Virtual reality as a countermeasure for astronaut motion sickness during simulated post-flight water landings.

Entry motion sickness (EMS) affects crewmembers upon return to Earth following extended adaptation to microgravity. Anticholinergic pharmaceuticals (e.g., Meclizine) are often taken prior to landing; however, they have operationally adverse side effects (e.g., drowsiness). There is a need to develop non-pharmaceutical countermeasures to EMS. We assessed the efficacy of a technological countermeasure providing external visual cues following splashdown, where otherwise only nauseogenic internal cabin visual references are available. Our countermeasure provided motion-congruent visual cues of an Earth-fixed scene in virtual reality, which was compared to a control condition with a head-fixed fixation point in virtual reality in a between-subject design with 15 subjects in each group. We tested the countermeasure's effectiveness at mitigating motion sickness symptoms at the end of a ground-based reentry analog: approximately 1 h of 2Gx centrifugation followed by up to 1 h of wave-like motion. Secondarily, we explored differences in vestibular-mediated balance performance between the two conditions. While Motion Sickness Questionnaire outcomes did not differ detectably between groups, we found significantly better survival rates (with dropout dictated by reporting moderate nausea consecutively over 2 min) in the visual countermeasure group than the control group (79% survival vs. 33%, t(14) = 2.50, p = 0.027). Following the reentry analogs, subjects demonstrated significantly higher sway prior to recovery (p = 0.0004), which did not differ between control and countermeasure groups. These results imply that providing motion-congruent visual cues may be an effective mean for curbing the development of moderate nausea and increasing comfort following future space missions.

Exhibition of stochastic resonance in vestibular tilt motion perception.

BACKGROUND: Stochastic Resonance (SR) is a phenomenon broadly described as "noise benefit". The application of subsensory electrical Stochastic Vestibular Stimulation (SVS) via electrodes behind each ear has been used to improve human balance and gait, but its effect on motion perception thresholds has not been examined. OBJECTIVE: This study investigated the capability of subsensory SVS to reduce vestibular motion perception thresholds in a manner consistent with a characteristic bell-shaped SR curve. METHODS: We measured upright, head-centered, roll tilt Direction Recognition (DR) thresholds in the dark in 12 human subjects with the application of wideband 0-30 Hz SVS ranging from ±0-700 µA. To conservatively assess if SR was exhibited, we compared the proportions of both subjective and statistical SR exhibition in our experimental data to proportions of SR exhibition in multiple simulation cases with varying underlying SR behavior. Analysis included individual and group statistics. RESULTS: As there is not an established mathematical definition, three humans subjectively judged that SR was exhibited in 78% of subjects. "Statistically significant SR exhibition", which additionally required that a subject's DR threshold with SVS be significantly lower than baseline (no SVS), was present in 50% of subjects. Both percentages were higher than simulations suggested could occur simply by chance. For SR exhibitors, defined by subjective or statistically significant criteria, the mean DR threshold improved by -30% and -39%, respectively. The largest individual improvement was -47%. CONCLUSION: At least half of the subjects were better able to perceive passive body motion with the application of subsensory SVS. This study presents the first conclusive demonstration of SR in vestibular motion perception.

Close-coupling calculations of low-energy inelastic and elastic processes in 4He collisions with H2: A comparative study of two potential energy surfaces.

The two most recently published potential energy surfaces (PESs) for the HeH2 complex, the so-called MR (Muchnick and Russek) and BMP (Boothroyd, Martin, and Peterson) surfaces, are quantitatively evaluated and compared through the investigation of atom-diatom collision processes. The BMP surface is expected to be an improvement, approaching chemical accuracy, over all conformations of the PES compared to that of the MR surface. We found significant differences in inelastic rovibrational cross sections computed on the two surfaces for processes dominated by large changes in target rotational angular momentum. In particular, the H2(nu=1,j=0) total quenching cross section computed using the BMP potential was found to be a factor of 1000 larger than that obtained with the MR surface. A lesser discrepancy persists over a large range of energies from the ultracold to thermal and occurs for other low-lying initial rovibrational levels. The MR surface was used in previous calculations of the H2(nu=1,j=0) quenching rate coefficient and gave results in close agreement with the experimental data of Audibert et al. which were obtained for temperatures between 50 and 300 K. Examination of the rovibronic coupling matrix elements, which are obtained following a Legendre expansion of the PES, suggests that the magnitude of the anisotropy of the BMP potential is too large in the interaction region. However, cross sections for elastic and pure rotational processes obtained from the two PESs differ typically by less than a factor of 2. The small differences may be ascribed to the long-range and anharmonic components of the PESs. Exceptions occur for (nu=10,j=0) and (nu=11,j=1) where significant enhancements have been found for the low-energy quenching and elastic cross sections due to zero-energy resonances in the BMP PES which are not present in the MR potential.

Male rat sexual behavior compared after 6-OHDA and electrolytic lesions in the dorsal NA bundle region of the midbrain.

Forebrain catecholamine depletion and midbrain histological damage in adult male rats were investigated as a function of 6-hydroxydopamine dosage in the range 4 microgram in 2 microliter to 8 micrograms in 4 microliter, stereotaxically injected at 0.43 microliter/min bilaterally in the region of the ascending dorsal noradrenaline bundle of the locus coeruleus, without and with a 30-60 min earlier 25 mg/kg intraperitoneal dose of desmethylimipramine (DMI). Sexual behavior of the male rat was compared for treatment with 4 microgram in 2 microliter 6-OHDA, without and with 25 mg/kg protective dose of DMI, and alternatively for 1 mA 30 sec bilateral electrolytic lesions at the same location. For the behaviorally tested rats receiving 6-OHDA treatment, cortical noradrenaline was depleted to 17% and to 81% of control, without and with DMI, respectively. Hypothalamic NA was depleted to 60% and 102% (no depletion), respectively. Caudate dopamine depletion did not reach significance at P = 0.05. For rats with electrolytic lesions cortical NA was depleted to 46% of control and caudate dopamine was not depleted. For the electrolytically lesioned rats, the first 3 post-ejaculatory intervals decreased by an average of 24%, while the 1 h ejaculatory frequency increased by 17%, which confirms a prior finding. However, no measured sexual behavioral effects were observed with 6-OHDA. Thus, interrupting the dorsal noradrenaline bundle has not been shown to have any effect on sexual behavior in the male rat.

Sexual inhibition is reduced by rostral midbrain lesions in the male rat.

Electrolytic lesions in a circumscribed area of the rostral midbrain of rats shortened the inhibitory period following ejaculation, thereby increasing the number of ejaculations achieved in 1-hour tests. These lesions also interrupted the dorsal norepinephrine bundle as reflected in a 63 percent reduction in telencephalic or cortical norepinephrine.