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A joint NASA and Institute of Biomedical Problems (IBMP) study, designated as the Field Test, was designed to investigate how the immediate post-flight effects of long duration spaceflight impact performance on vestibular and sensorimotor-related functional tasks. One unique feature of this study was the use of functional tests typically associated with everyday living to track recovery. These tasks are also expected of crewmembers during recovery operations and include sit-to-stand and prone-to-stand transitions, translating objects, and jumping down from a platform. This paper provides an overview of the methodology used for the Field Test. As an example of the functional deficits observed, we present results for a seat egress and walking task that involved turning 180 degrees and stepping over obstacles. We observed significant increases in the time-to-complete this task on landing day. We recommend this task being incorporated into Standard Measures to evaluate the efficacy of countermeasures. The decrements observed at landing day have implications for the deconditioned crew during exploration missions where crewmembers will be unassisted after landing on a planetary surface.

BACKGROUND: The vestibulo-sympathetic reflex operates during orthostatically challenging movements to initiate cardiovascular responses in advance of a baroreceptor-mediated response. The objective of this study was to determine whether there was an association between changes in vestibular function and cardiovascular responses during a prone-to-stand movement in astronauts after return from long-duration spaceflight.METHODS: Thirteen crewmembers who participated in International Space Station missions were tested before spaceflight and 1 d after landing. Vestibular function was evaluated by computerized dynamic posturography while their head was erect and while they performed dynamic head tilts. Heart rate and mean arterial blood pressure were measured while the subjects were in prone and standing positions.RESULTS: The 21.4% increase in the astronauts’ heart rate during the prone to stand maneuver after spaceflight correlated significantly with their spaceflight-induced 48.7% decrease in postural stability during dynamic head tilts. The larger mean arterial pressure in the prone position after spaceflight compared to preflight (+7%) also correlated with the postflight decrease in postural stability during dynamic head tilts.CONCLUSION: These results indicate that an appropriate vestibular function is important to evoke optimum vestibulo-sympathetic response during orthostatically challenging voluntary movements performed after spaceflight. They also suggest that there may be a greater need to generate an anticipatory cardiovascular response after spaceflight.Deshpande N, Laurie SS, Lee SMC, Miller CA, Mulavara AP, Peters BT,Reschke MF, Stenger MB, Taylor LC, Wood SJ, Clément GR, Bloomberg JJ. Vestibular and cardiovascular responses after long-duration spaceflight. Aerosp Med Hum Perform. 2020; 91(8):621–627.

The incidence of presyncopal events is high soon after a long-duration spaceflight;>60% of returning astronauts could not complete a 10-min 80° head-up tilt test on landing day (R+0) after ~6 months of spaceflight. The objective of this study was to demonstrate the ability of a lower body gradient compression garment (GCG) to protect against an excessive increase in heart rate and a decrease in blood pressure during standing after long-duration spaceflight. Methods: Eleven astronauts (9 M, 2 F) volunteered to participate. The stand test protocol consisted of 2 min of prone rest followed by 3.5 min of standing. Subjects completed one familiarization session, two preflight data collection sessions in standard clothing, and three tests on landing day while wearing GCG. Postflight tests were conducted 1–4 h (R+0A), ~12 h (R+0B), and ~28 h after landing (R+0C). Results: All astronauts completed the stand test preflight. Three astronauts were unable to attempt the stand test at R+0A, and one of these was unable to start the test at R+0B. One astronaut was unable to complete 3.5 min of standing at R+0B (test ended at 3.3 min). Review of the individual’s blood pressure data revealed no hypotension but the astronaut reported significant motion sickness. Of the astronauts who participated in testing on landing day, the heart rate and mean arterial pressure responses to standing (stand-prone) were not different than preflight at any of the postflight sessions. Conclusion: Wearing the GCG after spaceflight prevented the tachycardia that normally occurs while standing after spaceflight without compression garments and protected against a decrease in blood pressure during a short stand test.

Space travel presents a number of environmental challenges to the central nervous system, including changes in gravitational acceleration that alter the terrestrial synergies between perception and action, galactic cosmic radiation that can damage sensitive neurons and structures, and multiple factors (isolation, confinement, altered atmosphere, and mission parameters, including distance from Earth) that can affect cognition and behavior. Travelers to Mars will be exposed to these environmental challenges for up to 3 years, and space-faring nations continue to direct vigorous research investments to help elucidate and mitigate the consequences of these long-duration exposures. This article reviews the findings of more than 50 years of space-related neuroscience research on humans and animals exposed to spaceflight or analogs of spaceflight environments, and projects the implications and the forward work necessary to ensure successful Mars missions. It also reviews fundamental neurophysiology responses that will help us understand and maintain human health and performance on Earth.

Intermittent artificial gravity (AG) treatments may reduce bone, muscle, and cardiovascular deconditioning during prolonged space flight; however, the effects of repeated centrifugation on central processing of vestibular information remain unknown. This study investigated the effects of one intermittent AG prescription on balance control and neuromotor reflex function in a ground-based study of subjects exposed to bed rest. Fifteen male volunteers were exposed to 21 days of 6° head-down-tilt (HDT) bed rest (BR) to simulate some of the effects of space flight. Eight were treated with daily 1 h AG exposures aboard a short radius centrifuge that provided 1-g footward loading at heart level. The other seven served as control subjects. Balance control was assessed using a computerized dynamic posturography (CDP) protocol modified by adding low frequency pitch-plane head movements. Neuromotor reflex function was assessed using tendon (MSR) and functional stretch reflex (FSR) data collected from the triceps surae muscle group. CDP performance was degraded by BR in both groups, but was unaffected by AG. BR also degraded MSR and FSR functions in both groups, but AG blunted the decrement in MSR. This AG prescription had little functionally relevant effect on balance control, but may have had some salutary effect on neuromotor reflexes.

