Structural Brain Changes following Long-Term 6° Head-Down Tilt Bed Rest as an Analog for Spaceflight

Area of Science:

• Neuroscience
• Space Medicine
• Medical Imaging

Background:

• Astronauts experience visual impairment and increased intracranial pressure after long-term spaceflight (visual impairment and intracranial pressure syndrome).
• Head-down tilt bed rest serves as a terrestrial analog for microgravity's effects.

Purpose of the Study:

• To investigate structural brain changes induced by prolonged head-down tilt bed rest.
• To explore potential correlations between these changes and spaceflight-induced neurological conditions.

Main Methods:

• Volumetric analysis of pre- and post-bed rest brain Magnetic Resonance Imaging (MRI) scans.
• Assessment of gray matter (GM), white matter (WM), cerebrospinal fluid (CSF), and ventricular volumes.
• Analysis of brain tissue density and position relative to the skull.

Main Results:

• No significant changes in overall GM, WM, CSF, or ventricular volumes were detected.
• A notable upward shift and posterior rotation of the brain within the skull occurred.
• Increased brain tissue density at the vertex (frontoparietal lobes) and decreased density at the brain base (orbitofrontal cortex) were observed.
• Posterior brain rotation correlated significantly with changes in ventricular volume, suggesting altered CSF homeostasis.

Conclusions:

• Head-down bed rest induces widespread brain morphologic changes and tissue redistribution due to altered gravity.
• The correlation between ventricular volume changes and posterior brain rotation suggests a disruption in CSF homeostasis.
• Further volumetric analysis of astronaut scans is crucial to link these structural changes to visual impairment and intracranial pressure syndrome.