The Resting-State Brain Activity Change During Short Term Head Down Tilt Bed Rest

Space flight began fifty years ago, hundreds of astronauts had been sent into space to carry out a variety of space missions. In order to carry out space missions successfully, the researchers began to focus on what happens to humans while in space environment and how the performance of individual behavior is affected. These issues were hot among researchers from medicine, physiology, sports science, psychology and many other areas. Researchers attempt to explain the behavior and cognition change from different perspectives, these works could provide a basis to keep the safety during space missions.Continuous behavior monitoring during orbiting had found multiple impairment happened to individuals into space microgravity condition, such as attention, executive control, information processing and spatial motion control etc. Then researchers began to focus on interpreting the internal mechanisms of these behavioral impairment. The researchers initially focused on the behavior change from a physiological point, some works are meaningful. Such as the vestibular system disorders may impair spatial information processing and changes of the musculoskeletal system contributes to the impairment of motion control. Body fluid change, particularly change in the cardiovascular system will affect the implementation of executive control. These findings increase our understanding of the performance decline in microgravity. However, it should be noted that the human brain acts as a control center, few studies mentioned how brain function change in microgravity. This may due to the limited setup of advanced brain imaging equipment in confined environment. Currently only a few studies have documented EEG changes in microgravity. Such as, Alpha and mu frequency abnormal electrical activity may reflect brain activity is suppressed. But due to the spatial resolution of EEG recording technique is low, the functional activity change of the brain in microgravity is still not clear, other imaging techniques need to be brought in during the further study.In the current study, the space flight ground simulation model-6 ° HDBR model and resting-state functional magnetic resonance imaging techniques were combined to investigate individual’s resting state of brain function under short-term HDBR state. During a three-day and a seven-day round HDBR task, sixteen male subjets and twenty male subjects were recruited. Amplitude of low-frequency algorithm, regional homogeneity algorithms and functional connectivity were used to understand the changes of neural activity under HDBR. Through the above quantitative indicators of brain function data, the present study attempts to investigate whether individual’s resting state of brain activity will change and the temporal characteristics and meaning of these brain activity changes. The data may help the researchers understanding the performance decline and cognition impairment during spaceflight. The main results conclusions are summarized as follows.1. Short-term HDBR simulation will affect the resting state brain activity in ocal level. After a three-day head-down bed rest treatment, the amplitude of low-frequency were decreased in dorsomedial nucleus and ventrolateral nucleus of the thalamus region(p<0.05, correctted by Alpasim). Thalamus regional variations observed in research activities may be as a reasonable part of the explanation to motion control decline under microgravity. The more important part is that the local brain activity change in thalamus verified that brain activity do change in local level during simulated microgravity.2. Short-term HDBR simulation will affect functional connectivity among default mode network. After seven days HDBR, the connectivity among superior frontal gyrus, middle frontal gyrus, medial prefrontal cortex, inferior parietal lobule, the hippocampus, thalamus and cingulated were changed(p<0.05, correctted by Alpasim). In addition, pattern recognition calculations show that brain function during microgravity and normal gravity condition can be effectively separated, brain connectomics could used as biomarker to monitor brain activity changes during spaceflight This result meanwhile verified that brain activity do change in global level during simulated microgravity.3. The resting state of brain activity during short-term head-down tilted bed rest shows a trend of adaptive change. The brain activity shows a sudden change in the first a few HDT days and then began to keep stable or recovery. During the seven-day head-down bed rest simulation, amplitude of low-frequency in posterior cingulate, paracentral lobule, anterior cingulate and posterior cerebellar lobe region during HDT is significantly lower than baseline(p<0.05, correctted by Alpasim).4. The resting state brain activity change during short-term head-down bed rest may partly explain the variation of cognitive behavioral performance during spaceflight. In the current study, the mental transformation was investigated as an example to verify the relationship between resting state brain activity change and performance decline. The regional homogeneity change in inferior parietal lobule was found has high correlation with the performance variation in mental transformation(r=- 0.59,p<0.05). This result furthered our understanding of the meaning of brain activity change during HDT.Overall, the results of the current study found that resting-state brain activity do change during short-term simulated microgravity and the resting state of brain activity during short-term head-down tilted bed rest shows a trend of adaptive change. By use mental transformation as an example, the relationship between resting state brain activity change and performance decline has been verified. These findings would help the researcher monitor the brain activity change in real microgravity during spaceflight and develop countermeasure to response performance decline.