Daily artificial gravity is associated with greater neural efficiency during sensorimotor adaptation.

Altered vestibular signaling and body unloading in microgravity results in sensory reweighting and adaptation. Microgravity effects are well-replicated in head-down tilt bed rest (HDBR). Artificial gravity (AG) is a potential countermeasure to mitigate the effects of microgravity on human physiology and performance. We examined the effectiveness of daily AG for mitigating brain and/or behavioral changes in 60 days of HDBR. One group received AG for 30 minutes daily (AG; n = 16) and a control group spent the same time in HDBR but received no AG (CTRL; n = 8). All participants performed a sensorimotor adaptation task five times during fMRI scanning: twice prior to HDBR, twice during HDBR, and once following HDBR. The AG group showed similar behavioral adaptation effects compared with the CTRLs. We identified decreased brain activation in the AG group from pre to late HDBR in the cerebellum for the task baseline portion and in the thalamus, calcarine, cuneus, premotor cortices, and superior frontal gyrus in the AG group during the early adaptation phase. The two groups also exhibited differential brain-behavior correlations. Together, these results suggest that AG may result in a reduced recruitment of brain activity for basic motor processes and sensorimotor adaptation. These effects may stem from the somatosensory and vestibular stimulation that occur with AG.

Changes in working memory brain activity and task-based connectivity after long-duration spaceflight.

We studied the longitudinal effects of approximately 6 months of spaceflight on brain activity and task-based connectivity during a spatial working memory (SWM) task. We further investigated whether any brain changes correlated with changes in SWM performance from pre- to post-flight. Brain activity was measured using functional magnetic resonance imaging while astronauts (n = 15) performed a SWM task. Data were collected twice pre-flight and 4 times post-flight. No significant effects on SWM performance or brain activity were found due to spaceflight; however, significant pre- to post-flight changes in brain connectivity were evident. Superior occipital gyrus showed pre- to post-flight reductions in task-based connectivity with the rest of the brain. There was also decreased connectivity between the left middle occipital gyrus and the left parahippocampal gyrus, left cerebellum, and left lateral occipital cortex during SWM performance. These results may reflect increased visual network modularity with spaceflight. Further, increased visual and visuomotor connectivity were correlated with improved SWM performance from pre- to post-flight, while decreased visual and visual-frontal cortical connectivity were associated with poorer performance post-flight. These results suggest that while SWM performance remains consistent from pre- to post-flight, underlying changes in connectivity among supporting networks suggest both disruptive and compensatory alterations due to spaceflight.

Artificial gravity during a spaceflight analog alters brain sensory connectivity.

Spaceflight has numerous untoward effects on human physiology. Various countermeasures are under investigation including artificial gravity (AG). Here, we investigated whether AG alters resting-state brain functional connectivity changes during head-down tilt bed rest (HDBR), a spaceflight analog. Participants underwent 60 days of HDBR. Two groups received daily AG administered either continuously (cAG) or intermittently (iAG). A control group received no AG. We assessed resting-state functional connectivity before, during, and after HDBR. We also measured balance and mobility changes from pre- to post-HDBR. We examined how functional connectivity changes throughout HDBR and whether AG is associated with differential effects. We found differential connectivity changes by group between posterior parietal cortex and multiple somatosensory regions. The control group exhibited increased functional connectivity between these regions throughout HDBR whereas the cAG group showed decreased functional connectivity. This finding suggests that AG alters somatosensory reweighting during HDBR. We also observed brain-behavioral correlations that differed significantly by group. Control group participants who showed increased connectivity between the putamen and somatosensory cortex exhibited greater mobility declines post-HDBR. For the cAG group, increased connectivity between these regions was associated with little to no mobility declines post-HDBR. This suggests that when somatosensory stimulation is provided via AG, functional connectivity increases between the putamen and somatosensory cortex are compensatory in nature, resulting in reduced mobility declines. Given these findings, AG may be an effective countermeasure for the reduced somatosensory stimulation that occurs in both microgravity and HDBR.

