An intriguing new study has clarified the phenomenon of using sound to relieve pain. An international team of researchers has discovered the neuronal process through which sound lowers pain sensitivity. Surprisingly, modest volumes were more helpful than turning the music up loud. This was revealed using cutting-edge brain imaging techniques.
Wallace Gardner, a dentist, released an odd study in 1960 that claimed sound might be used to relieve pain. He claimed to have performed more than 200 teeth extraction procedures with sound as the sole painkiller. In addition, eight other dentists who used “audio analgesia” successfully were mentioned in his study.
Since then, scientists have repeatedly observed the phenomena, but little is understood about how the brain might be causing these analgesic effects. According to Yuanyuan Liu, co-senior author of the current study, earlier studies suggested potential brain mechanisms at work. Still, this new study pinpoints the actual neural circuitry for the first time.
Liu, from the National Institute of Dental & Craniofacial Research, explained:
Human brain imaging studies have implicated certain brain areas 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.
The researchers first considered the widely held hypothesis that soothing classical music might have inherent pain-relieving effects. Then, to evaluate mice’s pain tolerance, a solution was injected into their paws while they were being played a piece of music by Johann Sebastian Bach titled Réjouissance.
The music’s volume was raised in 5-dB steps across various experiments. However, the only volume that worked as an analgesic was the quietest one, at 50 dB, just 5 dB above the room’s ambient noise. This was the study’s first unexpected finding.
The following test examined several sound sources. Therefore, the studies were conducted using white noise and a pitch-shifted version of the classical piece that sounded unpleasant in place of the original’s pleasant tones. The second surprise discovery the researchers made was that all sounds had analgesic effects on the animals.
Volume was the only factor that mattered. Any sound worked as long as it was played at a volume just a whisper louder than the room’s background noise. “We were really surprised that the intensity of sound, and not the category or perceived pleasantness of sound would matter,” Liu said.
The researchers also sought to identify precisely which brain circuits were responsible for these sound-induced analgesic effects. The team found a direct link between the thalamus and the auditory cortex using various advanced approaches to focus on active brain circuits.
The low-intensity sound appeared to reduce neuronal activity at the thalamus end of this circuit. Later experiments that suppressed activity in this neural pathway without sound similarly reduced pain. This is intriguing because it shows that science has found a mechanism by which music directly reduces pain perceptions.
The discovery may support Gardner’s 1960 research, which formulated the perceptive hypothesis that music directly reduced pain sensation by perhaps interfering with communication between auditory brain regions and the thalamus.
Gardner wrote 60 years ago:
In thinking toward an explanation, we note that parts of the auditory and pain systems come together in several regions of the reticular formation and lower thalamus. The interactions between the two systems are largely inhibitory. Both the direct suppressive effect and the effects mediated through relaxation, reduction of anxiety, and diversion of attention, can be explained by assuming that acoustic stimulation decreases the ‘gain’ of pain relays upon which branches of the auditory system impinge.
According to a commentary on the current study by researchers Thomas Kunar and Rohini Kunar, the results partially defy earlier theories that claimed sound-induced anesthesia in humans might only be caused by psychological variables like being relaxed or distracted by music.
The researchers added:
Previous concepts on using music and sounds for pain relief attributed their effects to distraction-associated analgesia and anxiety reduction. Although sound likely contributes to distraction, the study by Zhou et al. reveals that sound-induced analgesia is a specific mechanistic entity in its own right, supported by the observation that suppression of pain outlasted the application of sound by several days.
Yet, Liu is mindful not to ignore such additional psychological aspects. He did note that compared to rodents, humans find music far more sophisticated, with factors like emotion, memory, and pleasing harmony probably having significant pain-reducing effects on any analgesic impact. “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,” Liu noted.
Future research must first focus on determining whether the same brain circuit seen in mice also functions in people. And if it is confirmed, it might pave the way for many novel non-pharmacological pain management techniques.
Harvard neurobiologist Clifford Woolf said in an interview with Science that the findings suggest low-volume noise, rather than the more conventional idea of playing soothing classical music, could be an effective painkiller. “Many would have anticipated you need to listen to Mozart for pain relief. But maybe all we need to do is give patients a tiny level of buzzing noise,” Clifford noted.
The new study was published in the Science journal on July 7, 2022.
