berlin spending long periods in space may not only lead tomuscle atrophy and reduction in bone density but also have lasting effects on the brain the first longterm study in russian cosmonauts has warnedlittle is known about how different tissues of the brain react to exposure to microgravity said researcher from ludwig maximilian university of munich lmu in germanyit remains unclear whether and to what extent the neuroanatomical changes so far observed persist following return to normal gravity they saidthe study which appears in the new england journal of medicine shows that differential changes in the three main tissue volumes of the brain remain detectable for at least half a year after the end of their last missionthe study was carried out on ten cosmonauts each of whom had spent an average of 189 days on board the international space station issthe researchers used magnetic resonance tomography mrt to image the brains of the subjects both before and shortly after the conclusion of their longterm missionsin addition seven members of the cohort were reexamined seven months after their return from spacethis is actually the first study in which it has been possible to objectively quantify changes in brain structures following a space mission also including an extended followup period said peter zu eulenburg a professor at lmuthe mrt scans performed in the days after the return to earth revealed that the volume of the grey matter the part of the cerebral cortex that mainly consists of the cell bodies of the neurons was reduced compared to the baseline measurement before launchin the followup scans done 7 months later this effect was partly reversed but nevertheless still detectablein contrast the volume of the cerebrospinal fluid which fills the inner and outer cavities of the brain increased within the cortex during longterm exposure to microgravitymoreover this process was also observable in the outside spaces that cover the brain after the return to earth while the cerebrospinal fluid spaces within returned to near normal sizethe white matter tissue volume those parts of the brain that are primarily made up of nerve fibres appeared to be unchanged upon investigation immediately after landinghowever the subsequent examination 6 months later showed a widespread reduction in volume relative to both earlier measurementsin this case the researchers postulate that over the course of a longer stint in space the volume of the white matter may slowly be replaced by an influx of cerebrospinal fluidupon return to earth this process is then gradually reversed which then results in a relative reduction of white matter volumetaken together our results point to prolonged changes in the pattern of cerebrospinal fluid circulation over a period of at least seven months following the return to earth said zu eulenburghowever whether or not the extensive alterations shown in the grey and the white matter lead to any changes in cognition remains unclear at present he saidaccording to the researchers to minimise the risks associated with longterm missions and to characterise any clinical significance of