The orientation of Listing’s Plane (LP) was examined under one-g and zero-g conditions during parabolic flight. Ten healthy subjects participated in the experiment. In zero-g the orientation of LP was consistently altered. LP elevation was tilted backwards by approx. 10° (p = 0.003). The azimuth angles of the left and right eyes also diverged in zero-g, with a statistically significant change (p = 0.04) in the vergence angle between 6.1° and 11.8°. A discernible dissociation in torsional eye position was also observed, which proved to be statistically significant (p = 0.03). The thickness of LP was found to be of the order of 1°, and was not significantly altered by the transitions between one-g and zero-g. Additional control experiments involving repeated measurements of LP under normal laboratory conditions demonstrated that the parameters of LP remain stable in the individual. The parabolic flight results demonstrate that in contrast to re-orientation in the one-g gravitational field, the elimination of gravity represents a qualitative change for the vestibular and oculomotor systems. It appears that given the lack of voluntary control of ocular torsion, the tonic otolith afferences are instrumental in the stabilisation of torsional eye position and consequently of Listing’s Plane. The observed torsional divergence also provides support for the so-called otolith asymmetry hypothesis.
Research Containing: Microgravity
Transitions to and from microgravity, as experienced during a spaceflight mission, radically alter the demands on sensorimotor coordination. In this contribution, attention is directed to the vestibulo-oculomotor response to active head roll-tilt, generally referred to as ocular counterroll (OCR). Results are presented from a single-case longitudinal study over a 435-day spaceflight and from three further subjects over a 30-day period in microgravity. 1. Under one-g test conditions, with the head initially in the comfortable-upright position, active head-to-trunk roll tilt elicits a combined canal- and otolith-mediated oculomotor response, which manifests as a volley of torsional nystagmus beats combined with a tonic OCR. In microgravity it appears that only the transitory canal-mediated torsional nystagmus response remains. In both conditions the initial nystagmus response commences with an anticompensatory torsional fast phase. 2. Under zero-g conditions the head movements were comparable to those under one-g conditions but a consistent reduction in head velocity was observed. Despite this, eye velocity and eye-head velocity gain for the torsional component were found to be enhanced by up to 50% over the first thirty days in prolonged microgravity. 3. The results obtained from the 435-day mission indicate that the initially enhanced response decreases–over the course of several months–to preflight baseline level. The findings indicate that otolith- and canal-ocular responses are not simply added linearly, but rather that the afferent otolith signal also plays an inhibitory, or stabilising role on the canal-mediated response. Further, presuming a re-weighting of otolithic afferent information during prolonged microgravity, it is proposed that a corollary inverse re-weighting of corollary neck-proprioceptive afferences provides an effective substitute. In contrast to the idea that the torsional VOR is an evolutionary relic, it is postulated from the above findings that the anticompensatory saccade and the inherent low gain of OCR result as a compromise between intended reorientation to a tilted visual field and VOR compensation.
Exposure to microgravity during spaceflight is known to elicit orientation illusions, errors in sensory localization, postural imbalance, changes in vestibulo-spinal and vestibulo-ocular reflexes, and space motion sickness. The objective of this experiment was to investigate whether an alteration in cognitive visual-spatial processing, such as the perception of distance and size of objects, is also taking place during prolonged exposure to microgravity. Our results show that astronauts on board the International Space Station exhibit biases in the perception of their environment. Objects' heights and depths were perceived as taller and shallower, respectively, and distances were generally underestimated in orbit compared to Earth. These changes may occur because the perspective cues for depth are less salient in microgravity or the eye-height scaling of size is different when an observer is not standing on the ground. This finding has operational implications for human space exploration missions.