Australian–New Zealand IODP Consortium Ocean Planet Workshop; Canberra, Australia, 14–16 April 2019

Impairments in balance control are inevitable following exposure to microgravity. However, the role of particular sensory system in postural disorders at different stages of the exposure to microgravity still remains unknown. We used a method called Dry Immersion (DI), as a ground-based model of microgravity, to elucidate the effects of 6-h of load-related afferent inputs on kinematic characteristics of postural corrective responses evoked by pushes to the chest of different intensities during upright standing. The structure of postural corrective responses was altered following exposure to DI, which was manifested by: (1) an increase of the ankle and knee flexion during perturbations of medium intensity, (2) the lack of the compensatory hip extension, as well as diminished knee and ankle flexion with a further increase of the perturbation intensity to submaximal level. We suggest that the lack of weight-bearing increases the reactivity of the balance control system, whereas the ability to scale the responses proportionally to the perturbation intensity decreases. Disrupted neuromuscular coordination of postural corrective responses following DI can be attributed to adaptive neural modifications on the spinal and cortical levels. The present study provides evidence that even a short-term lack of load-related afferent inputs alters kinematic patterns of postural corrective responses, and can result in decreased balance control. Because vestibular input is not primarily affected during the DI exposure, our results indicate that activity and the state of the load-related afferents play critical roles in balance control following real or simulated microgravity.

The free-fall of orbital spaceflight effectively removes the gravitational vector used as a primary spatial orientation reference on Earth. Sustained absence of this reference drives adaptive changes in the internal perception-action models of the central nervous system (CNS), most notably in the processing of the vestibular otolith inputs. Upon landing, the return of the gravitational signal triggers a re-adaptation that restores terrestrial performance; however, during this period, the individual suffers from a functional vestibular deficiency. Here we provide evidence of a transient increase of the weighting of somatosensory inputs in postural control while the CNS resolves these vestibular deficiencies. Postural control performance was measured before and after spaceflight in 11 Shuttle astronauts and 11 matched controls and nine elderly who did not experience spaceflight. A quiet-stance paradigm was used that eliminated vision, modulated the lower extremity somatosensory cues by subtly modulating the orientation of the support surface beneath feet of subjects in all groups. Additionally, in astronauts and matched controls, we challenged the vestibular system with dynamic head tilts. Postural stability on the landing day (R+0) was substantially decreased for trials with absent visual and altered somatosensory cues, especially those also requiring dynamic head tilts ( ± 5° @ 0.33 Hz) during which 20/22 trials ended prematurely with a fall. In contrast, none of the astronauts fell during eyes-closed, dynamic head tilt trials with unaltered somatosensory cues, and only 3/22 trials resulted in falls with eyes-closed and altered somatosensory cues, but static upright head orientation. Furthermore, postural control performance of astronauts was either statistically not different or worse than that of healthy elderly subjects during the most challenging vestibular conditions on R+0. Overall, our results demonstrate a transient reweighting of sensory cues associated with microgravity-induced vestibular deficiencies, with a significant increase in reliance on somatosensory cues, which can provide an effective reference even without vision and with dynamic vestibular challenges. The translation of these results to aging population suggests that elderly individuals with visual and vestibular deficits may benefit from therapeutic interventions enhancing sensorimotor-integration to improve balance and reduce the risk of falling.

INTRODUCTION The purpose of this study was to determine how short- and long-duration spaceflight affects astronauts' performance on functional tests that challenge the balance control system (Seated Egress and Walk; Object Translation; Recovery from Fall/Stand; and Jump Down) and on clinical tests of balance function (Computerized Dynamic Posturography and Tandem Walk). In addition, we examined how exercise affects functional performance after long-term axial body unloading during 70 d of bed rest at 6° head-down tilt. METHODS Data were collected twice during the 2-mo period before spaceflight or during the 2-wk period before bed rest, and four times after flight or bed rest: on the day of landing or the day bed rest ended, 1 d and 6 d later, and a final session 12 d after bed rest or 30 d after spaceflight. RESULTS For bed rest subjects, long-term axial unloading alone caused functional performance deficits immediately after bed rest. However, the addition of an exercise regimen did not significantly improve median functional performance immediately after this axial unloading. For spaceflight subjects, the length of the space mission was directly related to the severity of functional performance deficits within 1 d of landing and during the subsequent recovery period after flight. DISCUSSION The performance data suggest that an additional sensorimotor-based countermeasure may be necessary to maintain functional performance at preflight levels immediately after spaceflight.Miller CA, Kofman IS, Brady RR, May-Phillips TR, Batson CD, Lawrence EL, Taylor LC, Peters BT, Mulavara AP, Feiveson AH, Reschke MF, Bloomberg JJ. Functional task and balance performance in bed rest subjects and astronauts. Aerosp Med Hum Perform. 2018; 89(9):805-815.

BACKGROUND It has been proposed that individual susceptibility to motion sickness is related to the vestibulo-ocular reflex (VOR) through the activation of the velocity storage mechanism. OBJECTIVE We investigated whether motion sickness level was related to the gain and phase of the VOR. METHODS VOR gain and phase were measured in 214 subjects while they rotated in yaw at 0.01 Hz, 0.02 Hz, 0.04 Hz, 0.08 Hz, and 0.16 Hz in darkness, and results were compared to the severity of symptoms the subjects experienced during subsequent tests to provoke motion sickness. These tests included cross-coupled angular accelerations, sudden stops in light or in dark, off-vertical axis rotation, and parabolic flight. The subjects were grouped according to the motion sickness level reached during these tests (none, low, medium, or high). RESULTS No correlation was found between the horizontal VOR gain and motion sickness level. However, for the subjects with high motion sickness level, the VOR phase lead was significantly lower during rotation at frequencies ranging from 0.04 Hz to 0.16 Hz (i.e. the VOR time constant was longer) than the other motion sickness groups. CONCLUSION These results support the theory that the longer the time constant for velocity storage, the more severe the motion sickness.

