Investigation of the mastoid electrode contribution to the brain stem auditory evoked response

The auditory nerve and bran stem responses recorded at the vertex and mastoids were closely examined in normal subjects using a larynx electrode as a neutral reference point. With monaural stimulation, significant activity was found at the vertex and both mastoids, and the wave-forms at the ipsi- and contralateral mastoids were consistently different. With binaural stimulation the small amplitude mastoid response were largely in phase with the vertex response. The implications of the findings are discussed.