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Humans perceive sound very differently than previously believed

Washington, Nov 21 : Researchers at Stanford University School of Medicine claim that the model used for the past 30 years to help explain how humans perceive sound is wrong.


The long-held theory helped to explain a part of the hearing process called "adaptation," or how humans can hear everything from the drop of a pin to a jet engine blast with high acuity, without pain or damage to the ear.

Anthony Ricci, PhD, the Edward C. and Amy H. Sewall Professor of Otolaryngology and senior author of the study said that he would argue that adaptation is probably the most important step in the hearing process, and this study shows that we have no idea how it works.

Inside the ear, specialized cells called hair cells detect vibrations caused by air pressure differences and convert them into electrochemical signals that the brain interprets as sound.

Adaptation is the part of this process that enables these sensory hair cells to regulate the decibel range over which they operate.

The process helps protect the ear against sounds that are too loud by adjusting the ears' sensitivity to match the noise level of the environment.

The traditional explanation for how adaptation works is that it is controlled by at least two complex cellular mechanisms both requiring calcium entry through a specific, mechanically sensitive ion channel in auditory hair cells.

However, the new study finds that calcium is not required for adaptation in mammalian auditory hair cells and posits that one of the two previously described mechanisms is absent in auditory cochlear hair cells.

Experimenting mostly on rats, the Stanford scientists used ultrafast mechanical stimulation to elicit responses from hair cells as well as high-speed, high-resolution imaging to track calcium signals quickly before they had time to diffuse.

After manipulating intracellular calcium in various ways, the scientists were surprised to find that calcium was not necessary for adaptation to occur.

Ricci said that this somewhat heretical finding suggests that at least some of the underlying molecular mechanisms for adaptation must be different in mammalian cochlear hair cells as compared to that of frog or turtle hair cells, where adaptation was first described.

The study is published in the journal Neuron

--ANI (Posted on 21-11-2013)

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