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 occured 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.