Laboratory of Sensory Neuroscience
February 12, 2013
Shedding light on the elusive mechanics of hearing in the mammalian cochlea
Human hearing is exquisitely sensitive over a vast range of sounds. We can hear faint sounds down to the level of thermal fluctuations in the ear, and our ability to discern subtle differences in tone allows us to distinguish human voices of nearly identical timbre. We additionally perceive sounds of vastly differing intensities on a similar scale, enabling us to clearly hear the distant strumming of nylon strings from a classical guitar playing in concert with a full orchestra. These remarkable capabilities are largely lost in
individuals with sensorineural hearing loss, which stems primarily from the failure of mechanosensory hair cells. Such hearing loss is associated with changes in the traveling waves that transmit acoustic signals along the cochlea. However, the connection between cochlear mechanics and the amplificatory function of hair cells remains unclear. Using an optical technique that permits the targeted inactivation of prestin, a protein of outer hair cells that generates forces on the basilar membrane, we find that these forces locally
interact with cochlear traveling waves to achieve enormous mechanical amplification. Analysis of these results indicates that cochlear amplification produces negative damping that counters the viscous drag impeding traveling waves; targeted photoinactivation locally interrupts this compensation. These results reveal the locus of amplification in cochlear traveling waves and connect the characteristics of normal hearing to molecular forces.