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Background: Aging is characterized by substantial changes in sleep architecture that negatively impact physical fitness, quality of life, mood or cognitive functioning. Older adults often fail to reach the recommended amount of physical activity to prevent the age-related decline sleep function, partly because of geographical barriers. Home-based interventions could overcome these barriers preventing older adults from being active, and administration through videoconference may be an optimal solution. Increasing the availability of synchronisers such as physical activity, light exposure or vestibular stimulation is a good non-pharmacological strategy for circadian rhythms entrainment and could strengthen the sleep-wake cycle and thus improve sleep in the ageing subject. The aims of this study are (1) to evaluate the effects of a remote physical exercise training and a remote physical exercise training combined with bright light exposure, and (2) to study the specific contribution of galvanic vestibular stimulation on sleep in healthy older adults with sleep complaint. Methods: One hundred healthy older adults (60-70 years old) with sleep complaint will be randomized to a physical exercise training group (n=25), a physical exercise training combined with bright light exposure group (n=25), a galvanic vestibular stimulation group (n=25) or a control group (i.e. health education) (n=25). While physical exercise training and health education will be supervised by videoconference at home, bright light exposure (from the physical exercise training combined with bright light exposure group) and vestibular stimulation will be self-administered at home. Pre- and post- tests will be performed to assess: sleep (polysomnography, subjective questionnaires), circadian rhythms (actigraphy, temperature), physical fitness (VO2peak, muscular function, postural control and functional mobility), cognition (executive function, long-term memory), quality of life and mood (anxiety and depression). Discussion: The results should support the development of recommendations and non-pharmaceutical preventive strategies to maintain or even improve sleep quality in older adults and, consequently, to improve physical fitness, cognition, quality of life and mood throughout aging. Trial registration: Clinicaltrials.gov ID: NCT05030389. Registered on September - retrospectively registered.

Background Older adults often fail to reach the recommended amount of physical activity to prevent the age-related decline in metabolic, cardiorespiratory, and muscular function. Effective home-based physical training programs could neutralize barriers preventing older adults from being active, and administration/supervision through videoconference may be an optimal solution. The present randomized controlled trial aimed to test the non-inferiority of training program administered through videoconference against the same program administered face-to-face in healthy older adults. Methods Participants were randomized in a no-training control group (n = 13), a face-to-face training group (n = 15), and a videoconference training group (n = 13). The intervention groups completed the same home-based, structured, progressive and combined training program for 16 weeks, 1-hour twice a week. Pre-intervention and post-intervention evaluations included body composition, cardiorespiratory fitness and muscle function measures. The non-inferiority margin was calculated by comparing the face-to-face training group to the no-training control group. Results Non-inferiority of videoconferencing against face-to-face training was observed for changes in body weight (p>.01), fat mass (p=.015), maximal aerobic power (p=.013), maximal heart rate (p=.034), maximal oxygen consumption (p>.01), knee extension strength (p=.044) and lower limb power (p=.019), but not for muscle mass (p=.067), handgrip strength (p=.171), trunk extension strength (p=.241) and knee flexion strength (p=.462). Conclusion A training program administered through videoconferencing was not inferior to the same program administered face-to-face for reducing body weight and fat mass, and for improving maximal aerobic power and oxygen consumption as well as lower limb power and knee extension strength in healthy elderly subjects. However, videoconferencing training was not as effective as face-to-face training for improving handgrip, trunk extension and knee flexion isometric strength, possibly because of a higher motivation related to the physical presence of the trainer in the face-to-face training group.

