14 DAY TRIAL // Data obtained while carrying out experiments on rats indicates that long-term exposure to loud noises is likely to affect the human brain in such ways that it can no longer properly process speech and distinguish among various speech sounds.
As part of these experiments, researchers with the University of Texas at Dallas exposed one group of laboratory rats to moderate levels of noise for a full hour. One other group was exposed to intense noise for the same amount of time.
Later, the scientists examined activity patterns in the auditory cortex of rats in both the first and the second group. The focus was on how long it took neurons in this area of the brain to respond to stimuli, provided that they were able to respond, to begin with.
It was thus discovered that in the case of rats exposed to intense noise, i.e. 124 decibels, merely one third of the auditory cortex was able to react to stimuli. What's more, the neurons that did respond showed peculiar patterns of activity.
Specifically, they took longer to react and needed exposure to louder sounds to generate a response. Besides, the rats were found to have trouble completing a behavioral task involving telling speech sounds apart that they previously had no trouble carrying out.
In the case of the rodents exposed to moderate noise, most of the auditory cortex remained responsive. However, neurons in charge of handling high frequencies needed more intense stimulation to react and took longer than normal to produce a reaction. Still, these rodents were able to complete the behavioral task.
In light on these findings, researchers with the University of Texas at Dallas wish to draw attention to the fact that, contrary to what some might assume, loud noises do not affect the ear alone. On the contrary, this form of environmental pollution appears to also take its toll on a person's brain.
Commenting on the outcome of this series of experiments, Dr. Michael Kilgard said, “Although the ear is critical to hearing, it is just the first step of many processing stages needed to hold a conversation. We are beginning to understand how hearing damage alters the brain and makes it hard to process speech, especially in noisy environments.”
Furthermore, “As we have made machines and electronic devices more powerful, the potential to cause permanent damage has grown tremendously. Even the smaller MP3 players can reach volume levels that are highly damaging to the ear in a matter of minutes.”
Data provided by the National Institutes of Deafness and Other Communication Disorders indicates that, in this day and age, about 15% of the people between the ages of 20 and 69 living in the United States are suffering from noise-induced hearing loss.