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18Concordia station in Antarctica is one of the most remote human outpost on Earth. Because of 19 its geographical location, a winterover at Concordia shares a lot of stressors with a space mission. 20 Following a recent study on the markers of sleep pressure during wakefulness on board of the 21 International Space Station, we were investigating if long term isolation in a space analogue station 22 shows similar effects on sleep pressure. Unlike in space, markers of sleep pressure did not increase 23 during isolation's constant darkness period in Antarctica. When measures of sleep pressure were 24 high in the evening, psychological strain was increased, emphasising the importance of keeping sleep 25 pressure under physiological levels during the mission. As a first indication for a countermeasure, 26 we showed that one hour of bicycle exercise during lunch time could decrease sleep pressure. All 27 these observations need to be further studied in a more controlled environment. 28 Keywords 29Sleep pressure, wake electroencephalographic recordings, Antarctica space analogue station, long 30 term isolation, psychological strain, space countermeasure, physical activity 31 32 Sleep quality and sleep quantity are regulated by two interacting process, the homeostatic and 33 the circadian process (1): i) The homeostatic process builds up with time awake. Good sleep 34 quality is defined by an efficient dissipation of sleep pressure overnight which in turn decreases the 35 propensity to fall asleep and improve alertness the following day (2; 3). ii) The circadian process is 36 oscillating on a 24 hours cycle (4). The master clock is regulated by the suprachiasmatic nucleus 37 and constantly adjusted by environmental cues (5). Daylight is one of the main cues to the master 38 clock. Circadian rhythms exert a strong impact on sleep quality and sleep timing (6). Interestingly, 39 EEG theta activity (5-7Hz) in the waking EEG (1) reflects both the homeostatic and the circadian 40 process. The circadian impact can be seen by diurnal fluctuations of theta activity, peaking in the 41 afternoon and again at bed time (7). The homeostatic component, on the other hand, becomes 42 obvious after prolonged wakefulness (i.e. sleep deprivation), which is associated with a significant 43 increase in theta power. (8; 9; 10; 11; 12). 44Astronauts are subject to very irregular schedules and workloads (e.g. launchings or dockings of 45 a vehicule) and while orbiting Earth, the International Space Station (ISS) crew witness a sun 46 rise every 90 minutes which can lead to a misalignment of their 24-hour sleep-wake cycle (13). 47Accordingly, chronic sleep restriction has been reported during space missions (14). We recently 48 provided first evidence for increased of sleep pressure markers during wakefulness in space, i.e 49 measured waking EEG in the theta frequency range, and showed that reaction times were slower 50 when markers of sleep pressure were high (15). To understand the cause of changes in markers of 51 sleep pressure i...