Background & Aims
New treatment approaches for chronic pain are urgently needed. As pain is associated with neuronal oscillations in the brain, their modulation might represent a novel treatment approach. As neuronal oscillations at alpha frequencies (8-13 Hz) are thought to represent a gating mechanism that shapes sensory processing [3] including pain [4 to 7], modulating alpha oscillations is a straightforward approach to modulate pain. Sensory entrainment is a non-invasive neuromodulation technique, where a subject is exposed to a rhythmic sensory stimulus to enhance neuronal oscillations at the applied frequency [9,10]. As proof-of-concept, this preregistered work (https://osf.io/2yurg), aimed to entrain alpha activity in the somatosensory cortex through rhythmic somatosensory stimuli. With accessibility and scalability in mind, we used transcutaneous electrical nerve stimulation (TENS), for which clinical devices are widely available, inexpensive, and already in use to alleviate pain [11 to 13].
Methods
31 healthy participants (all right-handed, µ age = 24.07, 17 f) received electrical stimulation through two electrodes at the left wrist [14] while brain activity was measured using EEG. In between two 5 min resting-state recordings, participants received three types of stimulation for 5 min with different stimulation frequencies: alpha regular (based on the individual alpha frequency (IAF)), beta (20 Hz), and alpha irregular (IAF triangularly changing within 2 Hz range). All stimulations were followed by one minute of rest to investigate post-stimulation effects. In addition, ratings of the perceived intensity of stimulations were gathered. After preprocessing [15] of the EEG data [16], power at the alpha regular stimulation frequency was estimated at electrodes CP3, CP5, and C3 during (online) and after (offline) stimulations. Power values and intensity ratings were statistically compared between stimulation types using one-sided Bayesian Wilcoxon signed-rank tests.
Results
Comparisons of percieved intensity ratings revealed very strong evidence that stimulation was perceived as stronger for beta stimulation than alpha regular (BF10 = 313.86) and alpha irregular (BF10 = 134.49) but evidence against a difference of ratings between alpha regular and alpha irregular (BF10 = 0.11). Next, we investigated potential online effects during the last 60 s of stimulation. Power at the alpha stimulation frequency was highest for the alpha regular stimulation (mean 437 mV^2), followed by alpha irregular (420 mV^2) and beta (332 mV^2). Moderate evidence in favor of higher power during alpha regular stimulation against beta was found (BF10= 7.20). While there was evidence against a difference between alpha regular and irregular (BF10 = 0.15), comparing alpha irregular against beta yielded anecdotal evidence (BF10 = 1.44). Corresponding offline analyses of the 60 s following stimulation mostly yielded inconclusive results (BF10 ranging from 0.31 to 0.8).
Conclusions
The current proof-of-concept study aimed to demonstrate entrainment of alpha oscillations in the somatosensory cortex using TENS in healthy participants. It revealed evidence that stimulating at the individual alpha frequency can enhance brain activity at the same frequency in the somatosensory cortex. Longer stimulation times might be needed to yield lasting effects after stimulation. Overall, we proved the feasibility of neuromodulating alpha activity in the somatosensory cortex. Thus, our work opens the way for further studies with a potential perspective for treatments of chronic pain, using a widely available and easily purchasable device that can be directly used at home.
References
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Presenting Author
Nicolò Bruna
Poster Authors
Nicolò Bruna
MSc
Klinikum Rechts der Isar
Lead Author
Elisabeth S. May
Dr.
Lead Author
Laura Tiemann Dr.
Lead Author
Cristina Gil Àvila
PhD
Lead Author
Felix Bott
Technical University of Munich
Lead Author
Markus Ploner
Technische Universitaet Munchen
Lead Author
Topics
- Treatment/Management: Interventional Therapies – Neuromodulation