The neural basis of motion sickness

Temporal Changes in Fixational Eye Movements After Concussion in Adolescents and Adults: Preliminary Findings

Concussions often involve ocular impairment and symptoms such as convergence insufficiency, accommodative insufficiency, blurred vision, diplopia, eye strain, and pain. Current clinical assessments of ocular function and symptoms rely on subjective symptom reporting and/or involve lengthy administration time. More objective, brief assessments of ocular function following concussion are warranted. The purpose of this study was to evaluate changes in fixational eye movements (FEMs) and their association with clinical outcomes including recovery time, symptoms, cognitive and vestibular/ocular motor impairment. Thirty-three athletes (13-27 years of age; 54.5% female) within 21 days of a diagnosed concussion participated in the study. A tracking scanning laser ophthalmoscope (TSLO) evaluated FEMs metrics during fixation on a center and corner target. Participants completed symptom (Post-Concussion Symptom Scale [PCSS]), cognitive (Immediate Post-concussion Assessment and Cognitive Testing [ImPACT], and Vestibular/Ocular Motor Screening (VOMS) evaluations. All measures were administered at the initial visit and following medical clearance, which was defined as clinical recovery. Changes in FEMs were calculated using paired-samples t tests. Linear regression (LR) models were used to evaluate the association of FEMs with clinical recovery. Pearson product-moment correlations were used to evaluate the associations among FEMs and clinical outcomes. On the center task, changes across time were supported for average microsaccade amplitude (p = 0.005; Cohen's d = 0.53), peak velocity of microsaccades (p = 0.01; d = 0.48), peak acceleration of microsaccades (p = 0.02; d = 0.48), duration of microsaccade (p < 0.001; d = 0.72), and drift vertical (p = 0.017; d = -0.154). The LR model for clinical recovery was significant (R2 = 0.37; p = 0.023) and retained average instantaneous drift amplitude (β = 0.547) and peak acceleration of microsaccade (β = 0.414). On the corner task, changes across time were supported for drift proportion (p = 0.03; d = 0.43). The LR model to predict clinical recovery was significant (R2 = 0.85; p = 0.004) and retained average amplitude of microsaccades (β = 2.66), peak velocity of microsaccades (β = -15.11), peak acceleration of microsaccades (β = 12.56), drift horizontal (β = 7.95), drift vertical (β = 1.29), drift amplitude (β = -8.34), drift proportion (β = 0.584), instantaneous drift direction (β = -0.26), and instantaneous drift amplitude (β = 0.819). FEMs metrics were also associated with reports of nausea and performance within the domain of visual memory. The FEMs metric were also associated with PCSS, ImPACT, and VOMS clinical concussion outcomes, with the highest magnitude correlations between average saccade amplitude and VOMS symptoms of nausea and average instantaneous drift speed and ImPACT visual memory, respectively. FEMs metrics changed across time following concussion, were useful in predicting clinical recovery, and were correlated with clinical outcomes. FEMs measurements may provide objective data to augment clinical assessments and inform prognosis following this injury.

A Combination of Gamma-Aminobutyric Acid, Glutamic Acid, Calcium, Thiamine, Pyridoxine, and Cyanocobalamin vs Ginger Extract in the Management of Chronic Motion Sickness: A Clinical Evaluation

Background

Motion sickness (kinetosis) is a common and temporarily incapacitant ailment, manageable with behavioral as well as pharmacological measures.

Objective

To assess the effectiveness and safety of a combination of gamma-aminobutyric acid, glutamic acid, calcium, thiamine, pyridoxine, and cyanocobalamin (Group A) (n = 170) and extract of Zingiber officinale (ginger) (Group B) (n = 165) in the management of chronic complaints consistent with motion sickness.

Methods

Both groups were tested according to the following end points, under self-paired as well as comparative study designs: reduction of ≥20 score points in the total motion sickness assessment questionnaire (MSAQ) score, percentage of patients presenting a reduction of the total MSAQ score, absolute MSAQ score reduction, physician's assessment scores, final overall assessment of study medication, and willingness to continue treatment. Safety was also evaluated.

Results

There was a statistically significant better performance under both study designs for Group A (P = 0.05 using different statistical tests) in all end points. Both regimens were safe, with different neurological and gastrointestinal tolerability outcomes.

