The Impact of 6 and 12 Months in Space on Human Brain Structure and Intracranial Fluid Shifts

Abstract

As plans develop for Mars missions, it is important to understand how long-duration spaceflight impacts brain health. Here we report how 12-month (n = 2 astronauts) versus 6-month (n = 10 astronauts) missions impact brain structure and fluid shifts. We collected MRI scans once before flight and four times after flight. Astronauts served as their own controls; we evaluated pre- to postflight changes and return toward preflight levels across the 4 postflight points. We also provide data to illustrate typical brain changes over 7 years in a reference dataset. Twelve months in space generally resulted in larger changes across multiple brain areas compared with 6-month missions and aging, particularly for fluid shifts. The majority of changes returned to preflight levels by 6 months after flight. Ventricular volume substantially increased for 1 of the 12-month astronauts (left: +25%, right: +23%) and the 6-month astronauts (left: 17 ± 12%, right: 24 ± 6%) and exhibited little recovery at 6 months. Several changes correlated with past flight experience; those with less time between subsequent missions had larger preflight ventricles and smaller ventricular volume increases with flight. This suggests that spaceflight-induced ventricular changes may endure for long periods after flight. These results provide insight into brain changes that occur with long-duration spaceflight and demonstrate the need for closer study of fluid shifts.

Keywords: cortical thickness; free water; gray matter volume; spaceflight; ventricular volume.

Figure 1

Astronaut Testing Timeline. MRI scan day is shown in relation to flight start and end. Average scanning day ± standard deviation is presented. Day = 0 is the start of flight. R = Return. To protect their privacy, individual data are not presented here for the 12-month astronauts.

Figure 2

Ventricular volume changes with spaceflight and comparison with aging. Twelve-month astronaut data are shown in orange (TM-1) and yellow (TM-2). Six-month astronaut data are shown in gray. Volume changes are expressed as a percent change from baseline scan. Top: Numeric values on the left “Spaceflight Changes” panels indicate slope of change in units of volume (% of baseline ventricular volume). For the 6-month group, slopes are the group median slope. Error bars indicate standard error. Structural ROIs are overlaid onto slices and a rendered template brain in standard space. Bottom: The average brain change over time for the control participants is indicated by the blue line with blue 95% confidence interval. The control group median slope is indicated in blue text. Error bars indicate standard error. The dMRI control scans were collected over an average of 1.4 ± 0.6 years and thus entire trajectory of change for the dMRI control data is depicted in the figure. ROI Image: Structural ROIs are overlaid onto slices and a rendered template brain in standard space.

Figure 3

Pre-/postcentral gyri FW changes with spaceflight and aging. Twelve-month astronaut data are shown in orange (TM-1) and yellow (TM-2). Six-month astronaut data are shown in gray. Control data are shown in blue. FW is expressed as mean FW fraction change per year. Top: Numeric values in the left “Spaceflight Changes” panels indicate slope of change in units of mean FW fraction per year. For the 6-month group, these slopes are the group median slope. Error bars indicate standard error. Bottom: The average FW change over time for the control participants is indicated by the blue line with blue 95% confidence interval. The control group median slope is indicated in blue text. Error bars indicate standard error. The dMRI control scans were collected over an average of 1.4 ± 0.6 years and thus entire trajectory of change for the dMRI control data is depicted in the figure. ROI Image: Structural ROIs are overlaid onto slices and a rendered template brain in standard space.

Figure 4

SMA and frontal pole FW changes with spaceflight and aging. Twelve-month astronaut data are shown in orange (TM-1) and yellow (TM-2). Six-month astronaut data are shown in gray. Control data are shown in blue. FW is expressed as mean FW fraction change per year. Top: Numeric values in the left “Spaceflight Changes” panels indicate slope of change in units of mean FW fraction per year. For the 6-month group, these slopes are the group median slope. Error bars indicate standard error. Bottom: The average FW change over time for the control participants is indicated by the blue line with blue 95% confidence interval. The control group median slope is indicated in blue text. Error bars indicate standard error. While the T₁ control scans were collected over an average of 7.2 ± 1.5 years, the x-axis here only continues out to 2.75 years in order to provide better visual comparison with the astronaut data. ROI Image: Structural ROIs are overlaid onto slices and a rendered template brain in standard space.

Figure 5

Pre-/postcentral gyri, SMA, and frontal pole GMv and CT changes with spaceflight and aging. Twelve-month astronaut data are shown in orange (TM-1) and yellow (TM-2). Six-month astronaut data are shown in gray. Control data are shown in blue. GMv changes are expressed as a percentage of preflight total intracranial volume (TIV) at baseline scan. CT is expressed as thickness (mm) change per year. Spaceflight Graphs: Numeric values in the left “Spaceflight Changes” panels indicate slope of change in units of volume (% of baseline TIV) or thickness (mm) per year. For the 6-month group, these slopes are the group median slope. Error bars indicate standard error. Control Group Graphs: The average FW change over time for the control participants is indicated by the blue line with blue 95% confidence interval. The control group median slope is indicated in blue text. Error bars indicate standard error. While the T₁ control scans were collected over an average of 7.2 ± 1.5 years, the x-axis here only continues out to 2.75 years in order to provide better visual comparison with the astronaut data.

Figure 6

Cerebellar volume changes with spaceflight and aging. Twelve-month astronaut data are shown in orange (TM-1) and yellow (TM-2). Six-month astronaut data are shown in gray. Volume changes are expressed as a percent change from baseline scan. Top: Numeric values on the left “Spaceflight Changes” panels indicate slope of change in units of % of baseline volume per year. For the 6-month group, these slopes are the group median slope. Error bars indicate standard error. Bottom: The average brain change over time for the control participants is indicated by the blue line with blue 95% confidence interval. The control group median slope is indicated in blue text. Error bars indicate standard error. While the T1 control scans were collected over an average of 7.2 ± 1.5 years, the x-axis here only continues out to 2.75 years in order to provide better visual comparison with the astronaut data. ROI Image: ROIs are indicated on template in CERES space. Warm-colored regions indicate those included in anterior cerebellum ROI. Cool-colored regions indicate those included in posterior cerebellum ROI.