0256 IMPROVEMENT IN COGNITION DURING THE WAKE MAINTENANCE ZONE FOLLOWING SLEEP LOSS IS DEPENDENT ON COGNITIVE DOMAIN

Abstract

The wake-promoting signal from the circadian system enhances alertness in the early evening when the homeostatic signal for sleep is increasing. This ‘wake maintenance zone’ (WMZ), which precedes the onset of evening melatonin secretion, is associated with improved vigilant attention even under conditions of elevated sleep pressure, such as 40 hours of sleep deprivation (SD). The impact of the WMZ on different cognitive domains during SD is not well established, and forms the basis of this study. Twenty-three healthy volunteers (18 males; mean age=25.4 ± 5.7y) underwent 40 hours of SD under constant routine conditions. The Psychomotor Vigilance Test (PVT) and Karolinska Sleepiness Scale (KSS) were completed bi-hourly. An additional test battery assessing the cognitive domains of processing speed, visual learning, visual attention, and working memory was administered at 3h, 13h, 27h, and 37h after habitual wake time. Melatonin onset timing confirmed that tests administered at 13h and 37h occurred during the WMZ. Paired t-tests compared performance during SD with performance at a circadian matched control, during the morning (3h versus 27h post-wake) and early evening/WMZ (13h versus 37h). As expected, PVT mean reaction time and number of lapses significantly increased at 27h and 37h, relative to control. This effect was also observed for processing speed. In contrast, measures of visual attention, visual learning, and working memory significantly deteriorated after 27h of SD (relative to 3hr post-wake), yet no effect of SD was observed at 37h (relative to 13h post wake). Vigilant attention and processing speed deteriorated with SD, with no improvement observed during the WMZ. In contrast, visual attention, visual learning, and working memory were also adversely impacted by SD (27h awake), but preserved in the WMZ despite increased homeostatic sleep pressure (37h awake). These data highlight the need to examine a variety of cognitive domains when examining the impact of sleep and circadian factors on performance. The study was supported by the Cooperative Research Centre for Alertness, Safety and Productivity.