Supraspinal neural mechanisms of the analgesic effect produced by transcutaneous electrical nerve stimulation

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ORIGINAL ARTICLE

Supraspinal neural mechanisms of the analgesic effect produced by transcutaneous electrical nerve stimulation Yanzhi Bi1,2 · Zhaoxing Wei2,3 · Yazhuo Kong2,3 · Li Hu1,2,4 Received: 11 December 2019 / Accepted: 9 November 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract Although the analgesic effects of conventional transcutaneous electrical nerve stimulation (TENS) and acupuncture-like TENS are evident, their respective neural mechanisms in humans remain controversial. To elucidate and compare the supraspinal neural mechanisms of the analgesic effects produced by conventional TENS (high frequency and low intensity) and acupuncture-like TENS (low frequency and high intensity), we employed a between-subject sham-controlled experimental design with conventional, acupuncture-like, and sham TENS in 60 healthy human volunteers. In addition to assessing the TENS-induced changes of subjective ratings of perceived pain, we examined the TENS associated brainstem activities (fractional amplitude of low frequency fluctuations, fALFF) and their corresponding resting state functional connectivity (RSFC) with higher-order brain areas using functional magnetic resonance imaging. The analgesic effect of conventional TENS was only detected in the forearm that received TENS, coupled with decreased pons activity and RSFC between pons and contralateral primary somatosensory cortex. In contrast, acupuncture-like TENS produced a spatially diffuse analgesic effect, coupled with increased activities in both subnucleus reticularis dorsalis (SRD) and rostral ventromedial medulla (RVM), and decreased RSFC between SRD and medial frontal regions as well as between SRD and lingual gyrus. To sum up, our data demonstrated that conventional TENS and acupuncture-like TENS have different analgesic effects, which are mediated by different supraspinal neural mechanisms. Keywords  Transcutaneous electrical nerve stimulation (TENS) · Pain · Functional magnetic resonance imaging (fMRI) · Analgesic effect · Subnucleus reticularis dorsalis (SRD) · Rostral ventromedial medulla (RVM)

Introduction Through delivering electrical pulses to activate peripheral somatosensory afferents, transcutaneous electrical nerve stimulation (TENS) has been widely offered as a noninvasive and non-addictive pain treatment in various acute * Li Hu [email protected] 1



CAS Key Laboratory of Mental Health, Institute of Psychology, Chinese Academy of Sciences, Beijing, China

2



Department of Psychology, University of Chinese Academy of Sciences, Beijing, China

3

CAS Key Laboratory of Behavioral Science, Institute of Psychology, Chinese Academy of Sciences, Beijing, China

4

Department of Pain Management, The State Key Clinical Specialty in Pain Medicine, The Second Affiliated Hospital of Guangzhou Medical University, Guangzhou, China



and chronic pain conditions (Hurlow et al. 2012; Johnson 2007; Mokhtari et al. 2020; Nnoaham and Kumbang 2008; Sluka and Walsh 2003; von Deneen et al. 2020). In practice, TENS can be implemented