Multiple spaceflights with shorter recovery time impact brain structure

·   Spaceflight experience, in particular longer missions and shorter inter-mission recovery time, induce fluid changes in the brain that may not return to normal before subsequent flights, reports a study published in Scientific Reports. Ventricles — cavities in the brain filled with cerebrospinal fluid — expand increasingly with longer spaceflight missions up to six months, and inter-mission intervals of less than three years may not allow sufficient time for the ventricles to fully recover. 

·    Spaceflight induces widespread changes in the human brain including ventricle volume expansion, but it is unclear if these changes differ with varying mission duration or number of previous spaceflight missions. Rachael Seidler and colleagues scanned the brains of 30 astronauts using MRI, pre- and post-spaceflight, including those on two-week missions (eight astronauts), six-month missions (18 astronauts) and longer (four astronauts). They found that longer spaceflight missions resulted in greater ventricular enlargement, which tapered off after six months in space.

·   They found that there were no statistically reliable associations between the number of previous missions completed and post-fight gray matter volume (GMv) shifts or ventricular volume changes.

·      The authors found that for 11 astronauts who had more than three years to recover in between missions, there was an associated increase in ventricle volume after their most recent mission. However, the authors found that in seven astronauts who had a shorter recovery time in between missions there was little to no enlargement of the ventricles post-flight compared to pre-flight. They propose that less than three years between spaceflights may not be enough time to allow ventricles to recover their compensatory capacity to accommodate the increase in intracranial fluid and they remain enlarged when the astronauts return to space within this time frame.

·  “Among the experienced astronauts, the number of years since the previous mission was significantly associated with post-fight volume changes for all four ventricles. Longer time between successive missions was associated with greater increases in left and right lateral and third ventricle volumes following spaceflight. The fourth ventricle showed the opposite pattern with longer inter-mission delays being associated with greater volumetric decreases following spaceflight,” they write.

·       As spaceflight becomes more frequent and of longer duration, the findings provide insight into how spaceflight experience, both previous and current, may influence brain changes.