It has been known since the 1960s that sound can have analgesic effects on people. Accounts from dental operations indicated that music and noise relieved pain to some extent, and music that is used as an intervention can alleviate postoperative pain and bring relief. Because diverse genres of music and even nature sounds can relieve pain to an equal extent, the inherent characteristics of sound, as well as contextual factors, have been hypothesized to drive these analgesic effects. However, the neural mechanism by which this occurs is still not understood.
New research published in the journal Science has investigated whether sound brings relief to mice with inflammatory pain induced by hindpaw injection of complete Freund’s adjuvant. Inspired by observations in humans, Wenjie Zhou and colleagues evaluated the phenomenon in mice using a suite of methods, including behavioral tests, viral tracing, microendoscopic calcium imaging, and multielectrode recordings.
The researchers found that sounds with a low-signal to ambient noise ratio, specifically a 5 decibel increase in sound intensity over ambient sound levels, caused relief from pain in the experimental mice. This involved inhibitory inputs from the auditory cortex to distinct regions of the somatosensory thalamus, depending on whether the pain was administered in the forepaw or hindpaw.
Furthermore, artificial manipulation of the identified circuits both mimicked and suppressed sound-induced analgesic effects. According to the researchers, their study revealed the corticothalamic circuits underlying sound-promoted analgesia by deciphering the role of the auditory system in pain processing.”
“The neural mechanisms underlying music-induced analgesia in humans are doubtlessly more complicated than those revealed in mice,” said the study authors. In humans, multiple brain areas are involved in pain processing and this warrants further investigation. However, this study suggests that music-induced analgesia could be developed as an alternative or complementary intervention for treating and relieving pain in humans.
“Although this experimental paradigm is not equivalent to using music and pleasant sounds to evoke analgesia in humans, the study of Zhou et al. opens up new directions for research on sound-induced analgesia by creating a model in which the mechanistic underpinnings can be investigated,” wrote Rohini Kuner and Thomas Kuner in a related Perspective.