Altered Scale-Free Dynamics of Spontaneous Brain Activity in Post-Traumatic Stress Disorder: Relationship to Impaired Functional Connectivity

Objective: Post-traumatic stress disorder (PTSD) has been linked to reduced functional brain connectivity, but it is unclear if altered local network properties contribute to these disruptions in functional coupling. Computational studies have demonstrated that dynamical states characterized by scale-free local activity optimize the long-range functional coupling in neuronal networks. Our study uses resting-state magnetoencephalographic recordings to investigate if characteristics of scale-free dynamics of local cortical activity are associated with alterations in long-range functional connectivity in PTSD. Methods: Participants (n = 96) were service members with combat exposure and various levels of post-traumatic stress severity (PTSS). We estimated the amplitude envelopes of beta-band cortical activity in 134 cortical regions and we characterized their scale-free dynamics using the power-law scaling exponent determined by detrended fluctuation analysis. We assessed the correlation between PTSS, scaling exponents, and functional coupling between homologous anatomical areas of the two hemispheres. Results: We found negative correlations between PTSS and scaling exponents as well as between PTSS and inter-hemispheric coupling (IHC) predominantly in prefrontal and temporal regions. Positive correlations between scaling exponents and IHC were present in a large number of regions, with high correlations across primary and unimodal association cortices and lower correlations across high-order heteromodal processing areas. Conclusions: Our findings suggest that mechanisms that regulate scale-free dynamics of local cortical activity may contribute to alterations of long-range functional connectivity in PTSD. Significance: Therapies with the potential to normalize local scale-free brain activity may lead to the restoration of functional brain connectivity, offering a promising avenue for PTSD treatment.