The Role of Effort Discounting in the Link between Insomnia and Depression

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Two-thirds of individuals with depression have also been shown to meet criteria for insomnia, the presence of which is associated with poor clinical course, greater resistance to depression treatment and an increased risk for relapse and suicidality. Research aimed at identifying the shared biopsychosocial processes relevant to both depression and insomnia is necessary to develop the therapeutic tools to reduce these negative outcomes and improve the health and quality of life of Veterans. The proposed CDA-2 targets reward processing, specifically the processing of reward-relevant effort, as one such commonality. Individuals with depression have been shown to engage more readily in effort discounting than non-depressed individuals, meaning that they are more likely to devalue rewards that require greater effort to obtain. There is some preliminary evidence that sleep disturbance may lead to effort discounting, but this effect has not been tested in adults with clinically significant insomnia, nor have previous studies of effort discounting in depression adequately characterized the severity and prevalence of insomnia among participants. This CDA-2 aims to evaluate the extent to which the processing of reward-relevant effort is meaningfully related to insomnia. The study will involve 132 Veterans ages 18 – 55 selected to represent a continuum of depression and insomnia symptom severity utilizing a quadrant approach. This approach will ensure a good distribution of Veterans with low insomnia/low depression, high insomnia/low depression, low insomnia/ high depression, and high insomnia/high depression severity for an analysis that utilizes continuous predictors to maximize power and explore the component effects of insomnia and depression on effort discounting. Veterans will participate in a week of subjective (sleep diary) and objective (actigraphy) assessments of sleep followed by assessments of effort discounting. Effort discounting will be measured with the Effort Expenditure for Rewards and the Progressive Ratio Tasks, behavioral measures that provide estimates of the effort subjects are willing to put forth for monetary rewards. To assess the specificity of the relationship of insomnia and reward processing, Veterans will also complete the delayed discounting task (a measure of reward valuation), and the probabilistic reversal learning task (a measure of reward learning). The Behavioral Inhibition/Behavioral Activation Scales and The Sensitivity to Punishment/Sensitivity to Reward Questionnaire are self-report measures of reward sensitivity and will also be administered. Veterans with clinically significant insomnia (i.e., Veterans in the high insomnia/low depression and high insomnia/high depression groups) will be randomly assigned to Cognitive Behavioral Therapy for Insomnia (CBT-I) or to a 6-week waitlist control period, after which they will receive CBT-I. Post-treatment/waitlist assessments of sleep and reward processing will be conducted to explore whether changes in insomnia severity are related to both changes in depression and effort discounting. Insomnia is hypothesized to be related to increased effort discounting (i.e., reduced effort to pursue rewards), and improvements in insomnia are hypothesized to be correlated with both improvements in depression and reduced effort discounting. As assessments of the specificity of the insomnia/effort discounting relationship are exploratory, there are no a priori hypotheses as to the effects of insomnia on reward valuation or learning. This CDA-2 will provide the applicant with focused training in translational sleep and mental health research (primary mentor Dr. Philip Gehrman), clinical trial methods and advanced statistics (co-mentor Dr. Michael Thase), assessment and analysis of reward guided behavior (co-mentor Dr. Robin Nusslock) and grantsmanship and professional development (co-mentor Dr. Steven Sayers). Findings from this study could enhance clinical practice guidelines for the treatment of Veterans with depression and insomnia.