A 30-year scientific debate over how specialized cells in the inner ear amplify sound in mammals appears to have been settled more in favor of bouncing cell bodies rather than vibrating, hair-like cilia, according to investigators at St. Jude Children’s Research Hospital.
The finding could explain why dogs, cats, humans and other mammals have such sensitive hearing and the ability to discriminate among frequencies. The work also highlights the importance of basic hearing research in studies into the causes of deafness. A report on this work appears in the advanced online issue of “Proceedings of the National Academy of Science.”
“Our discovery helps explain the mechanics of hearing and what might be going wrong in some forms of deafness,” said Jian Zuo, Ph.D., the paper’s senior author and associate member of the St. Jude Department of Developmental Neurobiology. “There are a variety of causes for hearing loss, including side effects of chemotherapy for cancer. One strength of St. Jude is that researchers have the ability to ask some very basic questions about how the body works, and then use those answers to solve medical problems in the future.”
The long-standing argument centers around outer hair cells, which are rod-shaped cells that respond to sound waves. Located in the fluid-filled part of the inner ear called the cochlea, these outer hair cells sport tufts of hair-like cilia that project into the fluid. The presence of outer hair cells makes mammalian hearing more than 100 times better than it would be if the cells were absent.
As sound waves race into the inner ear at hundreds of miles per hour, their energy—although dissipated by the cochlear fluid—generates waves in the fluid, somewhat like the tiny waves made