It's the Sound not the Pulse: Peripheral Magnetic Stimulation Reduces Central Sensitization through Auditory Modulatory Effects

Repetitive peripheral magnetic stimulation (rPMS) is a non-pharmacological, non-invasive analgesic modality with limited side effects. However, there is a paucity of controlled studies demonstrating its efficacy compared to existing pain management tools. Here, in an initial sample of 100 healthy participants (age 18-40), we compared the analgesic efficacy of two rPMS stimulation protocols--continuous theta burst stimulation (ctbPMS) and intermittent TBS (itbPMS)--against transcutaneous electric nerve stimulation (TENS), a peripheral stimulation technique that is commonly used for pain management. We also included a sham rPMS protocol where participants heard the sound of rPMS stimulation while the coil was placed over their arm, but received no peripheral stimulation. We hypothesized that itbPMS and ctbPMS--but not sham--would reduce pain intensity, pain unpleasantness, and secondary hyperalgesia evoked by a phasic heat pain (PHP) paradigm on the volar forearm with similar efficacy to TENS. Neither rPMS nor TENS reduced reported pain intensity or unpleasantness (p>0.25). However, ctbPMS and itbPMS significantly reduced the area of secondary hyperalgesia, whereas TENS did not (F3,96= 4.828, p= 0.004). Unexpectedly, sham rPMS, which involved auditory but no peripheral nerve stimulation, also significantly reduced secondary hyperalgesia compared to TENS. We performed a second study (n=32) to investigate auditory contributions to rPMS analgesia. Masking the rPMS stimulation sound with pink noise eliminated its analgesic effect on secondary hyperalgesia (p=0.5). This is the first study to show that the analgesic properties of rPMS in acute experimental pain may be largely attributed to its auditory component rather than peripheral nerve stimulation.