Purpose of the study
Following sound deprivation or stimulation, our hearing system is able to adapt by increasing or decreasing its sensibility, respectively. In the literature, this modulation of the auditory “gain” is described as being a phenomenon occurring in the brainstem. Yet, no study has yet looked at the structures involved in the process all along the hearing system.
Our study aims to document the changes in “gain” at every level of the hearing system, before and after sound deprivation (ear plugs) or enrichment (noise generators).
Who was this study for?
People from 18 to 35 years old who do not have hearing loss or any other hearing problems (e.g., tinnitus, dizziness). Participants have been assigned to either the “ear plug” group or the “noise generator” group.
What was paticipants had to do?
We have tested participant’s hearing, from periphery (auditory canal, audiometry, cochlea) up to the auditory cortex (magnetoencephalography, see below), before and after wearing ear plugs or noise generators.
What’s magnetoencephalography (MEG) ?
Magnetoencephalography allows to record magnetic fields produced by the brain electric activity. The more active cells in the brain produce a magnetic field more intense than the less active cells at a precise moment. By recording magnetic fields while making a cognitive task, it is possible to produce an image of brain functional activity.
The use of EEG’s electrodes is also necessary, first to watch the movements of eyes during experiment and, second, to establish links between electrophysiologic activity and magnetic activity of the brain during the task.
How often did participants have to go to the BRAMS?
In a first meeting we had determined the eligibility of each participant for the study according to our precise hearing criterias. If the participant was eligible, he/she was invited to come to a second meeting (about 4 hours), during which several clinical hearing tests have been realized in the BRAMS laboratory. Then, magnetoencephalography have been run in the psychology department (5 minutes walk from the BRAMS). This test involved fitting a helmet with sensors to record the brain activity during a listening task (the sensors do not produce waves). No harmful sound has been presented. Besides the helmet, three additional self-adhesive sensors have been placed on the forehead and behind ears to record brainstem electric activity.
Exactly one week after wearing ear plugs or noise generators, the participant had to come back to the BRAMS to redo the same tests as before. He/She could not remove earplugs or generators before that time.
Every participant received a 60-dollar amount for participation. Also, if desired, he/she received custom-made earplugs to be worn in noisy environments to protect their hearing.
Recruitment and evaluation periods are now completed. All data collected during this study are curently in analysis!