Eye eccentricity modifies the perception of whole-body rotation

International audienceIn 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

Motion sickness: physiopathology, therapeutic and rehabilitation

Abstract: Technological evolution of modern transports significantly increases motion sickness symptoms occurrence. Motion sickness is defined by a set of four main symptoms that regularly appear: facial pallor, cold sweats,nausea and vomiting. Other additional signs such as dizziness, headache, fatigue and postural instability can be also observed. One of the most established theories to explain in which circumstances motion sickness arises is the ‘sensory conflict’ theory. This theory postulates that motion sickness originates from a sensory mismatch between actual versus expected invariant patterns of vestibular, visual and somatosensory inputs. It has been accepted that the vestibular system influences individual motion sickness susceptibility since patients with bilateral vestibular deficit have greatly reduced susceptibility or do not become motion sick at all. This sensory mismatch leads to an activation of vestibule-autonomic pathways, which have been shown to be also involved in producing nausea and vomiting during motion sickness and those that generate illness after ingestion of toxins. The characteristics of movements that induce motion sickness have been defined: otolith stimulations around 0.2 Hz are involved probably because the signals at this frequency are ambiguous and difficult to interpret by the brain in terms of inclination or translational movements perception. Other factors such as vestibular reflex characteristics, gender, age are involved; strong smells, temperature are often reported. Preventive and curative pharmacological treatments are the same as 30 years ago. New pharmacological classes without undesirable side effects have to be tested on humans. Behavioral measures can be useful

Sensorial countermeasures for vestibular spatial disorientation

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

The complexity of center of pressure positions during quiet stance and its relationship to cognition, aging and falls

International audienceBACKGROUND In a secondary analysis of data taken from a publicly available database, we examined cognitive performance, postural sway, and relations between them for four groups: younger and older individuals with versus without a recent history of falls. Our objective was to compare linear versus nonlinear measures of postural activity as post-hoc predictors of cognitive performance and falling. METHODS We evaluated standing body sway in 147 participants (18 to 85 years-old) over 60 seconds, separately with eyes-open and with eyes-closed. We evaluated cognitive performance using portions of the Trail Making Test. We evaluated postural activity in terms of standard deviation, velocity, and amplitude of the CoP. Separately, we used detrended fluctuation analysis (DFA) to examine the complexity of CoP displacements. Using analysis of variance, we conducted separate analyses of cognitive performance and postural activity comparing Younger and Older Adults and Non-fallers and Fallers, taking into account Vision (eyes-closed vs. open) and the direction of postural movements (AP vs. ML) while also controlling for participants' characteristics. We used moderation analyses to evaluate whether relationships between Trail Making Test scores and the linear and nonlinear outcomes were moderated by Age group or Fall status. RESULTS For postural activity, only DFA differed between Non-fallers and Fallers. Older adults exhibited increased complexity associated with better processing speed function, while fallers show an opposite association, relying on processing speed to increase postural rigidity instead of facilitating adaptive control of balance. CONCLUSIONS We conclude that DFA can provide information regarding postural activity and cognitive performance that cannot be obtained from more traditional, linear measures of postural activity, and that DFA may be a valuable tool for assessing fall risk

Vestibulo-Ocular Responses, Visual Field Dependence, and Motion Sickness in Aerobatic Pilots

International audienceBACKGROUND: 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

Non-linear analysis of posturography data: a better reflection of aging, cognitive flexibility, fear of falling and falls?

Introduction: Understanding the mechanisms and factors affecting balance control is crucial for improving postural control, particularly in older adults where the ability to maintain balance decreases and can be influenced by factors such as cognition, fear of falling, and physical conditions. Postural control is often evaluated by measuring the spatial variation of the Center of Pressure (CoP) measured by posturography, but these technics do not capture the dynamics of balance, including its fluctuations and stability over time. Detrended Fluctuation Analysis (DFA), a non-linear mathematical method can capture the dynamic fluctuation of signals over time. DFA could provide a more comprehensive evaluation of postural control and could be a valuable tool in understanding the relationships between balance and age, cognition, fear of falling or falls. Methods: 163 subjects from the public Human Balance Evaluation Database (116 females and 47 males) participated in the study.1 The ages of the subjects ranged from 18 to 85 years. The subjects' balance was evaluated while standing still for 60s with eyes open (looking at a 5 cm round black target placed on the subject's eye-height on a wall 3 m ahead) and with eyes closed. Each condition was performed three times and the order was randomized. Traditional linear analysis of the posturography data was used and CoP Area, anteroposterior (AP), and médiolateral (ML) standard deviation, velocity, and maximum excursion were calculated. Non-Linear Analysis (DFA) was used to calculate the AP and ML alpha coefficients of orders 1 and 2. In addition, the number of falls in the past year, Short Falls Efficacy Scale; International Physical Activity Questionnaire Short Version; and Trail Making Test were collected. Given the non-normal distribution of most data, Kendall's Tau Correlations were used to explore the relationship between the posturography parameters, age, fear of falling, and trail-making tests times and errors, Kruskal-Wallis with Games-Howell posthoc were used to analyze differences in posturography outcomes depending on the level of physical activity, and Mann-Whitney U to test the differences in posturography outcomes between fallers and non-fallers. Results and discussion : In eyes opened condition, compared to linear analysis, order 1 DFA of ML showed the strongest relationship with age, and was the only outcome associated with fear of falling and cognitive errors representing cognitive flexibility. In the eyes-closed condition, DFA did not seem more associated with those outcomes than linear analysis. Order 1 DFA of ML displacement was also the only parameter differing according to the level of physical activity, with an alpha significantly lower in participants with a high level of physical activity compared to those with a low level. DFA order 2 of ML displacement in eyes opened condition was also the only parameter differing between participants who sustained a fall in the past year and participants who did not. Conclusions et perspectives: The use of DFA could be an analysis better reflecting the multiple sensory and neuropsychological integration during standing balance. It could also be a better tool to assess fall risks in the population. 1.Santos, D. A. & Duarte, M. A public data set of human balance evaluations. PeerJ 4, e2648 (2016)

Vestibulo-sympathetic reflex in patients with bilateral vestibular loss

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Impact of Galvanic Vestibular Stimulation on Anxiety Level in Young Adults

International audienceGalvanic vestibular stimulation (GVS) is a non-invasive method used to stimulate the vestibular system. The vestibular system includes the sensors, neural pathways, vestibular nuclei and the cortical areas receiving integrated vestibular inputs. In addition to its role in postural control or gaze stabilization, the vestibular system is involved in some cognitive functions and in emotion processing. Several studies have revealed a modulating effect of vestibular stimulation on mood state, emotional control, and anxiety level. Nevertheless, GVS is known to induce motion sickness symptoms such as nausea. The aim of the present study was to evaluate the tolerability and efficacy of a GVS protocol to be used potentially as a treatment for anxiety, and also to test the impact of stimulation parameters (duration) on anxiety. Twenty-two students underwent three stimulation conditions: (1) a sham session (no stimulation); (2) a single-duration session (38 min of GVS); and (3) a double-duration session (76 min of GVS). Before and after each stimulation, participants completed a Graybiel Scale form for motion sickness symptoms evaluation and a visual analog scale form for anxiety. We observed a significant diminution of anxiety level after a 38-min session of GVS, while a low level of motion sickness was only found following a 76-min session of GVS. Our preliminary study confirms the feasibility of using GVS to modulate anxiety and corroborates the involvement of the vestibular system in the emotional process

Impact of galvanic vestibular stimulation on mood

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