Anhedonia in melancholic and non-melancholic depressive disorders

Background: Anhedonia represents a core symptom of major depression and may be a potential marker for melancholia. However, current understanding of this construct in depressive sub types is limited. Method: Participants were recruited from the Black Dog Institute (Sydney) arid Massachusetts General Hospital (Boston). Diagnostic groups were derived on the basis of agreement between clinician and DSM-IV diagnosis from structured interviews. Currently depressed unipolar melancholic, non melancholic and healthy control participants were administered a probabilistic reward task (PRT) to assess a behavioural correlate of anhedonia-blunted reward based learning. Self reported measures of anhedonia, approach and avoidance motivation were completed by the Sydney sample. Results: Relative to healthy controls and non-melancholic participants, melancholic depressed participants had reduced response bias, highlighting blunted reward teaming. Moreover, although non-melancholic participants were characterized by a delayed response bias, melancholic depressed participants Failed to develop a bias throughout blocks. Response bias showed 110 associations with self-report measures of hedonic tone in depressed participants. Positive associations were observed between response bias, approach and avoidance motivation in non-melancholic participants only. Limitations: Possible medication, fatigue and anxiety effects were not controlled; small sample sizes; inclusion criteria may have excluded those with severe melancholia and led to underestimation of group differences. Conclusions: Melancholia is characterised by a reduced ability to modulate behaviour as a function of reward, and the motivational salience of rewarding stimuli may differ across depressive sub-types. Results support the view that melancholia is a distinct sub-type. Further exploration of reward system functioning in depressive sub-types is warranted. (C) 2015 Elsevier B.V. All rights reserved.