Morning stimulant administration reduces sleep and overnight working memory improvement.

The goal of cognitive enhancement is to improve mental functions using interventions including cognitive training, brain stimulation and pharmacology. Indeed, psychostimulants, commonly used for cognitive enhancement purposes, while preventing sleep, have been shown to increase working memory (WM) and attention. Sleep, however, is also important for cognitive function; thus, understanding the interaction between stimulants, sleep and cognition may inform current approaches to cognitive enhancement. We used a double-blind, placebo controlled, repeated measure design to investigate the effect of morning administration of a commonly used stimulant, dextroamphetamine (DEX, 20 mg), on repeated, within-day and overnight WM performance, as well as on sleep in healthy young adults. Compared with placebo (PBO), we found no within-day benefit of DEX on WM. After sleep, DEX performed worse than PBO and the overnight improvement in performance in the PBO condition was absent in the DEX condition. Moreover, sleep quality was negatively affected by DEX administration. In summary, we found no cognitive boost from psychostimulants across a day of wake and a blockade of overnight WM increases with the stimulant, compared to PBO.