Scientists discover why soft sounds relieve pain

(ORDO NEWS) — Experiments on mice have shown that a low sound background reduces the activity of the thalamus and reduces the response to painful stimuli.

Even more than half a century ago, doctors noticed that playing music during dental operations relieves pain so much that some patients did not even need conventional anesthesia.

Perhaps, this effect is familiar to everyone – it is not without reason that parents soothe suffering babies with the softest voice they are capable of.

It attracts great interest from scientists, and since then they have repeatedly confirmed that music can relieve both acute and chronic pain. To find out the mechanisms underlying such a reaction, American neuroscientists set up experiments.

Yuanyuan Liu and her colleagues conducted experiments on laboratory mice. For 20 minutes, they played pleasant (at least for the human ear) music – the overture Rejouissance (“Fun”) to the orchestral suite by Johann Sebastian Bach.

The sound volume varied from 50 to 60 decibels, while the background noise in the room was 45 decibels. In the limbs, the mice were given injections with different strengths. If the animal pulled away or began to lick the paw, this indicated that it felt pain.

Experiments showed that if the music sounded quiet enough, then for a pain reaction it was necessary to act on the paw three times stronger than without it. And if the play was played loudly, the sensitivity to pricks remained the same as without music.

Moreover, a similar effect was observed with the sound of “ugly”, atonal music (the same overture, but specially processed on a computer) and even with the usual “white noise”, if only it was a little louder than the background sounds.

The experiments were repeated using fluorescent dyes and microelectrodes, which made it possible to monitor the brain activity of the experimental mice.

As it turned out, soft sounds reduce the flow of signals coming from the auditory cortex to the thalamus – the area where the integration of sensory data takes place. Indeed, if the connection between these parts of the brain was artificially blocked, the animals showed a weakened response to pain stimuli.

The scientists concluded that a low sound background reduces the activation of the thalamus by signals from the neurons of the auditory cortex, reducing the intensity of pain sensations.

Perhaps in the future such “sound anesthesia” will find application in real medical practice. But for now, the authors plan to investigate its effects in humans by monitoring thalamic activity using MRI.

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