Averaged evoked potentials in cats with lesions of auditory pathway

Averaged evoked activity was recorded from needle electrodes placed at the vertex of the calvaria and adjacent to each bulla in anesthetized cats in response to click stimuli. The portion of the response from 0 to 10 msec was analyzed. Activity during the first 3 msec was greatly reduced on the side ipsilateral to a lesion involving destruction of the cochlea or section of the eighth nerve and its blood vessels. Activity after 4 msec was greatly reduced on the side ipsilateral to destruction of the cochlear nuclei. No effect was found with destruction of both inferior colliculi. The bulla-vertex evoked responses were also compared to those recorded from the round window. The results support the premise that change in the wave-form of the early evoked potential can be used to determine site of loss of acoustic information along the auditory pathway.