Brain displacement and nonlinear deformation following human spaceflight.

Area of Science:

• Neuroscience
• Space Medicine
• Human Physiology

Background:

• Spaceflight alters fluid distribution in the human body, including the brain.
• Previous studies noted average brain position shifts, but detailed regional changes were unclear.

Purpose of the Study:

• To quantify brain regional shifts and deformations after spaceflight and bed rest.
• To investigate behavioral correlates of these brain changes.
• To compare spaceflight effects with a head-down tilt bed rest analog.

Main Methods:

• Analysis of MRI data from 26 astronauts and 24 bed rest participants.
• Rigid body registration to measure brain position changes relative to the skull.
• Quantification of regional deformations and correlations with exposure duration and behavior.

Main Results:

• The brain shifted backward, upward, and rotated pitch post-spaceflight/bed rest, correlating with duration.
• Nonlinear regional deformations and symmetrical left-right shifts were observed.
• Supplementary motor cortex showed largest upward displacement (2.52 mm) after one year in space.
• Recovery occurred within 6 months post-flight, with posterior insula shifts correlating with balance decline.

Conclusions:

• Spaceflight induces comprehensive brain shifts and deformations within the cranial compartment.
• These changes are partially mimicked by head-down tilt bed rest but show distinct differences.
• Findings are crucial for understanding spaceflight's impact on brain structure, function, and behavior.