Brain connectivity and behavioral changes in a spaceflight analog environment with elevated CO2.

Astronauts are exposed to microgravity and elevated CO2 levels onboard the International Space Station. Little is known about how microgravity and elevated CO2 combine to affect the brain and sensorimotor performance during and after spaceflight. Here we examined changes in resting-state functional connectivity (FC) and sensorimotor behavior associated with a spaceflight analog environment. Participants underwent 30 days of strict 6o head-down tilt bed rest with elevated ambient CO2 (HDBR+CO2). Resting-state functional magnetic resonance imaging and sensorimotor assessments were collected 13 and 7 days prior to bed rest, on days 7 and 29 of bed rest, and 0, 5, 12, and 13 days following bed rest. We assessed the time course of FC changes from before, during, to after HDBR+CO2. We then compared the observed connectivity changes with those of a HDBR control group that underwent HDBR in standard ambient air. Moreover, we assessed associations between post-HDBR+CO2 FC changes and alterations in sensorimotor performance. HDBR+CO2 was associated with significant changes in functional connectivity between vestibular, visual, somatosensory and motor brain areas. Several of these sensory and motor regions showed post-HDBR+CO2 FC changes that were significantly associated with alterations in sensorimotor performance. We propose that these FC changes reflect multisensory reweighting associated with adaptation to the HDBR+CO2 microgravity analog environment. This knowledge will further improve HDBR as a model of microgravity exposure and contribute to our knowledge of brain and performance changes during and after spaceflight.

The effects of a spaceflight analog with elevated CO2 on sensorimotor adaptation.

Aboard the International Space Station (ISS), astronauts must adapt to altered vestibular and somatosensory inputs due to microgravity. Sensorimotor adaptation on Earth is often studied with a task that introduces visuomotor conflict. Retention of the adaptation process, known as savings, can be measured when subjects are exposed to the same adaptive task multiple times. It is unclear how adaptation demands found on the ISS might interfere with the ability to adapt to other sensory conflict at the same time. In the present study, we investigated the impact of 30 days' head-down tilt bed rest combined with elevated carbon dioxide (HDBR + CO2) as a spaceflight analog on sensorimotor adaptation. Eleven subjects used a joystick to move a cursor to targets presented on a computer screen under veridical cursor feedback and 45° rotated feedback. During this NASA campaign, five individuals presented with optic disk edema, a sign of spaceflight-associated neuro-ocular syndrome (SANS). Thus, we also performed post hoc exploratory analyses between subgroups who did and did not show signs of SANS. HDBR + CO2 had some impact on sensorimotor adaptation, with a lack of savings across the whole group. SANS individuals showed larger, more persistent after-effects, suggesting a shift from relying on cognitive to more implicit processing of adaptive behaviors. Overall, these findings suggest that HDBR + CO2 alters the way in which individuals engage in sensorimotor processing. These findings have important implications for missions and mission training, which require individuals to adapt to altered sensory inputs over long periods in space.NEW & NOTEWORTHY This is the first bed rest campaign examining sensorimotor adaptation and savings in response to the combined effect of HDBR + CO2 and to observe signs of spaceflight-associated neuro-ocular syndrome (SANS) in HDBR participants. Our findings suggest that HDBR + CO2 alters the way that individuals engage in sensorimotor processing. Individuals who developed signs of SANS seem to rely more on implicit rather than cognitive processing of adaptive behaviors than subjects who did not present signs of SANS.

Ophthalmic changes in a spaceflight analog are associated with brain functional reorganization.

