[A study on three components of auditory evoked brainstem response]

Under adequate stimulus intensities, the power spectra of normal auditory evoked brainstem responses (ABR) are mainly composed of three major parts, i.e. component A (0 approximately 350Hz), B (350-700Hz). and C (700-1200Hz). By means of digital filter using fast Fourier transform, three derived ABR waveforms consist of each component of the power spectrum were obtained and named component waves A, B, and C, respectively. For the purpose of discussing the possibilities of clinical use of derived ABR waveforms, these three component waveforms were analized in normal hearing subjects and patients with central disorders. In addition, the changes of these waveforms were studied in a series of lesion experiments of brainstem auditory pathway in cats. Before and after destructions of cochlear nerve, cochlear nuclei, superior olivary nuclei, lateral lemniscus and inferior colliculus, these three derived waveforms were compared. The following results were obtained: 1) In normal subjects, the changes in ABR waveforms according to the changes of the rise-time, interstimulus interval and frequency of the stimulus were mainly attributed to component wave C. 2) In patients with central disorders, component wave C were initially affected. Therefore, it seemed that the earliest waveform alterations in ABR occur in high frequency parts of the power spectrum. 3) The resultant experimental data in cats indicated that component wave C seems to be the most sensitive to reveal the lesion sites. 4) It was suggested that the analysis of ABR by three component waveforms was useful to detect the neurological disorders.