Squeak up – my hearing isn’t so good these days Panther Media GmbH/Alamy Stock Photo

Have you noticed that learning languages or musical instruments becomes harder as you get older? It may be because your brain’s ability to distinguish between sounds is declining. But research in mice suggests we may be able to reverse this.

Previously, Jay Blundon at St Jude Children’s Research Hospital in Memphis, Tennessee, and his colleagues discovered that levels of a chemical called adenosine in the thalamus – a part of the brain involved in sensory processing – rise as mice age. This activates a pathway that impairs learning in the brain’s auditory cortex, so when old mice are played two tones that are close in pitch, they are unable to discriminate between them.

The team has now found that using genetic tools or drugs to reduce adenosine signalling makes the mice able to tell the difference.


Neuronal changes

To demonstrate this, the researchers exposed old mice to a continuous sound as background noise. Then, they played a slightly different tone in addition. The mice were startled by the new sound, showing they were able to hear it as being different from the background tone.

When the team blocked adenosine signalling, they observed an increase in the number of neurons in the auditory cortex that responded to sounds – a process called neuroplasticity. This may be why tone discrimination improved in the aged mice, says Blundon.

If neuroplasticity and tone discrimination could be enhanced in elderly people, it might be easier for them to learn new musical skills or languages, says Blundon. “Learning a second language later in life can often be more difficult because of your inability to accurately hear differences in phonemes,” he says. Phonemes are the distinct units of sound that make up languages.

Train the brain

Improving auditory plasticity could also help in conditions like stroke and tinnitus, says Blundon. Different auditory neurons could potentially be trained to take over the role of those destroyed by stroke, or to replace those that become hyperactive in tinnitus, he says. “But we’re far, far away from any human studies,” he says.

Another possible application is in people with cochlear implants, says Gary Housley at the University of New South Wales, Australia. Children adapt quickly to these implants, whereas adults are slower – possibly due to reduced auditory plasticity, he says. “You might be able to target adenosine to speed up this adaptation process.”

Adenosine signalling is also involved in many other functions in the body, says David Ryugo at the Garvan Institute of Medical Research in Australia. As a result, administering an adenosine-blocking drug could have a range of unwanted side effects, he says.

Blundon and his colleagues are now investigating whether there are ways to precisely control the adenosine pathway so that clinical treatments can be developed. “There are still many unanswered questions, but it’s fascinating to speculate at this point,” he says.

Journal reference: Science, DOI: 10.1126/science.aaf4612