Following long-duration spaceflight, some astronauts exhibit ophthalmic structural changes referred to as Spaceflight Associated Neuro-ocular Syndrome (SANS). Optic disc edema is a common sign of SANS. The origin and effects of SANS are not understood as signs of SANS have not manifested in previous spaceflight analog studies. In the current spaceflight analog study, 11 subjects underwent 30 days of strict head down-tilt bed rest in elevated ambient carbon dioxide (HDBR+CO2 ). Using functional magnetic resonance imaging (fMRI), we acquired resting-state fMRI data at 6 time points: before (2), during (2), and after (2) the HDBR+CO2 intervention. Five participants developed optic disc edema during the intervention (SANS subgroup) and 6 did not (NoSANS group). This occurrence allowed us to explore whether development of signs of SANS during the spaceflight analog impacted resting-state functional connectivity during HDBR+CO2 . In light of previous work identifying genetic and biochemical predictors of SANS, we further assessed whether the SANS and NoSANS subgroups exhibited differential patterns of resting-state functional connectivity prior to the HDBR+CO2 intervention. We found that the SANS and NoSANS subgroups exhibited distinct patterns of resting-state functional connectivity changes during HDBR+CO2 within visual and vestibular-related brain networks. The SANS and NoSANS subgroups also exhibited different resting-state functional connectivity prior to HDBR+CO2 within a visual cortical network and within a large-scale network of brain areas involved in multisensory integration. We further present associations between functional connectivity within the identified networks and previously identified genetic and biochemical predictors of SANS. Subgroup differences in resting-state functional connectivity changes may reflect differential patterns of visual and vestibular reweighting as optic disc edema develops during the spaceflight analog. This finding suggests that SANS impacts not only neuro-ocular structures, but also functional brain organization. Future prospective investigations incorporating sensory assessments are required to determine the functional significance of the observed connectivity differences.

Optic flow improves adaptability of spatiotemporal characteristics during split-belt locomotor adaptation with tactile stimulation.

Human locomotor adaptation requires feedback and feed-forward control processes to maintain an appropriate walking pattern. Adaptation may require the use of visual and proprioceptive input to decode altered movement dynamics and generate an appropriate response. After a person transfers from an extreme sensory environment and back, as astronauts do when they return from spaceflight, the prolonged period required for re-adaptation can pose a significant burden. In our previous paper, we showed that plantar tactile vibration during a split-belt adaptation task did not interfere with the treadmill adaptation however, larger overground transfer effects with a slower decay resulted. Such effects, in the absence of visual feedback (of motion) and perturbation of tactile feedback, are believed to be due to a higher proprioceptive gain because, in the absence of relevant external dynamic cues such as optic flow, reliance on body-based cues is enhanced during gait tasks through multisensory integration. In this study, we therefore investigated the effect of optic flow on tactile-stimulated split-belt adaptation as a paradigm to facilitate the sensorimotor adaptation process. Twenty healthy young adults, separated into two matched groups, participated in the study. All participants performed an overground walking trial followed by a split-belt treadmill adaptation protocol. The tactile group (TC) received vibratory plantar tactile stimulation only, whereas the virtual reality and tactile group (VRT) received an additional concurrent visual stimulation: a moving virtual corridor, inducing perceived self-motion. A post-treadmill overground trial was performed to determine adaptation transfer. Interlimb coordination of spatiotemporal and kinetic variables was quantified using symmetry indices and analyzed using repeated-measures ANOVA. Marked changes of step length characteristics were observed in both groups during split-belt adaptation. Stance and swing time symmetries were similar in the two groups, suggesting that temporal parameters are not modified by optic flow. However, whereas the TC group displayed significant stance time asymmetries during the post-treadmill session, such aftereffects were absent in the VRT group. The results indicated that the enhanced transfer resulting from exposure to plantar cutaneous vibration during adaptation was alleviated by optic flow information. The presence of visual self-motion information may have reduced proprioceptive gain during learning. Thus, during overground walking, the learned proprioceptive split-belt pattern is more rapidly overridden by visual input due to its increased relative gain. The results suggest that when visual stimulation is provided during adaptive training, the system acquires the novel movement dynamics while maintaining the ability to flexibly adapt to different environments.

Plantar tactile perturbations enhance transfer of split-belt locomotor adaptation.

