Scientists studying the brains of old and young mice believe that the brain might be trained to filter out background sound, potentially helping to solve the challenges people with a hearing impairment experience when listening to speech in background noise.
Researchers from the Johns Hopkins University School of Medicine found that old mice were less able than young mice to suppress actively firing brain cells in the midst of ambient noise making it difficult for the brain to focus on one type of sound — such as spoken words — and filter out surrounding noise.
Researchers recorded the activity of 8,000 brain cells, or neurons, in the auditory cortex brain region of 12 old mice (16–24 months old) and 10 young mice (2–6 months old). They conditioned the mice to lick a water spout when they heard a tone and then got them to do the same exercise while the researchers played white noise.
Without the white noise, the old mice licked the water spout just as well as the young mice when they heard the tone. With the white noise the old mice were worse at detecting the tone and licking the spout than the young mice.
When studying the auditory cortex of each mouse, some neuron activity increased when the mice heard the tone and, at the same time, other neurons were repressed or switched off. In most of the old mice, however, the neurons were mostly active and failed to turn off in white noise. In older animals, ambient noise seems to make neuron activity more ‘fuzzy,’ disrupting the ability to distinguish individual sounds.
However, the mammalian brain’s flexible learning potential means that it might be re-trained to tamp down the many firing neurons and focus on individual sounds amid background noise.
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