Alterations of Functional Brain Connectivity After Long-Duration Spaceflight as Revealed by fMRI

Abstract

The present study reports alterations of task-based functional brain connectivity in a group of 11 cosmonauts after a long-duration spaceflight, compared to a healthy control group not involved in the space program. To elicit the postural and locomotor sensorimotor mechanisms that are usually most significantly impaired when space travelers return to Earth, a plantar stimulation paradigm was used in a block design fMRI study. The motor control system activated by the plantar stimulation involved the pre-central and post-central gyri, SMA, SII/operculum, and, to a lesser degree, the insular cortex and cerebellum. While no post-flight alterations were observed in terms of activation, the network-based statistics approach revealed task-specific functional connectivity modifications within a broader set of regions involving the activation sites along with other parts of the sensorimotor neural network and the visual, proprioceptive, and vestibular systems. The most notable findings included a post-flight increase in the stimulation-specific connectivity of the right posterior supramarginal gyrus with the rest of the brain; a strengthening of connections between the left and right insulae; decreased connectivity of the vestibular nuclei, right inferior parietal cortex (BA40) and cerebellum with areas associated with motor, visual, vestibular, and proprioception functions; and decreased coupling of the cerebellum with the visual cortex and the right inferior parietal cortex. The severity of space motion sickness symptoms was found to correlate with a post- to pre-flight difference in connectivity between the right supramarginal gyrus and the left anterior insula. Due to the complex nature and rapid dynamics of adaptation to gravity alterations, the post-flight findings might be attributed to both the long-term microgravity exposure and to the readaptation to Earth’s gravity that took place between the landing and post-flight MRI session. Nevertheless, the results have implications for the multisensory reweighting and gravitational motor system theories, generating hypotheses to be tested in future research.

Macro- and microstructural changes in cosmonauts’ brains after long-duration spaceflight

“…The few studies that previously have found signs of functional neuroplasticity after spaceflight have often observed changes in the activity of or connectivity with the cerebellum and primary motor cortex, although these changes have not yet been noted in the basal ganglia ( 10 , 11 ). In addition, one previous study has used dMRI to investigate changes in the brain as a result of long-duration spaceflight, and they found fractional anisotropy decreases in the cerebellum, which the authors ascribe to disrupted WM structural connectivity ( 6 ).…”

Neural Correlates of Vestibular Processing During a Spaceflight Analog With Elevated Carbon Dioxide (CO2): A Pilot Study

“…past work investigating vestibular processing in astronauts. Two previous studies suggest changes from pre-to postspaceflight in resting-state (Demertzi et al, 2016) and taskbased connectivity (Pechenkova et al, 2019) in brain networks that support vestibular function. Our past work has identified disrupted white matter structural connectivity in several tracts that underlie sensory integration and vestibular processes and associations of these brain changes with balance declines (Lee et al, 2019b).…”

“…Astronauts also present with decreased skin sensitivity on the soles of the feet following spaceflight (Lowrey et al, 2014), which has been attributed to in-flight sensory reweighting (i.e., the process of adjusting the magnitude of different sensory contributions to motor control) (Assländer and Peterka, 2014) in compensation for unreliable vestibular inputs in microgravity. A single-subject case study (Demertzi et al, 2016) and recent study of 11 cosmonauts (Pechenkova et al, 2019) examining resting-state and task-based functional magnetic resonance imaging (fMRI) connectivity found evidence for vestibular cortex reorganization and multisensory reweighting following longduration spaceflight. This work provides preliminary evidence of flight-related central vestibular plasticity.…”

Effects of galvanic vestibular stimulation on resting state brain activity in patients with bilateral vestibulopathy

“…Transient experimental vestibular deprivation has been shown to elicit (a) changes in the functional connectivity of the right supramarginal gyrus (SMG) of cosmonauts (Pechenkova et al, ) which correlated with the severity of motion sickness and (b) altered responsivity in the vestibular cortical network (Yuan et al, ). Prolonged head‐down‐tilt bed rest over >2 months (HDBR) is utilized as a spaceflight analog research condition to study related behavioral and neural changes in the absence of gravitational modifications (Yuan et al, ).…”