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See Inside February/March 2008

The Sound of Silence

Before we can hear, specialized ear cells ready our brain for noise

From the moment we begin to hear, our auditory system is precisely tuned, able to distinguish subtle differences between sounds. But how does it get that way? New research reveals how developing ears generate their own noise, a process that may help calibrate our auditory system.

Johns Hopkins University researchers studied the auditory systems of rats, which are deaf until about 12 days of age. During this prehearing period, the scientists discovered, the rodents have bursts of activity in certain cells—called support cells—in their cochleas. These nonnerve cells spontaneous­ly release a chemical messenger called ATP, sending signals to other cells in the inner ear and eventually to the brain.

“It appears that this activity plays an important role in the development of the auditory system,” lead researcher Dwight E. Bergles says. For instance, it seems to be necessary for refining the brain maps that differentiate among auditory frequencies. The spontaneous activity—which, in humans, would take place in utero—may also shed light on tinnitus, or the perception of phantom sound, and explain how certain genetic mutations can cause deafness.

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