BACKGROUND: Aerobatic flight is a challenge for the vestibular system, which is likely to lead to adaptive changes in the vestibular responses of pilots. We investigated whether aerobatic pilots, as individuals who experience intense vestibular stimulation, present modifications of the vestibular-ocular reflex, motion sickness susceptibility and intensity, visual vertical estimation, and visual dependence as compared to normal volunteers.METHODS: To evaluate vestibulo-ocular reflexes, eye movements were recorded with videonystagmography while subjects were rotated on a rotatory chair with the axis of rotation being vertical (canal-ocular reflex) or inclined to 17° (otolith-ocular reflex). Motion sickness was evaluated after the rotatory test using the Graybiel diagnostic criteria. General motion sickness susceptibility and visual field dependence were also evaluated.RESULTS: Averaged data did not show significant difference in canal-ocular reflex and otolith ocular-reflex between groups. However, a significant asymmetry in otolith-driven ocular responses was found in pilots (CW 0.50 ± 1.21° · s−1 vs. CCW 1.59 ± 1.12° · s−1), though visual vertical estimation was not altered in pilots and both groups were found field independent. Pilots were generally less susceptible to motion sickness (MSSQ scores: 2.52 ± 5.59 vs. 13.5 ± 11.36) and less affected by the nauseogenic stimulation (Graybiel diagnostic criteria 3.36 ± 3.81 vs. 8.39 ± 7.01).DISCUSSION: We did not observe the expected habituation in the group of aerobatic pilots. However, there was a significant asymmetry in the otolith-driven ocular responses in pilots, but not in the controls, which may result from the asymmetry in piloting protocols.Kuldavletova O, Tanguy S, Denise P, Quarck G. Vestibulo-ocular responses, visual field dependence, and motion sickness in aerobatic pilots. Aerosp Med Hum Perform. 2020; 91(4):326–331.

Insomnia symptoms are common among patients with breast cancer (BC; 20–70%) and are predictors of cancer progression and quality of life. Studies have highlighted sleep structure modifications, including increased awakenings and reduced sleep efficiency and total sleep time. Such modifications may result from circadian rhythm alterations consistently reported in this pathology and known as carcinogenic factors, including lower melatonin levels, a flattened diurnal cortisol pattern, and lower rest-activity rhythm amplitude and robustness. Cognitive behavioral therapy and physical activity are the most commonly used non-pharmacological interventions to counter insomnia difficulties in patients with BC. However, their effects on sleep structure remain unclear. Moreover, such approaches may be difficult to implement shortly after chemotherapy. Innovatively, vestibular stimulation would be particularly suited to tackling insomnia symptoms. Indeed, recent reports have shown that vestibular stimulation could resynchronize circadian rhythms and improve deep sleep in healthy volunteers. Moreover, vestibular dysfunction has been reported following chemotherapy. This perspective paper aims to support the evidence of using galvanic vestibular stimulation to resynchronize circadian rhythms and reduce insomnia symptoms in patients with BC, with beneficial effects on quality of life and, potentially, survival.

Introductionwith ageing, the risk of falling increases. It has been reported that fall frequency may depend on the time of the day, suggesting a possible circadian rhythm of postural control. The objective was to test whether postural control in older adults followed a circadian rhythm. Then, in order to examine the possible functions involved in circadian variations in balance performances, circadian rhythm of sleepiness and vertical perception were also tested.Methodseight participants (70.7 ± 4.7 years) were included. Baseline circadian rhythm profile was assessed through continuous core temperature measurement. Static and dynamic balance, subjective sleepiness and fatigue, and verticality perception were measured at 2:00, 6:00, 10:00, 14:00, 18:00 and 22:00, on separate weeks in a random order.Resultstemperature followed a circadian rhythm, with lowest temperature occurring at 03:50. Circadian rhythm was detected for the centre of pressure displacement length and velocity, in dynamic condition eyes closed, with lowest performances occurring at 18:33 and 16:59, respectively. Subjective sleepiness and fatigue also followed circadian rhythm with lowest sleepiness occurring at 15:46 and 15:50, for the Karolinska Sleeping Scale and the Visual Analogic Scale of fatigue, respectively. Finally, the vertical perception was not significantly following a circadian rhythm.Conclusionolder adults present a circadian rhythm of balance, in particular in more challenging conditions, and the lowest performances occurred in the late afternoon These circadian rhythms could explain some of the falls happening at this time in community-dwelling older adults.