The influence of cosmic radiation and/or microgravity on insect development was studied during the 7 day German Spacelab Mission D1. Eggs of Carausius morosus of five stages differing in sensitivity to radiation and in capacity to regeneration were allowed to continue their development in the BIORACK 22 degrees C incubator, either at microgravity conditions or on the 1 g reference centrifuge. Using the Biostack concept–eggs in monolayers were sandwiched between visual track detectors–and the 1 g reference centrifuge, we were able to separate radiation effects from microgravity effects and also from combined effects of these two factors in space. After retrieval, hatching rates, growth kinetics and anomaly frequencies were determined in the different test samples. The early stages of development turned out to be highly sensitive to single hits of cosmic ray particles as well as to the temporary exposure to microgravity during their development. In some cases, the combined action of radiation and microgravity even amplified the effects exerted by the single parameters of space. Hits by single HZE particles caused early effects, such as body anomalies, as well as late effects, such as retarded growth after hatching. Microgravity exposure lead to a reduced hatching rate. A synergistic action of HZE particle hits and microgravity was established in the unexpectedly high frequency of anomal larvae. However, it cannot be excluded, that cosmic background radiation or low LET HZE particles are also causally involved in damage observed in the microgravity samples.
This report is a detailed review of the current data on the mechanic and gravitational sensitivity of osteoblasts and osteogenic precursor cells in vitro. It summarizes the numerous responses of cells with an osteoblastic phenotype and osteogenic precursor cells and especially their responses to the alteration of their mechanic or gravitational surroundings. The review also discusses the osteogenic cell's pathways of signal transduction and the mechanisms of gravitational sensitivity. It was shown that the earliest multipotent stromal precursor cells of an adult organism's bone marrow can sense changes of intensity in a gravitational or mechanic field in model conditions, which may play a certain role in the development of osteopenia in microgravity.
<Go to ISI>://WOS:000208485500011
Background Back pain and intervertbral disc (IVD) damage are common problems experienced by astronauts. We hypothesize this is from paraspinal muscle deconditioning, ∼5 cm body lengthening from spinal swelling and straightening, and biochemical tissue changes.Objective Examine morphological changes in the lumbar spine induced by spaceflight.Design Prospective, case series clinical study.Setting We studied crewmembers from the National Aeronautics and Space Administration (NASA).Participants Recruitment from International Space Station NASA/European Space Agency/Canadian Space Agency crewmembers, starting 2011. We enrolled 8 NASA crewmembers. One crewmember completed the study. The others are in various stages of testing.Risk factors Assessment Crew members were studied before and after a ∼180 day mission in the International Space Station.Main outcome measurements In pre-flight and post-flight studies of the lumbar spine, evaluate: 1) degenerative changes using MRI, 2) compressibility using an upright MRI backpack loading protocol, 3) spinal kinematics with X-ray videography, 4) visual analog scale pain.Results Comparing pre-flight and post- flight data, there were 1) increased lumbar IVD heights in the supine position, 2) increased lumbar IVD compressibility in the upright position, 3) decreased flexibility, and 4) increased low back pain post-flight.⇓Spinal kinematics (angles in degrees) during flexion/extension. Pre-flight degenerate disks had less motion. Post-flight, all disks had less motion.Conclusions The data support the idea that decreased gravitational forces on the IVDs, during prolonged microgravity, increases their water content but decreases proteoglycan. This increases disk degeneration risk on Earth. We have a sample size of one for complete Pre- and Post-Flight testing. It's difficult to make conclusions with this preliminary data. However, the acquired images are very high quality and provide confidence for future tests. The next crewmember returns to Earth for final testing November, 2013. Testing of 4 crewmembers and ongoing recruitment are underway.
Effect of gravity on human spontaneous 10-Hz electroencephalographic oscillations during the arrest reaction
Electroencephalographic oscillations at 10 Hz (alpha and mu rhythms) are the most prominent rhythms observed in awake, relaxed (eye-closed) subjects. These oscillations may be considered as a marker of cortical inactivity or an index of the active inhibition of the sensory information. Different cortical sources may participate in the 10-Hz oscillation and appear to be modulated by the sensory context and functional demands. In microgravity, the marked reduction in multimodal graviceptive inputs to cortical networks participating in the representation of space could be expected to affect the 10-Hz activity. The effect of microgravity on this basic oscillation has heretofore not been studied quantitatively. Because the alpha rhythm has a functional role in the regulation of network properties of the visual areas, we hypothesised that the absence of gravity would affect its strength. Here, we report the results of an experiment conducted over the course of 3 space flights, in which we quantified the power of the 10-Hz activity in relation to the arrest reaction (i.e., in 2 distinct physiological states: eyes open and eyes closed). We observed that the power of the spontaneous 10-Hz oscillation recorded in the eyes-closed state in the parieto-occipital (alpha rhythm) and sensorimotor areas (mu rhythm) increased in the absence of gravity. The suppression coefficient during the arrest reaction and the related spectral perturbations produced by eye-opening/closure state transition also increased in on orbit. These results are discussed in terms of current theories on the source and the importance of the alpha rhythm for cognitive function.
