Exploring the neural processes through experiments, a team of researchers unravelled how sound reduces pain in mice. The findings are now likely to facilitate the development of safer methods to treat or manage pain. Earlier studies had indicated that music and other kinds of sound can help activate chronic pain in humans. However, the mechanism that goes behind this pain reduction could not be detected.
In the new study, researchers experimented on mice with inflamed paws and exposed them to different types of sounds. These included a pleasant piece of classical music, an unpleasant rearrangement of the same sound, and white noise.
The researchers noted that all three types of sounds eased the pain in the mice when played at low intensity. However, when high intensities of the same sound were played, it had no impact on the mice.
“Human brain imaging studies have implicated certain areas of the brain in music-induced analgesia, but these are only associations. In animals, we can more fully explore and manipulate the circuitry to identify the neural substrates involved,” said Yuanyuan (Kevin) Liu, PhD student and a Stadtman tenure-track investigator at the National Institute of Dental and Craniofacial Research and co-senior author of the study published in Science.
Liu added that the observations of the experiment were surprising as the pain relief depended upon the intensity of the sound rather than its nature.
To explore the mechanism behind the effect, researchers used non-infectious viruses along with fluorescent protein to zero in on the connections between brain regions. They were able to spot the route from the auditory cortex to the thalamus. While the cortex is responsible for receiving and processing information about sound, the thalamus works as a relay station for sensory signals that includes pain as well.
It was found that low-intensity white noise effectively reduced the neuron activity at the receiving end of the pathway in the thalamus. Researchers have noted that in the absence of sound, light and small molecules-based techniques suppressed the pathway and showed similar pain-blunting effects as low-intensity noise.
“We don't know if human music means anything to rodents, but it has many different meanings to humans — you have a lot of emotional components,” said Liu.
The findings are likely to come in handy for researchers in exploring better and safer alternatives to opioids for treating pain.