Patterns of human locomotion are highly adaptive and flexible and depend on the environmental context. Locomotor adaptation requires the use of multisensory information to perceive altered environmental dynamics and generate an appropriate movement pattern. In this study, we investigated the use of multisensory information during locomotor learning. Proprioceptive perturbations were induced by vibrating tactors, placed bilaterally over the plantar surfaces. Under these altered sensory conditions, participants were asked to perform a split-belt locomotor task representative of motor learning. Twenty healthy young participants were separated into two groups: no-tactors (NT) and tactors (TC). All participants performed an overground walking trial, followed by treadmill walking including 18 min of split-belt adaptation and an overground trial to determine transfer effects. Interlimb coordination was quantified by symmetry indices and analyzed using mixed repeated-measures ANOVAs. Both groups adapted to the locomotor task, indicated by significant reductions in gait symmetry during the split-belt task. No significant group differences in spatiotemporal and kinetic parameters were observed on the treadmill. However, significant group differences were observed overground. Step and swing time asymmetries learned on the split-belt treadmill were retained and decayed more slowly overground in the TC group whereas in NT, asymmetries were rapidly lost. These results suggest that tactile stimulation contributed to increased lower limb proprioceptive gain. High proprioceptive gain allows for more persistent overground after effects, at the cost of reduced adaptability. Such persistence may be utilized in populations displaying pathologic asymmetric gait by retraining a more symmetric pattern.

Screening people in the waiting room for vestibular impairments.

OBJECTIVE: Primary care physicians need good screening tests of the vestibular system to help them determine whether patients who complain of dizziness should be evaluated for vestibular disorders. The goal of this study was to determine whether current, widely used screening tests of the vestibular system predict subsequent performance on objective diagnostic tests of the vestibular system (ENG). METHODS: Of 300 subjects who were recruited from the waiting room of a primary care clinic and were screened there, 69 subjects subsequently volunteered for ENGs in the otolaryngology department. The screening study included age, history of vertigo, head impulse tests, Dix-Hallpike maneuvers, and the Clinical Test of Sensory Integration and Balance with the head still and the head pitching at 0.33 Hz. The ENG included Dix-Hallpike maneuvers, vestibular-evoked myogenic potentials, bithermal water caloric tests, and low-frequency sinusoids in the rotatory chair in darkness. RESULTS: The scores on the screening were related to the total ENG, but odds ratios were not significant for some variables, probably because of the small sample size. CONCLUSIONS: A larger sample may have yielded stronger results, but in general the high odds ratios suggest a relation between the ENG score and Dix-Hallpike responses and between the ENG scores and some Clinical Test of Sensory Integration and Balance responses.

Dynamic changes in perivascular space morphology predict signs of spaceflight-associated neuro-ocular syndrome in bed rest.

During long-duration spaceflight, astronauts experience headward fluid shifts and expansion of the cerebral perivascular spaces (PVS). A major limitation to our understanding of the changes in brain structure and physiology induced by spaceflight stems from the logistical difficulties of studying astronauts. The current study aimed to determine whether PVS changes also occur on Earth with the spaceflight analog head-down tilt bed rest (HDBR). We examined how the number and morphology of magnetic resonance imaging-visible PVS (MV-PVS) are affected by HDBR with and without elevated carbon dioxide (CO2). These environments mimic the headward fluid shifts, body unloading, and elevated CO2 observed aboard the International Space Station. Additionally, we sought to understand how changes in MV-PVS are associated with signs of Spaceflight Associated Neuro-ocular Syndrome (SANS), ocular structural alterations that can occur with spaceflight. Participants were separated into two bed rest campaigns: HDBR (60 days) and HDBR + CO2 (30 days with elevated ambient CO2). Both groups completed multiple magnetic resonance image acquisitions before, during, and post-bed rest. We found that at the group level, neither spaceflight analog affected MV-PVS quantity or morphology. However, when taking into account SANS status, persons exhibiting signs of SANS showed little or no MV-PVS changes, whereas their No-SANS counterparts showed MV-PVS morphological changes during the HDBR + CO2 campaign. These findings highlight spaceflight analogs as models for inducing changes in MV-PVS and implicate MV-PVS dynamic compliance as a mechanism underlying SANS. These findings may lead to countermeasures to mitigate health risks associated with human spaceflight.

