Trial-to-trial variance in choice reaction time as a measure of the effectof stimulants during sleep deprivation

Performance stability, as assessed by trial-to-trial variance in a choice r eaction time (RT) task, was evaluated as a measure of stimulant effects on performance during sleep deprivation. Administration of methylphenidate, pe moline, and a placebo began 16 hr into a 64-hr sleep-deprivation protocol. Performance stability deteriorated significantly, especially during the cir cadian nadirs. In absolute terms, sleep deprivation increased trial-to-tria l variance more than it increased the mean correct RT. In addition, this me asure demonstrated differing effects of the 2 drug regimens. Pemoline, at a dose of 37.5 mg every 12 hr, significantly reduced the overall average eff ects of sleep loss on performance stability during the first 24 hr of drug administration. Pemoline also reduced circadian-related instability in perf ormance throughout the study. Methylphenidate, at a dose of 10 mg every 6 h r, counteracted circadian-related instability in performance during the fir st 24-hr period of drug administration (16-40 hr of sleep deprivation) but not during the second 24-hr period (40-64 hr of sleep deprivation). Methylp henidate did not significantly affect the overall average effects of sleep loss on performance stability. Thus, trial-to-trial variance appears to be a valuable measure for elucidating stimulant effects during sleep deprivati on.