Effect of High Electrical Stimulus Intensities on the Auditory Nerve Using Brain Stem Response Audiometry

Abstract

The response of the auditory nerve to acute intracochlear electrical stimulation using charge-balanced biphasic current pulses was monitored using electrically evoked auditory brain stem responses (EABRs). Stimulation at moderate charge densities (64 μC cm−2 geom/phase; 0.8 mA, 200 μs/phase) for periods of up to 12 hours produced only minimal short-term changes in the EABR. Stimulation at a high charge density (144 μC cm−2 geom/phase; 1.8 mA, 200 μs/phase) resulted in permanent reductions in the EABR for high stimulus rates (> 200 pulses per second [pps]) or long stimulus durations (12 hours). At lower stimulus rates and durations, recovery to prestimulus levels was slow but complete. The mechanisms underlying these temporary and permanent reductions in the EABR are probably caused by neural adaptation and more long-term metabolic effects. These findings have implications for the design of speech-processing strategies using high stimulus rates.