title: Impaired probabilistic classification learning with feedback in patients with major depression.
abstract: BACKGROUND
  The function of basal ganglia (BG) in the pathophysiology of major depression (MD) is still unclear. Recent research found changes in BG regarding size, structure and cerebral perfusion in patients with MD. Neuroimaging shows recruitment of the striatum during feedback (FB) based incidental learning of probabilistic classification learning, while the medial temporal lobe (MTL) is associated with paired associate (PA) based incidental learning. The purpose of this study was to evaluate whether FB-based incidental learning is affected in MD.
  
  
  METHODS
  The FB and PA versions of the weather prediction task (WPT), a task of incidental probabilistic classification learning, were completed by patients with MD (n=44) and healthy controls (n=44). In FB-learning the participants received either a "thumbs-up" or "thumbs-down" message according to their right or wrong classification of cards to a certain kind of weather (either rainy or fine), while in PA learning no classification was required. Severity of MD was rated on the Beck Depression Inventory and Hamilton Rating Scale for depression.
  
  
  RESULTS
  Patients with MD were selectively impaired on the FB task relative to controls (p<0.05), while no significant difference was found for PA learning between the two groups. Furthermore, there were no significant differences between FB and PA-learning within the patient and control groups.
  
  
  CONCLUSIONS
  Our results indicate a distinct impairment on the FB-based version of the weather prediction task. These findings implicate disturbed reinforcement learning in this group of patients.
authors.affiliation: Department of Psychiatry, Graz Medical University, 8036 Graz, Austria.
authors.forename: S
authors.initials: S
authors.lastname: Mörkl
authors.affiliation: Department of Psychiatry, Graz Medical University, 8036 Graz, Austria.
authors.forename: C
authors.initials: C
authors.lastname: Blesl
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, University College London, Institute of Neurology, Queen Square, London WC1N3BG, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Jahanshahi
authors.affiliation: Department of Psychiatry, Graz Medical University, 8036 Graz, Austria. Electronic address: annamaria.painold@medunigraz.at.
authors.forename: A
authors.initials: A
authors.lastname: Painold
authors.affiliation: Department of Psychiatry, Graz Medical University, 8036 Graz, Austria.
authors.forename: A K
authors.initials: AK
authors.lastname: Holl
mesh_terms: D000293:Adolescent; D000328:Adult; D003865:Major Depressive Disorder / Q000523:psychology*; D005260:Female; D000068156:Formative Feedback; D006801:Humans; D008297:Male; D008875:Middle Aged; D011337:Probability Learning; D055815:Young Adult
keywords: Basal ganglia; Feedback; Learning; Major depression; Weather prediction task