What happens to the human brain when the force of gravity is removed from the equation? New research is beginning to reveal that not only is space travel a challenge to the human body’s muscles and skeletal system, but it actually causes the human brain to move positions within its cavity.
For many years, researchers have known about microgravity’s impact on bodily fluid distribution, muscle atrophy, and bone density. Today, sophisticated MRI research has discovered that even the brain itself migrates in measurable patterns during long-duration missions. After examining data from 26 astronauts, along with microgravity simulation experiments conducted in Earth’s gravity, researchers discovered that the brain migrates in an upward, backward, and slightly rotated fashion. In some cases, this migration exceeds 2.5 millimeters, particularly in areas related to sensory and motor functions, in direct relation to the length of time spent in space.
In microgravity environments, there is no force of gravity to hold it in place. The cerebrospinal fluid is able to move towards the brain. The brain is lifted slightly due to this. The brain is not lifted evenly. In fact, there is a region of the brain known as the supplementary motor area responsible for controlling movement. In this region of the brain, there has been a marked shift upwards after a year-long space mission.
Comparison with head-down tilt bed rest studies, a typical model of microgravity, shows similar trends, but some important differences are also observed. Bed rest volunteers demonstrate greater displacement in the backward direction, whereas in microgravity, a greater displacement in the upward direction is observed.
What is intriguing is that not all changes are necessarily negative. Structural changes may also include beneficial neuroplastic changes. The increase in volume of gray matter in sensorimotor areas may very well be a mechanism by which the brain is adjusting to new sensory inputs generated by microgravity conditions. Animal studies and concurrent studies on humans have found that these changes can result in an improvement in certain sensory processing functions during space travel, though functions such as balance may be temporarily compromised on return to Earth.
However, tracking such changes is difficult in space. Methods like optical coherence tomography (OCT) have already been employed on the International Space Station to monitor eye health and could be used for the early detection of fluid-related brain shifts. The advent of new compact imaging technology and the development of non-invasive intracranial pressure monitors will enable the future possibility of autonomous tracking of fluid-related changes in the brain for deep space missions where real-time feedback is difficult because of the presence of communication delays.
In terms of mission planning, it is essential to know the timeline of both the onset and recovery of these effects. When some of these changes happen in a matter of weeks, countermeasures can be implemented sooner. When a recovery time of several months is involved, the returning individuals will require some form of rehabilitation before they can take on high-demand activities on Earth if they come from Mars or lunar bases.
As the human species looks toward the long journey beyond low earth orbit, it has become clear through the findings of current studies that the effect of microgravity on the human brain is one that we are just beginning to understand. Whether it be a danger, an adaptation, or something in between, this will be one of the defining factors in ensuring the health and well-being of astronauts on the way toward making the human species a spacefaring one.
