Princeton Neuroscience Institute
Background: Cognitive control-related symptoms of Major Depressive Disorder (MDD) (e.g., difficulty concentrating) contribute substantially to disability. Often cognitive symptoms and poorer performance on cognitive control tasks are interpreted as a reduced ability to exert control. We propose instead that cognitive symptoms may be due, in part, to reduced motivation to exert control because of increased cognitive effort “costs”.
Methods: We developed a novel experiential learning task, using patch-foraging, to derive a quantitative estimate of people’s cognitive effort costs. This measure allows us to, 1) dissociate motivation from ability, 2) compare cognitive effort costs in MDD relative to controls, 3) assess specificity of impairment with respect to differences from physical effort costs, self-efficacy, and reward responsiveness, and 4) map these axes of motivation onto MDD symptom heterogeneity.
Results: Preliminary results (N=30, 20 MDD) showed participants avoided exerting cognitive and physical effort, as reflected by lower patch-leaving thresholds in high- relative to low-effort environments of each condition (physical: beta=-0.37, df=29.15, t=-2.58, p<0.015; cognitive: beta=-0.46, df=29.29, t=-2.41, p<0.023). More depressed participants assigned disproportionately higher cost to physical effort (beta=13.07, df=27, t=3.01, p0.719), cognitive ability (beta=-3.16, df=26, t=-0.54, p>0.59), or in physical ability (beta=-0.23, , df=27, t=-0.60, p>0.55).
Conclusions: Resolving the underlying mechanisms of cognitive impairments in MDD has implications for developing treatments. By our account, if MDD patients are found to assign higher cognitive effort costs, interventions should target willingness to engage control (e.g., by providing motivational input) rather than cognitive control performance (e.g., cognitive training).
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