Prolonged Microgravity Affects Human Brain Structure and Function

Abstract

Background and purpose: Widespread brain structural changes are seen following extended spaceflight missions. The purpose of this study was to investigate whether these structural changes are associated with alterations in motor or cognitive function.

Materials and methods: Brain MR imaging scans of National Aeronautics and Space Administration astronauts were retrospectively analyzed to quantify pre- to postflight changes in brain structure. Local structural changes were assessed using the Jacobian determinant. Structural changes were compared with clinical findings and cognitive and motor function.

Results: Long-duration spaceflights aboard the International Space Station, but not short-duration Space Shuttle flights, resulted in a significant increase in total ventricular volume (10.7% versus 0%, P < .001, n = 12 versus n = 7). Total ventricular volume change was significantly associated with mission duration (r = 0.72, P = .001, n = 19) but negatively associated with age (r = -0.48, P = .048, n = 19). Long-duration spaceflights resulted in significant crowding of brain parenchyma at the vertex. Pre- to postflight structural changes of the left caudate correlated significantly with poor postural control; and the right primary motor area/midcingulate correlated significantly with a complex motor task completion time. Change in volume of 3 white matter regions significantly correlated with altered reaction times on a cognitive performance task (bilateral optic radiations, splenium of the corpus callosum). In a post hoc finding, astronauts who developed spaceflight-associated neuro-ocular syndrome demonstrated smaller changes in total ventricular volume than those who did not (12.8% versus 6.5%, n = 8 versus n = 4).

Conclusions: While cautious interpretation is appropriate given the small sample size and number of comparisons, these findings suggest that brain structural changes are associated with changes in cognitive and motor test scores and with the development of spaceflight-associated neuro-optic syndrome.

Fig 1.

Ventricular volume increases depended on duration in flight, type of space flight, and astronaut age (A–C). Note that the following modifications were made to the figures to protect astronaut anonymity: Individual data points for mission duration and ISS astronaut ages are not plotted. Instead, the regression line and 95% confidence bands are shown. A, Boxplot showing %ΔVV versus mission duration. B, %ΔVV versus mission duration, including Shuttle and ISS astronauts. C, %ΔVV versus ISS astronaut age at launch.

Fig 2.

Spaceflight results in crowding of brain tissue at the vertex. Red voxels indicate regions along the brain surface where there was an increase in brain parenchyma pre- to postflight due to crowding of the brain tissue as the brain shifted upwards. Blue voxels indicate displaced brain tissue that occurred predominantly along the margins of the lateral and third ventricles due to enlargement of the ventricles postflight.

Fig 3.

Regional deformation of brain parenchyma that significantly predicted performance on motor function tests. A, Regional deformation of brain parenchyma that significantly predicted performance on the Recovery from Fall/Stand Test (P < .05). B, Regional deformation of brain parenchyma that significantly predicted performance on the Dynamic Postural Stability Test (P < .05). C, Regional deformation of brain parenchyma that significantly predicted performance on the Seated Egress and Walk Test (P < .05).

Fig 4.

Regional deformation of brain parenchyma that significantly predicted performance on the Continuous Performance Test (P < .05).