Conclusions

Group A and Group B regimens were effective and safe in the management of chronic complaints consistent with motion sickness and the Group A regimen was more effective than Group B.

Serial dependencies in visual stability during self-motion

Every time we move our head, the brain must decide whether the displacement of the visual scene is the result of external or self-produced motion. Gaze shifts generate the biggest and most frequent disturbance of vision. Visual stability during gaze shifts is necessary for both, dissociating self-produced from external motion and retaining bodily balance. Here, we asked participants to perform an eye-head gaze shift to a target that was briefly presented in a head-mounted display. We manipulated the velocity of the scene displacement across trials such that the background moved either too fast or too slow in relation to the head movement speed. Participants were required to report whether they perceived the gaze-contingent visual motion as faster or slower than what they would expect from their head movement velocity. We found that the point of visual stability was attracted to the velocity presented in the previous trial. Our data reveal that serial dependencies in visual stability calibrate the mapping between motor-related signals coding head movement velocity and visual motion velocity. This process is likely to aid in visual stability as the accuracy of this mapping is crucial to maintain visual stability during self-motion.NEW & NOTEWORTHY We report that visual stability during self-motion is maintained by serial dependencies between the current and the previous gaze-contingent visual velocity that was experienced during a head movement. The gaze-contingent scene displacement velocity that appears normal to us thus depends on what we have registered in the recent history of gaze shifts. Serial dependencies provide an efficient means to maintain visual stability during self-motion.

Could Vulnerability to Motion Sickness and Chronic Pain Coexist within a Sensorimotor Phenotype? Insights from over 500 Pre-Pain Motion Sickness Reports

BACKGROUND

The sensorimotor incongruence theory proposes that certain instances of pain result from conflicts in the brain's sensorimotor networks. Indeed, injuries may cause abnormalities in afferent and cortical signaling resulting in such conflicts. Motion sickness also occurs in instances of incongruent sensorimotor data. It is possible that a sensory processing phenotype exists that predisposes people to both conditions.

AIM

The aim of this study was to investigate whether participants with chronic pain recall greater susceptibility to motion sickness before chronic pain onset.

METHOD

Data were collected via an online LimeSurvey. A self-report tendency toward motion sickness was measured using the Motion Sickness Susceptibility Questionnaire. Group differences were analysed using analysis of covariance methods.

RESULTS

530 patients (low back pain, n = 198; neck pain, n = 59; whiplash-associated disorder, n = 72; fibromyalgia syndrome, n = 114; Migraine, n = 41) and 165 pain-free controls were surveyed. ANCOVA analysis, using sex and anxiety as covariates, suggested that childhood motion sickness susceptibility scores differed by group (F = 2.55 (6, 615), p = 0.019, (ηp2) = 0.024). Planned comparisons, with corrected p-values, suggested that childhood motion sickness was not statistically greater for low back pain, rheumatoid arthritis, migraine, neck pain or whiplash-associated disorder (ps > 0.05), although scores were on average 27%, 42%, 47%, 48% and 58% higher, respectively. Childhood susceptibility was statistically higher in people with FMS (p = 0.018), with scores on average 83% higher than controls. ANCOVA analysis, using sex and anxiety as covariates, suggested that adult motion sickness susceptibility scores did not differ by group (F = 1.86 (6, 613), p = 0.086), although average scores were, on average, at least 33% higher in persistent pain groups.

CONCLUSIONS

According to retrospective reporting, greater susceptibility to motion sickness appears to pre-date persistent pain in some conditions. This supports the possibility that motion sickness and chronic pain may, in some cases, have overlapping mechanisms related to the handling of incongruent sensorimotor data.

Study of clinical correlation of motion sickness in patients with vestibular migraine

Objective

In this study, clinical data from vestibular migraine (VM) patients and healthy control populations were collected to analyze the clinical data of VM patients, especially the history of motion sickness, and to understand their clinical characteristics.

Methods

According to VM diagnostic criteria, 140 patients diagnosed with confirmed VM (cVM) and probable VM (pVM) who attended the outpatient and inpatient ward of Jiaxing First Hospital between August 2017 and June 2021, as well as 287 healthy check-ups in the health management center, were analyzed and compared in terms of age, gender, and previous history of motion sickness.

