Insula functional connectivity at EEG resting-state as a biomarker linked to pain processing and severity of clinical symptoms in fibromyalgia

Brain areas and oscillations have been pointed out as markers of chronic pain. We used electroencephalography (EEG) to compare the linear and non-linear connectivity of regions of interest (ROIs) related to the pain matrix in people with fibromyalgia (FM) and healthy controls (HC). Sixty-four women (49 FM and 15 HC) volunteered to participate in a resting-state EEG session with eyes open (EO) and eyes closed (EC), as well as clinical, psychological, and serum brain-derived neurotrophic factor (BDNF). The connectivity of 10 ROIs was computed for 7 different EEG frequencies. In EC conditions, FM exhibits decreased non-linear connectivity in the beta-2 band between the right-insula and left mPFC (F=-4.09, p = .035). Considering the differences between EO and EC, FM present increased linear connectivity between the left insula and right thalamus in the beta-3 band (F = 3.46, p = .009 ) and increased non-linear connectivity between the right insula and left medial prefrontal cortex (mPFC) in the beta-2 band (F = 3.78, p = .025 ). These results mainly indicate the insula role in different circuits in FM and highlight the beta oscillations activity. Insular brain connectivity at rest could be an objective biomarker of how pain is processed, and it is related to the severity of clinical symptoms in fibromyalgia.