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.