Experimental and clinical study on the steady-state response elicited by sinusoidally amplitude-modulated tones.

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(1) Clinical studyThe reliability and frequency specificity of 80-Hz amplitude-modulation following response (80-Hz AMFR) detected by phase coherence to predict the hearing threshold during sleep was evaluated in 125 children with abrupt high-frequency, low frequency and mid-frequency hearing impairment. The 80-Hz AMFR at carrier frequency of 1000 Hz were performed in all patients and the auditory brainstem response (ABR) elicited by 1000 Hz tone pips in 93 ears. Both responses were examined during sleep and thresholds were compared with behavioral hearing threshold, which was determined by standard pure-tone audiometry or play audiometry. In children with various patterns of audiogram, the threshold patterns of 80-Hz AMFR clearly followed the corresponding audiogram patterns in all types of hearing impairment. The measurement of 80-Hz AMFR thus appeared to be accurate in hearing prediction and to have a good reliability and frequency specificity in children during sleep.In addition, t … More he stability of 80-Hz AMFR was evaluated in various stages of sleeping. The results suggested that the response was more clearly detected in deeper sleep stage in adults and children.The stimulus tones for multiple stimulation technique, by which hearing can be estimated in 4 frequencies simultaneously and the examination time for the prediction of hearing across the frequencies used for audiometry can be shortened, were generated by using computer and were begun to use clinically.(2) Experimental studyTo clarify the contribution of the cochlear nucleus (CN) and inferior colliculus (IC) to the scalp-recorded amplitude-modulation following response (AMFR), the near-field potentials elicited with the sinusoidally amplitude-modulated (SAM) tone, click and tone pip were recorded from CN and IC in cats. The carrier frequency of SAM tone was set at 1 kHz and the modulation depth was 95%. The modulation rates of SAM tones and the repetition rates of click and tone pip were 20,40,77 and 100 Hz. The waveforms were calculated by the summation of 100 sweeps.Near-field potentials elicited with SAM tones and recorded from CN and IC were consisted of two components ; one was the low-frequency component corresponding to modulation rate and the other was the high-frequency component resembled to SAM tone itself. On the other hand click and tone pip elicited the relatively short-duration potentials repeating as stimulus rate. The phase of the potentials elicited by SAM tone reversed in the ventral nucleus of CN and between the pericentral and the central nucleus of IC.These results suggest that CN and IC contribute to the generation of the scalp recorded AMFR. Less