title: Fear extinction as a model for synaptic plasticity in major depressive disorder.
abstract: BACKGROUND
  The neuroplasticity hypothesis of major depressive disorder proposes that a dysfunction of synaptic plasticity represents a basic pathomechanism of the disorder. Animal models of depression indicate enhanced plasticity in a ventral emotional network, comprising the amygdala. Here, we investigated fear extinction learning as a non-invasive probe for amygdala-dependent synaptic plasticity in patients with major depressive disorder and healthy controls.
  
  
  METHODS
  Differential fear conditioning was measured in 37 inpatients with severe unipolar depression (International Classification of Diseases, 10th revision, criteria) and 40 healthy controls. The eye-blink startle response, a subcortical output signal that is modulated by local synaptic plasticity in the amygdala in fear acquisition and extinction learning, was recorded as the primary outcome parameter.
  
  
  RESULTS
  After robust and similar fear acquisition in both groups, patients with major depressive disorder showed significantly enhanced fear extinction learning in comparison to healthy controls, as indicated by startle responses to conditioned stimuli. The strength of extinction learning was positively correlated with the total illness duration.
  
  
  CONCLUSIONS
  The finding of enhanced fear extinction learning in major depressive disorder is consistent with the concept that the disorder is characterized by enhanced synaptic plasticity in the amygdala and the ventral emotional network. Clinically, the observation emphasizes the potential of successful extinction learning, the basis of exposure therapy, in anxiety-related disorders despite the frequent comorbidity of major depressive disorder.
authors.affiliation: Department of Psychiatry and Psychotherapy, University Medical Center Freiburg, Freiburg, Germany.
authors.forename: Marion
authors.initials: M
authors.lastname: Kuhn
authors.affiliation: Department of Psychiatry and Psychotherapy, University Medical Center Freiburg, Freiburg, Germany.
authors.forename: Nora
authors.initials: N
authors.lastname: Höger
authors.affiliation: Department of Psychiatry and Psychotherapy, University Medical Center Freiburg, Freiburg, Germany.
authors.forename: Bernd
authors.initials: B
authors.lastname: Feige
authors.affiliation: Division of Clinical Psychology, Psychotherapy, and Health Psychology, Department of Psychology, University of Salzburg, Salzburg, Austria.
authors.forename: Jens
authors.initials: J
authors.lastname: Blechert
authors.affiliation: Department of Psychiatry and Psychotherapy, University Medical Center Freiburg, Freiburg, Germany.
authors.forename: Claus
authors.initials: C
authors.lastname: Normann
authors.affiliation: Department of Psychiatry and Psychotherapy, University Medical Center Freiburg, Freiburg, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Nissen
mesh_terms: D000328:Adult; D000679:Amygdala / Q000503:physiopathology; D016022:Case-Control Studies; D003214:Conditioning, Classical; D003865:Major Depressive Disorder / Q000503:physiopathology*; D005108:Extinction, Psychological; D005239:Fear; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D009473:Neuronal Plasticity