Science: Scientists decipher the reasons why “sounds” reduce pain

On July 8, Beijing time, the team of Professor Zhang Zhi of the School of Life Sciences and Medicine of the University of Science and Technology of China, the team of Professor Liu Yuanyuan of the National Institutes of Health, and the team of Associate Professor Tao Wenjuan of Anhui Medical University collaborated to publish a paper in Science, revealing the key factors and neural mechanisms of voice analgesia.

The low intensity acoustic-to-noise ratio relieves pain in mice by inhibiting glutamate neurons to thalamus projection.png

Schematic diagram of low-intensity sound relieving pain in mice by inhibiting neural projection from the auditory cortex to the somatosensory thalamus

In fact, as early as 1960, the journal Science published a paper that found that during dental procedures, music can regulate patients’ emotions. And it is pointed out that even noise, such as the sound of a surgical drill, can produce analgesic effects.

However, for more than half a century, the key factors in how sound can reduce pain, and the neural mechanisms by which sound affects our brains to reduce pain, are unclear.

In this study, the researchers first played 3 different types of sounds to mice with inflamed paws, namely soothing music, uncoordinated notes, and white noise. The results showed that these three sounds were effective in relieving pain in mice when played at low intensity (about the level of whispering), while there was no obvious analgesic effect during high-intensity playback.

Some studies hypothesize that the analgesic effects of sound may be closely related to the therapeutic environment. Therefore, the researchers placed the mice in an environment with different intensities of background sounds, and found that a sound about 5 decibels higher than the ambient noise could effectively relieve the pain of the mice. So far, the researchers have built a mouse model of vocal analgesia.

“Surprisingly, for mice, the faint difference in sound intensity between sound and ambient noise was crucial to the analgesic effect of the sound, rather than the melody of the sound.” Dr. Zhou Wenjie, the first author of the paper and a special associate researcher at the School of Life Sciences and Medicine of the University of Science and Technology of China, said.

So, what is the neural mechanism by which sound exerts analgesic effects?

The auditory cortex is the most advanced brain center for sound processing and performs a fine analysis of the sounds heard. Using the virus as a neural tracer, the researchers tracked the whole brain of the auditory cortex output in mice, found that auditory cortex neurons projected in large numbers into the somatosensory thalamus (responsible for receiving sensory signals from the body, including pain), and found that low-intensity sounds were able to inhibit this projection.

“The results suggest that low-intensity sounds play a role in relieving pain by inhibiting neural projection from the auditory cortex to the somatosensory thalamus.” Zhou Wenjie said that this is the corticothalamus circuit of sound analgesia. However, in addition to the intensity of the sound, the melody of the sound, the role of the human perception of pain also needs to be further studied.

In response to this study, the journal Science made a special review, pointing out that “by creating a model of the basis of the research mechanism, it opens up a new direction for the study of music/sound causing analgesia.” (Source: China Science Daily Wang Min)

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