A study determined that in the spaceflight under weightlessness condition, human's brain function may be affected by the changes of physiological effects along with the distribution of blood and body fluids to the head. This variation of brain function will influence the performance of astronauts and therefore create possible harm to flight safety.

This study employs 20 male subjects in a 7-day−6° head-down tilted (HDT) bed rest model to simulate physiological effects under weightlessness condition, and use behavioral, electrophysiological techniques to compare the changes of mental rotation ability (MR ability) before and after short-term simulated weightlessness state

Researchers have proposed that microgravity can harm human's cardiovascular system, endocrine system, the central nerve system and other systems. In addition, the changes of central nerve system will further influence the vestibular function, the visual and sensory – motor system, which as a result would affect human's cognitive function.

During the flight under weightlessness condition, brain function will be affected by the physiological effects of the redistribution of blood and body fluids to the head, which may influence the performance of astronauts. This requires astronaut to have extraordinary spatial cognitive ability.

Mental rotation (MR) was first revealed in behavioral experiments, which refers to a type of spatial ability in which a person imagines how an object or array would appear if rotated away from the presented orientation. In the present study, 20 healthy males participated in a 7-day MR task under −6° HDT model.

Behavioral data shows that the accuracy at baseline was higher than HDT period and post HDT period. This finding indicated that simulated microgravity may have negative effects on people's MR ability. Linear regression analysis showed that RT is in significantly liner relationship with RA. As RT is prolonged along with the increasing RA, which is consistent with previous research, they may draw the conclusion that simulated microgravity hasn't changed the basic regularity of mental rotation.

To sum up, 7-day simulated weightlessness does not change the basic process of mental rotation. The overall changing rate of processing speed has shown a down-and-up trend. After HDT, the mental rotation speed is slower than the baseline.

The influence of simulated weightlessness on individual's mental rotation ability reveals a neural adaptive mechanism. In the first 3 days of simulated weightlessness, the MR ability first decreased and then went back, changing like a “U” shape. In the rest days, it went into a state of random fluctuations.

The time series of MR ability changes observed in the current HDT study could help us clarify the performance damage occurred in the early stage of spaceflight. As indicated by the current result, the first 3 days may be the critical period for performance maintain during spaceflight.