Auditory evoked potentials

Abstract

This article describes the basic elements of auditory evoked potentials, including stimulus tone and recording condition, and clinical applications of auditory evoked potentials, such as ECochG, ABR and ASSR. The clinical applications of auditory evoked potentials are roughly classified into (1) objective audiometry and (2) neurological examination. ECochG is applied to the diagnosis of endolymphatic hydrops and inner ear hearing loss. ABR is still an important examination in the diagnosis of acoustic neurinoma, though the prevalence of MRI has reduced its importance. The elongation of the I-V inter-peak latency (I-V IPL) of ABR in lower brainstem lesion is mainly due to I-III IPL elongation, whereas I-V IPL elongation is mainly due to IH-V IPL elongation in upper brainstem lesions. Recruitment and conductive hearing loss can be estimated by the finding of the latency-intensity curve of wave V. Although ABR is the most popular device in objective audiometry, the prediction of hearing levels in the lower frequency range using ABR evoked by clicks is less accurate. The most important benefit of ASSR is to provide an accurate assessment of hearing at different frequencies in a frequency specific manner, if stimulation consists of a sinusoidally amplitude-modulated tone. However, ASSR is not appropriate to use as a diagnostic tool in neurological examinations, because the waveforms of ASSR consist of the interference of different wave components. Power spectrum analysis and phase coherence using fast Fourier transformation are useful for the automatic detection of ASSR, because of its sinusoidal waveform configuration. Because the detectability of ASSR changes under different arousal states, 40-Hz ASSR is suitable for waking adults and 80-Hz ASSR for sleeping children in the assessment of hearing. Its advantage is that the thresholds at 4 different frequencies in both ears can be predicted more rapidly than ABR using the multiple simultaneous stimulation technique.