Pharmaceutical enhancement of complex problem-solving in healthy adults

INTERVENTION: A single oral dose of a capsule containing 15 milligrams dextroamphetamine, 30 milligrams of methylphenidate, 200 milligrams of modafinil or placebo prior to cognitive testing in a repeated‐measures full crossover double‐blinded design in healthy volunteers. A washout period of at least seven days will be observed between testing sessions. Cognitive testing commences 90 minutes after dosage, and includes solving complex optimisation problems, spatial working memory tests, motor inhibition tests, reaction time and spatial problem solving. Cognitive testing will take between 60 and 90 minutes, depending on the speed of the individual participant. CONDITION: Cognitive enhancement PRIMARY OUTCOME: Performance in complex optimisation task as measured by accuracy scores. That is, are the items selected by the participant included in the optimal solution. This is also referred to as "computational perfomance". SECONDARY OUTCOME: "Economic performance" of the complex optimisation task, that is, how close the submitted solution is to the known optimal solution. ; Motor inhibition, as measured by error rate on the CANTAB stop‐signal task. Network analysis of the steps taken to solve the complex optimisation tasks. That is, analysis of which items are selected and deselected as the participant attempts to maximise ("optimise") the solution to the problem. This sequence of selection and deselection of items can be visualised in "decision space" and the number of steps taken to achieve a solution can be analysed. Reaction time, as measured on the CANTAB reaction time task. Spatial problem solving, as measured by accuracy rate on the CANTAB stockings of Cambridge task. Spatial working memory performance, as measured by error rate on the CANTAB spatial working memory task. INCLUSION CRITERIA: Healthy volunteers aged between 18 and 35 years old.