Sound only works as a painkiller in mice if it is not much louder than the ambient noise. This is shown by new research, which also sheds more light on how this form of pain relief works in the brain.

It has been known for decades that music, or more broadly: sound, can relieve pain. But how exactly is still a mystery. A team of Chinese and American scientists lift a corner of the veil now with experiments in mice.

In these animals it appears to make little difference whether classical music, ‘sounding’ music or noise is heard. However, what the mice hear must be slightly louder than the ambient noise.

Furthermore, the researchers have shown for the first time that there is a connection between the brain area where sound is processed and the area that transmits all kinds of information from the nerves, including pain.

Remodeled classical music

To see whether the type of sound made a difference in mice, the researchers got their lab animals to hear classical music, the same music but then converted into an unpleasant-sounding whole, or ‘white noise’. That turned out to make no difference.

It mattered how loud that sound was. If it was 5 decibels louder than the ambient noise, it had an analgesic effect on the mice (which the researchers had caused inflamed paws). If, for example, the difference with the ambient noise was 10, 15 or 20 decibels, the mice would not benefit from the noise.

Interestingly, the pain-relieving effect persisted for a few days after the mice were exposed to noise that was 5 decibels louder than the ambient noise. According to the researchers, this shows that the noise did not simply distract or calm the mice.

The Utrecht Central of the brain

The next question the researchers tackled was: what happens in the brain when mice hear a pain-relieving sound? Using non-infectious viruses containing luminescent proteins, they visualized a pathway of the auditory cortexwhere sounds are processed, to the thalamus†

That last brain region describes Bert Joostenprofessor of experimental anesthesiology and pain management at Maastricht University, as “the Utrecht Central Station of the brain: a kind of train station where almost all information from the nerve network, including pain stimuli, somehow converges or passes through”.

Joosten calls the fact that the researchers have shown a connection between auditory cortex and thalamus “an interesting and important finding, which helps us understand how sound can influence pain stimuli”.

New Pain Treatments

Now, of course, mice are not humans. “Mice have a very different sound range than humans,” says Joosten. “That way they can hear high tones that we don’t.” It is also easy to imagine that we react differently to music that we have learned to appreciate during our lives than animals.

The researchers themselves state that the mechanisms in the brain by which music can relieve pain in humans “are undoubtedly more complicated than in mice”. In humans, for example, there are all kinds of other brain areas involved in pain processing that are known to respond to music.

As a result, the conclusions from this study cannot simply be applied to humans. Nevertheless, the scientists express the hope that their research can contribute to the development of new pain treatments.