Results

A comparison of clinical data related to VM patients and the control population showed that there were more women in the VM group (P < 0.01) and that patients in the VM group were older (P < 0.05) and had a higher prevalence of history of motion sickness history (P < 0.01). Analysis after matching gender and age revealed that patients in the cVM group were older than those in the pVM group (P < 0.05), but the proportion of motion sickness was lower than in the pVM group (P < 0.05). The age of the patients in the cVM group was mainly distributed around 50 years of age, following a normal distribution, whereas the age distribution of the patients in the pVM group did not have a significant trend of age concentration and was distributed at all ages.

Conclusion

The history of motion sickness is significant in patients with VM and may be a potential suggestive factor for the diagnosis of VM.

EEG-based evaluation of motion sickness and reducing sensory conflict in a simulated autonomous driving environment

Autonomous driving offers significant potential for changes in the automotive industry. However, sensory conflict during autonomous driving can lead to motion sickness. Quantitative evaluation and effective preventions to predict and reduce motion sickness are needed. The goal of this study is to verify the objective indicator of motion sickness level based on encephalography (EEG) that we proposed before and investigate the influence of attenuating sensory conflict on motion sickness. A 6-degree of freedom (DOF) driving simulator platform was used to provide an autonomous driving environment to the subjects, and the subjective motion sickness level (MSL), as well as the EEG signals of 15 healthy subjects, were collected simultaneously during 3 conditions, i) autonomous driving, ii) autonomous driving with eyes blindfolded and iii) active driving. The MSLs were reported by the subjects every two minutes, providing a reference to the recorded EEG signals. The EEG signals were analyzed and compared among different conditions. Average MSLs were higher in autonomous driving than in autonomous driving with eyes blindfolded and active driving, together with the increase of the mean EEG frequency of theta band in the central, parietal and occipital areas (FC5, Cz, CP5, P3, and POz). These findings validated that EEG mean frequency of theta band could be an indicator of motion sickness, besides an attenuated visual input or active control of the vehicle can effectively reduce the generation of motion sickness.

Antiemetic effects of baclofen in a shrew model of postoperative nausea and vomiting: Whole-transcriptome analysis in the nucleus of the solitary tract

Aims

The molecular genetic mechanisms underlying postoperative nausea and vomiting (PONV) in the brain have not been fully elucidated. This study aimed to determine the changes in whole transcriptome in the nucleus of the solitary tract (NTS) in an animal model of PONV, to screen a drug candidate and to elucidate the molecular genetic mechanisms of PONV development.

Methods

Twenty‐one female musk shrews were assigned into three groups: the Surgery group (shrew PONV model, n = 9), the Sham group (n = 6), and the Naïve group (n = 6). In behavioral studies, the main outcome was the number of emetic episodes. In genetic experiments, changes in the transcriptome in the NTS were measured. In a separate study, 12 shrews were used to verify the candidate mechanism underlying PONV.

Results

A median of six emetic episodes occurred in both the Sham and Surgery groups. Whole‐transcriptome analysis indicated the inhibition of the GABA_B receptor‐mediated signaling pathway in the PONV model. Baclofen (GABA_B receptor agonist) administration eliminated emetic behaviors in the shrew PONV model.

Conclusions

Our findings suggest that the GABA_B receptor‐mediated signaling pathway is involved in emesis and that baclofen may be a novel therapeutic or prophylactic agent for PONV.

Reduced Gain and Shortened Time Constant of Vestibular Velocity Storage as a Source of Balance and Movement Sensitivities in Gravitational Insecurity

Gravitational insecurity (GrI) involves lifetime movement and balance concerns whose pathophysiological origins are unclear. We tested whether balance symptoms in mild GrI might involve anomalies in vestibular velocity storage (VVS), a brainstem/cerebellar circuit that amplifies gain and prolongs the persistence of weak vestibular signals from small/slow head movements. A Provisional Gravitational Insecurity Index (PGrI) was developed, evaluated for psychometrics/demographics, and used to identify otherwise healthy adults with life-long balance challenges as well as sex, age, and ethnicity-matched comparison adults without such challenges. Balance confidence, sensory hypersensitivities, spatial orientation, anxiety, and hearing loss were self-reported. Standing balance under visual/proprioceptive restrictions and perrotary vestibulo-ocular nystagmus were evaluated. The PGrI showed approximated test-retest reliability and convergent and discriminant validity. When only vestibular input was available, mild GrI participants on a tilting platform used effortful hip strategies for balance significantly more than did comparison participants. Rotation testing revealed that mild GrI participants had significantly less low frequency gain and shortened VVS persistence. Combined, these two parameters correlated significantly with PGrI. The PGrI also correlated with problematic spatial orientation, but surprisingly, not to anxiety. Balance/movement issues in GrI are likely due to VVS deficiencies. Additional mechanisms may account for other GrI symptoms. Better understanding of GrI’s pathophysiological basis will be useful in informing the larger health-provider community about this condition.

