Effect Of72Hours Simulated Weightlessness On Processing Ability Of Mental Rotation: An ERP Research

During space flight, astronauts have to face various kinds of environmental inter-ference factors that are different from the ground, such as microgravity, radiation,vacuums, noise, etc. Among them, microgravity impacted the human body most. Whilethe real space flight was tight in time and heavy in tasks, it’s difficult to conduct too muchexperiments, hence ground simulation was wildly adopted to explore how space flightenvironment influence the astronauts. Researches had confirmed that head-down tilt（HDT）bed rest simulated microgravity model can effectively simulated the physio-logical effects of body fluid redistribution caused by microgravity, and became inter-nationally recognized human experimentation model.A good spatial ability is fundamental for astronauts to keep a appropriate flightcondition and carry on spatial orientation. Mental rotation test was always been regardedas a typical test to measure the spatial visualization capacity. Although there were someresearches about the alteration of individual mental rotation capacity in microgravity,these researches were based on behavioristics, and were difficult to reveal the cognitive neural mechanism behind. Since the brain function research techniques become more andmore mature, making it possible to investigate the brain mechanism of mental rotation.Therefore, this study was from the perspective of cognitive neuroscience, adoptedhead-down tilt（HDT）bed rest model to simulate weightlessness physiology effects, andused the Event Related Potential technologies to discusses the alteration and neuralmechanisms of individual mental rotation capacity under simulated weightlessness.16healthy volunteer subjects participated in a72hours HDT test, accomplishedstimulate mental rotation tests which with letter "F" and subject "hand" pictures asstimulation, in one day before the HDT（HDT/0D）and continuous three days after HDT（HDT/1D, HDT/2D, HDT/3D）respectively, then compared and analysis the behaviorand ERP data.Main results:1. When the letter "F" was used as surface stimulus to research on mental rotation,the rotation angle of stimulation pictures and the response time had significant linearrelationship. from the HDT/0D to HDT/3D, the linear fitting intercept of mental rotationtime changing with angle didn’t reach statistically significant level,（F（3,45）=1.216, P=0.309）, the fitting of slope also didn’t reach the statistically significant,（F（3,45）=0.235,P=0.817. ERP results indicate that the main effect of rotation angle reached statisticallysignificant（,F（3,45）=44.478, P <0.001）, and the average amplitude among4angles hadsignificant difference; Main effect of HDT time factor reached statistically significant（F（3,45）=6.585, P=0.004）, and average amplitude between HDT/1D HDT/0D hadsignificant difference, other time points had no statistical difference; The main effect ofelectrode point was significant,（F（2,30）=7.771, P=0.003）, the average amplitude ofPz was significantly greater than in P3, P4had no difference between either Pz or P3.2. When the "Hand" picture was used as surface stimulus to research on mentalrotation, the rotation angle of stimulation pictures and the response time had significantlinear relationship. from the HDT/0D to HDT/3D, the linear fitting intercept of mentalrotation time changing with angle didn’t reach statistically significant level,（F（3,14）= 0.551, P=0.650）, the fitting of slope reached the statistically significant,（F（3,45）=4.338,P=0.009）. ERP results indicate that the main effect of rotation angle reachedstatistically significant（,F（3,45）=43.482, P <0.001）, and the average amplitude among4angles had significant difference; Main effect of HDT time factor reached statisticallysignificant（F（3,45）=8.284, P=0.003）, and average amplitude between HDT/1DHDT/0D had significant difference, other time points had no statistical difference; Themain effect of electrode point was significant,（F（2,30）=6.928, P=0.007）, the averageamplitude of P3was significantly less than P3and P4, Pz and P4had no statisticaldifference.Main conclusions:Simulated weightlessness didn’t change the process of individual mental rotation, thegreater of the rotation angle, the longer the reaction time and the more psychologicalresources it required. However, the duration of the simulated weightlessness significantlyaffect the individuals’ mental rotation capacity. After HDT, individuals’ mental rotationcapacity fell first and then recovered. Overall, the foundation reaction time, the rotatingreaction and the average amplitude, all showed a inverted "U" trend, indicating brainfunction had a adaptive change under physiological effect of weightlessness. Thephysiological effect of weightlessness impact more on the body mental rotation than onthe the object mental rotation, both body and object mental rotation appeared righthemisphere advantage, and latter was more apparent.