Pharmaceutical enhancement of complex optimisation


This project aims to investigate the role of the neurotransmitter dopamine in complex decision making, and how three prescription stimulant medications that modulate dopamine levels in the brain in slightly different ways can affect the quality of complex decision making. These medications (dextroamphetamine, methylphenidate and modafinil) are increasingly used by healthy people for non-medical, cognitive enhancement purposes; however, their effects on basic cognition are often found to be inconsistent, and their effects on more naturalistic, complex optimisation behaviours are not known.

This project used a double-blinded placebo-controlled crossover design, recruiting healthy participants who participated in four testing sessions. At each session, the participant received either a single dose of one of the three pharmaceuticals or the placebo. Participants completed a series of computerised complex optimisation tasks and basic cognition tasks.

Several reviews and meta-analyses have examined the effects of these medications on basic cognitive functions including memory, attention and cognitive control in healthy people. Results of these analyses have been mixed, with just as many studies finding a small positive effect of these medications as those who found no effect at all. Far fewer studies have examined the effects of these medications on more complex, multifactorial cognitive processes.  Studies that examined effects of these medications on aspects of creative combinatorial or adaptive thinking, risk-taking under varying levels of uncertainty, and approach verses avoidance behaviour in problem solving found that performance may be hindered rather than enhanced by stimulant medications. It is clear that more research on the effects of these medications on the quality of complex decision making is urgently needed.

The knapsack task is a complex (NP-hard) optimisation task involving selection of items to maximise value while remaining within a weight constraint. This task recapitulates the kind of constrained problem-solving seen in many real-life situations, also allowing analysis of the path participants take through the "solution space" of each instance of a problem. This offers an important opportunity to assess how humans make combinatorial decisions in a goal-directed process. Using these medications to probe how perturbations to the dopamine system affect the quality of decision making will also have implications for the use of such drugs in attempts at cognitive enhancement in healthy people


Do stimulant medications, that increase dopamine in the brain, enhance, or have a deleterious effect, on the completion of a complex decision making task?


Peter Bossaerts, Elizabeth Bowman, David Coghill (Department of Paediatrics, The University of Melbourne; Royal Childrens' Hospital), Carsten Murawski

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