Long-term effects of an environmental noise on the auditory system – DAILYNOISE

We will quantify i) impairment in hair cell function; ii) classical audiometry measures of subcortical neural processing; iii) cortical spectral and temporal processing, including processing of communication sounds such as conspecific and heterospecific vocalizations; iv) robustness of neural responses to noise, which is attenuated in people suffering from hearing loss related to aging or exposure to traumatic sounds; v) modifications of thalamocortical inhibitory processes, which are also known to be down-regulated by either noise-induced or aging-induced hearing loss. Techniques ranging from the cellular (immunohistochemistry) to more integrated levels (in-vivo electrophysiology, computational neuroscience, behavioral training) will be deployed and integrated for this project. This ambitious set of experiments is made possible by the broad range of expertise of the DAILYNOISE team.

Preliminary results suggest that the adult auditory cortex is more resistant than suspected to long lasting daily exposure to environmental noise. Our data, obtained with a “real-world noise”, suggest that not all types of noise exposure impact the properties of auditory cortical neurons. Further investigations are currently in progress, for instance dealing with stress levels of animals.

Epidemiologic as well as animal studies suggest (without proving) that long-term environmental noise damages and significantly modifies auditory processing in our animals. This project will for the first time determine whether environmental noise actually induces hearing impairment. In addition to its innovative methodology, DAILYNOISE will have significant impact on public policy and health, providing empirical data that will inform the development of better regulations, and influencing better-informed lifestyle choices, potentially improving the living conditions and health of hundreds of millions of inhabitants inside and outside the workplace.

In addition to an important background work of methods design for analysis of auditory cortical responses to complex sounds, the above preliminary results have been presented in many important international meetings: SfN 2015, 2016; ARO 2016, 2017 for instance. The analysis of the huge amount of data generated by this project is still currently under progress.

Over the last decades, people have been exposed to increasing noise from multiple sources, including transportation noise, amplified music, concerts, TV and video games. Regulations dealing with occupational or leisure noise in western countries do not consider the cumulative effect of daily exposure at loud but non-traumatic sound pressure levels (80dB SPL), which is still considered harmless. Recent studies suggest that this complacency is misplaced: significant damage to the peripheral auditory system is not necessarily accompanied by immediate impairments that can be measured with audiometry. It is thus possible that auditory function could be progressively degraded by environmental noise, but this damage would remain undetected in epidemiologic studies based solely on audiometry.

The purpose of the project DAILYNOISE is to assess the long-term effects of daily 8 hour exposure to noise at 80dB SPL, which mimics noise levels routinely encountered in everyday life. To this end, we use an animal model with a short lifespan (the Sprague-Dawley rat, 2 years) to follow degradation to the whole auditory system over the course of a lifespan. First, modifications of the auditory nerve output due to peripheral damage and frequent stimulation may lead to plasticity-related changes at upper stages of the auditory system. Also, age-related changes will interfere with neural processing of natural sounds and background noise. The DAILYNOISE project proposes to track for the first time peripheral, subcortical, cortical and behavioral changes in auditory function in individual animals from young adulthood to old age.

We will quantify i) impairment in hair cell function; ii) classical audiometry measures of subcortical neural processing; iii) cortical spectral and temporal processing, including processing of communication sounds such as conspecific and heterospecific vocalizations; iv) robustness of neural responses to noise, which is attenuated in people suffering from hearing loss related to aging or exposure to traumatic sounds; v) modifications of thalamocortical inhibitory processes, which are also known to be down-regulated by either noise-induced or aging-induced hearing loss. Techniques ranging from the cellular (immunohistochemistry) to more integrated levels (in-vivo electrophysiology, computational neuroscience, behavioral training) will be deployed and integrated for this project. This ambitious set of experiments is made possible by the broad range of expertise of the DAILYNOISE team.

Epidemiologic as well as animal studies suggest (without proving) that long-term environmental noise damages and significantly modifies auditory processing in our animals. This project will for the first time determine whether environmental noise actually induces hearing impairment. In addition to its innovative methodology, DAILYNOISE will have significant impact on public policy and health, providing empirical data that will inform the development of better regulations, and influencing better-informed lifestyle choices, potentially improving the living conditions and health of hundreds of millions of inhabitants inside and outside the workplace.