Cognitive demand of human sensorimotor performance during an extended space mission: a dual-task study
INTRODUCTION: Two previous single-case studies found that the dual-task costs of manual tracking plus memory search increased during a space mission, and concluded that sensorimotor deficits during spaceflight may be related to cognitive overload. Since dual-task costs were insensitive to the difficulty of memory search, the authors argued that the overload may reflect stress-related problems of multitasking, rather than a scarcity of specific cognitive resources. Here we expand the available database and compare different types of concurrent task. METHODS: Three subjects were repeatedly tested before, during, and after an extended mission on the International Space Station (ISS). They performed an unstable tracking task and four reaction-time tasks, both separately and concurrently. Inflight data could only be obtained during later parts of the mission. RESULTS: The tracking error increased from pre- to in flight by a factor of about 2, both under single- and dual-task conditions. The dual-task costs with a reaction-time task requiring rhythm production was 2.4 times higher than with a reaction-time task requiring visuo-spatial transformations, and 8 times higher than with a regular choice reaction-time task. CONCLUSIONS: Long-term sensorimotor deficits during spaceflight may reflect not only stress, but also a scarcity of resources related to complex motor programming; possibly those resources are tied up by sensorimotor adaptation to the space environment.
Differential gene expression patterns in white spruce newly formed tissue on board the International Space Station
White spruce (Picea glauca [Moench] Voss) seedlings produced by somatic embryogenesis were grown both at the Kennedy Space Center and in weightlessness in the ISS for 30 days. Plants were placed in closed environment incubators (Advanced Biological Research System) under controlled light, temperature, humidity and CO2 conditions. At the end of the experiment, the leading shoot from three plantlets of each of the three lines tested were sampled and pooled in Kennedy Space Center Fixation Tubes (KFT) containing a RNA stabilization solution. Transcript levels were determined by quantitative real-time polymerase chain reaction (RT-qPCR) for 27 candidate genes and three reference genes on the nine seedlings grown in each environment. About two-thirds of the 27 genes produced a larger number of transcript molecules in microgravity conditions. However, only three genes showed significant differences between the two environments, and all of them were up-regulated in microgravity. These genes appear to be involved in important processes such as cell propagation, plant development and response to stress, and their up-regulation has likely contributed to influencing seedling growth patterns.
After spaceflight, astronauts sometimes suffer a variable degree of reduced orthostatic tolerance. Although many studies have addressed this problem, many aspects remain unclear. Also, it is unknown how long the cardiovascular system needs to recover from short duration spaceflights. The scope of the present study was to determine a long-term follow-up of cardiovascular control up to 25 days after spaceflight under control conditions in five astronauts using heart rate variability, blood pressure variability and baroreflex sensitivity (BRS) indices. In standing position heart rate after spaceflight was significantly higher compared with pre-flight (R+1: 99 (SD 9) BPM vs L-30: 77 (SD 3) BPM; p<0.001). At the same time high frequency modulation of heart rate was extremely depressed (R+1: 70 (SD 334) ms2 vs L-30: 271 (SD 68) ms2; p<0.01), as was BRS: (R+1: 5 (SD 1) vs L-30: 10 (SD 2) ms/mmHg, p<0.05). These changes had largely recovered after 4 days upon return to Earth. Orthostatic blood pressure control was well maintained from the first day after landing. The decrease in BRS and in vagal heart rate modulation following short-duration spaceflight appear to constitute an adequate autonomic neural response to restored gravity. After 4 days upon return to Earth, vagal heart rate modulation is almost completely recovered to the pre-flight level. The findings of the present study demonstrate that the decrease in vagal heart rate modulation in standing position should not be characterised as some kind of cardiovascular deconditioning, but rather as the normal response to orthostatic stress after spaceflight.