753: Theta Oscillations in Fibromyalgia: Repetition-Related Rather Than tACS-Specific Effects

Topic: Experimental (Non-clinical) Human Studies
Subtopic: Pain Category (ICD-11), Chronic widespread pain, Neuromodulation (e.g. rTMS, tDCS, FUS, DBS, biofeedback)

Background and Aims: Background: Fibromyalgia is increasingly understood as a disorder involving altered central pain processing, with pain-related, affective, and cognitive dimensions interacting in the central nervous system. Neuroimaging studies highlight the relevance of regions involved in pain processing, including somatosensory, prefrontal, cingulate, and insular areas, although findings remain heterogeneous across modalities and designs. Theta-band activity is also closely linked to cognitive control and task demands, with frontal-midline theta increasing when greater control is required. Transcranial alternating current stimulation may influence cortical oscillations in a frequency-specific manner, making it a candidate tool for probing oscillatory mechanisms in chronic pain.
Objective: This study examined whether tACS modulates theta-band event-related oscillations during an implicit affective-cognitive task in patients with fibromyalgia.

Methods: A total of 105 patients with fibromyalgia participated in the study. Participants were assigned to one of three stimulation conditions: 4-Hz tACS, 10-Hz tACS, or sham stimulation. Stimulation was delivered for 20 minutes at 1 mA over F3/F4. EEG was recorded before and after stimulation while participants performed a color-detection task. In this task, emotional faces were presented as task-irrelevant distractors: each face expressed neutral, pain, anger, or happy emotion and appeared inside a colored rectangular frame. Participants were instructed to ignore the facial expression and respond to the frame color as quickly and accurately as possible. Event-related oscillatory activity in the 4–8 Hz range was examined using wavelet-based analyses across different regions of interest and time windows, including 0–500 ms, 50–250 ms, and 250–500 ms.

Results: Across the analyzed regions of interest and time windows, significant main effects of Time were observed, indicating that theta-band event-related oscillatory activity changed from the pre- to post-stimulation assessment. However, no significant Time × Group interactions were found. Thus, the magnitude of pre–post change did not differ reliably between the 4-Hz, 10-Hz, and sham groups.

Conclusions: In this sample of patients with fibromyalgia, theta-band event-related oscillatory activity changed between the first and second task administration. However, because these changes were not specific to active stimulation and did not differ between stimulation groups, the findings do not support a frequency-specific effect of tACS on theta-band responses in the present task. A more plausible interpretation is that the observed Time effects reflect repetition-related processes, such as practice, habituation, or changes in cognitive engagement across repeated exposure to the task.

References: Müller, M., Wüthrich, F., Federspiel, A., Wiest, R., Egloff, N., Reichenbach, S., Exadaktylos, A., Jüni, P., Curatolo, M., & Walther, S. (2021). Altered central pain processing in fibromyalgia—A multimodal neuroimaging case-control study using arterial spin labelling. PLOS ONE, 16(2), Article e0235879. https://doi.org/10.1371/journal.pone.0235879
Eisma, J., Rawls, E., Long, S., Mach, R., & Lamm, C. (2021). Frontal midline theta differentiates separate cognitive control strategies while still generalizing the need for cognitive control. Scientific Reports, 11, Article 14641. https://doi.org/10.1038/s41598-021-94162-z
Herrmann, C. S., Rach, S., Neuling, T., & Strüber, D. (2013). Transcranial alternating current stimulation: A review of the underlying mechanisms and modulation of cognitive processes. Frontiers in Human Neuroscience, 7, Article 279. https://doi.org/10.3389/fnhum.2013.00279
Antal, A., & Paulus, W. (2013). Transcranial alternating current stimulation (tACS). Frontiers in Human Neuroscience, 7, Article 317. https://doi.org/10.3389/fnhum.2013.00317
Crivelli-Decker, J., Hsieh, L.-T., Clarke, A., & Ranganath, C. (2018). Theta oscillations promote temporal sequence learning. Neurobiology of Learning and Memory, 153, 92–103. https://doi.org/10.1016/j.nlm.2018.05.001

Presenting Author: Behzad Rostami Sani
Submitting Author: Behzad Rostami Sani

Senior Author: Pedro José Montoya Jiménez

IASP 2026 Global Year theme of Neuropathic Pain: Yes

• Daniel Cabello Coscarón: MSc - University of the Balearic Islands(UIB)
• Juan Lorenzo Terrasa Navarro: PhD - University of the Balearic Islands(UIB)
• Ana María González Roldán: PhD - University of the Balearic Islands(UIB)
• Pedro José Montoya Jiménez: PhD - University of the Balearic Islands(UIB)