Prolonged exposure to loud noise alters how the brain processes speech, which may affect the ability to distinguish speech, a study has found.
Neuroscientists at the University of Texas in the US have demonstrated how noise-induced hearing loss affects the brain's recognition of speech.
To stimulate two types of noise traumas, the researchers exposed rats to moderate or intense levels of noise for an hour. One group heard a high-frequency noise at 115 dB, inducing moderate hearing loss. The second group heard low-frequency noise at 124 dB causing severe hearing loss.
The researchers observed how the two types of hearing loss affected sound processing in the auditory cortex.
Two different results
In the group with severe hearing loss, less than one-third of the tested auditory cortex sites that normally respond to sound reacted to the stimulation. In the sites that did respond, there were unusual patterns of activity.
In the group with moderate hearing loss, the area of the cortex responding to sounds didn’t change, but the neurons’ reactions did. A larger area of the auditory cortex responded to low-frequency sounds and the neurons reacting to high-frequencies needed more intense sound stimulation and responded slower.
The scientific paper was published in the journal Ear and Hearing.
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