Astronauts are asked to perform at a very high level in a very demanding situation, under constant supervision and scrutiny; this doesn’t help with the stress level. Beyond such external factors, the high standards they set for themselves may lead to self-imposed stress. A mission is often the peak of one’s professional career, a position of high visibility in which errors of judgement can have immediate and dire consequences. Astronauts are well-prepared and highly trained to overcome and cope with stressors that would be unbearable for most of us. Nevertheless, they are human. Stress takes a toll, especially over the long run and when downtime for rest and recovery is hard to come by. While we understand a great deal about these stressors individually (even if we do not yet know how to counter them effectively), their combination, over an extended period, could lead to problems that we do not yet foresee. In this regard, human spaceflight is not only an exploration of space itself, but also of human limits and capabilities. Effects of Stress What are the effects of these myriad stressors on brain function and mental performance? We know some, and others might become apparent on more ambitious missions such as a trip to Mars. A common observation among astronauts refers to a phenomenon known as “space fog” or “space stupids”—a sense of cognitive slowing and the need for increased mental effort to perform routine tasks . Disrupted sleep and elevated CO 2 alone, in a demanding setting under intense pressure to perform, could easily produce such cognitive problems. Add all the other spaceflight stressors described above, and it is not hard to imagine having even greater difficulty concentrating and a sense of mental lethargy. Related to this is the phenomenon of “neurasthenia”: a vaguely defined sense of fatigue, lack of motivation, irritability, and related somatic sensations. Strangely, though, objective testing of cognitive function in space does not fully support these subjective observations. In- flight cognitive testing shows variable effects and is hampered by a small number of astronaut subjects and poorly controlled conditions (differences in flight experience, fatigue level, sleep, etc.). A laboratory experiment provides a much better- controlled setting, but it cannot reproduce the reality of space travel that we desire to capture. In fact, what space data we do have show few, if any, significant decrements in objective measures of cognitive function . There are some changes in reaction time, for example, but their significance is uncertain . This is similar to the case in which a terrestrial patient has a complaint but testing yields no anomalous results in the clinic. Is the test
Working in zero gravity means a shift of body fluids and could lead to changes in cognitive function and vision.
types of things that are conducive to working with others in a small space. The radiation level is also elevated—although not as high as it is on the moon or Mars, or in deep space on the journey there. The primary long-term risk from radiation is an increased lifetime likelihood of cancer, but there are possible short-term effects as well. There is some evidence from animal studies that a large acute radiation dose (as might result from a solar flare) could cause a deficit in cognitive function. While this remains to be verified in humans, the prospect of a drop in mental capacity when it is most needed—for example, in mid-journey to Mars—should give one pause. Finally, there is weightlessness itself. It is perhaps odd to think of this as a stressor, when we see astronauts cavorting in zero gravity, free to explore the full three-dimensional scope of their confines. But this freedom comes with challenges. Objects, including people, float away if not held in place. Debris floats and can get into the eyes. There are also physiological consequences of the shift of body fluids to the head, which might lead to changes in cognitive function, and certainly contribute to sinus congestion and alterations in the senses of taste and smell.
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