INTRODUCTION Exposure to microgravity causes alterations in multiple physiological systems, potentially impacting the ability of astronauts to perform critical mission tasks. The goal of this study was to determine the effects of spaceflight on functional task performance and to identify the key physiological factors contributing to their deficits. METHODS A test battery comprised of seven functional tests and 15 physiological measures was used to investigate the sensorimotor, cardiovascular, and neuromuscular adaptations to spaceflight. Astronauts were tested before and after 6-month spaceflights. Subjects were also tested before and after 70 d of 6° head-down bed rest, a spaceflight analog, to examine the role of axial body unloading on the spaceflight results. These subjects included control and exercise groups to examine the effects of exercise during bed rest. RESULTS Spaceflight subjects showed the greatest decrement in performance during functional tasks that required the greatest demand for dynamic control of postural equilibrium which was paralleled by similar decrements in sensorimotor tests that assessed postural and dynamic gait control. Other changes included reduced lower limb muscle performance and increased HR to maintain blood pressure. Exercise performed during bed rest prevented detrimental change in neuromuscular and cardiovascular function; however, both bed rest groups experienced functional and balance deficits similar to spaceflight subjects. CONCLUSION Bed rest data indicate that body support unloading experienced during spaceflight contributes to postflight postural control dysfunction. Further, the bed rest results in the exercise group of subjects confirm that resistance and aerobic exercises performed during spaceflight can play an integral role in maintaining neuromuscular and cardiovascular functions, which can help in reducing decrements in functional performance. These results indicate that a countermeasure to mitigate postflight postural control dysfunction is required to maintain functional performance.

Ocular counter-rolling (OCR) is a reflex generated by the activation of the gravity sensors in the inner ear that stabilizes gaze and posture during head tilt. We compared the OCR measures that were obtained in 6 astronauts before, during, and after a spaceflight lasting 4–6 days with the OCR measures obtained from 6 astronauts before and after a spaceflight lasting 4–9 months. OCR in the short-duration fliers was measured using the afterimage method during head tilt at 15°, 30°, and 45°. OCR in the long-duration fliers was measured using video-oculography during whole body tilt at 25°. A control group of 7 subjects was used to compare OCR measures during head tilt and whole body tilt. No OCR occurred during head tilt in microgravity, and the response returned to normal within 2 hours of return from short-duration spaceflight. However, the amplitude of OCR was reduced for several days after return from long-duration spaceflight. This decrease in amplitude was not accompanied by changes in the asymmetry of OCR between right and left head tilt. These results indicate that the adaptation of otolith-driven reflexes to microgravity is a long-duration process.

Objectives(1) To assess vestibular changes and related sensorimotor difficulties, especially instability of posture and gait, among astronauts immediately after they return from space and to compare the effects experienced after short- and long-duration space missions. (2) To determine whether any difficulties experienced were severe enough to impair the astronauts’ ability to leave the spacecraft in the event of an emergency.Study DesignProspective cohort study.SettingNational Aeronautics and Space Administration’s Kennedy Space Center and Johnson Space Center.Subjects and MethodsFourteen crewmembers of 3 Space Shuttle missions that lasted about 1 week and 18 crewmembers of 8 International Space Station missions that lasted about 6 months were given brief vestibular examinations 1 to 5 hours after landing. These examinations focused on the presence of vestibular and motor coordination difficulties, as well as motion sickness and motion sensations. Standardized tests included the observation of abnormal e...

Introduction The effects of repeated centrifugation in association with head-down tilt (HDT) bed rest (BR) on the mediation of basic reflexes associated with the major postural muscles was investigated as a potential countermeasure for maintaining balance control and neuromotor reflex function. Methods There were 15 male volunteers who were exposed to 21 d of 6° HDT-BR. Eight were treated with daily 1-h artificial gravity (AG) exposures aboard a short radius centrifuge that provided 1-g footward loading at heart level. The other seven served as HDT-BR control subjects. Balance control was assessed using a standard computerized dynamic posturography (CDP) protocol that was modified by adding low-frequency pitch-plane head movements. Neuromotor reflex function was assessed using tendon stretch reflexes (MSR) and functional stretch reflex (FSR) data collected from the triceps surae muscle group. Results CDP performance was degraded by HDT-BR in both groups (ranging from 24 to 26%), but was unaffected by AG. BR also degraded MSR and FSR functions in both groups, with increased peak reflex latencies between 1.5 and 1.95 ms, but AG maintained pre-BR latencies for the MSR subjects. Discussion AG exposure did not modify balance control from pre-BR responses, but did help prevent decrements in FSR latencies post-BR.Paloski WH, Reschke MF, Feiveson AH. Bed rest and intermittent centrifugation effects on human balance and neuromotor reflexes. Aerosp Med Hum Perform. 2017; 88(9):812-818.

Between 1989 and 1995, NASA evaluated how increases in flight duration of up to 17 days affected the health and performance of Space Shuttle astronauts. Thirty-one Space Shuttle pilots participating in 17 space missions were tested at 3 different times before flight and 3 different times after flight, starting within a few hours of return to Earth. The astronauts moved their head and eyes as quickly as possible from the central fixation point to a specified target located 20°, 30°, or 60° off center. Eye movements were measured with electro-oculography (EOG). Head movements were measured with a triaxial rate sensor system mounted on a headband. The mean time to visually acquire the targets immediately after landing was 7–10% (30–34 ms) slower than mean preflight values, but results returned to baseline after 48 hours. This increase in gaze latency was due to a decrease in velocity and amplitude of both the eye saccade and head movement toward the target. Results were similar after all space missions, regardless of length.

