Noise Induced Hearing Loss Alters Brain Responses to Speech

In a recent study published in Ear and Hearing, researchers from the University of Texas at Dallas demonstrated how noise-induced hearing loss affects the brain’s recognition of speech. Exposure to intensely loud sounds leads to permanent damage of the hair cells, and once damaged, the hair cells do not grow back. “As we have made machine and electronic devices more powerful, the potential to cause permanent damage has grown tremendously,” said the study’s lead author. “Even the smaller MP3 players can reach volume levels that are highly damaging to the ear in a matter of minutes.” To simulate two types of noise trauma that clinical populations face, scientists exposed rats to moderate or intense levels of noise for an hour, with one noise frequency at 115 decibels — inducing moderate hearing loss —and the other at 124 decibels — causing severe hearing loss. Researchers observed how the two types of hearing loss affected speech sound processing in the rats by recording the neuronal response in the auditory cortex a month after noise exposure. In the group of mice with severe hearing loss, less than one-third of the tested auditory cortex sites that normally respond to sound reacted to stimulation, showing unusual patterns of activity. The neurons reacted slower, the sounds needed to be louder and the neurons responded to frequency ranges more narrow than normal. Additionally, the rats could not tell the speech sounds apart in a behavioral task that they were previously able to completely successfully. To read more about this study, click here.