We know hearing loss can cause permanent damage to the fragile structures inside our ears, but what if it could change the way auditory nerve cells work as well? According to a recent study published in the Journal of Neuroscience, even temporary hearing loss can cause measurable changes in the behavior of the nerve cells that transmit signals from the ear to the brain.
So what do we mean by “temporary” hearing loss?
Think about the hearing loss you experience when you’re congested from a cold, or suffering from an ear infection. This type hearing loss might only last for a few days, but it can still have a significant influence on the way nerve cells behave.
To test the way hearing loss affects nerve cell behavior, scientists at the University at Buffalo studied mice that had their ears surgically blocked for a period lasting between three days and more than a week. After examining the deafened mice and comparing them to mice in a control group, the researchers found that the nerve cells in the ears of the deafened mice used their limited supply of neurotransmitters faster, and ultimately depleted their reserves. Subsequently, the vesicles (small, sac-like structures) where neurotransmitters are stored shrank as well.
“When it’s quiet, the demands on the auditory nerve cells are not great, so it makes sense that you would see these changes” said lead researcher Matthew Xu-Friedman. “You no longer need as much neurotransmitter, so why invest a lot of storage? If you’re not that active, you don’t need a big gas tank. And you’re not as afraid to use up what you have. This is one plausible explanation for what we observed.”
Now, the scientists are conducting additional research to determine whether or not the nerve cells completely recover once hearing is restored. In preliminary research they found that the cells “do seem to mostly bounce back,” but they don’t know yet if they fully return to their pre-deafened state. This follow-up research could provide physicians and audiologists with a more comprehensive picture of how hearing loss affects the brain.