Impacts of spaceflight experience on human brain structure.

Area of Science:

• Neuroscience
• Space Medicine
• Human Physiology

Background:

• Spaceflight causes significant alterations in human brain structure.
• The impact of mission duration and prior spaceflight experience on these changes remains unclear.

Purpose of the Study:

• To investigate how mission duration and astronaut experience influence spaceflight-induced brain morphology changes.
• To quantify changes in gray matter, white matter, free water, and ventricular volume.

Main Methods:

• Voxelwise analysis of brain gray matter volume, white matter microstructure, and extracellular free water (FW) distribution.
• Measurement of ventricular volumes from pre- to post-flight in 30 astronauts.
• Correlation of brain changes with mission duration and inter-mission intervals.

Main Results:

• Longer missions correlated with greater expansion of the lateral and third ventricles, primarily within the first six months.
• Extended inter-mission intervals (over 3 years) were associated with greater ventricle expansion post-flight.
• Astronauts with less than 3 years between missions showed minimal ventricle enlargement.

Conclusions:

• Ventricle expansion in the brain continues with increasing space mission duration.
• Inter-mission intervals shorter than 3 years may impede full recovery of the brain's adaptive capacity.
• These findings suggest potential limits to human brain adaptation during prolonged or repeated spaceflight.