APPLICATION OF DIGITAL FILTERING AND PHASE SPECTRAL ANALYSIS TO MIDDLE LATENCY RESPONSE AND 40HZ EVENT RELATED POTENTIAL
IN CENTRAL NERVE SYSTEM DISORDERS
1990 Volume 93 Issue 7 Pages 1046-1054
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1990 Volume 93 Issue 7 Pages 1046-1054
40Hz event related potential, or 40Hz-ERP, described by Galambos in 1981 has been considered as the useful potential in predicting hearing threshold across the audiometric frequencies. Although 40Hz-ERP was reported by Galambos as the summation of middle latency responses (MLR), its origin has not been clarified. Moreover reports of the clinical use of 40Hz-ERP in patients with the neurological disorders were rare. Therefore, we recorded ABR, MLR and 40Hz -ERP in 35 patients with central nerve system disorders, or CNS disorders, and analysed the relation between central lesions and modality of MLR or 40Hz-ERP from the view point of phase spectral analysis compairing with the digital filtered waveform analysis. For the phase spectral analysis, synchrony measure method described by Fridman in 1984 was applied to MLR and 40Hz-ERP.
Following results were obtained.
1) By the digital filtered waveform analysis, the latencies of Po, Na, Pa and the amplitudes of Po, Na, Pa, Nb were recorded clearly in normal cases. In cases with the central lesions, many of them were revealed reduction of the amplitude of Po, but other parameters were not useful for the detection of CNS disorders because of their wide normal ranges.
2) The parameters of the phase spectral analysis were obtained from 17 records of the normal subjects. The SM(30+40+5OHz), which is the average of CSM 30Hz, CSM 40Hz and CSM 50Hz, was applied to MLR, and the SM(40+80+120Hz) was applied to 40Hz-ERP. The criteria was adopted as the SM value subtracted 2 standard deviations from mean value of the normal subjects at 80dBnHL stimulation.
3) The phase spectral analysis of MLR were abnormal in 6 out of 35 cases with central lesions, but 11 cases were judged abnormal by the waveform analysis. On the contrally, abnormal findings in 40Hz-ERP were observed in 24 cases, and 8 of those were cases with no response by the phase spectral analysis, although only 4 cases were judged abnormal by the waveform analysis.
4) Out of 15 cases with disorders of midbrain or thalamus revealed by CT and the neurological examinations, 14 cases showed abnormal findings of 40Hz-ERP in the phase spectral analysis.
Therefore, phase spectral analysis, especially of 40Hz-ERP, was useful for the detection of CNS disorders.