Study protocol to examine the effects of spaceflight and a spaceflight analog on neurocognitive performance: extent, longevity, and neural bases.

BACKGROUND: Long duration spaceflight (i.e., 22 days or longer) has been associated with changes in sensorimotor systems, resulting in difficulties that astronauts experience with posture control, locomotion, and manual control. The microgravity environment is an important causal factor for spaceflight induced sensorimotor changes. Whether spaceflight also affects other central nervous system functions such as cognition is yet largely unknown, but of importance in consideration of the health and performance of crewmembers both in- and post-flight. We are therefore conducting a controlled prospective longitudinal study to investigate the effects of spaceflight on the extent, longevity and neural bases of sensorimotor and cognitive performance changes. Here we present the protocol of our study. METHODS/DESIGN: This study includes three groups (astronauts, bed rest subjects, ground-based control subjects) for which each the design is single group with repeated measures. The effects of spaceflight on the brain will be investigated in astronauts who will be assessed at two time points pre-, at three time points during-, and at four time points following a spaceflight mission of six months. To parse out the effect of microgravity from the overall effects of spaceflight, we investigate the effects of seventy days head-down tilted bed rest. Bed rest subjects will be assessed at two time points before-, two time points during-, and three time points post-bed rest. A third group of ground based controls will be measured at four time points to assess reliability of our measures over time. For all participants and at all time points, except in flight, measures of neurocognitive performance, fine motor control, gait, balance, structural MRI (T1, DTI), task fMRI, and functional connectivity MRI will be obtained. In flight, astronauts will complete some of the tasks that they complete pre- and post flight, including tasks measuring spatial working memory, sensorimotor adaptation, and fine motor performance. Potential changes over time and associations between cognition, motor-behavior, and brain structure and function will be analyzed. DISCUSSION: This study explores how spaceflight induced brain changes impact functional performance. This understanding could aid in the design of targeted countermeasures to mitigate the negative effects of long-duration spaceflight.

Influence of muscle strength to weight ratio on functional task performance.

Existing models of muscle deconditioning such as bed rest are expensive and time-consuming. We propose a new model utilizing a weighted suit to manipulate muscle strength, power, or endurance relative to body weight. The aims of the study were to determine as to which muscle measures best predict functional task performance and to determine muscle performance thresholds below which task performance is impaired. Twenty subjects performed seven occupational astronaut tasks (supine and upright seat egress and walk, rise from fall, hatch opening, ladder climb, object carry, and construction board activity), while wearing a suit weighted with 0-120 % of body weight. Models of the relationship between muscle function/body weight and task completion time were developed using fractional polynomial regression and verified with pre- and post-flight astronaut performance data. Spline regression was used to identify muscle function thresholds for each task. Upright seat egress and walk was the most difficult task according to the spline regression analysis thresholds. Thresholds normalized to body weight were 17.8 N/kg for leg press isometric force, 17.6 W/kg for leg press power, 78.8 J/kg for leg press work, 5.9 N/kg isometric knee extension and 1.9 Nm/kg isokinetic knee extension torque. Leg press maximal isometric force/body weight was the most reliable measure for modeling performance of ambulatory tasks. Laboratory-based manipulation of relative strength has promise as an analog for spaceflight-induced loss of muscle function. Muscle performance values normalized to body weight can be used to predict occupational task performance and to establish relevant strength thresholds.

Sharpening the tandem walking test for screening peripheral neuropathy.

