The placebo effect on psychomotor performance and working memory capacity: randomized single blind cross-over trial

BACKGROUND: Imaging studies show that placebo enhance release of dopamine in the mesolimbic and mesocortical tracts. Dopamine in these areas are involved in attention and working memory function. PURPOSE: We wanted to investigating the effect of placebo on psychomotor function and working memory capacity. METHOD: 31 medical students participated in this single blind, crossover trial. Choice reaction time, critical flicker fusion threshold, n-back working memory tasks measured before and after one hour of the students receiving placebo in three different occasions as stimulant, unknown, and inert substance. RESULTS: Placebo, as stimulant, significantly enhanced choice reaction time and working memory function (P < 0.05) while showed no significant effect on critical flicker fusion threshold (P > 0.05). Placebo as unknown significantly deteriorates working memory capacity (P < 0.05). Placebo as inert substance shows no significant changes regarding choice reaction time, critical flicker fusion threshold, and working memory task. CONCLUSION: Placebo, as stimulant enhanced attention and improved working memory capacity, while as unknown may deteriorate working memory function.