|Research Impact/Earth Benefits:
|| The need to assess safe limits of exposure to CO2 with respect to adverse effects upon cognitive functions are particularly urgent in a setting in which even small decrements in cognitive functions, such as those utilized in complex decision making, could pose significant risk to outcomes in which substantial resources and even lives are invested. One such setting is human space flight. Crew reports and other anecdotal evidence (Law, et al., 2010; Cronyn et al., 2012; Strangman et al., 2012) suggest that the space flight environment may depress mental faculties. However, it seems probable that the measures historically available to space flight crews (Spaceflight Cognitive Assessment Tool for Windows (WinSCAT) and MiniCog) lacked the sensitivity needed to detect deficits in cognitive functions experienced or observed as instances of “mental viscosity,” due to the ceiling effect, which occurs when subjects achieve perfect scores on subtests in these batteries and so there is no difference measurable among subjects at the ceiling level (Cowings et al., 2006). Thus for several reasons, including small sample size, learning effects, and lack of sensitivity, “our knowledge about cognitive effects of space flight is superficial” (De La Torre et al., 2012). Given that CO2-like symptoms, such as difficulty in concentrating and headache, are among the most common symptoms reported by crews (Strangman, 2010), are experienced at lower than expected levels of CO2 (4,000 to 8,000 PPM, or 3 to 6 mm Hg), and resolve when the spacecraft CO2 is reduced, the possibility exists that CO2 sensitivity may be enhanced in the space environment (Law et al., 2010, 2014), it is possible that the threshold for cognitive effects attributable to CO2 in space may be lower than that observed by Satish et al. (2012). If this holds true, it may result in the need to establish lower space flight limits for CO2 and in turn drive the development of new technologies for CO2 control onboard spacecraft. Although not impacted by physiological changes associated with microgravity, submariners experience similar isolated quarters with recycled resources and higher than average baseline CO2 levels. In addition, they are another population where minor effects on cognition and decision-making can have life threatening consequences.
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