Effects of adaptation on electrocochleography and auditory brain-stem responses in the elderly.

Changes in the amplitude and latency of the evoked potentials in electrocochleography (ECochG) and auditory brainstem responses (ABR) produced by increased stimulus rates (adaptation) were investigated using an extratympanic ECochG technique with simultaneous recording of the ABR in 12 elderly patients, and compared with those of eight normally hearing young adult subjects. Although the absolute latencies of the action potential (AP) and ABR waves were delayed in the elderly, the shift in latency of these components with increased stimulus rate was similar in both groups of subjects. Amplitudes of the AP and wave III component were reduced with increased stimulus rate to a degree which again was similar in both the elderly and young adults. On this basis we suggest that synaptic connections to nerve fibres from surviving hair cells in the elderly are functioning so that disturbance of this part of the acoustic nerve is not a feature of presbycusis.