Bilaterally recorded brain stem auditory evoked responses. Their asymmetric abnormalities and lesions of the brain stem

I. Hashimoto, Y. Ishiyama and G. Tozuka

Simultaneous bilateral recordings (C3 to A1 and C4 to A2) of brain stem auditory evoked responses have been studied in 67 supratentorial lesions, nine midbrain lesions, 21 intrinsic pontine lesions, and 23 extrinsic compressions of the pons. The responses in supratentorial lesions showed completely normal records. In midbrain lesions, wave V was specifically altered. As wave 1 has been shown to be a far-field seventh nerve potential, and wave V the midbrain potential, waves II to IV can be inferred to originate in the central auditory pathway between the seventh nerve and the midbrain. Alterations of waves II to IV correlated well with localization of pontine lesions, and asymmetric alterations of the bilaterally recorded responses were associated with unilateral lesions of the brain stem auditory pathway and/or lesions of the crossed auditory projections.