A New Vestibular Stimulation Mode for Motion Sickness With Emphatic Analysis of Pica

Motion sickness (MS) was frequently introduced for rodents in research work through passive motion that disturbed vestibular signals in the presence of visual and aleatory, proprioceptive inputs. Inducement of MS in this way causes conflicting signals that activate intermixed neural circuits representing multimodal stimulation. From reductionism, a lab setup to elicit rat MS via vestibular stimulation was configured in the present study for MS study in connection with dissection of the central vestibular component causally underlying MS. The individual animal was blinded to light with a custom-made restrainer, and positioned at an inclination of 30° for otolith organs to receive unusual actions by gravitoinertial vector. Following a 2-h double-axis (earth–vertical) rotation involving angular acceleration/deceleration, a suit of behaviors characterizing the MS was observed to be significantly changed including pica (eating non-nutritive substance like kaolin), conditioned taste avoidance and locomotion (p < 0.05). Notably, for the statistical hypothesis testing, the utility of net increased amount of kaolin consumption as independent variables in data processing was expounded. In addition, Fos-immunostained neurons in vestibular nucleus complex were significantly increased in number, suggesting the rotation-induced MS was closely related to the vestibular activation. In conclusion, our work indicated that the present setup could effectively elicit the MS by disturbing vestibular signals in rat in the context of well-controlled proprioceptive inputs and lack of visual afference.

Multi-Dimensional and Objective Assessment of Motion Sickness Susceptibility Based on Machine Learning

Background

As human transportation, recreation, and production methods change, the impact of motion sickness (MS) on humans is becoming more prominent. The susceptibility of people to MS can be accurately assessed, which will allow ordinary people to choose comfortable transportation and entertainment and prevent people susceptible to MS from entering provocative environments. This is valuable for maintaining public health and the safety of tasks.

Objective

To develop an objective multi-dimensional MS susceptibility assessment model based on physiological indicators that objectively reflect the severity of MS and provide a reference for improving the existing MS susceptibility assessment methods.

Methods

MS was induced in 51 participants using the Coriolis acceleration stimulation. Some portable equipment were used to digitize the typical clinical manifestations of MS and explore the correlations between them and Graybiel's diagnostic criteria. Based on significant objective parameters and selected machine learning (ML) algorithms, several MS susceptibility assessment models were developed, and their performances were compared.

Results

Gastric electrical activity, facial skin color, skin temperature, and nystagmus are related to the severity of MS. Among the ML assessment models based on these variables, the support vector machine classifier had the best performance with an accuracy of 88.24%, sensitivity of 91.43%, and specificity of 81.25%.

Conclusion

The severity of symptoms and signs of MS can be objectively quantified using some indicators. Multi-dimensional and objective assessment models for MS susceptibility based on ML can be successfully established.

The Role of Different Afferent Systems in the Modulation of the Otolith-Ocular Reflex After Long-Term Space Flights

Background

The vestibular (otolith) function is highly suppressed during space flight (SF) and the study of these changes is very important for the safety of the space crew during SF missions. The vestibular function (particularly, otolith-ocular reflex–OOcR) in clinical and space medicine is studied using different methodologies. However, different methods and methodologies can influence the outcome results.

Objective

The current study addresses the question of whether the OOcR results obtained by different methods are different, and what the role is of the different afferent systems in the modulation of the OOcR.

Methods

A total of 25 Russian cosmonauts voluntarily took part in our study. They are crewmembers of long duration space missions on the International Space Station (ISS). Cosmonauts were examined in pre- and post-flight “Sensory Adaptation” and “Gaze Spin” experiments, twice before (preflight) and three times after SF (post-flight). We used two different video oculography (VOG) systems for the recording of the OOcR obtained in each experiment.

