Sources of electrocochleographic responses as studied in patients with brain damage

With electrodes on the ear lobe and vertex, the earliest (within 10 msec after the stimulus) average response to click stimuli consists of five successive waves in both cat and man (electrocochleography). It has been conclusively demonstrated that the first wave in both man and cat represents the compound cochlear action potential. Experimental studies on cats in this laboratory have demonstrated that waves 2-5 are generated in the various brain-stem auditory nuclei. The purpose of the present study was to confirm these sites of generation for man by comparing electrocochleographic responses with clinical evidence in patients with various types of brain lesion, e.g., brain-stem tumours in adults and brain-stem damages in severely retarded infants. The electrocochleograms were compared with attempts to localize the sites of brain lesions by means of neurological examination, skull X-ray, pneumoencephalogram, EEG, surgery or autopsy. In cases in which abnormal electrocochleographic patterns were recorded, clinical evidence either hinted at or confirmed the presence of a brain-stem lesion. Thus, the first electrocochleographic wave represents the response of the auditory nerve and the later four waves are generated in the brain-stem auditory nuclei.