Targeting the Autonomic Nervous System Balance in Patients with Chronic Low Back Pain using Transcranial Alternating Current Stimulation: A Randomized, Crossover, Double-Blind, Placebo-Controlled Pilot Study

Abstract

BackgroundChronic low back pain (CLBP) is characterized by an alteration in pain processing by the central nervous system that may affect autonomic nervous system (ANS) balance. Heart rate variability (HRV) reflects the balance of parasympathetic and sympathetic ANS activation. In particular, respiratory sinus arrhythmia (RSA) solely reflects parasympathetic input and is reduced in CLBP patients. Yet, it remains unknown if non-invasive brain stimulation can alter ANS balance in CLBP patients.ObjectiveTo evaluate if non-invasive brain stimulation modulates the ANS, we analyzed HRV metrics collected in a previously published study of transcranial alternating current stimulation (tACS) for the modulation of CLBP through enhancing alpha oscillations. We hypothesized that tACS would increase RSA.MethodsA randomized, crossover, double-blind, sham-controlled pilot study was conducted to investigate the effects of 10Hz-tACS on metrics of ANS balance calculated from electrocardiogram (ECG). ECG data were collected for 2 minutes before and after 40 minutes of 10Hz-tACS or sham stimulation.ResultsThere were no significant changes in RSA or other frequency-domain HRV components from 10Hz-tACS. However, exploratory time-domain HRV analysis revealed a significant increase in the standard deviation of normal RR intervals (SDNN) for 10Hz-tACS relative to sham.Conclusion(s)Although tACS did not significantly increase RSA, we found in an exploratory analysis that tACS modulated an integrated HRV measure of both ANS branches. These findings support the further study of how the ANS and alpha oscillations interact and are modulated by tACS.

Modulating Brain Rhythms of Pain using Transcranial Alternating Current Stimulation (tACS)? A Sham-controlled Study in Healthy Human Participants

“…Bayesian statistics to strengthen the interpretability of negative findings [7]. However, complementing the weak tACS effects on pain in previous studies [1,5,35], we did not find significant tACS effects on tonic experimental pain in healthy human participants.…”

“…However, tACS induced changes of alpha activity which correlated with pain intensity [1]. In addition, exploratory analyses of autonomic activity recorded in this study indicated that heart rate variability was increased [35]. Our study extends these findings in two important aspects.…”

“…However, just like any single chronic pain treatment approach, tACS will likely not represent a stand-alone treatment but rather a valuable part of a combined bio-psycho-social treatment approach. Based on the present and previous studies [1,5,35], the most promising target for future tACS studies are alpha oscillations in somatosensory cortices. Supplementary Fig.…”

“…To assess tACS effects on longer-lasting pain, we applied a tonic heat pain paradigm which resembles chronic pain conditions more closely than usual phasic pain stimuli [32]. Based on previous evidence on the role of neural oscillations in the processing of pain [1,5,24,27,30,35,39], we systematically applied tACS at alpha and gamma oscillations over somatosensory and prefrontal cortices in healthy human participants. To control for unspecific tACS effects, we additionally performed sham stimulation at both locations.…”