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Abstract:
There is abundant evidence that humans and other animals employ multiple control systems to solve complex decision-making tasks. Conventional dichotomies such as model-free or habitual systems, versus model-based or goal-directed systems are under debate and revision, but remain useful for designing and analyzing tasks and can be exploited to cast light on psychiatric disorders. One particular issue that has attracted less study, although it is likely to be of great importance in the control that we exert over the deployment of these control systems, is the meta-cognitive question of self-monitoring and self-evaluation, i.e., control over control. Given the known involvement of the neuromodulators dopamine and norepinephrine in aspects of both control and metacognition, we used neuropharmacological perturbations to examine interactions between control and control over control. In particular, we used the systemic administration in healthy human volunteers of Propranolol which suppresses the operation of norepinephrine and putatively enhances meta-cognitive accuracy, and Levodopa-B, which boosts dopamine and, although there are conflicting results in the literature, has been reported to boost the influence of model-based control.
We examined the effects of the drugs on choice and confidence ratings in two tasks: a conventional perceptual decision-making task used to study to confidence judgements, and a two-outcome task that offers an exquisitely fine decomposition of model-free and model-based choice and credit assignment. Using hierarchical Bayesian fitting, we found that Propranolol significantly decreased meta-cognitive ability, particularly among individuals with lower weight (and so a higher effective dose), while there was a very weak trend for Levodopa-B to improve it. However, performance was not significantly affected by drugs in either task. In the two-outcome task, Propranolol increased model-based behavior but had no effect on model-free behavior, while Levodopa-B had no effect on either.
Regarding control over control, when control systems disagree, meta-control might naturally be exerted to determine which one should be favored. For instance, when decision-makers lack confidence, the model-based controller should be preferred because it is statistically superior. However, if decision-making is uncertain, the model-based system may not be reliable. In support of this hypothesis, we found that model-based behavior was less likely to increase after low confidence, as an effect of Levodopa-B. We assessed the validity of our findings by comparing results from randomly permuted drug conditions with our empirical drug conditions. Overall, we suggest that our study sheds new light on the role of noradrenergic and dopaminergic systems in different levels of control and points to potential avenues for mitigating dysfunction within and between these systems.
