3CLT ABR analyses in a human subject with unilateral extirpation of the inferior colliculus

Reported are the results of analyses of three-channel Lissajous trajectories (3CLTs) of the auditory brain stem responses (ABRs) in a human subject in whom a focal lesion of the brain stem was caused by stereotactic radiosurgery, the 'gamma knife'. The surgery caused total destruction of the right inferior colliculus. The results, using multiple measures for defining ABR components, confirm findings from more conventional 2-channel recordings which, in turn, suggested the presence of an intact wave IV but a negligible, if not totally absent, wave V with stimulation of the left (contralateral) ear. The results thus support theories that wave V is generated by crossed pathways and that wave IV is an independent wave generated by the lateral lemniscus. Since magnetic resonance imaging suggested no destruction of tissue below the inferior colliculus, the findings also support theories of wave V generation at or rostral to the inferior colliculus. In practical terms, the results demonstrate the value of multichannel recordings of the ABR in component identification and in interpreting ABR abnormalities.