International audience; Videoconference-based adapted physical exercise combines the benefits of supervised exercise training with staying at home, when conventional training is inaccessible. However, exercising with the use of a screen can be considered an optokinetic stimulation, and could therefore induce changes in sensory processing, affecting postural stability. The objectives of this study were to compare the effectiveness of the training delivered Face-to-Face and by Videoconferencing in improving physical capacities of older adults, and to evaluate the possible effects of the Videoconference mode on the processing of sensory information that could affect postural control. Twenty eight older adults underwent the supervised exercise program for sixteen weeks either Face-to-Face or by Videoconference. Muscular strength of knee and ankle flexors and extensors, maximum oxygen uptake, postural stability and horizontal rotational vestibulo-ocular reflex were evaluated before and after the training. Both modes of training similarly increased the VO2 peak and strength of the motor muscles of lower limbs in all participants. The use of the Videoconference did not modify the vestibulo-ocular reflex in subjects or the importance of vision for postural control. Therefore, the Videoconference-based exercise training can be considered a safe and effective way to maintain good functional capacity in seniors.

Background Patients with schizophrenia (SZ) present a higher level of cardiovascular morbidity than the general population due to poor physical fitness and a sedentary lifestyle. Moreover, despite major therapeutic advances in the management of SZ, some clinical symptoms remain resistant to pharmacological approaches. A large number of studies support the effectiveness of physical activity (PA) for both physical and mental health in SZ. The main objective of the present study is to assess the effects of a remote, web-based adapted PA program (e-APA) compared to a health education program (e-HE) on brain plasticity in SZ and healthy volunteers (HV). The secondary objectives are to assess the effects of e-APA on other cerebral variables as well as clinical, neurocognitive, circadian, biological, and physiological variables. Methods: The study is an interventional, multicenter, randomized open-label controlled trial. Forty-two SZ will be randomized to either the active group (e-APA, N = 21) or non-active group (e-HE, N = 21), and 42 HV will be matched to SZ according to age, gender, and level of PA. Interventions will consist of 32 sessions (2x60 minutes/week, for 16 weeks) via supervised home-based videoconferencing. The active group will carry out an individualized PA program of moderate to vigorous intensity. Pre- and post-intervention cerebral magnetic resonance imaging (MRI) will be performed to evaluate changes in global hippocampal volume. Other cerebral assessments using diffusion tensor imaging, arterial spin labelling, spectroscopy and resting-state functional MRI will be performed. In addition, clinical, neurocognitive and circadian rhythms assessments as well as physical tests and biological analyses will be conducted. Discussion: To our knowledge, this is the first study aiming to evaluate the efficacy of APA delivered by supervised home-based videoconferencing in SZ. Moreover, using multimodal MRI, this study could clarify the pathophysiological mechanisms underlying the efficacy of APA. Finally, this innovative approach (remote, web-based APA) might also increase participation in long-term PA since PA-based programs are known to have low adherence and early dropout. The results of this study should promote the inclusion of PA interventions as a novel adjunctive therapy for SZ. Trial registration: ClinicalTrials.gov identifier: NCT03261817. Registered on 16 August 2017.

International audience; Animal and human studies demonstrate anatomical and functional links between the vestibular nuclei and the circadian timing system. This promotes the hypothesis of a circadian rhythm of vestibular function. The objective of this study was to evaluate the vestibular function through the vestibulo-ocular reflex using a rotatory chair at different times of the day to assess circadian rhythmicity of vestibular function. Two identical studies evaluating temporal variation of the vestibulo-ocular reflex (VOR) were performed, the first in young adults (age: 22.4 ± 1.5 y), and the second in older adults (70.7 ± 4.7 y). The slow phase velocity and time constant of the VOR were evaluated in six separate test sessions, i.e., 02:00, 06:00, 10:00, 14:00, 18:00, and 22:00 h. In both studies, markers of circadian rhythmicity (temperature, fatigue, and sleepiness) displayed expected usual temporal variation. In young adults, the time constant of the VOR showed variation throughout the day (p < .005), being maximum 12:25 h (06:00 h test session) before the acrophase of temperature circadian rhythm. In older adults, the slow phase velocity and time constant also displayed temporal variation (p < .05). Maximum values were recorded at 10:35 h (06:00 h test session) before the acrophase of temperature circadian rhythm. The present study demonstrates that vestibular function is not constant throughout the day. The implication of the temporal variation in vestibular system in equilibrium potentially exposes the elderly, in particular, to differential risk during the 24 h of losing balance and falling.

