Head down tilt bed rest (HDBR) has been effectively used to assess the physiological changes related to space flight. It has also been employed to assess the impact of immobility on cognitive functioning. Given the positive relationship between physical activity and cognitive function, it is expected that bed rest negatively affects cognitive performance. In addition, it is expected that the effects are most pronounced for executive functions, working memory, and spatial cognition as physical activity interventions predominantly affect the hippocampus, cingulate cortex, and prefrontal cortex.
The main objective of this study is to investigate the effects of 60 days of HDBR with and without two different artificial gravity (AG) protocols as a countermeasure on structural and functional neuroplasticity and their behavioral significance. The investigators will assess the relationship with key neurotrophic factors to better understand the underlying mechanisms of the detrimental effects of HDBR and compare these data to historic data of two European Space Agency (ESA) sponsored HDBR studies of identical duration. Investigators will include neuroimaging protocols that overlap with ongoing and future studies on the International Space Station (ISS) and other space analogs such as the Human Exploration Research Analog (HERA) and Antarctica.
APPROACH:
Twenty-four subjects will be randomly assigned to one of the following three groups: (1) bed rest without any countermeasure, (2) bed rest combined with a continuous AG protocol, and (3) bed rest with an intermittent protocol. The primary outcomes are to assess within-subject changes in left and right hippocampal volumes induced by stress associated with bed rest immediately after before bed rest, and to analyze between-subject changes in left and right hippocampal volume between the bed rest control group and the AG countermeasure groups. Prior to bed rest subjects will be familiarized and trained on HYPER.Campus tasks by going through practice tests and trials. Subjects will also be asked to complete questionnaires.
Bed rest subjects will be assessed with quantitative structural and functional MRIs before, during and after HDBR. The neuroimaging approach employs highly unique imaging sequences, including ultra-high resolution imaging of the hippocampus. To assess the relation between neurostructural and functional changes and changes in cognitive performance, investigators will perform a unique set of unobtrusive cognitive measurement tools with and without an MRI before, during, and after HDBR. The tasks are designed and scheduled to avoid any masking effects due to repetitive testing and/or changing body posture, and specifically probe the anatomical correlates that are expected to be most vulnerable to the detrimental effects of HDBR, such as the hippocampus, the cingulate cortex and the prefrontal cortex.
Saliva samples will be collected in the morning and evening to assess cortisol concentration. In addition, blood samples will be drawn in the morning after an overnight fast as well as immediately after AG on the same day before, during, and after bed rest.
Cognitive performance will be assessed pre-bed rest, during bed rest, and post bed rest using the Cognition software which is comprised of 10 brief cognitive tests that cover a wide range of cognitive domains. In addition, a battery of tests will assess cognitive performance, spatial updating, memory performance, dual task performance, topographical memory, spatial memory, wayfinding performance, navigation strategies, and orientation preference pre-bed rest, during bed rest, and post bed rest.
RESULTS:
This study is in progress. Results will be available at a later date.
