Abstract
Our earlier study found patients with depression to show a preference for larger reward as measured by the Iowa Gambling Task (IGT). In this IGT version, larger rewards were associated with even larger consequent losses. In the light of the clinical markers defining depressive disorder, this finding might appear controversial at first. Performance of depressed patients on various decision-making (DM) tasks is typically found to be impaired. Evidence points toward reduced reward learning, as well as the difficulty to shift strategy and integrate environmental changes into DM contingencies. This results in an impaired ability to modulate behavior as a function of reward, or punishment, respectively. Clinical symptoms of the disorder, the genetic profile, as well as personality traits might also influence DM strategies. More severe depression increased sensitivity to immediate large punishment, thus predicting future decisions, and was also associated with higher harm avoidance. Anhedonic features diminished reward learning abilities to a greater extent, even predicting clinical outcome. Several questions about how these aspects relate remain to be clarified. Is there a genetic predisposition for the DM impairment preceding mood symptoms? Is it the consequence of clinical signs or even learned behavior serving as a coping strategy? Are patients prone to develop an aversion of loss or are they unable to sense or deal with reward or the preference of reward? Does the DM deficit normalize or is a persisting impairment predictor for clinical outcome or relapse risk? To what extent is it influenced by medication effects? How does a long-lasting DM deficit affect daily life and social interactions? Strikingly, research evidence indicates that depressed patients tend to behave less deceptive and more self-focused, resulting in impaired social DM. The difficulty in daily interpersonal interactions might contribute to social isolation, further intensifying depressive symptoms.
Highlights
Depression is traditionally considered an affective disorder
We propose that depressed patients with anhedonic symptoms tend to expect an inevitable punishment after obtaining a large reward during the Iowa Gambling Task (IGT)
An excessive firing of the habenula typically detected in the absence of an expected reward does not occur
Summary
Depression is traditionally considered an affective disorder. Yet, research in the past decades has drawn attention to the substantial impairment in cognitive function. Various aspects of cognitive disturbance have frequently been reported in the acute phase of the illness (Harvey et al, 2004; Rogers et al, 2004) These include domains of executive function, such as planning and problem solving (Naismith et al, 2003), inhibition and semantic fluency (Ravnkilde et al, 2002; Gohier et al, 2009) – present even in first episode major depressive disorder (Schmid and Hammar, 2013) – decision-making (DM; Chamberlain and Sahakian, 2006) and various aspects of memory processes (Rose and Ebmeier, 2006; Taylor Tavares et al, 2007). The DM capacity might have a fundamental effect on social skills and coping strategies, influencing vulnerability, preventing symptoms or even enhancing relapse risk
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