Background: The study aimed to determine whether improved muscle strength after 12 weeks of neuromuscular electrical stimulation (NMES) of plantar and dorsiflexors could result in better limits of stability in older adults. Methods: Twenty-seven participants were divided into a control group and a neuromuscular home-based training group. The training group performed a 3-month long NMES training of both plantar and dorsiflexors. Ankle flexor strength and limits of stability were measured. A mediation analysis was conducted to determine whether the NMES effect on the limits of stability was mediated by increased strength. Results: The NMES training increased plantar flexor strength (+47%; β = 0.217, P = .02), and this increase predicted the anterior limits of stability improvement (+27%; β = 0.527, P = .02). The effect of the NMES on the limits of stability was fully mediated by the plantar flexor strength increase (indirect effect: β = 0.1146; 95% confidence interval, 0.020–0.240). Conclusion: It seems that NMES improves the limits of stability through its positive effect on muscle strength. NMES may be utilized in fall-prevention programs.

Les altérations physiologiques et fonctionnelles liées au vieillissement peuvent avoir un impact sur l’autonomie des personnes dans les activités de la vie quotidienne. Afin de prévenir et de limiter ces effets délétères, il est recommandé d’avoir une activité physique adaptée régulière. Cependant, l’accès à un entraînement efficace n’est pas toujours possible pour les seniors. Dans une première partie, nous examinons donc l’état des connaissances scientifiques sur les différentes modalités d’entraînement au domicile d’un public âgé. En l’absence de supervision, il apparaît que les bénéfices associés à la pratique sont moindres et que l’adhésion au programme est réduite. Dans le cadre d’entraînements à domicile semi-supervisés, il semble que les bénéfices sur la santé soient encore une fois faibles. Lors d’entraînements à domicile avec supervision à distance, l’adhésion et les effets sur la santé semblent cette fois plus importants. Ainsi, afin de répondre aux problématiques relevées par cette revue, dans la seconde partie de ce travail nous présentons un projet novateur d’accompagnement à distance par un professionnel au moyen d’un système de visioconférence collectif. La mise en place de ce projet est prometteuse puisque les résultats préliminaires montrent des taux d’adhésion, d’observance et un niveau de satisfaction très élevés.

International audience; The vestibular system is responsible for sensing every angular and linear head acceleration, mainly during periods of motor activity. Previous animal and human experiments have shown biological rhythm disruptions in small rodents exposed to a hypergravity environment, but also in patients with bilateral vestibular loss compared to a control population. This raised the hypothesis of the vestibular afferent influence on circadian rhythm synchronization. The present study aimed to test the impact of vestibular stimulation induced by a rotatory chair on the rest/activity rhythm in human subjects. Thirty-four healthy adults underwent both sham (SHAM) and vestibular stimulation (STIM) sessions scheduled at 18:00 h. An off-vertical axis rotation on a rotatory chair was used to ecologically stimulate the vestibular system by head accelerations. The rest/activity rhythm was continuously registered by actigraphy. The recording started one week before the first session (BASELINE), continued in the week between the two sessions and one week after the second session. Vestibular stimulation caused a significant decrease in the average activity level in the evening following the vestibular stimulation. A significant phase advance in the rest/activity rhythm occurred two days after the 18:00 h vestibular stimulation session. Moreover, the level of motion sickness symptoms increased significantly after vestibular stimulation. The present study confirms previous results on the effect of vestibular stimulation and the role of vestibular afferents on circadian biological rhythmicity. Our results support the hypothesis of the implication of vestibular afferents as non-photic stimuli acting on circadian rhythms.

