ELEVATION OF AUDITORY-THRESHOLDS BY SPONTANEOUS COCHLEAR OSCILLATIONS

THE inner ear sometimes acts as a robust sound generator, continuously broadcasting sounds (spontaneous otoacoustic emissions) which can be intense enough to be heard by other individuals standing nearby(1-4). Paradoxically, most individuals are unaware of the sounds generated within their ears, Two hypotheses could explain this paradox: (1) the spontaneous emissions may not be transmitted to the central nervous system; or (2) the spontaneous emission produces a continuous, high rate of neural activity, which, like the natural pattern of spontaneous activity, is ignored by the central nervous system. Here we demonstrate that high-intensity spontaneous otoacoustic emissions can vigorously activate auditory nerve fibres in mammals (Chinchilla laniger). This 'internal biological noise' creates a 'line busy' signal that significantly degrades a neuron's ability to respond to sound and results in a hearing loss completely different from that caused by damage to sensory cells(1,4).