Brain network hubs in the somatosensory cortex display differing provincial and connector qualities in bipolar disorder

Brain regions rarely act independently but form functional networks to address specific tasks. Recent studies suggest that psychiatric illnesses are associated with impaired functional integration across large-scale brain networks. ‘Hubs’ are brain regions that are highly connected to widespread areas of the brain, serving as important relay stations, or integrate information from specialized brain networks. The aim of this study was to investigate brain hub functioning in the somatomotor network in clinically remitted bipolar patients.We analyzed resting-state fMRI data from 96 euthymic individuals with bipolar disorder and 61 healthy control individuals. We characterized the hub quality of a-priori defined regions of interest in relation to within- or between-network integration. Provincial hubs mainly integrate information within their own brain network while connector hubs share information between different brain networks. In a novel time-varying analysis, we determined if hubs follow the trajectory of their own brain network or aberrantly follow other brain networks. In healthy controls, we found that the somatomotor network comprised mainly provincial hubs. In bipolar disorder patients by contrast, hubs located in the primary somatosensory cortex displayed weaker provincial hub function or had more connector hub qualities. Furthermore, hubs in bipolar disorder showed weaker allegiances with their own brain network and started following the trajectories of the limbic, the salience, and the frontoparietal network. Our findings suggest that these hub aberrancies possibly contribute to previously shown functional connectivity alterations in bipolar disorder and may thus constitute the neural substrate to persisting impairments in sensory integration despite clinical remission.