Studying How Sound Suppresses Pain
Research has long supported the notion that music and other kinds of sound can help alleviate acute and chronic pain. In a new study, published in Science, an international team of scientists used mice to explore neural pathways through which sound blunts pain.
The scientists 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. All three reduced pain sensitivity in the mice when played just slightly louder than background noise (about the level of a whisper). The effect lasted well beyond the sound itself—for at least 2 days after exposure to the sound 3 days in a row for 20 minutes. When played louder, the sounds had no effect on the animals’ pain responses.
Pain perception can be affected by emotions and stress. However, the scientists discovered that low-intensity sound affected the animal’s perception of pain through another mechanism.
To explore the brain circuitry underlying this effect, the team used techniques 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 in the thalamus at the receiving end of this pathway.
Suppressing the pathway in the absence of sound, the team found, mimicked the pain-blunting effects of low-intensity noise. In contrast, activating the pathway restored the animals’ sensitivity to pain in the presence of sound. The scientists also identified distinct brain circuits through which sound blunted pain from hind paws and forepaws.
It is still unclear if similar brain processes are involved in humans. Other aspects of sound, such as its perceived harmony or pleasantness, may be important for human pain relief. “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 Dr. Yuanyuan Liu of NIDCR.
“By uncovering the circuitry that mediates the pain-reducing effects of sound in mice,” said NIDCR director Dr. Rena D’Souza, “this study adds critical knowledge that could ultimately inform new approaches for pain therapy.”
The team was led by researchers at NIDCR; the University of Science and Technology of China, Hefei; and Anhui Medical University in Hefei, China.—adapted from NIH Research Matters