November 1, 2007 -- How We Can Hear Without Sound
Listen to this. Hear that? The ringing? Yeah, I don’t hear it either. But some people might if they’d been at an “AC/DC” concert, or worse, suffer from tinnitus – that tortuous ringing in the absence of sound. But how is ringing without sound possible?
Well research published in Nature this week reveals that sound without sound happens in the pre-developed ears of rats. Researchers isolated auditory nerves that fire without sound, in fact even without a fully formed ear.
There are supporting nerve cells in the developing cochlea that spontaneously release cell energy, or ATP, and this ATP causes neighboring hair cells to fire and activate the auditory neurons that spike as if they heard something, like a tree falling in the forest.
The researchers say this process, before the ear has formed is like developing the choreography and performing rehearsals for hearing. The system is warming up, and refining a detailed auditory map.
While the spontaneous firing stops as soon as ears is complete, researchers say cells continue to express ATP when exposed to loud sounds, and this ATP might produce the effect of sound when there is none…like that ringing.