Space week day 5: A bit more gravity for my brain, please

Microgravity is the condition when astronauts experience weightlessness in space. While orbiting the Earth, astronauts aboard the International Space Station experience just that.

A lack of gravitational force is known to affect multiple physiological functions of astronauts, particularly damage to the central nervous system.

Notably, it affects the brain, where fluid shifts can alter brain shape, structure, and function. Research indicates that astronauts’ brains undergo noticeable changes of shape in space.

In this review, the researchers analyzed all available studies on brain scans of astronauts, comparing scans taken before they departed from Earth and after their return from space. Here’s what they discovered.

Structural changes to the brain
Space missions, especially those of long duration, can significantly alter brain structure. Studies using MRI have revealed that astronauts experience changes in both gray matter (brain cells) and white matter (connections) volumes. Some of the astronaut's brain regions expand while others shrink.

Astronauts also see a shift in the brain fluids. The brain fluid normally envelops and protects the brain. It is located around the brain and within the brain in cavities called the ventricles.

When the brain fluid shifts upwards due to the absence of gravity, it can lead to actual changes in the shape and size of the brain. That may affect neural functions. Due to the changes in fluid dynamics, the brain tissue shifts and crowds in certain areas, and the cavities within the brain may expand. These changes are similar to those seen in aging ..

The question of how these changes relate to mission duration and prior spaceflight experience remains complex and unresolved. It seems that long-term exposure to microgravity might exacerbate brain changes, but the relationship between mission duration and brain alterations is not straightforward.

Impact on cognition
The structural changes in the brain caused by spaceflight may not only alter its appearance on scans but could also impact astronauts' physical and cognitive abilities.

Changes in brain volume and fluid dynamics, such as those observed in the cerebellum, the little brain responsible for balance, may impact balance and reaction times. This is especially important in astronauts’ performance on tasks requiring coordination and may very well explain the balance changes seen in the astronauts from before spaceflight to after spaceflight.

In particular, the deep-seated caudate nucleus, which plays a key role in motor control, appears to undergo structural changes due to microgravity. These changes can contribute to motor impairments and body alignment issues.

Furthermore, connections between different brain regions seem to change during spaceflight. An example is the connection between the brain cells involved in spatial awareness (vision) and motor control. Studies showed altered connectivity after space missions. That suggests that spaceflight-induced changes in the brain are not only a matter of visually changed anatomy but also how the brain is wired.

The role of neuroplasticity and long-term effects
The brain's ability to adapt to the stress of microgravity during space travel without the astronaut going bonkers is partly explained by neuroplasticity.

Neuroplasticity is the brain's ability to change, reorganize, and adapt by forming new connections, helping it learn, heal, and adjust to new situations.

For example, a normal "earth brain" compensates for age-related changes by increasing the surface area of certain regions despite thinning in others. This adaptive response could help the "astronaut brain" counteract some of the negative effects of spaceflight on brain structure.

However, this process may not be perfect, and there could be long-term consequences for cognitive function, especially if multiple space missions are undertaken or, in the future, much longer extraterrestrial space travel. The brain seems to adapt, but these adjustments may come with trade-offs, such as impairments in certain functions, like vision and motor control.

The effects of repeated spaceflight, particularly on the ventricles and fluid dynamics, may limit the brain's ability to adapt. While astronauts with more spaceflight experience show less compliance in their brain's fluid dynamics, those new to spaceflight seem to have a more flexible brain that can more easily accommodate the changes induced by microgravity. The cumulative effect of repeated space missions could have lasting consequences on astronauts' mental and physical performance.

So. The impacts of spaceflight on the brain extend beyond simple structural alterations. Connections are changed. Function altered.

These findings suggest that as we look to longer missions, such as those to Mars, understanding the brain’s capacity to adapt to the unique environment of space is crucial for ensuring astronaut health and safety.

About the scientific paper:

First author Sahar Rezaei, Iran
Published in: Brain Imaging and Behaviour, October 2024
Link to paper: https://link.springer.com/article/10.1007/s11682-024-00894-7