Effect of Simulated Microgravity on Human Brain Gray Matter and White Matter--Evidence from MRI.

Ke Li,Xiaojuan Guo,Jinsheng Feng,Li Yao,Xin Ouyang,Yawei Zeng,Yu Wang,Lin Ma,Zhen Jin,Huiguang He

doi:10.1371/journal.pone.0135835

Abstract

BackgroundThere is limited and inconclusive evidence that space environment, especially microgravity condition, may affect microstructure of human brain. This experiment hypothesized that there would be modifications in gray matter (GM) and white matter (WM) of the brain due to microgravity.MethodEighteen male volunteers were recruited and fourteen volunteers underwent -6° head-down bed rest (HDBR) for 30 days simulated microgravity. High-resolution brain anatomical imaging data and diffusion tensor imaging images were collected on a 3T MR system before and after HDBR. We applied voxel-based morphometry and tract-based spatial statistics analysis to investigate the structural changes in GM and WM of brain.ResultsWe observed significant decreases of GM volume in the bilateral frontal lobes, temporal poles, parahippocampal gyrus, insula and right hippocampus, and increases of GM volume in the vermis, bilateral paracentral lobule, right precuneus gyrus, left precentral gyrus and left postcentral gyrus after HDBR. Fractional anisotropy (FA) changes were also observed in multiple WM tracts.ConclusionThese regions showing GM changes are closely associated with the functional domains of performance, locomotion, learning, memory and coordination. Regional WM alterations may be related to brain function decline and adaption. Our findings provide the neuroanatomical evidence of brain dysfunction or plasticity in microgravity condition and a deeper insight into the cerebral mechanisms in microgravity condition.

Highlights

Over the last two decades, there have been a lot of long-duration spaceflights
Fractional anisotropy (FA) changes were observed in multiple white matter (WM) tracts
These regions showing gray matter (GM) changes are closely associated with the functional domains of performance, locomotion, learning, memory and coordination

Summary

Introduction

Over the last two decades, there have been a lot of long-duration spaceflights. Studies have shown that astronauts’ cognitive and behavioral activities would be impaired in space environment where there are some harmful factors, such as microgravity, radiation, noise and changed circadian rhythm [1,2,3,4]. Physiology experiments have successfully observed changes in volumes of cerebrospinal fluid, cerebral blood flow and intracranial pressure caused by the redistribution of an astronaut’s body fluid toward head in a weightless environment [7,8,9]. These changes in turn may lead to structural remodelling and alter cerebral autoregulation [10]. There is limited and inconclusive evidence that space environment, especially microgravity condition, may affect microstructure of human brain. This experiment hypothesized that there would be modifications in gray matter (GM) and white matter (WM) of the brain due to microgravity.

Methods

Discussion

Conclusion