LAUSR

Sleep inertia is a state of impaired cognitive performance upon awakening that dissipates with time awake. Manipulation of the distal-to-proximal skin temperature gradient using cold water has been hypothesized as a potential countermeasure to sleep inertia, but not previously explored (Krauchi et al., 2004). This study examined the effects of cold-water hand immersion on subsequent cognitive performance and sleepiness during sleep inertia. Ten healthy adults (mean±standard deviation [SD] age 23.2±4.96 years; 6M, 4F) have thus far completed an ongoing 8-day protocol. Prior to an overnight in-laboratory visit, participants maintained habitual 8h sleep schedules for 1 week at home. In-laboratory sleep opportunities were timed to coincide with habitual sleep time. Following at least 5-min of electroencephalogram (EEG) verified continuous slow wave sleep (SWS), participants were awakened twice during the night to submerge their non-dominant hand in warm (34 C) or ice-cold water (0 C) for 3 min in a randomized, crossover design. Sleep inertia was assessed with a Mathematical Addition Test (ADD) and the Karolinska Sleepiness Scale (KSS) at ~ 5, 15, and 25 min after each awakening. Outcomes included number of correct responses and median reaction time for correct responses on the ADD and KSS scores. Data were analyzed with mixed-model ANOVA with condition, condition order and time since awakening as fixed factors and subject as a random factor. The average (Mean±SD) amount of SWS prior awakening was similar before the cold 7.0±2.3 min and warm 6.6±1.0min conditions (p>0.10). Following cold water immersion, subjective sleepiness was reduced and the median reaction time for correct responses was faster compared with warm water immersion (main effects of condition, p’s< 0.05). The number of correct responses was not significantly different between conditions, nor were there any significant interaction effects among the fixed factors. These preliminary findings indicate that cold-water hand immersion may reduce sleepiness and increase the speed of arithmetic calculations during sleep inertia, which could have important implications for military and first responders performing after awakenings from sleep. Office of Naval Research MURI N00014-15-1-2809; NIH RHL165343A and CTSA Grant UL1 TR002535; Undergraduate Research Opportunities Grant, University of Colorado Boulder.