Background: Imaging studies show that placebo enhance release of dopamine in the mesolimbic and mesocortical tracts. Dopamine in these areas involved in attention and working memory function.  Purpose: investigating the effect of placebo on psychomotor function and working memory capacity. Method: 31 medical students participate 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 enhance choice reaction time and working memory function (P < 0.05) while show 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 enhance attention and improve working memory capacity, while as unknown may deteriorate working memory function.

doi : 10.5214/ans.0972.7531.1118403

Competing interests: None.  Source of Funding: None

Received Date : 17 June 2011     Revised Date: 29 July 2011     Accepted Date : 23 August 2011