Electrically evoked emissions and acoustic trauma

By studying the nature of the cochlea´s ability to produce an acoustic response to electrical current stimuli the authors analyze the mechanism of the active process present in mammalian hearing. A microelectrode is inserted into scala media and sinusoidal electrical current is passed through the organ of Corti. This produces an acoustic emission at the frequency of electrical stimulation. The authors investigated the effect of acoustic trauma on the magnitude and phase of the electrically evoked emissions. Gerbils were exposed to traumatizing tones of 110 dB SPL for 7 min at 4500, 1800, and 800 Hz. The experimental results show that for low electrical frequency, below the characteristic frequency of the electrode location, emissions increase in magnitude. For high electrical frequency, near the characteristic frequency of the electrode, emissions decrease in magnitude due to acoustic trauma. The effects are more pronounced when the locations including the electrode place are traumatized