Looking at rat brains to study age-related hearing loss

A new study looking at the brain activity of rats hopes to shed light on why some people’s hearing begins to deteriorate as they age.

Researchers from Johns Hopkins Medicine looked at the brain activity of older mice compared to younger mice and found that older mice were less likely to silence certain actively-activating brain cells extremes in the presence of background noise, making it harder for them to focus on specific sounds than it was for younger mice.

Patrick Kanold, professor of biomedical engineering at Johns Hopkins University and School of Medicine and one of the study’s authors, said in a press release: “There’s more to hearing than hearing.

While previous research has determined that age-related hearing loss is partly related to changes in hair cells in the inner ear, this new study is published in the Journal of Neuroscience. in December demonstrated that it is the brain itself that plays a role in this listening process. loss is good.

The researchers looked at brain activity in 12 16-24 month old mice compared with 10 2-6 month old mice. In total, they looked at the activity of more than 8,000 neurons across all of the mice.

To see if the mice could correctly pick up a meaningful sound while other, more distracting noises were being played, the researchers had the rats lick a faucet when they heard a sound. specific bar. They then played sounds to the mice with and without background noise playing in the background.

All of the mice performed well at perceiving sounds and licking the faucet when it was the only sound. But when there was background noise, the older mice had more difficulty making sounds and were less likely to lick their faucets than younger mice.

Smaller mice also tended to recognize sounds immediately, while some of the larger rats licked their faucets before the sound was heard, suggesting they mistakenly thought they were hearing a sound. there.

So what is going on in the brain that might be related to these results?

When the researchers looked at the neurons, they found that when there was no background noise playing, certain neurons activated when they heard that sound, while neurons Other nerves will be suppressed or temporarily turned off, similar to turning off the radio to hear someone better. speak.

However, in the older mice, many neurons remained active regardless of the tone, which suggests that the aged mice were less likely to turn off some of the neurons that are meant to be inactive when alarm is playing. The researchers noted that their higher levels of neuronal activation could also make them think they were hearing a sound when they weren’t.

“In old mice, the brain can ‘play’ or act as if there is a certain sound, when it is not,” said Kanold.

“In older animals, background noise seems to make neuronal activity more ‘faint’, disrupting the ability to distinguish individual sounds.”

If these findings also hold true for humans, the researchers suggest, it could be good news for people who are struggling to hear things clearly as they age.

“There could be many ways to train the brain to focus on individual sounds amid a series of noises,” says Kanold.

However, this study only establishes a correlation – more research needs to be done to determine the mechanism that leads to this inability to turn off certain neurons and whether it actually causes it. hearing loss or not.


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