Are head-down tilt bedrest studies capturing the true nature of spaceflight-induced cognitive changes? A review

Although a number of studies have examined cognitive functions in space, the reasons behind the observed changes described by space research and anecdotal reports have not yet been elucidated. A potential source of cognitive changes is the cephalad fluid shift in the body caused by the lack of hydrostatic pressure under microgravity. These alterations can be modeled under terrestrial conditions using ground-based studies, such as head-down tilt bedrest (HDBR). In this review, we compare the results of the space and HDBR cognitive research. Results for baseline and in-flight/in-HDBR comparisons, and for baseline and post-flight/post-HDBR comparisons are detailed regarding sensorimotor skills, time estimation, attention, psychomotor speed, memory, executive functions, reasoning, mathematical processing, and cognitive processing of emotional stimuli. Beyond behavioral performance, results regarding brain electrical activity during simulated and real microgravity environments are also discussed. Finally, we highlight the research gaps and suggest future directions

Late bedtime is associated with decreased hippocampal volume in young healthy subjects

Hippocampal volume loss has been described in several pathological conditions including sleep disorders. Whether differences in normal sleep are associated with differences in hippocampal volume is unknown. Here we designed a study to assess volume of the hippocampus with regard to bedtime, wake up time and sleep duration in 90 healthy university students. To assess hippocampal volumes we applied semi-automatic user-independent magnetic resonance volumetry. We found a significant association between delayed bedtime and smaller hippocampal volumes, a non-significant tendency for smaller hippocampal volumes in the late wake up time group and significantly smaller hippocampal volumes for both short and long sleepers. These results suggest the importance of adequate sleep timing and especially bedtime in determining hippocampal volume

Alexithymia is associated with low level of vitamin D in young healthy adults.

Objective Vitamin D plays an important role in brain development and functioning. Low levels of vitamin D have been described in several psychiatric and neurologic conditions including autism spectrum disorder. Alexithymia that shows high comorbidity with autism is also present in the general population as well as hypovitaminosis D. Methods Here we assessed the relation between alexithymia as measured by the Toronto Alexithymia Scale-20 and vitamin D level in healthy young adults. Results We found an inverse correlation between the levels of alexithymia and vitamin D. Discussion These data suggest the association between disturbed emotional processing and low levels of vitamin D to be present in young healthy subjects