Results

Comparison of the two VOG systems didn’t result into significant and systematic differences in the OOcR measurements. Analysis of the static torsion otolith–ocular reflex (OOR), static torsion otolith–cervical–ocular reflex (OCOR) and static torsion otolith–ocular reflex during eccentric centrifugation (OOREC) shows that the OOREC results in a lower OOcR response compared to the OOR and OCOR (before flight and late post-flight). However, all OOcRs were significantly decreased in all cosmonauts early post-flight.

Conclusion

Analysis of the results of ocular counter rolling (OCR) obtained by different methods (OOR, OCOR, and OOREC) showed that different afferent systems (tactile-proprioception, neck-cervical, visual and vestibular afferent input) have an impact on the OOcR.

Vestibular-autonomic interactions: beyond orthostatic dizziness

PURPOSE OF REVIEW

This review aims to summarize the current literature describing vestibular-autonomic interactions and to describe their putative role in various disorders' clinical presentations, including orthostatic dizziness and motion sensitivity.

RECENT FINDINGS

The vestibular-autonomic reflexes have long been described as they relate to cardiovascular and respiratory function. Although orthostatic dizziness may be in part related to impaired vestibulo-sympathetic reflex (orthostatic hypotension), there are various conditions that may present similarly. A recent clinical classification aims to improve identification of individuals with hemodynamic orthostatic dizziness so that appropriate recommendations and management can be efficiently addressed. Researchers continue to improve understanding of the underlying vestibular-autonomic reflexes with recent studies noting the insular cortex as a cortical site for vestibular sensation and autonomic integration and modulation. Work has further expanded our understanding of the clinical presentation of abnormal vestibular-autonomic interactions that may occur in various conditions, such as aging, peripheral vestibular hypofunction, traumatic brain injury, and motion sensitivity.

SUMMARY

The vestibular-autonomic reflexes affect various sympathetic and parasympathetic functions. Understanding these relationships will provide improved identification of underlying etiology and drive improved patient management.

The behavior of the optokinetic system

Optokinetic responses in several species are compared, describing differences in afoveate and foveate animals, and the effects of visual testing conditions, including directions of stimulus motion. Smooth pursuit contributes to responses to full-field visual motion in foveate species; in the latter, measurement of optokinetic after-nystagmus in darkness allows investigation of the optokinetic system. The concept of optokinetic-vestibular symbiosis and velocity storage are discussed, pertinent electrophysiological studies (such as vestibular nucleus neurons that respond to both optokinetic and vestibular stimuli) are reviewed and a model is developed. The different purposes and properties of optokinetic responses (to maintain clear vision during self-rotation) and smooth pursuit (to visually track a moving target) are clarified.

The Predictive Role of ADRA2A rs1800544 and HTR3B rs3758987 Polymorphisms in Motion Sickness Susceptibility

Motion sickness is a common central nervous system response, the primary sign of which is vomiting. Its susceptibility varies between individuals. To find predictive factors, we investigated the association of ADRA2A rs1800544 and HTR3B rs3758987 with motion sickness susceptibility and examined their mRNA changes during actual voyages. A total of 315 healthy college students were enrolled for SNP genotyping by the PCR-RFLP method. Blood samples were collected from another 42 subjects during two separate voyages to detect their mRNA expression changes at three time points. The frequency of the rs1800544 GG genotype in the susceptibility group was significantly higher (52.26%), and allele G increased the risk of motion sickness (OR = 1.585, 95% CI = 1.136-2.208). In the logistic regression model, the rs3758987 CC+TC genotype and rs1800544 GG genotype increased the risk of motion sickness-induced vomiting (OR = 2.105, 95% CI = 1.112-3.984; OR = 1.992, 95% CI = 1.114-3.571). The ADRA2A mRNA baseline was lower in the GG carriers and the HTR3B mRNA baseline was lower in the TC/CC carriers before sailing, then increased significantly within 24 h and then decreased after a long-term voyage. People carrying the rs1800544 GG genotype seem more susceptible to motion sickness. In combination with the incidence of vomiting during the actual-voyage experiments, our results indicate the involvement of rs1800544 and rs3758987 in motion sickness-induced vomiting.

