitability of auditory nerve. These results supported to provide data for the envisaged introduction of a speech-processing strategy based on high stimulus rates.
Liu
Aiguo
A
Department of Otolaryngology, EENT Hospital of Fudan University, Shanghai, 200031, China. aiguo309cn@yahoo.com.cn
Wang
Zhengmin
Z
Cui
Yonghua
Y
Zhou
Liang
L
Chi
Fanglu
F
D000818:Animals; D003054:Cochlear Implants; D003056:Cochlear Nerve / Q000502:physiology*; D004558:Electric Stimulation; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology*; D005260:Female; D006168:Guinea Pigs; D008297:Male