Sex and gender differences have long been a research topic of interest, yet few studies have explored the specific differences in neurological responses between men and women during and after spaceflight. Knowledge in this field is limited due to the significant disproportion of sexes enrolled in the astronaut corps. Research indicates that general neurological and sensory differences exist between the sexes, such as those in laterality of amygdala activity, sensitivity and discrimination in vision processing, and neuronal cell death (apoptosis) pathways. In spaceflight, sex differences may include a higher incidence of entry and space motion sickness and of post-flight vestibular instability in female as opposed to male astronauts who flew on both short- and long-duration missions. Hearing and auditory function in crewmembers shows the expected hearing threshold differences between men and women, in which female astronauts exhibit better hearing thresholds. Longitudinal observations of hearing thresholds for crewmembers yield normal age-related decrements; however, no evidence of sex-related differences from spaceflight has been observed. The impact of sex and gender differences should be studied by making spaceflight accessible and flying more women into space. Only in this way will we know if increasingly longer-duration missions cause significantly different neurophysiological responses in men and women.

The study was designed to investigate target acquisition in the vertical plane with emphasis on establishing strategy differences associated with acquisition triggering methods. Eight subjects were tested. Measurements consisted of target acquisition time, eye-head latency differences, velocity of gaze, eyes and head, and head amplitude. Using 3-way repeated measures analyses of variance the results show that the strategy for acquisition of predictable visual targets in vertical plane with the head unrestrained significantly depended on (a) the direction of the gaze motion with respect to the gravity vector (i.e., there is significant up-down asymmetry), (b) the angular distance of the target, and (c) the method of triggering the command to acquire the target-external versus internal. The data also show that when vertical acquisition is compared with triggering methods in the horizontal plane there is a difference in overall strategy for the acquisition of targets with the same spatial distances from straight ahead gaze when both the eyes and head are used. Among the factors contributing to the difference in strategy for vertical target acquisition are the gravitational vector, the relationship of target displacement and vestibular activitation, biomechanical and neural control asymmetries, and the difference in the vertical field of view.

Prior studies indicate that the human translational vestibulo-ocular reflex (tVOR) generates eye rotations approximately half the magnitude required to keep the line of sight pointed at a stationary object--a compensation ratio (CR) of ∼0.5. We asked whether changes of visual or vestibular stimuli could increase the CR of tVOR. First, subjects viewed their environment through an optical device that required eye movements to increase by ∼50% to maintain fixation of a stationary visual target. During vertical translation, eye movements did increase, but tVOR CR remained at ∼0.5. Second, subjects viewed through LCD goggles providing 4 Hz strobe vision that minimized retinal image motion; this reduced tVOR CR. Finally, subjects were rotated in roll while they translated vertically; no increase in tVOR occurred. Taken with prior studies, we conclude that tVOR is optimally set to generate eye rotations that are about 50% of those required to stabilize the line of sight.

The purpose of the study was to explore the effects of long-duration space flight on the acquisition of specific visual targets in the horizontal plane. Seven cosmonauts (4 high performance pilots and 3 non-pilots) who had flown between 186–198 days on Mir served as subjects. Baseline testing was performed 4 times prior to launch and 4 times following landing at different intervals totrack recovery. During testing the subjects were required to acquire targets that were randomly presented with both a head and eye movement using a time optimal strategy. Prior to flight two unique head movement strategies, related primarily to piloting experience, were used for target acquisition. Non-pilots employed a Type-I strategy consisting of high velocity head movements with large peak amplitudes, while high performance pilots used primarily low velocity, small amplitude head movements (Type-II) to acquire the targets (p

Purpose During locomotion, head perturbations, consisting of rotations and translations (linear movements), occur with predominant frequencies of 0.5-5.0 Hz. The vestibular reflexes act at short latency to safeguard clear vision and stable posture during locomotion. Much is known about the angular vestibulo-ocular reflex (aVOR) in response to head rotations, which depend on the semicircular canals of the vestibular labyrinth. However, the means to test reliably the linear or translational vestibulo-ocular reflex (tVOR), which depends on the otolithic organs, has only become available more recently. Methods We used a moving platform to translate normal human subjects vertically at frequencies similar to those occurring during locomotion, under ambient illumination. Results Our findings suggested that, whereas aVOR is concerned with stabilizing images of visual targets on the retina to optimize visual acuity, tVOR seems best suited to minimize retinal image motion between objects lying in different depth planes, in order to optimize motion parallax information. We then asked whether the tVOR functioned abnormally in patients with two neurological disorders that often cause falls: progressive supranuclear palsy (PSP) and cerebellar ataxia. We found that patients with PSP cannot adjust tVOR responses appropriately during viewing of near objects, nor converge their eyes. Vestibular-evoked myogenic potentials (VEMPs), an otolith-spinal reflex, are also impaired in PSP patients. Patients with cerebellar ataxia also lack the ability to adjust tVOR for near viewing, even though they may be able to converge. Conclusions Taken together, our studies suggest that abnormal otolithic vestibular reflexes contribute to postural instability in PSP and cerebellar ataxia, and deserve further investigation.

Introduction Spaceflight has functionally significant effects on sensorimotor behavior, but it is difficult to separate the effects of ascending somatosensory changes caused by postural muscle and plantar surface unloading from descending visual-vestibular neural changes. To differentiate somatosensory changes from graviceptor changes in post-spaceflight sensorimotor behavior, bed rest may serve as an exclusionary analog to spaceflight. Methods Four separate tests were used to measure changes in sensorimotor performance: 1) the monosynaptic stretch reflex (MSR); 2) the functional stretch reflex (FSR); 3) balance control parameters associated with computerized dynamic posturography (CDP); and 4) a functional mobility test (FMT). Results A mixed model regression analysis showed significant increases in median MSR start and peak latencies, while the median FSR latency showed no significant increase. Median MSR peak magnitude showed a significant increase during the middle bed rest period (19-60 d). There were no significant effects of bed rest on balance control, but some indication that dynamic head movements may affect posture after bed rest. Time to complete the course for the FMT increased significantly with bed rest. Discussion The four primary tests indicate that long-duration head-down bed rest, through unloading and modification of the body's support surface, serves as an exclusionary analog for sensorimotor responses to spaceflight. Furthermore, the data suggest that procedures designed to alleviate modifications to the sensory substrate serving the soles of the feet may provide a countermeasure to help maintain support afferentation of the postural muscles.

