Researchers at Johns Hopkins Medicine found that older mice were less able than younger mice to “turn off” specific brain cells that were actively firing in the presence of environmental noise. This creates a “fuzzy” soundstage that makes it difficult for the brain to focus on specific sounds and filter out ambient noise. Researchers suggest that age-related hearing loss could be treated by retraining the brain to reduce the activity of these neurons.
Studies of hearing in aged and young mice suggest that the brain may be trained to filter out background sounds.
Researchers at Johns Hopkins Medicine, who were looking for answers about how the brain works during age-related hearing loss, found that older mice fire more actively in ambient noise than younger mice. I found that I was less able to “turn off” certain brain cells that were The result, they say, creates a “fuzzy” soundstage that makes it difficult for the brain to focus on one type of sound (such as spoken words) and filter out surrounding “noise.”
Scientists have long linked the inevitable age-related hearing loss to the damage or destruction of hair cells in the inner ear over time.
But researchers at Johns Hopkins University said in their new study, published Dec. neuroscience journalhave shown that the brain has a lot to do with this condition, and retraining the brain to suppress the neurons that fire too hard could potentially treat such hearing loss.
When Grandpa can’t hear a word at a raucous holiday gathering, too many brain cells may be firing at once, researchers say.
“Hearing is more than ears,” says Patrick Kanold, PhD, professor of biomedical engineering at Johns Hopkins University and School of Medicine. Canold says most people experience some form of hearing loss after he turns 65, such as being unable to hear individual conversations in a bar or restaurant.
Kanold and his team recorded the activity of 8,078 brain cells, or neurons, in the auditory cortical brain regions of 12 old mice (16–24 months old) and 10 young mice (2–6 months old). Did.
First, researchers conditioned mice to lick a water spout when they heard the sound. I then performed the same exercise while playing “white noise” in the background.
In the absence of ambient noise, older rats licked the spout in the same way as younger rats when they heard the sound.
When researchers introduced white noise, older mice were, overall, worse at detecting tones and licking their mouths than younger mice.
Also, young mice tended to lick the spout at the beginning or end of the tone. Older mice licked at the onset of the tone cue, but also showed licking before the tone was presented.
Next, to see how auditory neurons function directly during such audiometry, researchers peered into the auditory cortex of mice using a technique called two-photon imaging. This technique uses fluorescence to identify and measure the activity of hundreds of neurons simultaneously.
Under normal conditions, if brain circuits are functioning correctly in the presence of ambient noise, some neuronal activity increases when mice hear a sound, while others are simultaneously inhibited or turned off. However, most aged mice were out of balance and had mostly active neurons, turning off neurons that should have turned off when a tone was played in the presence of a noisy background. did not become
Additionally, the researchers found that just before the tone cue, there was up to twice as much neuronal activity in young mice as in young mice, and that animals licked their mouths before the tone started, especially among males. .
A possible reason for that result is, “In older mice, the brain may be ‘firing’ or behaving as if a tone exists,” Canold said.
Experiments with ambient noise revealed that young mice had altered ratios of active to inactive neurons, while older mice had a whole set of neurons that were consistently active. Therefore, younger mice were able to suppress the effects of environmental noise on neural activity, but older mice were not, the researchers said.
“In older animals, ambient noise appears to make neuronal activity more ‘blurred,’ impairing the ability to distinguish individual sounds,” says Kanold.
On the other hand, Canold believes that the flexible learning capacity of mammalian brains can be ‘taught’ to deal with ambiguity in older animals, including humans.
“There may be ways to train the brain to focus on individual notes in a cacophony,” he says.
Canold points out that more research is needed to precisely map the relationship between the inability to block specific neurons and hearing loss in ambient sounds. This includes relevant brain circuits and age-related changes, as well as potential differences between male and female animals. .
See: “Diminished Modulation of Population Correlations in the Auditory Cortex is Associated with Diminished Auditory Detection Performance in Aged Mice,” Kelson Shilling-Scrivo, Jonah Mittelstadt, and Patrick O. Kanold, December 7, 2022. , Journal of Neuroscience.
DOI: 10.1523/JNEUROSCI.0955-22.2022
Other contributors to this research are Kelson Shilling-Scrivo and Jonah Mittelstadt from the University of Maryland.
Funding for the study was provided by the National Institutes of Health (P01AG055365, RO1DC009607, RO1DC017785).
