Abstract

Computational approaches are increasingly being used to model behavioral and neural processes in mood and anxiety disorders. Here we explore the extent to which the parameters of popular learning and decision-making models are implicated in anhedonic symptoms of major depression. We first highlight the parameters of reinforcement learning that have been implicated in anhedonia, focusing, in particular, on the role that choice variability (i.e., “temperature”) may play in explaining heterogeneity across previous findings. We then turn to neuroimaging findings implicating attenuated ventral striatum response in anhedonic responses and discuss possible causes of the heterogeneity in the literature. Taken together, the reviewed findings highlight the potential of the computational approach in teasing apart the observed heterogeneity in both behavioral and functional imaging results. Nevertheless, considerable challenges remain, and we conclude with five unresolved questions that seek to address issues highlighted by the reviewed data.

Highlights

  • Mood and anxiety disorders are a major worldwide health burden across individual, social, and economic levels (Beddington et al, 2008)

  • We focus on the application of computational modeling to anhedonia— diminished reward processing—in major depression

  • We review findings from two primary classes of models (Figure 1) that have been implicated in anhedonia: (a) reinforcement learning models and (b) reaction time models

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Summary

INTRODUCTION

Mood and anxiety disorders are a major worldwide health burden across individual, social, and economic levels (Beddington et al, 2008). Despite a number of effective therapies and growing neuroscientific understanding of disease processes, resistance to established treatment strategies remains high (Yonkers, Warshaw, Massion, & Keller, 1996) This may be, at least in part, because current clinical diagnoses of these disorders rely primarily on subjective symptoms and behaviors, while the goal of neuroscience is to understand objective (i.e., observer-independent) biological mechanisms. Mapping these two approaches onto one another is exceptionally difficult and fraught with potential bias but is critical if we want to improve our ability to develop new treatments and target current treatments more effectively. It has been suggested that computational modeling of behavior—the focus of this review—can provide a means of bridging the gap between observable symptoms and behavior to underlying neurobiological mechanisms (Huys, Maia, & Frank, 2016; Montague, Dolan, Friston, & Dayan, 2012)

Computational Modeling of Behavior
Reduced learning rate if outcome is appetitive
Little direct examination in MDD
Sensitivity to Value
Learning Rate
Pavlovian Bias
NEUROIMAGING OF THE ANHEDONIC PHENOTYPE
Striatum differences
Differences not within striatum
Integrating Computational Approaches and Brain Imaging
FIVE QUESTIONS FOR FUTURE RESEARCH
What Is the Role of Temperature?
Can We Disentangle Responses to Outcome Versus Cue?
What Is the Role of Patient Heterogeneity?
How Does Anxiety Interact With Anhedonia?
What Are the Clinical Implications?
Findings
OVERALL SUMMARY

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