This paper is a continuation of an earlier work that analyzed the elastic stability of a homogeneous, isotropic, Bell constrained cylindrical tube of uniform cross section subjected to axial end thrust. Here, the focus is on some applications. Four kinds of material models are considered: a simple hyperelastic Bell material model, Bell's empirical material model, and two new theoretical models, one being similar to a wellknown biomaterial model. Numerical results for a thick-walled tube and a solid bar are illustrated graphically The thin-walled tube problem, however, is studied analytically for a general class of Bell constrained materials, and the critical stretch and corresponding critical load are derived. The load result is shown to be consistent with the classical solution obtained by Southwell and Dean.

Spatial transformations of the vestibular-optokinetic system must account for changes in head position with respect to gravity in order to produce compensatory oculomotor responses. The purpose of this experiment was to study the influence of gravity on the vestibulo-ocular reflex (VOR) in darkness and on visual-vestibular interaction in the pitch plane in human subjects using two different comparisons: (1) Earth-horizontal axis (EHA) rotation about an upright versus a supine body orientation, and (2) Earth-horizontal versus Earth-vertical (EVA) rotation axes. Visual-vestibular responses (VVR) were evaluated by measuring the slow phase velocity of nystagmus induced during sinusoidal motion of the body in the pitch plane (at 0.2 Hz and 0.8 Hz) combined with a constant-velocity vertical optokinetic stimulation (at ±36°/s). The results showed no significant effect on the gain or phase of the VOR in darkness or on the VVR responses at 0.8 Hz between EHA upright and EHA supine body orientations. However, there was a downward shift in the VOR bias in darkness in the supine orientation. There were systematic changes in VOR and VVR between EHA and EVA for 0.2 Hz, including a reduced modulation gain, increased phase lead, and decreased bias during EVA rotation. The same trend was also observed at 0.8 Hz, but at a lesser extent, presumably due to the effects of eccentric rotation in our EVA condition and/or to the different canal input across frequencies. The change in the bias at 0.2 Hz between rotation in darkness and rotation with an optokinetic stimulus was greater than the optokinetic responses without rotation. During EHA, changes in head position relative to gravity preserve graviceptor input to the VVR regardless of body orientation. However, the modifications in VVR gain and phase when the rotation axis is aligned with gravity indicate that this graviceptive information is important for providing compensatory eye movements during visual-vestibular interaction in the pitch plane.

During viewing of a near target, the gain of the visually modulated vestibulo-ocular reflex (vVOR) exceeds 1.0. We investigated whether retinal image slip contributes to this gain increase by measuring responses during strobe illumination. Subjects showed greater gain values during normal versus strobe illumination of the near target, even during rotation at frequencies above 1.0 Hz, indicating that retinal image velocity information is used to optimize vVOR.

In an operational setting acquisition of visual targets using both head and eye movements can be driven by memorized sequence of commands – internal triggering (IT) or by commands issued through secondary operator – external triggering (ET). The primary objective of our research was to examine differences in target acquisition using IT compared with ET. Using a forced time optimal strategy eight subjects were required to acquire targets with angular offsets of ±20°, 30° and 60° along the horizontal plane in both IT and ET conditions. The data showed that the eye/head latency difference in IT condition is longer than that for ET, the target acquisition time is also longer for IT commands. Consistent with this finding were similar results when examining the peak head velocity and peak head acceleration. Under IT protocol head amplitude is higher than when using ET. In conclusion, the study demonstrates that the pattern of performance of target acquisition task is influenced by the way of command triggering.

Neglecting the eccentric position of the eyes in the head can lead to erroneous interpretation of ocular motor data, particularly for near targets. We discuss the geometric effects that eye eccentricity has on the processing of target-directed eye and head movement data, and we highlight two approaches to processing and interpreting such data. The first approach involves determining the true position of the target with respect to the location of the eyes in space for evaluating the efficacy of gaze, and it allows calculation of retinal error directly from measured eye, head, and target data. The second approach effectively eliminates eye eccentricity effects by adjusting measured eye movement data to yield equivalent responses relative to a specified reference location (such as the center of head rotation). This latter technique can be used to standardize measured eye movement signals, enabling waveforms collected under different experimental conditions to be directly compared, both with the measured target signals and with each other. Mathematical relationships describing these approaches are presented for horizontal and vertical rotations, for both tangential and circumferential display screens, and efforts are made to describe the sensitivity of parameter variations on the calculated results.

This work characterizes a new methodologic and pharmacologic approach to control terrestrial and space motion sickness (SMS). The experimental design allowed separate evaluation of drug action on susceptibility and adaptability, and used repeated measures to approximate the chronic stressful motion of microgravity. Daily exposure to cross-coupled angular acceleration for 5 consecutive days demonstrated that the efficacy of doxepin and scopolamine plus amphetamine in the prevention of autonomic system dysfunction was not only apparent on the first test day (P < .01), but was also evident in the substantially enhanced resistance developed over the 5-day test period (P < .01) as compared with placebo. This indicates that daily use of these medications does not diminish therapeutic efficacy (tolerance). The efficacy of doxepin was anticipated because it possesses pharmacologic properties similar to those of established anti-motion sickness drugs. Comparable efficacy after doxepin loading for 4 hours, 3 days, or 21 days suggests a mechanism distinct from its antidepressant effects, possibly related to its potent antihistaminergic actions. Use of doxepin has operational significance to the National Aeronautics and Space Administration, in comparison with current preparations of scopolamine plus amphetamine, because of doxepin's minimal impact on cognitive performance, and most importantly, its favorable pharmacokinetic profile, particularly its long half-life.

