Toward an Etiology of Spaceflight Neuroplastic Syndrome: Evolutionary Science Leads to New Hypotheses and Program Priorities.

Evolutionary theory is applied to recent neuroscientific findings on factors associated with risk-and-reward systems, and consequently, aspects of human decision making in spaceflight. Factors include enzymes aiding metabolic pathways of dopamine and serotonin; neurotrophic factors supporting neuronal functioning and plasticity; and genes associated with serotonin and dopamine systems. Not all factors are at risk in spaceflight. Some remain stable. It is hypothesized that neural deconditioning in spaceflight arises from faulty signals sent to the brain and gut in attempting to adapt phenotypically to a novel space environment. There is a mismatch between terrestrial selection pressures during human evolution and conditions of cosmic radiation, microgravity, and higher CO2, which together cause scattered results. A contrary question is broached: Given these findings, why are human sequelae not worse? Discussion of programmatic issues then focuses on methodologies to determine the suitability of civilians for spaceflight, an issue that grows more pressing while more varied populations prepare for spaceflight in LEO and on, and in orbit around the Moon.