OBJECTIVE: Few tests of functional motor behavior are useful for rapidly screening people for lower extremity peripheral neuropathy. The goal of this study was to improve the widely used tandem walking (TW) test. METHODS: We tested "normal" (control) adult and ambulatory patients with peripheral neuropathy (PN) with their eyes open and eyes closed while they performed TW on industrial carpeting in sock-covered feet. Each subject wore a torso-mounted inertial motion unit to measure kinematic data. The data of subjects with PN also were compared with historical data on patients with vestibular impairments. RESULTS: The normal and PN groups differed significantly on TW and on the number of steps completed. PN and vestibular impairments data also differed significantly on both visual conditions. Kinematic data showed that patients with PN were more unstable than normal patients in the group. For the number of steps taken during the eyes open condition, receiver operating characteristic (ROC) values were only 0.81 and for the number of steps taken during the eyes closed condition, ROC values were 0.88. Although not optimal, this ROC value is better. Sensitivity and specificity at a cutoff of two steps were 0.81 and 0.92, respectively, and at a cutoff of three steps were 0.86 and 0.75, respectively. ROC values for kinematic data were <0.8, and when combined with the ROC value for the number of steps, the total ROC value did not improve appreciably. CONCLUSIONS: Although not ideal for screening patients who may have PN, counting the number of steps during TW is a quick and useful clinical test. TW is most sensitive to patients with PN when they are tested with eyes closed.

Sensorimotor adaptation training's effect on head stabilization in response to a lateral perturbation in older adults.

The goal of this study was to determine if exposure to sensorimotor adaptation training improved head stabilization in older adults. Sixteen participants, age 66-81 yr, were assigned at random to the control group (n = 8) or the experimental group (n = 8). Both groups first completed 6 trials of walking a foam pathway consisting of a moveable platform that induced a lateral perturbation during walking. Head-in-space and trunk-in-space angular velocities were collected. Participants from both groups then trained twice per week for 4 wk. Both groups walked on a treadmill for 20 min. The control group viewed a static scene. The experimental group viewed a rotating visual scene that provided a perceptual-motor mismatch. After training, both groups were retested on the perturbation pathway test. The experimental group used a movement strategy that preserved head stabilization compared with the controls (p < .05). This training effect was not retained after 4 wk.

Adaptation in locomotor stability, cognition, and metabolic cost during sensory discordance.

BACKGROUND: Locomotor instability may affect planetary extravehicular activities during the initial adaptation to the new gravitational environment. The goal of this study was to quantify the locomotor, cognitive, and metabolic effects of exposure to a discordant sensory environment. METHODS: A treadmill mounted on a 6-degree-of-freedom motion base was used to present 15 healthy subjects with a destabilizing support surface while they walked. Dependent measures of locomotor stability, cognitive load, and metabolic cost were stride frequency (SF), reaction time (RT), and the volume of oxygen consumed (Vo2), respectively. Subjects completed an 8-min baseline walk followed by 20 min of walking with a continuous, sinusoidal, laterally oscillating support-surface perturbation. Data for minutes 1, 7, 13, and 20 of the support-surface perturbation period were compared with the baseline. RESULTS: SF, RT, and Vo2 were significantly greater during support-surface motion than during the baseline walking condition and showed a trend toward recovery to baseline levels during the perturbation period. Results demonstrated that adaptation to walking in a discordant sensory environment has quantifiable and significant costs in SF, RT, and Vo2 as shown by mean increases of 9%, 20%, and 4%, respectively, collected during the first minute of exposure. By the fourth minute of exposure, mean Vo2 consumption had increased to 20% over its baseline. DISCUSSION: We believe that preflight sensorimotor adaptation training paradigms will impart gains in stability and the ability to multitask, and might increase productive mission time by extending work time in extravehicular activity suits where metabolic expenditure is a limiting factor.

Impacts of spaceflight experience on human brain structure.