Geometric considerations indicate that the human translational vestibulo-ocular reflex (tVOR) should have substantially different properties than the angular vestibulo-ocular reflex (aVOR). Specifically, tVOR cannot simultaneously stabilize images of distant and near objects on the retina. Most studies make the tacit assumption that tVOR acts to stabilize foveal images even though, in humans, tVOR is reported to compensate for less than 60% of foveal image motion. We have determined that the compensation gain (eye rotational velocity/required eye rotational velocity to maintain foveal target fixation) of tVOR is held steady at approximately 0.6 during viewing of either near or distant targets during vertical (bob) translations in ambient illumination. We postulate that tVOR evolved not to stabilize the image of the target on the fovea, but rather to minimize retinal image motion between objects lying in different depth planes, in order to optimize motion parallax information. Such behavior is optimized when binocular visual cues of both near and distant targets are available in ambient light. Patients with progressive supranuclear palsy or cerebellar ataxia show impaired ability to increase tVOR responses appropriately when they view near targets. In cerebellar patients, impaired ability to adjust tVOR responses to viewing conditions occurs despite intact ability to converge at near. Loss of the ability to adjust tVOR according to viewing conditions appears to represent a distinct disorder of vestibular function.

For several decades, the study of eye movements has been a source of valuable information to both scientists and clinicians. The singular value of studying eye movements stems from the fact that they are restricted to rotations in three planes and the eyeball offers very little inertia. This facilitates accurate measurement, for example using video eye recording in near infrared light, a prerequisite for quantitative analysis. Eye movements must continuously compensate for head movements so that the image of the world is held fairly steady on the retina, and thus appears clear and stationary.

In a prior study we reported that the human translational vestibulo-ocular reflex (tVOR) in response to vertical (bob) 2 Hz oscillations generated eye rotations of only 60% of those required to keep the eyes pointed at a stationary visual target, whether located at near (∼17 cm) or far (2 m). Best responses occurred in ambient illumination and we concluded that relative image motion between the target and background was an important determinant of tVOR behaviour. To investigate further how visual conditions influenced tVOR, we measured responses as subjects binocularly viewed the bridge of their own nose in a mirror at ∼8.5 cm, a visual condition that required similar convergence to viewing the near target, but cancellation of tVOR. Median tVOR cancellation gain [(near-viewing response−mirror viewing response)/near-viewing response] was 0.81 (range 0.55−0.97), which was substantially greater than the gain of smooth visual tracking of a large visual display moving at 2 Hz (median gain 0.27, range 0.09−0.42). Thus, visual inputs other than smooth tracking must contribute to tVOR cancellation. We then compared tVOR response to 2 Hz bob as subjects fixed upon a visual target at 17 cm and viewed a large textured background at 1.5 m that was either stationary or moving at 2.1 Hz. Vertical eye rotations waxed and waned as a function of the difference between platform and background oscillations. These findings support our hypothesis that tVOR evolved not to stabilize the image of the target on the fovea, but rather to minimize retinal image motion between objects lying in different planes, in order to optimize motion parallax information. A geometrically based optimization function is proposed to account for tVOR responses at different target distances.

This chapter provides a brief history of space flight, with an emphasis on the role of life sciences in the space program. A detailed table including the nearly 400 neuroscience experiments performed by all countries from Vostok-3 (August 1962) to the ISS Expedition-15 on board the International Space Station (from June to October 2007) completes this overview.

Prior studies of the human translational vestibulo-ocular reflex (tVOR) report that eye rotations amount to less than 60% of those required to keep the eyes pointed at a stationary visual target, unlike the angular VOR (aVOR) which is optimized to maintain stable gaze. Our first goal was to determine if the performance of the tVOR improves when head translations are combined with head rotations in ambient lighting. A second goal was to measure tVOR during vertical head translations (bob), which has not received systematic study. We measured tVOR alone and in combination with the aVOR in 20 normal human subjects, aged 25-72 years, as they sat on a moving platform that bobbed at 2.0 Hz while rotating horizontally (yaw) at 1.0 Hz. When subjects viewed a visual target at 2 m, median "compensation gain" (eye rotational velocity/required eye rotational velocity to maintain foveal target fixation) was 0.52 during pure bob and 0.59 during combined bob-yaw; during viewing of a near target at approximately 17 cm, compensation gain was 0.58 for pure bob and 0.60 for combined bob-yaw. Mean phase lag of eye-in-head velocity for the tVOR was approximately 19 degrees with respect to the ideal compensatory response, irrespective of whether translation was accompanied by rotation. Thus, the tVOR changed only slightly during translation-rotation versus pure translation, and our subjects' ocular rotations remained at about 60% of those required to point the eyes at the target. Comparison of response during binocular or monocular viewing, and ambient or reduced illumination, indicated that relative image motion between the target and background was an important determinant of tVOR behavior. We postulate that tVOR evolved not to stabilize the image of the target on the fovea, but rather to minimize retinal image motion between objects lying in different planes, in order to optimize motion parallax information.

