A study led by UB biologist Matthew Xu-Friedman shows how limber and adaptable the brain is when it comes to processing sound. Put the organ in a loud environment, and it starts receiving information in a new way—a discovery that could impact everyone from city dwellers to truck drivers, frequent flyers and anyone else who lives or works in noisy surroundings.
What we saw is that the auditory nerve cells dial themselves down. These cells, which carry information from the ear to the brain, start economizing resources. They start behaving in ways that conserve supplies of neurotransmitters—chemicals that help send signals to the brain.
If the cells ran out of neurotransmitters, they would have no way of talking to the brain. So we think they’re acting to preserve their resources.
We see two kinds of changes. One is that under high activity—in noise—the cells increase their supply of sack-like structures called vesicles that hold neurotransmitters. You don’t want to deplete your stock, so it makes sense to have a larger storehouse. The other major change is that each vesicle has a lower probability of releasing its neurotransmitters in response to noise. This helps ensure that cells have chemicals left to alert the brain to new sounds.
Our study was done on mice. But if I had to speculate, I’d say that what our results might mean for humans is that if you are in loud conditions for some period of time, as many of us are—people who work in machine shops, etc—your auditory system may adjust to that level of activity.
It’s good at some level; it’s meant to help you hear. But what happens when you go home from work or step off of the airplane? You’re left with this hyper-excitable auditory system: Everything is cranked up. Your cells have huge stocks of neurotransmitters, but now they aren’t being used because it’s quiet. Under these conditions, I think it’s possible that cells could become overloaded and trigger inappropriately, causing some form of tinnitus where your brain “hears” things it shouldn’t.