Researchers reverse the hypothesis behind the sensitivity of the mammalian hearing system

A new study from the University of Colorado Anschutz Medical Campus challenges a decades-old hypothesis about adaptation, a key feature of how sensory cells in the inner ear (hair cells) detect sound.

Paper, today in Scientific advances, examines how hair cells transform mechanical forces resulting from sound waves into a neural electrical signal, a process called mechanical-electrical transduction (MET). Hair cells have an intrinsic ability to fine-tune the sensitivity of the MET process (called adaptation), which underlies our ability to detect a wide range of sound intensities and frequencies with extremely high accuracy. So far, more than 30 years of research has convinced auditory scientists that the molecules and proteins responsible for adaptation have been identified. First published in 1987, the predominant model of how adaptation worked claimed that the sound-sensitive “antenna” of the hair cell (called the hair bundle) undergoes a mechanical change during adaptation, so that A decrease in the stiffness of the hair bundle caused a decrease in MET sensitivity.

Ancillary experiments conducted over the following decades suggested that a motor protein, myosin 1c, is required for MET adaptation. Through multiple experiments and a variety of checks, Anschutz researchers determined that this existing hypothesis needs to be reconsidered; that although adaptation requires myosin motors, it does not involve a mechanical change in the hair bundle.

Anschutz researchers performed a series of sophisticated experiments to examine the relationship between the mechanical properties of the hair bundle and the electrical response of the hair cell. Using a personalized high-speed imaging technique, Giusy Caprara, Ph.D., a postdoctoral researcher at the University of Colorado School of Medicine and lead author of the study, simultaneously performed a recording electrical and hair cell imaging in a variety of mammalian species at 10,000 frames per second to examine mechanical changes in the hair bundle during adaptation, an extreme break compared to the 1987 experiments that used photodiodes. “The reason this was not discovered earlier is that there are very few experiments that have tested the mechanical properties of the hair bundle,” explains Anthony Peng, Ph.D., supervising author and professor. assistant of physiology and biophysics at the University of Colorado School of Medicine. “Technology drove and made this discovery possible.”

Understanding the coping mechanism is important in determining how sensory cells in the inner ear work. Although the research is not directly translational, it is an important first step in fixing and replacing cochlear function, potentially leading to technological improvements for better sound processing and treatment of hearing dysfunction on down the line.

“The discovery that the original adaptation model was incorrect is important in several ways,” Peng says. “In basic science, this has opened avenues for more research, including proposing a new model of how adaptation works. Most importantly, hearing sensitivity and the range of hearing we can achieve is based on this process, so understanding this will help us better understand the different types of hearing loss that people experience. ”