International audience; Ocular counter-rolling (OCR) induced by whole body tilt in roll has been explored after spaceflight as an indicator of the adaptation of the otolith function to microgravity. It has been claimed that the overall pattern of OCR responses during static body tilt after spaceflight is indicative of a decreased role of the otolith function, but the results of these studies have not been consistent, mostly due to large variations in the OCR within and across individuals. By contrast with static head tilt, off-vertical axis rotation (OVAR) presents the advantage of generating a sinusoidal modulation of OCR, allowing averaged measurements over several cycles, thus improving measurement accuracy. Accordingly, OCR and the sense of roll tilt were evaluated in seven astronauts before and after spaceflight during OVAR at 45 degrees/s in darkness at two angles of tilt (10 degrees and 20 degrees). There was no significant difference in OCR during OVAR immediately after landing compared to preflight. However, the amplitude of the perceived roll tilt during OVAR was significantly larger immediately postflight, and then returned to control values in the following days. Since the OCR response is predominantly attributed to the shearing force exerted on the utricular macula, the absence of change in OCR postflight suggests that the peripheral otolith organs function normally after short-term spaceflight. However, the increased sense of roll tilt indicates an adaptation in the central processing of gravitational input, presumably related to a re-weighting of the internal representation of gravitational vertical as a result of adaptation to microgravity.

The development of a class of capacitors which use the interface between large surface area materials such as activated carbon to store charge is discussed. The key parameters of interest for the capacitor double layer (CDL) as an energy storage media are the value of the relative dielectric constant associated with the region in which the charge is stored, the thickness of the layer and the voltage at which the layer fails. These parameters are functions of the electrolyte species, and its concentration. This has led to the development of capacitors with capacitance of the order of 20-50 microfarads per real square centimeter of surface area. A second electrochemical capacitor of potential use in electrical actuation is based upon pseudocapacitance. Materials such as ruthenium oxide are capable of absorbing charge in the form of hydrogen ions (protons) into the surface in a reversible way. Both technologies allow capacitors to be built with a capacitance of several farads in a volume on the order of a "dime". For pulsed electrical actuation, capacitor or a battery capacitor combination would appear to be particularly attractive. Electrochemical capacitor technology is a step in the right direction. This paper describes the near-term and the current state-of-the-art in CDL and pseudocapacitor technology for application to devices such as electric propulsion and electric actuation in terms of energy density, power density, availability and cost. Specific applications to NASA and Navy needs are presented.

Thermophotovoltaics (TPV) is the term applied to the technique for energy conversion whereby the energy emitted by an incandescent source is converted to electrical energy by a photovoltaic cell. One of the approaches used in TPV is selective emission used in conjunction with a low bandgap photovoltaic cell, such as InGaAs. Because the alloying fraction of indium and gallium can be varied, the energy bandgap of InGaAs cells can be varied. This allows more of the infrared spectrum to be utilized in the photoconversion process in the InGaAs cells for lowering bandgaps. Conversion efficiencies of InGaAs photovoltaic cells have been reported under various illumination conditions. However, their efficiencies have not been reported using composite selective emitters. This paper reports the conversion efficiencies of three different InGaAs cells with bandgaps of 0.75, 0.66, and 0.6 eV which have been illuminated with four different composite selective emitters. The conversion efficiencies of the three InGaAs cells under composite selective emitter emission will be compared to that of a blackbody-like emitter.

A thermophotovoltaic (TPV) energy converter is a system used to convert thermal energy to electric energy. The system consists of a thermally excited photon emitter and photovoltaic (PV) cell. A thermally excited selective line emitter (rare earth oxide emitter) is a photon source which provides photons at elevated temperatures with a narrow energy band that can be matched with the PV cell bandgap energy. The PV cells can then convert photon energy to electricity at high efficiency. Past research on fibrous rare earth oxide selective emitters has shown that high emitter efficiency was attained at the expense of emitter mechanical strength. Therefore, an improvement of the emitter strength without sacrificing its emitter efficiency becomes one of the key issues in TPV research. This paper describes novel material processing approaches to produce reasonably strong rare earth emitters with high efficiency. The effect of the amount of rare-earth oxide and the material structure (fibrous and solid) on the selective efficiency of the emitters has been addressed in some detail.

Symptomatic reporting has been used in quantifying the severity of motion sickness including Coriolis sickness. This study was designed to objectively examine if the dynamic changes of salivary protein concentration relate to the severity of Coriolis sickness. Healthy adults with normal vestibular function underwent a modified Coriolis Sickness Susceptibility Index (CSSI) test, utilizing a staircase profile. Salivary samples were obtained prior to stimulation, 15, 30, and 45 min following stimulus onset, and/or upon reaching "nausea-II" endpoint. Total protein concentration tended to rise over the initial 30 min of stimulation, and then level off or decline. A statistically significant difference was found between the pre-stimulation and 30 min samples. Although some variability existed among the subjects, the general pattern of changes along the time course was similar. An inverse correlation approaching statistical significance was found between control (non-stimulus) total protein levels, and minutes of Coriolis stimulation required to reach the "nausea-II" endpoint. Thus, baseline salivary total protein levels can be of use in predicting susceptibility of Coriolis sickness and other forms of motion sickness.

Space motion sickness (SMS) and spatial orientation and motion perception disturbances occur in 70-80% of astronauts. People select "rest frames" to create the subjective sense of spatial orientation. In microgravity, the astronaut's rest frame may be based on visual scene polarity cues and on the internal head and body z axis (vertical body axis). The data reported here address the following question: Can an astronaut's orientation rest frame be related and described by other variables including circular vection response latencies and space motion sickness? The astronaut's microgravity spatial orientation rest frames were determined from inflight and postflight verbal reports. Circular vection responses were elicited by rotating a virtual room continuously at 35 degrees/s in pitch, roll and yaw with respect to the astronaut. Latency to the onset of vection was recorded from the time the crew member opened their eyes to the onset of vection. The astronauts who used visual cues exhibited significantly shorter vection latencies than those who used internal z axis cues. A negative binomial regression model was used to represent the observed total SMS symptom scores for each subject for each flight day. Orientation reference type had a significant effect, resulting in an estimated three-fold increase in the expected motion sickness score on flight day 1 for astronauts who used visual cues. The results demonstrate meaningful classification of astronauts' rest frames and their relationships to sensitivity to circular vection and SMS. Thus, it may be possible to use vection latencies to predict SMS severity and duration.