Spaceflight induces widespread changes in human brain morphology. It is unclear if these brain changes differ with varying mission duration or spaceflight experience history (i.e., novice or experienced, number of prior missions, time between missions). Here we addressed this issue by quantifying regional voxelwise changes in brain gray matter volume, white matter microstructure, extracellular free water (FW) distribution, and ventricular volume from pre- to post-flight in a sample of 30 astronauts. We found that longer missions were associated with greater expansion of the right lateral and third ventricles, with the majority of expansion occurring during the first 6 months in space then appearing to taper off for longer missions. Longer inter-mission intervals were associated with greater expansion of the ventricles following flight; crew with less than 3 years of time to recover between successive flights showed little to no enlargement of the lateral and third ventricles. These findings demonstrate that ventricle expansion continues with spaceflight with increasing mission duration, and inter-mission intervals less than 3 years may not allow sufficient time for the ventricles to fully recover their compensatory capacity. These findings illustrate some potential plateaus in and boundaries of human brain changes with spaceflight.

Gait adaptability training is affected by visual dependency.

As part of a larger gait adaptability training study, we designed a program that presented combinations of visual flow and support-surface manipulations to investigate the response of healthy adults to walking on a treadmill in novel discordant sensorimotor conditions. A visual dependence score was determined for each subject, and this score was used to explore how visual dependency was linked to locomotor performance (1) during three training sessions and (2) in a new discordant environment presented at the conclusion of training. Performance measures included reaction time (RT), stride frequency (SF), and heart rate (HR), which respectively served as indicators of cognitive load, postural stability, and anxiety. We hypothesized that training would affect performance measures differently for highly visually dependent individuals than for their less visually dependent counterparts. A seemingly unrelated estimation analysis of RT, SF, and HR revealed a significant omnibus interaction of visual dependency by session (p < 0.001), suggesting that the magnitude of differences in these measures across training day 1 (TD1), training day 3 (TD3), and exposure to a novel test is dependent on subjects' levels of visual dependency. The RT result, in particular, suggested that highly visually dependent subjects successfully trained to one set of sensory discordant conditions but were unable to apply their adapted skills when introduced to a new sensory discordant environment. This finding augments rationale for developing customized gait training programs that are tailored to an individual. It highlights one factor--personal level of visual dependency--to consider when designing training conditions for a subject or patient. Finally, the link between visual dependency and locomotor performance may offer predictive insight regarding which subjects in a normal population will require more training when preparing for specific novel locomotor conditions.

Cortical thickness of primary motor and vestibular brain regions predicts recovery from fall and balance directly after spaceflight.

Motor adaptations to the microgravity environment during spaceflight allow astronauts to perform adequately in this unique environment. Upon return to Earth, this adaptation is no longer appropriate and can be disruptive for mission critical tasks. Here, we measured if metrics derived from MRI scans collected from astronauts can predict motor performance post-flight. Structural and diffusion MRI scans from 14 astronauts collected before launch, and motor measures (balance performance, speed of recovery from fall, and tandem walk step accuracy) collected pre-flight and post-flight were analyzed. Regional measures of gray matter volume (motor cortex, paracentral lobule, cerebellum), myelin density (motor cortex, paracentral lobule, corticospinal tract), and white matter microstructure (corticospinal tract) were derived as a-priori predictors. Additional whole-brain analyses of cortical thickness, cerebellar gray matter, and cortical myelin were also tested for associations with post-flight and pre-to-post-flight motor performance. The pre-selected regional measures were not significantly associated with motor behavior. However, whole-brain analyses showed that paracentral and precentral gyri thickness significantly predicted recovery from fall post-spaceflight. Thickness of vestibular and sensorimotor regions, including the posterior insula and the superior temporal gyrus, predicted balance performance post-flight and pre-to-post-flight decrements. Greater cortical thickness pre-flight predicted better performance post-flight. Regional thickness of somatosensory, motor, and vestibular brain regions has some predictive value for post-flight motor performance in astronauts, which may be used for the identification of training and countermeasure strategies targeted for maintaining operational task performance.