This study assessed cardiovascular control during head-down neck flexion (HDNF) in a group of patients suffering from total bilateral idiopathic vestibular loss (BVL) for 7 ± 2 yr. Nine adult patients (age 54 ± 6 yr) with BVL were recruited. Calf blood flow (CBF), mean arterial pressure (MAP), and heart rate (HR) were measured with subjects’ eyes closed in two lying body positions: ventral prone (VP) and lateral (LP) on the left side. Vascular resistance (CVR) was calculated as MAP/CBF. The HDNF protocol consisted in passively changing the head position: head up (HU)–head down (HD)–HU. Measurements were taken twice at each head position. In VP CBF significantly decreased in HD (3.65 ± 0.65 mL·min−1·100 mL−1) vs. HU (4.64 ± 0.71 mL·min−1·100 mL−1) ( P < 0.002), whereas CVR in VP significantly rose in HD (31.87 ± 6.93 arbitrary units) vs. HU (25.61 ± 6.36 arbitrary units) ( P < 0.01). In LP no change in CBF or CVR was found between the two head positions. MAP and HR presented no difference between HU and HD in both body positions. Age of patients did not significantly affect the results. The decrease in CBF of the BVL patients was similar to the decrease observed with the same HDNF protocol in normal subjects. This suggests a sensory compensation for the lost vestibular inputs that could originate from the integration of inputs from trunk graviceptors and proprioceptive and cutaneous receptors. Another possibility is that the HDNF vascular effect is evoked mostly by nonlabyrinthine sensors.NEW & NOTEWORTHY The so-called vestibulo-sympathetic reflex, as demonstrated by the head-down neck flexion (HDNF) protocol, is present in patients with total bilateral vestibular idiopathic loss, equally in young and old subjects. The origin of the sympathetic effect of HDNF is questioned. Moreover, the physiological significance of the vestibulo-sympathetic reflex remains obscure, because it acts in opposition to the orthostatic baroreflex. It may serve to inhibit the excessively powerful baroreflex.

International audience; Daytime activity is largely regulated by the day/night pattern. Various physiological and cognitive functions display a variation during the diurnal period, where individuals manage their balance, spatial orientation and consequently their perception of the vertical. However, findings concerning daytime changes of postural control quality remain contradictory, mainly due to methodogical considerations. The aim of our study is to evaluate the effect of time of day on postural control and perception of the vertical. Fifteen male subjects underwent six test sessions over a 24-hour period. Each session involved a postural balance test (static/dynamic; eyes open/closed) and a subjective evaluation of sleepiness, fatigue and subjective visual vertical (SVV) (light stick tilted from 10 to 40°; eight trials). No time-of-day effect was observed on postural balance. However, perception of the vertical fluctuates during the day and is better at 10 a.m. than at 10 p.m. Despite the gradual perception of the vertical deterioration over the day, postural balance does not show any fluctuation. This postural balance consistency throughout the day may be the result of compensation mechanisms.

Spatial disorientation is defined as an erroneous body orientation perceived by pilots during flights. Limits of the vestibular system provoke frequent spatial disorientation mishaps. Although vestibular spatial disorientation is experienced frequently in aviation, there is no intuitive countermeasure against spatial disorientation mishaps to date. The aim of this review is to describe the current sensorial countermeasures and to examine future leads in sensorial ergonomics for vestibular spatial disorientation. This work reviews: 1) the visual ergonomics, 2) the vestibular countermeasures, 3) the auditory displays, 4) the somatosensory countermeasures, and, finally, 5) the multisensory displays. This review emphasizes the positive aspects of auditory and somatosensory countermeasures as well as multisensory devices. Even if some aspects such as sensory conflict and motion sickness need to be assessed, these countermeasures should be taken into consideration for ergonomics work in the future. However, a recent development in aviation might offer new and better perspectives: unmanned aerial vehicles. Unmanned aerial vehicles aim to go beyond the physiological boundaries of human sensorial systems and would allow for coping with spatial disorientation and motion sickness. Even if research is necessary to improve the interaction between machines and humans, this recent development might be incredibly useful for decreasing or even stopping vestibular spatial disorientation.

