title: Switching between executive and default mode networks in posttraumatic stress disorder: alterations in functional connectivity.
abstract: Working memory processing and resting-state connectivity in the default mode network are altered in patients with posttraumatic stress disorder (PTSD). Because the ability to effortlessly switch between concentration on a task and an idling state during rest is implicated in both these alterations, we undertook a functional magnetic resonance imaging study with a block design to analyze task-induced modulations in connectivity.
  
  
  METHODS
  We performed a working memory task and psychophysiologic interaction analyses with the posterior cingulate cortex and the medial prefrontal cortex as seed regions during fixation in 12 patients with severe, chronic PTSD and 12 healthy controls.
  
  
  RESULTS
  During the working memory task, the control group showed significantly stronger connectivity with areas implicated in the salience and executive networks, including the right inferior frontal gyrus and the right inferior parietal lobule. The PTSD group showed stronger connectivity with areas implicated in the default mode network, namely enhanced connectivity between the posterior cingulate cortex and the right superior frontal gyrus and between the medial prefrontal cortex and the left parahippocampal gyrus.
  
  
  CONCLUSIONS
  Because we were studying alterations in patients with severe, chronic PTSD, we could not exclude patients taking medication. The small sample size may have limited the power of our analyses. To avoid multiple testing in a small sample, we only used 2 seed regions for our analyses.
  
  
  CONCLUSIONS
  The different patterns of connectivity imply significant group differences with task-induced switches (i.e., engaging and disengaging the default mode network and the central-executive network).
authors.affiliation: Department of Psychiatry, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ont., Canada.
authors.forename: Judith K
authors.initials: JK
authors.lastname: Daniels
authors.forename: Alexander C
authors.initials: AC
authors.lastname: McFarlane
authors.forename: Robyn L
authors.initials: RL
authors.lastname: Bluhm
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: Moores
authors.forename: C Richard
authors.initials: CR
authors.lastname: Clark
authors.forename: Marnie E
authors.initials: ME
authors.lastname: Shaw
authors.forename: Peter C
authors.initials: PC
authors.lastname: Williamson
authors.forename: Maria
authors.initials: M
authors.lastname: Densmore
authors.forename: Ruth A
authors.initials: RA
authors.lastname: Lanius
mesh_terms: D000328:Adult; D056344:Executive Function / Q000502:physiology*; D005260:Female; D006179:Gyrus Cinguli / Q000503:physiopathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology; D008875:Middle Aged; D009415:Nerve Net / Q000473:pathology*; D020534:Parahippocampal Gyrus / Q000502:physiology; D010296:Parietal Lobe / Q000502:physiology; D017397:Prefrontal Cortex / Q000502:physiology; D011569:Psychiatric Status Rating Scales; D013313:Stress Disorders, Post-Traumatic / Q000503:physiopathology* / Q000523:psychology*