Caffeine eliminates psychomotor vigilance deficits from sleep inertia

Study Objectives: This study sought to establish the effects of caffeine on sleep inertia, which is the ubiquitous phenomenon of cognitive performance impairment, grogginess and tendency to return to sleep immediately after a wakening. Design: 28 normal adult volunteers were administered sustained low-dose caf feine or placebo (randomized double-blind) during the last 66 hours of an 8 8-hour period of extended wakefulness that included seven 2-hour naps durin g which polysomnographical recordings were made. Every 2 hours of wakefulne ss, and immediately after abrupt awakening from the naps, psychomotor vigil ance performance was tested. Setting: N/A Participants: N/A Interventions: N/A Measurements and Results: In the placebo condition, sleep inertia was manif ested as significantly impaired psychomotor vigilance upon awakening from t he naps. This impairment was absent in the caffeine condition. Caffeine had only modest effects on nap sleep. Conclusions: Caffeine was efficacious in overcoming sleep inertia. This sug gests a reason for the popularity of caffeine-containing beverages after aw akening. Caffeine's main mechanism of action on the central nervous system is antagonism of adenosine receptors. Thus, increased adenosine in the brai n upon awakening may be the cause of sleep inertia.