Andrew Westbrook, PhD - US grants

DESCRIPTION (provided by applicant): Sustained, intensive cognitive effort can yield substantial benefits in terms of improved decision-making and generally enhanced cognitive performance. Cognitive effort, however, is often treated as aversive, as evidenced by substantial behavioral biases against effortful engagement. Among healthy adults, there appear to be measurable differences in how aversive individuals find cognitive effort, contributing to differences in performance, unexplained by measures of intelligence. Effort may be particularly aversive in disorders of anergia and apathy. It may explain why individuals with Major Depression, for example, demonstrate average performance on low effort tasks yet perform below average on demanding tasks. Despite the import of this central bias against cognitive engagement among healthy individuals and those with mental disorder, little is understood about why cognitive effort is aversive, or about the neural systems involved in decisions about task engagement. To address this gap, this project utilizes a novel behavioral economic paradigm towards the development of a neuroeconomics of cognitive effort. The novel paradigm yields first-ever, quantitative, between and within individual estimates of the cost of cognitive effort. The first Aim of this study seeks to validate the novel paradigm by demonstrating correlations of subjective cost estimates with traditional physiological and self-report measures of cognitive effort. Next, the paradigm will be used to investigate individual and task specific factors which make cognitive effort subjectively costly. Combined fMRI and pupillometry will be used to probe specific hypotheses about physiological markers of cognitive effort. Finally, following recent advances in neuroeconomics, the novel cost estimates will be used in parametric tests of fMRI data collected as individuals decide whether to engage in demanding tasks. This approach will be used to test specific hypotheses about the neural systems involved in on-going and prospective decisions to expend cognitive effort among healthy adults. This work will also thereby provide a foundation for elucidating why cognitive effort may be particularly aversive in depression.

Project Summary Tasks with cognitive control demands are treated as subjectively costly. Individuals will avoid higher demands, just like they avoid physical effort. Subjectively exaggerated costs sap motivation for cognitive control, undermining task performance ? an effect that has been examined in schizophrenia, depression, Parkinson?s disease, and depression. Yet, despite widespread significance, little is known about mechanisms tracking effort costs or mediating decisions to engage or persist with demanding cognitive tasks. Numerous lines of evidence suggest that dopamine signaling, conveying momentary incentive state, can offset effort costs and thus promote physical and cognitive effort. However, while dopamine has been shown to enhance cognitive control, it also appears to, paradoxically, undermine control by promoting impulsive action. The purpose of this project is to test a hypothesis that can reconcile conflicting effects of dopamine on cognitive control by unifying action selection mechanisms in the cognitive and physical domain. Namely, I will test the hypothesis that dopamine biases benefit over cost information during action selection, but it does so preferentially for ?proximal? actions (those that are immediately suggested by the environment). This hypothesis unifies domains in that physical actions are typically suggested by the environment (e.g. levers at hand, or stairs underfoot), while control actions are not. Instead, in the cognitive domain, control actions must compete with what the environment suggests, and will only win out when control mechanisms respond quickly enough. An important corollary of the hypothesis is that very high dopamine levels can amplify even small differences in proximity, thus potentiating proximal ?habits? over ?controlled? actions and explaining why dopamine can sometimes undermine control rather than promote it. I will test this hypothesis by formalizing the principles in biologically-constrained neural network models, and testing whether they can explain neurophysiological and behavioral dynamics in existing data sets. In a series of experiments, I will measure and manipulate dopamine (with PET imaging and pharmacological interventions) and measure and manipulate proximity (with eye gaze and task design), to determine whether proximity and dopamine determine cognitive action selection as hypothesized. Finally, I test whether the neural network models can predict performance in my experimental data using a common set of parameters. A long-term benefit of this work will be to precisely articulate the mechanisms by which dopamine can affect effortful cognitive action, and generate targets for pharmacological interventions that promote desirable effortful action without also promoting impulsivity.