title: Graph theory reveals hyper-functionality in visual cortices of Seasonal Affective Disorder patients.
abstract: OBJECTIVE
  Seasonal affective disorder (SAD) is a subtype of recurrent unipolar or bipolar depressive disorder with a higher prevalence in winter than in summer. The biological underpinnings of SAD are so far poorly understood. Studies examining SAD have found disturbances between the molecular and connectivity scales. The aim of the study was to explore changes in functional connectivity typical for SAD.
  
  
  METHODS
  We investigated unmedicated, untreated SAD patients and healthy controls using resting-state functional magnetic resonance imaging (rs-fMRI) utilizing graph theory, a data driven and hypothesis free approach, to model functional networks of the brain.
  
  
  RESULTS
  Comparing whole brain network properties using graph theory we observed globally affected network topologies with increasing pathlength in SAD. Nodal changes, however, were highly restricted to bilateral inferior occipital cortex. Interestingly, we found a lateralization where hyper-connectedness was restricted to right inferior occipital cortex and hyper-efficiency was found in the left inferior occipital cortex. Furthermore, we found these nodes became more "hub like" in patients, suggesting a greater functional role.
  
  
  CONCLUSIONS
  Our work stresses the importance of abnormal intrinsic processing during rest, primarily affecting visual areas and subsequently changing whole brain networks, and thus providing an important hint towards potential future therapeutic approaches.
authors.affiliation: Leibniz Institute for Neurobiology , Magdeburg , Germany.
authors.forename: Viola
authors.initials: V
authors.lastname: Borchardt
authors.forename: Anna Linda
authors.initials: AL
authors.lastname: Krause
authors.forename: Tuomo
authors.initials: T
authors.lastname: Starck
authors.forename: Juuso
authors.initials: J
authors.lastname: Nissilä
authors.forename: Markku
authors.initials: M
authors.lastname: Timonen
authors.forename: Vesa
authors.initials: V
authors.lastname: Kiviniemi
authors.forename: Martin
authors.initials: M
authors.lastname: Walter
mesh_terms: D000328:Adult; D001714:Bipolar Disorder / Q000503:physiopathology*; D001921:Brain / Q000000981:diagnostic imaging*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D059906:Neuroimaging; D009778:Occipital Lobe / Q000000981:diagnostic imaging*; D011877:Radionuclide Imaging; D016574:Seasonal Affective Disorder / Q000503:physiopathology*
keywords: Affective disorders; MRI; brain imaging; depression; seasonal affective disorder