After 11 years of intensive research, scientists at the University of Michigan Medical School succeeded in growing new auditory hair cells in order to restore hearing in the deafened adult guinea pigs.

Results from the study -- the first to demonstrate restoration of auditory hair cells at the structural and functional levels in mature living mammals -- will be published February 13 on Nature Medicine's advance online publication Web site.

Role of Hair Cells in Hearing

Hair cells are the sensory cells of the auditory and balance organs in the inner ear. Auditory hair cells reside in the organ of Corti, which is part of the cochlea -- a spiral-shaped bony organ in the inner ear. They get their name from the numerous microscopic hair-like projections that grow from each cell.

When sound waves reach the inner ear, they cause these projections to move. This triggers electrical signals, which are picked up by auditory nerve fibers and carried to the brain. If hair cells are damaged or missing, the connection between sound waves and the brain's auditory processing center is broken, making it impossible to hear.

Aging, infections, certain medications, autoimmune diseases, and exposure to loud sounds can destroy the delicate hair cells, leading to irreversible sensorineural hearing loss -- a condition affecting millions of people worldwide.

For years, scientists have been searching for a way to regenerate functioning hair cells.

Activating Atoh1

Yehoash Raphael, Ph.D., an associate professor of otolaryngology at U-M's Kresge Hearing Research Institute, who directed the U-M study, credits advances made by other scientists worldwide for his team's success.