Efficacy of caffeine and modafinil in counteracting sleep deprivation in the marmoset monkey

Background and purpose The effects of sleep deprivation are a burden in our 24-h society. The use of wake-promoting compounds could improve the performance in situations where sleep cannot be allowed. In this study, the efficacy of the wake-promoting compounds, modafinil and caffeine, in counteracting the effects of 24-h sleep deprivation in the marmoset monkey were tested. As caffeine is habitually used, the efficacy of both compounds after short- and long-term use was investigated. Materials and methods After a normal active day, the animals were kept awake and received wake-promoting compounds during the whole night. Three times during the sleep-deprived night, putative fatigue was assessed with an activity test and the vigilance and ability to execute a task was assessed with a hand–eye coordination (HEC) task. Results Both compounds were able to counteract to some extent the decline in performance. Modafinil was able to keep the activity at baseline performance, but performance on the HEC task was not improved. Caffeine was able to keep performance in the HEC task at a level just below daytime level but was not able to keep activity at daytime levels during the last part of the night. Caffeine and modafinil administration for 2 weeks showed a comparable effect on activity as acute use. The performance on the HEC task was similar after chronic caffeine and improved after chronic modafinil. Conclusion It is therefore concluded that modafinil and caffeine were both able to postpone or prevent the decline in vigilance and psychomotor performance and increase in fatigue induced by sleep deprivation.