Fig. 1. Regional abnormalities of baseline (pre-treatment) BOLD signal variability (SD_BOLD) in fibromyalgia (FM) compared to healthy controls (HC).

(A) Baseline group differences of resting-state SD_BOLD in the slow-5 (0.01 – 0.027 Hz) and slow-4 (0.027 – 0.073 Hz) frequency bands. Blue (FM) and black lines (HC) indicate the representative time-course of band-pass filtered BOLD signal in each slow frequency band. Brain regions displaying increased (hot scale bar) and decreased (cool scale bar) SD_BOLD in FM patients compared with HC were overlaid on the MNI standard brain. All statistical images are displayed with significant clusters (voxel-level threshold p < 0.001 and cluster-level extent threshold p < 0.025, FWE-corrected*). Grey bars represent FM patients (n = 12), white bars represent HC subjects (n = 15). Bar graphs were expressed as mean ± standard error of the mean. (B) Correlation between baseline SD_BOLD (slow-5 and slow-4) in the ventromedial prefrontal cortex (vmPFC) and changes in VAS pain score between active-tDCS and baseline. Higher SD_BOLD of the vmPFC at baseline predicted a greater reduction in clinical pain. VAS, visual analog scale; aINS, anterior insula; pINS, posterior insula; S2, secondary somatosensory cortex.