Individually unique dynamics of cortical connectivity reflect the ongoing intensity of chronic pain

Chronic pain diseases are characterised by an ongoing and fluctuating endogenous pain, yet it remains to be elucidated how this is reflected by the dynamics of ongoing functional cortical connections. In this study, we investigated the cortical encoding of 20 patients with chronic back pain and 20 chronic migraineurs in 4 repeated fMRI sessions. A brain parcellation approach subdivided the whole brain into 408 regions. Linear mixed-effects models were fitted for each pair of brain regions to explore the relationship between the dynamic cortical connectivity and the observed trajectory of the patients' ratings of fluctuating endogenous pain. Overall, we found that periods of high and increasing pain were predominantly related to low cortical connectivity. The change of pain intensity in chronic back pain was subserved by connections in left parietal opercular regions, right insular regions, as well as large parts of the parietal, cingular, and motor cortices. The change of pain intensity direction in chronic migraine was reflected by decreasing connectivity between the anterior insular cortex and orbitofrontal areas, as well as between the PCC and frontal and anterior cingulate cortex regions. Of interest, the group results were not mirrored by the individual patterns of pain-related connectivity, which rejects the idea of a common neuronal core problem for chronic pain diseases. The diversity of the individual cortical signatures of chronic pain encoding results adds to the understanding of chronic pain as a complex and multifaceted disease. The present findings support recent developments for more personalised medicine.