Several studies have suggested that anxiety may play a role in motion sickness susceptibility (MSS) variability. This study aimed to assess motion sickness susceptibility in healthy subjects and chronic vestibular patients and to investigate its relationship to gender, age and trait-anxiety. Healthy subjects (n=167) and chronic dizzy patients with various vestibulopathies (n=94), aged from 20 to 92 years old, were asked to complete Motion Sickness Susceptibility questionnaire (MSSQ) and trait-anxiety questionnaire (STAI-B). When patients were divided into those who had vestibular loss (n=51) vs. patients without vestibular loss (n=43), the MSSQ scores (mean ± SD) for patients with vestibular loss (18.8 ± 30.9) were lower than healthy subjects (36.4 ± 34.8), who were lower than vestibular patients without vestibular loss (59.0 ± 39.7). These significant differences could not be explained by gender, age, trait-anxiety, or interaction. Women had higher MSS than men, and MSS declined with age for healthy subjects and vestibular patients. The overall relationship between anxiety and MSS scores was weak and only reached significance in healthy subjects. These results support the conclusion that the vestibular system is heavily involved in MSS and that trait-anxiety may play a role in MSS but only in healthy subjects.

International audience

Les caracteristiques quantitatives du reflexe vestibulo-oculaire de 15 gymnastes ont ete comparees avec celles de 27 sujets controle d’âge similaire ne pratiquant pas d’activite physique ou une activite de loisir ne sollicitant pas le systeme vestibulaire de maniere importante. Les gymnastes avaient une vitesse initiale des phases lentes plus faible (p

The aim of this study was to evaluate the role of the vestibular system in cardiovascular control in a varying gravito-inertial field induced by parabolic flight. We measured variations in arterial pressure and heart rate in eight awake rats, four of which had undergone bilateral labyrinthectomy 3 months previously. While the control rats showed heart rate and mean arterial pressure modulations depending on gravity level, no such variation was observed in the lesioned rats. This study confirms the role of the vestibular system in cardiovascular control and opens up new prospects for interpreting cardiovascular variations observed during space flights.

International audience; Hypergravity disrupts the circadian regulation of temperature (Temp) and locomotor activity (Act) mediated through the vestibular otolithic system in mice. In contrast, we do not know whether the anatomical structures associated with vestibular input are crucial for circadian rhythm regulation at 1 G on Earth. In the present study we observed the effects of bilateral vestibular loss (BVL) on the daily rhythms of Temp and Act in semipigmented rats. Our model of vestibular lesion allowed for selective peripheral hair cell degeneration without any other damage. Rats with BVL exhibited a disruption in their daily rhythms (Temp and Act), which were replaced by a main ultradian period (τ

The purpose of this study was to test the hypothesis whereby eye movements as such may be an important factor in the development of motion sickness (MS). The horizontal eye movements of 27 subjects were measured during earth vertical axis rotation (EVAR) and during off vertical axis rotation (OVAR). Two groups were set up, one including subjects who suffered severe MS during the test, and the other including subjects with no MS symptoms. We found no differences in nystagmus parameters (EVAR: gain and time constant; OVAR: eye velocity modulation and eye position modulation) between the MS and the non-MS groups. We can conclude that eye movements are not involved in the development of MS.

Head posture and neck muscle activity (EMGs) were examined in unilateral (UL) and bilateral (BL) vestibularly lesioned rats in hypergravity (1.7 g) and hypogravity (0 g) during parabolic flights. Compared with BL rats taken as control, the head and the body of UL deviated toward the lesion side at 0 g and toward the intact side at 1.7 g. Recorded in head fixed condition, left and right EMGs remained symmetrical in BL while UL rats displayed an asymmetry between left and right muscles at 1.7 g, but not at 0 g. These results demonstrate that an experimental otolithic asymmetry, compensated on Earth, can become unbalanced in altered gravity. Paradoxically, the utricular system appears to play a major role in that process.

