Uncertainties of topodiagnosis of auditory nerve and brain-stem auditory evoked potentials due to rarefaction and condensation stimuli.

Auditory nerve and brain-stem auditory evoked potentials (AN and BAEP) were elicited after separate stimulation with rarefaction and condensation stimuli. There were only few persons with identical patterns in the two opposite phases. Rarefaction stimuli showed a tendency to evoke AN and BAEP with shorter latencies and better synchronization. In diseases of the auditory nerve and brain-stem the phase-dependent differences were even more prominent, indicating different topodiagnostic levels of lesions. The results point to the need for stimulus presentation with rarefaction and condensation stimuli separately and an evaluation of both curves. The alternating mode is the result of summating rarefaction and condensation stimuli.