Sleep Fragmentation Results in Novel Set-shifting Decrements in GCR-exposed Male and Female Rats.

The prolonged exposure to multiple spaceflight stressors during long-duration missions to the Moon and Mars will be challenging to the physical and mental health of the astronauts. Ground-based studies have reported that attentional set-shifting task (ATSET) performance is impaired after space radiation (SR) exposure. At certain times during deep-space missions, astronauts will likely have to contend with the combined impacts of SR and sleep perturbation. In rats, poor quality, fragmented sleep adversely impacts performance in multiple cognitive tasks, including the ATSET task. While both SR and sleep perturbations independently cause cognitive performance deficits, the incidence, severity and exact nature of those decrements following combined exposure to these flight stressors is largely unknown. This study established the impact that a single night of fragmented sleep has on ATSET performance in both male and female rats exposed to 10 cGy of galactic cosmic ray simulation (GCRsim). The GCRsim beam is a complex beam that mimics the mass and energy spectra of the SR particles that an astronaut will be exposed to within the spacecraft. Rats that had no obvious ATSET performance decrements when normally rested were subjected to fragmented sleep and their ATSET performance reassessed. Sleep fragmentation resulted in significant ATSET performance decrements in GCRsim-exposed rats, with specific performance decrements being observed in stages where attention or cue shifting is extensively used. Performance decrements in these stages are rarely observed after SR exposure. While both male and female rats exhibited latent sleep-related performance decrements, these were sex dependent, with male and female rats exhibiting different types of performance decrements (either reduced processing speed or task completion efficiency) in different stages of the ATSET task. This study suggests that SR-induced cognitive impairment may not be fully evident in normally rested rats, with an underestimation of both the incidence and nature of performance decrements that could occur when multiple space flight stressors are present. These data suggest that that there may be synergistic interactions between multiple space flight stressors that may not be easily predicted from their independent actions.