title: Abnormal brain responses to social fairness in depression: an fMRI study using the Ultimatum Game.
abstract: BACKGROUND
  Depression is a prevalent disorder that significantly affects the social functioning and interpersonal relationships of individuals. This highlights the need for investigation of the neural mechanisms underlying these social difficulties. Investigation of social exchanges has traditionally been challenging as such interactions are difficult to quantify. Recently, however, neuroeconomic approaches that combine multiplayer behavioural economic paradigms and neuroimaging have provided a framework to operationalize and quantify the study of social interactions and the associated neural substrates.
  
  
  METHODS
  We investigated brain activation using functional magnetic resonance imaging (fMRI) in unmedicated depressed participants (n = 25) and matched healthy controls (n = 25). During scanning, participants played a behavioural economic paradigm, the Ultimatum Game (UG). In this task, participants accept or reject monetary offers from other players.
  
  
  RESULTS
  In comparison to controls, depressed participants reported decreased levels of happiness in response to 'fair' offers. With increasing fairness of offers, controls activated the nucleus accumbens and the dorsal caudate, regions that have been reported to process social information and responses to rewards. By contrast, participants with depression failed to activate these regions with increasing fairness, with the lack of nucleus accumbens activation correlating with increased anhedonia symptoms. Depressed participants also showed a diminished response to increasing unfairness of offers in the medial occipital lobe.
  
  
  CONCLUSIONS
  Our findings suggest that depressed individuals differ from healthy controls in the neural substrates involved with processing social information. In depression, the nucleus accumbens and dorsal caudate may underlie abnormalities in processing information linked to the fairness and rewarding aspects of other people's decisions.
authors.affiliation: CIBPsi, Faculty of Psychology,Universidad de la República,Montevideo,Uruguay.
authors.forename: V B
authors.initials: VB
authors.lastname: Gradin
authors.affiliation: CIBPsi, Faculty of Psychology,Universidad de la República,Montevideo,Uruguay.
authors.forename: A
authors.initials: A
authors.lastname: Pérez
authors.affiliation: Medical Physics,NHS Tayside,University of Dundee,UK.
authors.forename: J A
authors.initials: JA
authors.lastname: MacFarlane
authors.affiliation: Medical Physics,NHS Tayside,University of Dundee,UK.
authors.forename: I
authors.initials: I
authors.lastname: Cavin
authors.affiliation: Aberdeen Biomedical Imaging Centre,University of Aberdeen,UK.
authors.forename: G
authors.initials: G
authors.lastname: Waiter
authors.affiliation: Department of Economics,University of Zurich,Switzerland.
authors.forename: J
authors.initials: J
authors.lastname: Engelmann
authors.affiliation: Department of Psychology,University of St Andrews,UK.
authors.forename: B
authors.initials: B
authors.lastname: Dritschel
authors.affiliation: Biophysics Section,Faculty of Sciences,Universidad de la República,Montevideo,Uruguay.
authors.forename: A
authors.initials: A
authors.lastname: Pomi
authors.affiliation: Division of Neuroscience,Medical Research Institute,University of Dundee,UK.
authors.forename: K
authors.initials: K
authors.lastname: Matthews
authors.affiliation: Division of Neuroscience,Medical Research Institute,University of Dundee,UK.
authors.forename: J D
authors.initials: JD
authors.lastname: Steele
mesh_terms: D000328:Adult; D059445:Anhedonia / Q000502:physiology; D002421:Caudate Nucleus / Q000503:physiopathology*; D003866:Depressive Disorder / Q000503:physiopathology*; D005260:Female; D005717:Games, Experimental; D006801:Humans; D007398:Interpersonal Relations; D008279:Magnetic Resonance Imaging; D008297:Male; D009014:Morals; D009714:Nucleus Accumbens / Q000503:physiopathology*; D012201:Reward; D055815:Young Adult
keywords: ultimatum game.