Background & Aims
The mechanisms through which pain arises from human brain activity have not yet been unraveled. It has been suggested that ongoing oscillatory activity could have a crucial role in the experience of pain. Previous studies from our lab, along with other significant research, have highlighted that altered theta and alpha oscillations could be related to pain perception1-9. Changes in alpha oscillations, in particular an increase in low-alpha activity, have been consistently reported in those suffering from chronic pain7-9. However, no line of research has yet clarified whether pain emerges from the modulation of these neural oscillations. Recent advances in neuromodulation techniques have provided new opportunities for understanding and manipulating these oscillatory activities10-14. The main goal of this study is to assess whether there is a causal link between ongoing neural oscillations and pain perception using transcranial alternating current stimulation (tACS) neuromodulation.
Methods
We used tACS to modulate ongoing oscillatory activities measured using scalp electroencephalography (EEG), with the aim of evaluating how this affects pain. To induce pain perception, we used sustained and periodic 0.2 Hz thermonociceptive stimuli (temperature baseline and peak were set to 35°C and 50.5°C, respectively)6 . tACS was delivered using a Starstim tES-EEG device that facilitates the switching between EEG recording and tACS stimulation protocols. The stimulation targeted the sensorimotor area of the contralateral dominant hand. We applied a high-definition montage (4X1) to achieve a more focal stimulation compared to standard tACS protocols. We explored the hypothesis that tACS can modulate pain perception by modulating EEG ongoing oscillations at alpha frequency bands, consistently associated with pain perception. The exact frequency of stimulation was set to the individual peak alpha frequency (PAF)7,8. A sham stimulation was used as a control condition.
Results
To this date, data was acquired from 15 healthy volunteers. A total of 40 participants will be tested before the IASP conference. Because the study is performed double-blind, only preliminary analyses that do not concern the effects of tACS on pain perception and neural oscillations could be performed at this point. On average warm detection threshold (WDT) before stimulation was 38.7°C ± 3.7°C and heat pain threshold (HPT) was 47.2°C ± 2.4°C. Also, the average PAF value before tACS was 10.07 Hz ± 0.16 Hz. In the EEG data recorded prior to tACS stimulation, the frequency-tagging related peaks were mostly observed in posterior and sensorimotor areas, including locations at or close to the stimulation target. Data collection is ongoing, and the full study will be presented at the conference. Analysis of these peaks after stimulation will enable us to better understand the connection between brain oscillations and pain.
Conclusions
This study investigates the causal relationship between pain perception and ongoing neural oscillations using tACS. Despite not being able to disclose preliminary results on the effects of tACS due to our double-blind protocol, the observed interindividual variability in baseline thresholds and PAF underscores the potential value of personalized strategies for understanding and managing pain. Analyses on the complete dataset will clarify the role of individual differences in neuromodulation efficacy and inform the development of targeted, oscillation-based pain management strategies.
References
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