Hyperconnectivity and High Temporal Variability of the Primary Somatosensory Cortex in Low-Back-Related Leg Pain: An fMRI Study of Static and Dynamic Functional Connectivity

OBJECTIVE: To investigate the functional connectivity (FC) and its variability in the primary somatosensory cortex (S1) of patients with low-back-related leg pain (LBLP) in the context of the persistent stimuli of pain and numbness. PATIENTS AND METHODS: We performed functional magnetic resonance imaging on LBLP patients (n = 26) and healthy controls (HCs; n = 34) at rest. We quantified and compared static FC (sFC) using a seed-based analysis strategy, with 6 predefined bilateral paired spherical regions of interest (ROIs) in the S1 cortex. Then, we captured the dynamic FC using sliding window correlation of ROIs in both the LBLP patients and HCs. Furthermore, we performed a correlational analysis between altered static and dynamic FC and clinical measures in LBLP patients. RESULTS: Compared with controls, the LBLP patients had 1) significantly increased static FC between the left S1(back) (the representation of the back in the S1) and right superior and middle frontal gyrus (SFG/MFG), between the left S1(chest) and right SFG/MFG, between right S1(chest) and right SFG/MFG, between the left S1(face) and right MFG, and between the right S1(face) and right inferior parietal lobule (P < 0.001, Gaussian random field theory correction); 2) increased dynamic FC only between the right S1(finger) and the left precentral and postcentral gyrus and between the right S1(hand) and the right precentral and postcentral gyrus (P < 0.01, Gaussian random field theory correction); and 3) a negative correlation between the Barthel index and the increased static FC between the left S1(face) and right inferior parietal lobule (P = 0.048). CONCLUSION: The present study demonstrated the hyperconnectivity of the S1 cortex to the default mode and executive control network in a spatial pattern and an increase in the tendency for signal variability in the internal network connections of the S1 cortex in patients with LBLP.