A study on the phase spectral analysis of middle latency response and 40-Hz event-related potential in central nervous system disorders.

The synchrony measure method, or SM method, a phase spectral analysis described by Fridman in 1984 for ABR, was applied to 40-Hz event-related potential (40-Hz ERP), and was found to be a useful method for automatic detection in predicting hearing thresholds across the audiometric frequencies. Although 40-Hz ERP was claimed by Galambos to be the summation of middle latency responses (MLR), its origin is still controversial. Moreover, only a few articles have reported on the clinical use of 40-Hz ERP in patients with neurological disorders. We recorded ABRs, MLRs, and 40-Hz ERPs in 59 patients with central nervous system (CNS) disorders, and analyzed the relationship between central lesions and MLR or 40-Hz ERP using phase spectral analysis. Abnormal findings in 40-Hz ERP were observed in 43 (72.9%) out of 59 cases with CNS disorders, and most of the abnormal cases had disorders involving the midbrain or thalamic lesions, especially on the side contralateral to stimuli. The results suggest that phase spectral analysis of 40-Hz ERP is useful in the detection of CNS disorders.