Juichi Yokoyama

Three frequency component waveforms of auditory evoked brainstem response in spinocerebellar degeneration

Under adequate stimulus intensities, the power spectra of normal auditory evoked brainstem responses (ABRs) are composed of three major components: 0-350 Hz, 350-700 Hz and 700-1200 Hz. By means of a digital filter using fast Fourier transform, three ABR waveforms consisting of each frequency component of the power spectrum were obtained. The significance of these three component waveforms in the analysis of ABR abnormality was estimated in 30 patients with spinocerebellar degeneration (SCD). In conventional wave latency analysis, 9 out of 30 patients (30%) had abnormal ABRs, the main abnormality being prolonged interpeak latencies of waves I-III, I-V and the disappearance of wave V. On the other hand, component waveforms were abnormal in 82.5% of the cases. These results suggest that analysis of ABRs by the use of component waveforms is useful for detecting abnormality in the brainstem auditory pathway in SCD patients.

Phase Spectral Analysis of Auditory Brainstem Response in Cats

In order to apply the phase spectral analysis of auditory brainstem response (ABR) to the clinical diagnostic test, the following studies in cats were performed. At first, the phase spectra of normal ABRs were investigated under adequate stimulus intensities. In addition the component synchrony measures (CSM) of ABRs were calculated at each stimulus level. Moreover the waveforms and phase spectra of ABRs were investigated before and after the destructions of cochlear nerve and brainstem auditory pathways in cats. The results were as follows; (1) In normal ABRs, the phase spectra were mainly composed of three frequency components at 0-300Hz (component A), 300-900Hz (component B) and 900-1500Hz (component C). The CSMs of component A represented the degree of synchrony for a slow component of the ABR and the CSMs of components B and C represented the degree of synchrony for a fast component. (2) A decrease in stimulus intensity resulted in a decrease in each average of the CSMs of the three components. (3) A greater decrease of the CSM occurred if ipsilateral destruction was performed in a peripheral lesion. Lesions of the auditory pathway were followed by a decrease of the CSM of component C to contralateral stimulation. These results suggest that the phase spectral analysis of ABRs has significant clinical value in the detection of brainstem lesions.

Cross-Correlation Function in the Analysis of Auditory Brainstem Response in Spinocerebellar Degeneration

Cross-correlation functions were derived from the analysis of auditory-evoked brainstem response (ABR) and compared with measurements of wave latency and computed tomography findings in the assessment of ABR findings in spinocerebellar degeneration (SCD). Gender-specific normative ABR templates were produced from 30 normal males and 30 normal females separately. The cross-correlation indices used were the correlation coefficient at time 0, the maximal correlation coefficient and the latency delay in milli-seconds. The technique was applied to 33 patients with SCD. The incidence of abnormal cross-correlation functions (81.8%) was greater than the incidence of abnormal ABR peak latencies assessed according to gender (75.8%) which, in turn, was more common than the abnormal peak latencies assessed conventionally (69.7%). Moreover, the incidence of abnormal cross-correlations and latencies in Menières disease was much lower (less than 8%). These results suggest that the evaluation of ABR waveform characteristics with cross-correlation functions using normative ABR templates of the same gender contributes to the precise detection of abnormality in the brainstem auditory pathway.