Sleep, cognition and neurophysiological responses during isolation

Space and isolation missions are stressful and negatively impact quality of sleep, mood and cognitive performance of crewmembers. Also important neurotropic factors, BDNF and IGF-1, are reduced with stress. The underlying neurophysiological mechanisms are unclear and efficient countermeasures missing. We aimed to investigate the effect isolation (30 days) on sleep, mood, cognition, neutrotrophic factors and brain cortical activity, to explore possible underlying neurophysiological mechanisms. 16 participants (aged: 37±7y) were isolated in 4 missions. During each mission 4 participants were isolated in the Human Exploration Research Analogue at NASA for 30 days. 17 non-isolated participants (control group, aged: 32±9y) were tested simultaneously. Both groups performed daily physical exercise throughout the interventions. Sleep was assessed with actigraphy (Respironics, Amsterdam). On mission days -5, 7, 28 and +5 sleep and awakening quality questionnaires (SSA), Positive Affect and Negative Affect Scale (PANAS-X), cognitive tasks and a five-minutes resting EEG (Brain Products, Munich) with closed eyes were completed. Intravenous morning cortisol, melatonin, BDNF and IGF-1 was compared between groups. Effects of the groups (isolation vs. non-isolation) and time were determined using repeated measures ANOVA. Cortisol was significantly increased during isolation in comparison to non-isolated group (p<0.01). Melatonin (p=0.37), BDNF (p=0.92) and IGF-1 (p=0.09) was similar between the groups and remained unchanged over time. No group effects for actigraphy total light exposure during sleep (p=0.61), sleep efficiency (p=0.54) and subjective sleep quality (SSA, p=0.10) were shown. Mood was similar between the groups (positive affect (p=0.38), negative affect (p=0.20)) and cognitive performance tests unaffected by the isolation (group effects: visuo-perceptual speed, p=0.22; arithmetical ability, p=0.75; special working memory, p=0.29). Frontal cortical current density was similar between the groups (p=0.40) and remained unchanged throughout the interventions (interaction, p=0.72). Sleep, mood and cognition were not impaired by 30 days of isolation, although increased levels of cortisol suggest high level of stress. Maintained sleep quality during isolation might have positively affected the CNS, as brain cortical activation and neurotropic factors remained unaffected by the isolation. An ongoing HERA campaign, might allow further analyses and insights into possible underlying neurophysiological mechanisms as well as the effect of physical activity as participants exercise less during isolation.