The aim of this study was to evaluate the relationship between olfaction and motion sickness. A sample of 18 participants was recruited and submitted to three sessions of nauseogenic stimulations: off vertical axis rotation (OVAR), performed under conditions of olfactory stimulation with limonene (pleasant odor), petrol (unpleasant odor) or distilled water (as a control). Motion sickness was assessed before, during and after each OVAR session. In addition, participants were asked to evaluate the intensity and hedonic valence of four odors (geraniol, limonene, butanol, petrol) as well as distilled water (as a control) before and after each OVAR session. Our analysis showed that OVAR has consistently increased the induced- motion sickness. However the addition of an odor that is pleasant or unpleasant during the rotation did not affect the occurrence of motion sickness symptoms compared to the control condition. Our results also showed that intensity of odors was significantly increased after OVAR and the intensity was significantly higher for unpleasant odors than for pleasant one. For the hedonicity, OVAR made unpleasant odors more unpleasant (p < 0.0001) while it made limonene odor slightly more pleasant (p < 0.05). The present study highlighted the lack of influence of odors in motion-induced sickness but an impact of a nauseogenic test on olfactory perception.

International audience; In order to explore the effect of gaze orientation on whole-body rotation perception, ten healthy participants were rotated in the dark while fixating on a visual target located either straight ahead or 15 degrees to the right. A vestibular-memory contingent saccade paradigm was used to estimate the rotation perception. The results attest to the participants' ability to accurately perceive their rotation, based solely on the intrinsic inputs (somesthetic and mainly vestibular), since the correlation between the imposed body rotation and the saccade amplitude was significant and positive. However, the rotation perception was less accurate and of lesser magnitude when the gaze was deviated in the opposite direction to the rotation than when it was either straight ahead or deviated in the direction of the rotation. This can be interpreted as the perceptual equivalent of Alexander's law.

In order to determine the effect of figure skating on the functional plasticity of the vestibular system, we quantified vestibulo-ocular reflex (VOR) and motion sickness (MS) intensity in 11 female figure skaters and 11 matched control subjects. Vestibular stimulation consisted of three cycles of sinusoidal rotation (0.025 Hz, +/-60 degrees /s) and two velocity steps of 60 degrees /s (acceleration 60 degrees /s(2)). Nauseogenic stimulation consisted of a constant velocity (60 degrees /s) off vertical axis rotation (OVAR) using a 15 degrees tilt angle. Subjective sickness symptoms were rated immediately after OVAR with the Pensacola diagnostic index. During sinusoidal stimulations, the skaters' VOR, as compared with that of the controls, demonstrates a gain that is 27% lower (0.44 +/- 0.12 vs. 0.58 +/- 0.10; P0.01) and a phase advance (10 +/- 12 degrees vs. -0.3 +/- 6.4 degrees ; P0.05). During velocity steps, the VOR gain is 32% lower among the skaters (0.52 +/- 0.14 vs. 0.71 +/- 0.12; P0.01), but there is no difference in time constant (10.8 +/- 1.8 s vs. 10.5 +/- 2.7 s; P = 0.78). Nauseogenic stimulation evokes significantly less MS in figure skaters than in control subjects (2.8 +/- 2.8 vs. 16.2 +/- 13.7; P0.01). Quantitative alterations in VOR parameters observed in figure skaters probably result from vestibular habituation induced by repeated unusual stimulations when practicing figure skating.

The aim of this study was to investigate whether figure skaters, as individuals who experience intense vestibular stimulation, presented modification of the otolith-ocular reflex. The reflexes of 12 figure skaters were assessed using off vertical axis rotation (OVAR). Horizontal otolith-ocular reflex during OVAR is characterized by two parameters: the eye velocity horizontal modulation, assumed to compensate for perceived lateral linear translation, and the bias, assumed to compensate for the perceived rotation. We observed that skaters presented smaller amplitude of modulation and truly compensatory bias compared with control participants. Thus, the otolithic signal during OVAR seems to be interpreted more as rotation and less as translation or inclination in figure skaters.

