Researchers identified the neural mechanisms through which sound reduces pain in mice. The findings could contribute to developing safer pain treatment methods in humans.
The study, published in Science, was led by researchers at the National Institute of Dental and Craniofacial Research (NIDCR), the University of Science and Technology of China, and Anhui Medical University.
The researchers first exposed mice with inflamed paws to three types of sound: a pleasant piece of classical music, an unpleasant rearrangement of the same piece, and white noise.
Researchers said they were surprised to find that all three types of sound reduced pain sensitivity in the mice when played at a low intensity relative to background noise (about the level of a whisper). At the same time, higher intensities of the same sounds had no effect on animals’ pain responses.
To explore the brain circuitry underlying this effect, the researchers used non-infectious viruses coupled with fluorescent proteins to trace connections between brain regions.
They identified a route from the auditory cortex, which receives and processes information about sound, to the thalamus, which acts as a relay station for sensory signals, including pain, from the body. In freely moving mice, low-intensity white noise reduced the activity of neurons at the receiving end of the pathway in the thalamus.
In the absence of sound, suppressing the pathway with light- and small molecule-based techniques mimicked the pain-blunting effects of low-intensity noise while turning on the pathway restored animals’ sensitivity to pain.
Researchers say it remains unclear if similar brain processes are involved in humans or whether other aspects of sound, such as its perceived harmony or pleasantness, are important for human pain relief.
“By uncovering the circuitry that mediates the pain-reducing effects of sound in mice, this study adds critical knowledge that could ultimately inform new approaches for pain therapy,” said NIDCR Director Rena D’Souza, D.D.S, Ph.D, in a press release.
Hope for treating chronic pain
With one in five adults in the US having chronic pain, and 7.4% suffering from high-impact chronic pain that limits life or work activities, scientists have previously explored the role of sound in reducing pain via animal models.
In a study published in the Journal of Neural Engineering, researchers from the University of Minnesota, Twin Cities, played broadband sound while electrically stimulating different body parts in guinea pigs.
They found that the combination of the two activated neurons in the brain’s somatosensory cortex, which is responsible for touch and pain sensations throughout the body.
While the researchers used needle stimulation in their experiments, one could achieve similar results using electrical stimulation devices, such as transcutaneous electrical nerve stimulation (TENS) units, which are widely available.
The researchers hope that their findings will lead to a treatment for chronic pain that’s safer and more accessible than drug approaches.
National Institutes of Health. Researchers discover how sound reduces pain in mice.
University of Minnesota, Twin Cities. Study finds that sound plus electrical body stimulation has potential to treat chronic pain.