The Effects of 30 Minutes of Artificial Gravity on Cognitive and Sensorimotor Performance in a Spaceflight Analog Environment.

The altered vestibular signaling and somatosensory unloading of microgravity result in sensory reweighting and adaptation to conflicting sensory inputs. Aftereffects of these adaptive changes are evident postflight as impairments in behaviors such as balance and gait. Microgravity also induces fluid shifts toward the head and an upward shift of the brain within the skull; these changes are well-replicated in strict head-down tilt bed rest (HDBR), a spaceflight analog environment. Artificial gravity (AG) is a potential countermeasure to mitigate these effects of microgravity. A previous study demonstrated that intermittent (six, 5-mins bouts per day) daily AG sessions were more efficacious at counteracting orthostatic intolerance in a 5 day HDBR study than continuous daily AG. Here we examined whether intermittent daily AG was also more effective than continuous dosing for mitigating brain and behavioral changes in response to 60 days of HDBR. Participants (n = 24) were split evenly between three groups. The first received 30 mins of continuous AG daily (cAG). The second received 30 mins of intermittent AG daily (6 bouts of 5 mins; iAG). The third received no AG (Ctrl). We collected a broad range of sensorimotor, cognitive, and brain structural and functional assessments before, during, and after the 60 days of HDBR. We observed no significant differences between the three groups in terms of HDBR-associated changes in cognition, balance, and functional mobility. Interestingly, the intermittent AG group reported less severe motion sickness symptoms than the continuous group during centrifugation; iAG motion sickness levels were not elevated above those of controls who did not undergo AG. They also had a shorter duration of post-AG illusory motion than cAG. Moreover, the two AG groups performed the paced auditory serial addition test weekly while undergoing AG; their performance was more accurate than that of controls, who performed the test while in HDBR. Although AG did not counteract HDBR-induced gait and balance declines, iAG did not cause motion sickness and was associated with better self-motion perception during AG ramp-down. Additionally, both AG groups had superior cognitive performance while undergoing AG relative to controls; this may reflect attention or motivation differences between the groups.

Longitudinal MRI-visible perivascular space (PVS) changes with long-duration spaceflight.

Humans are exposed to extreme environmental stressors during spaceflight and return with alterations in brain structure and shifts in intracranial fluids. To date, no studies have evaluated the effects of spaceflight on perivascular spaces (PVSs) within the brain, which are believed to facilitate fluid drainage and brain homeostasis. Here, we examined how the number and morphology of magnetic resonance imaging (MRI)-visible PVSs are affected by spaceflight, including prior spaceflight experience. Fifteen astronauts underwent six T1-weighted 3 T MRI scans, twice prior to launch and four times following their return to Earth after ~ 6-month missions to the International Space Station. White matter MRI-visible PVS number and morphology were calculated using an established, automated segmentation algorithm. We validated our automated segmentation algorithm by comparing algorithm PVS counts with those identified by two trained raters in 50 randomly selected slices from this cohort; the automated algorithm performed similarly to visual ratings (r(48) = 0.77, p < 0.001). In addition, we found high reliability for four of five PVS metrics across the two pre-flight time points and across the four control time points (ICC(3,k) > 0.50). Among the astronaut cohort, we found that novice astronauts showed an increase in total PVS volume from pre- to post-flight, whereas experienced crewmembers did not (p = 0.020), suggesting that experienced astronauts may exhibit holdover effects from prior spaceflight(s). Greater pre-flight PVS load was associated with more prior flight experience (r = 0.60-0.71), though these relationships did not reach statistical significance (p > 0.05). Pre- to post-flight changes in ventricular volume were not significantly associated with changes in PVS characteristics, and the presence of spaceflight associated neuro-ocular syndrome (SANS) was not associated with PVS number or morphology. Together, these findings demonstrate that PVSs can be consistently identified on T1-weighted MRI scans, and that spaceflight is associated with PVS changes. Specifically, prior spaceflight experience may be an important factor in determining PVS characteristics.