BACKGROUND Accurate measurement of beat-to-beat arterial blood pressure is essential for understanding the cardiovascular adaptation to weightlessness; however, the intra-arterial standard of beat-to-beat blood pressure measurement has never been used during space flight because of its invasive nature. OBJECTIVES The aim of the present study was to compare noninvasive radial artery tonometry blood pressure measurement with intra-radial pressure measurement during microgravity and hypergravity generated by parabolic flights. METHODS Two study participants, equipped with an intra-radial pressure line on the left arm and a Colin CBM-7000 (Colin Corp., Komaki City, Japan) beat-to-beat pressure measurement apparatus on the right arm, were studied in a supine position, during parabolic flights on board of the Airbus A300 OG of the Centre National d'Etudes Spatiales. The mean and standard deviations of the beat-to-beat difference between tonometric and intra-radial blood pressure were calculated for systolic and diastolic arterial pressure in the three gravity conditions (1g, 0 g and 1.8 g) experienced during parabolic flight. RESULTS The Colin CBM-7000 met the specifications required by the Association for the Advancement of Medical Instrumentation in the 0 g environment. Gravity, however, significantly affected the difference between tonometric and intra-arterial blood pressure, possibly owing to the effect of gravity on the apparent weight of the device and the corresponding calibration factor. CONCLUSION We conclude that the Colin CBM-7000 can be used with confidence during space flight.

The effect of sleep deprivation on the vestibular function is largely unknown. Some studies have found that postural balance or vestibular reflexes are decreased in sleep-deprived subjects while others found no change. The aim of this study was to evaluate the effect of sleep deprivation on the vestibulo-ocular reflex (VOR). Horizontal eye movements were recorded in healthy subjects during earth vertical axis rotation in darkness once after an ordinary night sleep and once after 26-29 h of sleep deprivation. In the first experiment (n = 8), for which rotation was a 60 degrees s(-1) velocity step, sleep deprivation induced a significant increase in VOR gain. In the second experiment (n = 12), for which rotation was sinusoidal (0.2 Hz +/- 25 degrees s(-1)), sleep deprivation induced no significant modification in VOR gain. The difference between the two studies was the abrupt onset of the step stimulation in comparison with the sinusoidal rotation. Because of its unexpected onset and the potential threat to postural balance, the step stimulation may activate the system specialized in reorienting attention towards salient or behaviourally relevant events. This system includes the right temporoparietal cortex, an area also involved in VOR control. A number of studies have found that sleep deprivation alters the activity of this cortical area during attentional tasks. It is therefore our hypothesis that the difference between the effects of these two vestibular stimulations results from a sleep deprivation-induced modulation of the right temporoparietal cortex.

Summary An electrical stimulation in man applied between the two mastoids could facilitate the distinction between labyrinthine and retrolabyrinthine lesions by stimulating directly the primary vestibular afferences. However, for this test to be really effective in current medical practice, the results obtained in normal subjects must be symmetrical and reproducible one day to another. The ocular responses induced by a constant electrical stimulation of 2.5 mA, applied between the two mastoids for 30 s (electrically evoked vestibulo-ocular reflex [EVOR]), in one direction and the other, were quantified in ten healthy subjects. Each subject was studied in two different sessions separated by 1 week. Horizontal eye movements were recorded in darkness by an infrared light reflection eye-tracking system. Slow-phase velocity and nystagmus frequency were about 20% higher when the cathode was on the right mastoid than when it was on the left mastoid. This directional preponderance (DP) displayed large individual differences between the two sessions. The reproducibility of the reflectivity (mean of right and left EVOR) was high ( r about 0.8). The weak reproducibility of the DP makes the EVOR at weak intensity inadequate to evaluate unilateral vestibular hypofunction. On the other hand, because of the high reproducibility of reflectivity, the EVOR should be effective in detecting bilateral vestibular hypofunction. Moreover, because of the weak intensity of stimulation, no local anaesthesia is needed so the manoeuvre is easy to repeat in case of chronic diseases.

Since motion sickness (MS) never occurs in individuals who lack functional vestibular apparatus, it has been suggested that MS susceptible individuals have more sensitive vestibular systems than non-susceptible people. However, previous investigations involving only stimulation of the semi-circular canals have been inconclusive. We measured gain and time constant (TC) of horizontal canal-ocular reflex (COR) and magnitude of otolith-ocular reflex (OOR). We found that MS susceptibility was not correlated to COR gain but was negatively correlated to OOR magnitude. Thus, MS susceptible individuals do not have more sensitive vestibular systems. We also found a positive correlation between MS susceptibility and TC. We hypothesize that central vestibular integration (velocity storage mechanism), by increasing low frequency vestibular inputs, would favour MS.