Cochlear enlightenment.

Of all mammalian receptor organs, the cochlea is the least understood. How it performs its most fundamental feat-the filtering of sound into different frequency bands over an enormous range of intensities-is still shrouded in mystery. Two of its neural systems, one a component of its dual output to the central nervous system (CNS) and the other a component of its dual feedback from the CNS, are in key cochlear positions but have escaped physiological study. At the same time, cochlear impairments affect an enormous and growing fraction of the population. Here we briefly highlight, from a system rather than molecular or biophysical viewpoint, recent breakthroughs that have forced a re-examination of assumptions deemed quite safe not too long ago and that herald a new renaissance in the study of this intricate sensory organ.