This article summarizes a variety of newly published findings obtained by the Neuroscience Laboratory, Johnson Space Center, and attempts to place this work within a historical framework of previous results on posture, locomotion, motion sickness, and perceptual responses that have been observed in conjunction with space flight. In this context, we have taken the view that correct transduction and integration of signals from all sensory systems is essential to maintaining stable vision, postural and locomotor control, and eye-hand coordination as components of spatial orientation. The plasticity of the human central nervous system allows individuals to adapt to altered stimulus conditions encountered in a microgravity environment. However, until some level of adaptation is achieved, astronauts and cosmonauts often experience space motion sickness, disturbances in motion control and eye-hand coordination, unstable vision, and illusory motion of the self, the visual scene, or both. Many of the same types of disturbances encountered in space flight reappear immediately after crew members return to earth. The magnitude of these neurosensory, sensory-motor and perceptual disturbances, and the time needed to recover from them, tend to vary as a function of mission duration and the space travelers prior experience with the stimulus rearrangement of space flight. To adequately chart the development of neurosensory changes associated with space flight, we recommend development of enhanced eye movement systems and body position measurement. We also advocate the use of a human small radius centrifuge as both a research tool and as a means of providing on-orbit countermeasures that will lessen the impact of living for long periods of time with out exposure to altering gravito-inertial forces. Copyright 1998 Elsevier Science B.V.

The primary goals of this research are to evaluate alternative energy storage technologies and power system options for pulsed plasma thrusters (PPT). This paper describes novel techniques to reduce the mass and volume of PPTs which are emerging as interesting propulsion options for small spacecraft applications. The emphasis is on efficient capacitor energy storage, namely multi-layer ceramic capacitors, and the Marx bank concept for voltage multiplication. NOMENCLATURE Parameter C = capacitance [F] E = energy [J] I = current [A] I = current (time dependent) R = resistance [Q] Q = charge [C] t = time [s] V = voltage [V] T = time constant [s] Indices P s n LR mea = parallel = series = number of stages/units = load resistance = measured

Recent advances in the technologies relevant to harvesting human power, as presented at the workshop, suggest that unobtrusive systems might be built in the range from microwatts to a few watts. As the Army becomes more mobile, a premium is to be paid for capability, reliability, autonomy and minimal mass systems. The frontline soldier, more often than not, does not have access to energy for recharging his power sources and therefore, must carry all his required power sources to complete his mission. The ability to harvest human energy, if favorable in terms of reliability, size, weight, and energy efficiency might translate immediately into increased autonomy time, increased capability, reduce or eliminate certain logistics items, and, perhaps, reduced cost. Fieldable technology rarely equals laboratory prototype or theoretical capability. Obstacles sometimes are fundamental and perhaps can be finessed through appropriate R&D, innovative techniques, and skillful engineering. This workshop attempted to explore some of the possibilities. As confirmed by the plenary speakers and the working groups, there are a number of potential applications where harvesting of human energy could be applied. Typical are: (1) Personal battery chargers, (2) Medical sensors, (3) Display power sources, (4) Gun sight power, and (5) Rangefinder.

A prototype of thermophotovoltaic (TPV) power generation was designed to study the influence of different emitters, e.g. blackbody emitter and selective emitters, on the photoconversion efficiency of InGaAs based 0.75 eV InGaAs photovoltaic (PV) cells. The prototype consists of a diffusion type burner which uses propane and forced air as the inlet fuels. The combustion process is forced to take place inside a cylindrical geometry emitter and heats the emitter. As a result, the emitter radiates the PV cells, which are arranged around the emitter. The PV cells then convert radiant energy to electricity. A thin quartz tube is placed between the emitter and the PV cells to prevent the combustion products from contaminating the PV cells. The PV cells are cooled using forced convection air. In this paper, the authors used novel material processing approaches to produce a cylindrical metallic alloy emitter ("blackbody" emitter) and a rare earth oxide emitter (selective emitters). The emitters are of a fibrous structure and have high porosity (about 90 vol.%). Highly porous emitters emits high emittance and also allows the combustion products through them. By using these emitters, the influence of emitter types on the overall TPV efficiency is determined.

An international, multidisciplinary community workshop convened to define scientific projects for the next decade of scientific ocean drilling utilizing unique capabilities afforded by the drilling vessel Chikyu ("Earth" in Japanese). The meeting, attended by 397 participants from 21 countries, featured 10 keynote lectures. Participants in working groups identified important projects that are fundamental to understanding the Earth system and that require deep penetration of the seafloor.

The present study was designed with two intentions; Are the effects of angular velocity detectable in the cardiovascular responses during the hyper-G? Another is object to examine how the otolith signal could modify the cardiovascular responses provoked by the exposure to the hyper-G. NASA/KC-135 hyper-gravity flight was used to generate high gravito-inertial forces to exclude a possible effect of angular velocity. Six healthy subjects was indicated to make dorsal flexion of the neck to reduce the otolith input. An exposure to +l.8Gz stress resulted in a remarkable increase of systolic and diastolic blood pressure, thereby pulse pressure became a little bit narrower. R-R interval revealed a tachycardia during the hyper-G except one subject. The present experiment bore the similar cardiovascular responses as those observed in the previous studies with a short rotating radius, suggesting that almost no effect of angular velocity acts on their responses. A weaker otolith input could possibly work on them. However a systematical observation can not recognize among the subjects for the vestibular effect on the cardiovascular responses. This fact of vestibular qualification leads us to speculate that it would depend on the subjects or other factors.