[Non-invasive electrical neuromodulation techniques: analgesic effects and neural mechanisms]

As non-pharmaceutical interventions, non-invasive electrical neuromodulation techniques are promising in pain management. With many advantages, such as low costs, high usability, and non-invasiveness, they have been exploited to treat multiple types of clinical pain. Proper use of these techniques requires a comprehensive understanding of how they work. In this article, we reviewed recent studies concerning non-invasive electrical peripheral nerve stimulation (transcutaneous electrical nerve stimulation and transcutaneous vagus/vagal nerve stimulation) as well as electrical central nerve stimulation (transcranial direct current stimulation and transcranial alternating current stimulation). Specifically, we discussed their analgesic effects on acute and chronic pain, and the neural mechanisms thereof. We then contrasted the four kinds of nerve stimulation techniques, pointing out limitations of existing studies and proposing directions for future research. With more extensive and in-depth research to overcome these limitations, we shall witness more clinical applications of non-invasive electrical nerve stimulations to alleviate patients' pain and ease the crippling medical and economic burden imposed on patients, their families, and the entire society.