title: Post-Traumatic Stress Constrains the Dynamic Repertoire of Neural Activity.
abstract: Post-traumatic stress disorder (PTSD) is an anxiety disorder arising from exposure to a traumatic event. Although primarily defined in terms of behavioral symptoms, the global neurophysiological effects of traumatic stress are increasingly recognized as a critical facet of the human PTSD phenotype. Here we use magnetoencephalographic recordings to investigate two aspects of information processing: inter-regional communication (measured by functional connectivity) and the dynamic range of neural activity (measured in terms of local signal variability). We find that both measures differentiate soldiers diagnosed with PTSD from soldiers without PTSD, from healthy civilians, and from civilians with mild traumatic brain injury, which is commonly comorbid with PTSD. Specifically, soldiers with PTSD display inter-regional hypersynchrony at high frequencies (80-150 Hz), as well as a concomitant decrease in signal variability. The two patterns are spatially correlated and most pronounced in a left temporal subnetwork, including the hippocampus and amygdala. We hypothesize that the observed hypersynchrony may effectively constrain the expression of local dynamics, resulting in less variable activity and a reduced dynamic repertoire. Thus, the re-experiencing phenomena and affective sequelae in combat-related PTSD may result from functional networks becoming "stuck" in configurations reflecting memories, emotions, and thoughts originating from the traumatizing experience.
  
  
  CONCLUSIONS
  The present study investigates the effects of post-traumatic stress disorder (PTSD) in combat-exposed soldiers. We find that soldiers with PTSD exhibit hypersynchrony in a circuit of temporal lobe areas associated with learning and memory function. This rigid functional architecture is associated with a decrease in signal variability in the same areas, suggesting that the observed hypersynchrony may constrain the expression of local dynamics, resulting in a reduced dynamic range. Our findings suggest that the re-experiencing of traumatic events in PTSD may result from functional networks becoming locked in configurations that reflect memories, emotions, and thoughts associated with the traumatic experience.
authors.affiliation: Department of Psychological and Brain Sciences, Indiana University, Bloomington, Indiana 47405, bmisic@indiana.edu.
authors.forename: Bratislav
authors.initials: B
authors.lastname: Mišić
authors.affiliation: Department of Diagnostic Imaging, Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada.
authors.forename: Benjamin T
authors.identifier: http://orcid.org/0000-0001-6173-1171
authors.initials: BT
authors.lastname: Dunkley
authors.affiliation: Directorate of Mental Health, Canadian Forces Health Services, Ottawa, Ontario K1K 0T2, Canada.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Sedge
authors.affiliation: Division of Neurosurgery, Sunnybrook Hospital, Toronto, Ontario M4N 3M5, Canada.
authors.forename: Leodante
authors.initials: L
authors.lastname: Da Costa
authors.affiliation: Research Institute, Baycrest Centre, Toronto, Ontario M6A 2E1, Canada.
authors.forename: Zainab
authors.initials: Z
authors.lastname: Fatima
authors.affiliation: Department of Psychology, University of Chicago, Chicago, Illinois 60637.
authors.forename: Marc G
authors.initials: MG
authors.lastname: Berman
authors.affiliation: Department of Diagnostic Imaging, Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada.
authors.forename: Sam M
authors.initials: SM
authors.lastname: Doesburg
authors.affiliation: Research Institute, Baycrest Centre, Toronto, Ontario M6A 2E1, Canada.
authors.forename: Anthony R
authors.initials: AR
authors.lastname: McIntosh
authors.affiliation: Canadian Forces Environmental Medicine Establishment, Toronto, Ontario M3K 2C9, Canada, and.
authors.forename: Richard
authors.initials: R
authors.lastname: Grodecki
authors.affiliation: Defence Research and Development Canada, Toronto, Ontario N3K 2C9, Canada.
authors.forename: Rakesh
authors.initials: R
authors.lastname: Jetly
authors.affiliation: Department of Diagnostic Imaging, Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada.
authors.forename: Elizabeth W
authors.initials: EW
authors.lastname: Pang
authors.affiliation: Department of Psychological and Brain Sciences, Indiana University, Bloomington, Indiana 47405.
authors.forename: Margot J
authors.initials: MJ
authors.lastname: Taylor
mesh_terms: D000328:Adult; D000465:Algorithms; D001683:Biological Clocks; D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping; D016022:Case-Control Studies; D019277:Entropy; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D008889:Military Personnel; D017711:Nonlinear Dynamics; D013057:Spectrum Analysis; D013313:Stress Disorders, Post-Traumatic / Q000473:pathology*
keywords: MEG; PTSD; TBI; connectivity; dynamics; network