Introduction
How stronger threat reshapes large-scale brain network organization remains untested. Heightened arousal via sympathetic activation has been proposed to increase functional integration, but no study has directly tested this (1-3). We compared two equivalent heat pain stimuli, a static ramp-and-hold and a dynamically escalating profile, the latter more strongly engaging pain, threat, and reward-punishment circuitry (Sunavsky, in review).
Methods
In 30 participants, we extracted epochs spanning 39 TRs from different stimulus conditions and computed region-to-region functional connectivity across a 131-node parcellation. Matrices were proportionally thresholded (0.05 to 0.5) and characterized using graph metrics: system segregation, Louvain modularity, nodal degree, and participation coefficient (4). Conditions were compared with paired t-tests at each threshold, FDR-corrected across all nodes and thresholds.
Results
Dynamically escalating threat reduced system segregation relative to the static condition, consistent with greater between-network integration under heightened arousal. Whole-brain FDR-corrected analysis showed increased participation coefficient in bilateral secondary somatosensory cortex (S2, parietal operculum), indicating stronger cross-network connector behavior. Among regions more strongly activated by the dynamic stimulus, only S2 and nucleus accumbens also showed increased hubness (binarized degree). Modularity did not differ between conditions.
Discussion
Escalating threat shifts network organization toward integration rather than reconfiguring module structure, since segregation fell while modularity was preserved. The convergence of higher participation and degree at S2 identifies it as a key integrative hub recruited by dynamic threat, with the accumbens implicating reward-punishment circuitry. These findings provide direct evidence that arousal-linked threat promotes functional integration in the human brain.
References
1. Shine, J.M., Bissett, P.G., Bell, P.T., Koyejo, O., Balsters, J.H., Gorgolewski, K.J., Moodie, C.A., & Poldrack, R.A. (2016). The dynamics of functional brain networks: integrated network states during cognitive task performance. Neuron, 92(2), 544-554.
2. Shine, J.M. (2019). Neuromodulatory influences on integration and segregation in the brain. Trends in Cognitive Sciences, 23(7), 572-583.
3. Chan, M.Y., Park, D.C., Savalia, N.K., Petersen, S.E., & Wig, G.S. (2014). Decreased segregation of brain systems across the healthy adult lifespan. Proceedings of the National Academy of Sciences, 111(46), E4997-E5006.
4. Rubinov, M., & Sporns, O. (2010). Complex network measures of brain connectivity: uses and interpretations. NeuroImage, 52(3), 1059-1069.
Acknowledgement
\nCanadian Institute of Health Research (CIHR) Project Grant [PJT-168878]* \nNSHA Fibromyalgia Research Fibromyalgia Grant*
