The wake maintenance zone shows task dependent changes in cognitive function following one night without sleep

Study Objectives: The interaction between homeostatic sleep pressure and circadian timing modulates the impact of sleep deprivation on cognition. We aimed to investigate how this interaction affects different cognitive functions. Methods: Twenty-three healthy volunteers (18 males; mean age = 25.4 +/- 5.7 years) underwent 40 hours of sleep deprivation under constant routine conditions. Performance on the Psychomotor Vigilance Test and a cognitive battery assessing vigilant attention, complex attention, recognition memory, and working memory was assessed in the morning (27 hours awake) and evening (37 hours awake) during sleep deprivation and compared to well-rested performance 24 hours earlier. Circadian phase assessments confirmed evening tests occurred in the wake maintenance zone (WMZ). Results: Increased time awake significantly impacted performance on all measures except recognition memory. Post hoc analyses found performance on all measures was significantly impaired in the morning following 27 hours of sleep deprivation compared to well-rested performance 24 hours earlier. In contrast, complex attention and working memory were preserved in the WMZ after 37 hours awake compared to 24 hours earlier, while vigilant attention and PVT performance were significantly impaired. During sleep deprivation, composite scores of speed and accuracy were both impaired in the morning, while only speed was impaired during the WMZ. Conclusions: We observed task-and time-dependent effects of sleep deprivation, such that vigilant attention was significantly impaired after both 27 hours and 37 hours awake (compared to when well-rested at the same circadian clock time). In contrast, complex attention and working memory were impaired at 27 hours awake, but preserved in the WMZ despite increased homeostatic sleep pressure (37 hours awake).