Anxiety and Motion Sickness Susceptibility May Influence the Ability to Update Orientation in the Horizontal Plane of Healthy Subjects

Few studies have evaluated the influence of idiosyncrasies that may influence the judgment of space-time orientation after passive motion. We designed a study to assess the influence of anxiety/depression (which may distort time perception), motion sickness susceptibility (which has been related to vestibular function, disorientation, and to the velocity storage mechanism), and personal habits on the ability to update orientation, after passive rotations in the horizontal plane. Eighty-one healthy adults (22–64 years old) accepted to participate. After they completed an in-house general health/habits questionnaire, the short Motion Sickness Susceptibility Questionnaire, the Hospital Anxiety and Depression Scale (HADS), the Pittsburgh Sleep Quality Index, and the short International Physical Activity Questionnaire, they were exposed to 10 manually driven whole-body rotations (45°, 90°, or 135°), in a square room, with distinctive features on the walls, while seated in the normal upright position, unrestrained, with noise-attenuating headphones and blindfolded. After each rotation, they were asked to report which wall or corner they were facing. To calculate the error of estimation of orientation, the perceived rotation was subtracted from the actual rotation. Multivariate analysis showed that the estimation error of the first rotation was strongly related to the results of the orientation test. The magnitude and the frequency of estimation errors of orientation were independently related to HADS anxiety sub-score and to adult motion sickness susceptibility, with no influence of age, but a contribution from the interaction of the use of spectacles, the quality of sleep and sex. The results suggest that idiosyncrasies may contribute to the space-time estimation of passive self-motion, with influence from emotional traits, adult motion sickness susceptibility, experience, and possibly sleep quality.

Vestibular Illusions and Alterations in Aerospace Environment

As the aerospace industry has grown rapidly over the years, aviators and astronauts have been exposed to some abnormal physiological changes arising from the dynamics of the aerospace environment. The vestibular system, encoding linear and angular movements of the head, is one of the main affected systems in which those abnormal changes can occur during flight. Despite the intricate and solid organization, vestibular units are such delicate structures that they can easily be deceived by aerial dynamics and gravity changes. Therefore, it is of vital importance for the continuity of flight safety to be aware of the detrimental alterations and impairments regarding the vestibular system and its reflex pathways. The aim of this paper was to present a review about how a healthy vestibular system is negatively affected within the aerospace environment and how some vestibular disorders become exaggerated or impaired during aviation and space activities.

Mechanisms of Nausea and Vomiting: Current Knowledge and Recent Advances in Intracellular Emetic Signaling Systems

Nausea and vomiting are common gastrointestinal complaints that can be triggered by diverse emetic stimuli through central and/or peripheral nervous systems. Both nausea and vomiting are considered as defense mechanisms when threatening toxins/drugs/bacteria/viruses/fungi enter the body either via the enteral (e.g., the gastrointestinal tract) or parenteral routes, including the blood, skin, and respiratory systems. While vomiting is the act of forceful removal of gastrointestinal contents, nausea is believed to be a subjective sensation that is more difficult to study in nonhuman species. In this review, the authors discuss the anatomical structures, neurotransmitters/mediators, and corresponding receptors, as well as intracellular emetic signaling pathways involved in the processes of nausea and vomiting in diverse animal models as well as humans. While blockade of emetic receptors in the prevention of vomiting is fairly well understood, the potential of new classes of antiemetics altering postreceptor signal transduction mechanisms is currently evolving, which is also reviewed. Finally, future directions within the field will be discussed in terms of important questions that remain to be resolved and advances in technology that may help provide potential answers.

The Importance of Being in Touch

This paper describes a series of studies resulting from the finding that when free floating in weightless conditions with eyes closed, all sense of one's spatial orientation with respect to the aircraft can be lost. But, a touch of the hand to the enclosure restores the sense of spatial anchoring within the environment. This observation led to the exploration of how light touch of the hand can stabilize postural control on Earth even in individuals lacking vestibular function, and can override the effect of otherwise destabilizing tonic vibration reflexes in leg muscles. Such haptic stabilization appears to represent a long loop cortical reflex with contact cues at the hand phase leading EMG activity in leg muscles, which change the center of pressure at the feet to counteract body sway. Experiments on dynamic control of balance in a device programmed to exhibit inverted pendulum behavior about different axes and planes of rotation revealed that the direction of gravity not the direction of balance influences the perceived upright. Active control does not improve the accuracy of indicating the upright vs. passive exposure. In the absence of position dependent gravity shear forces on the otolith organs and body surface, drifting and loss of control soon result and subjects are unaware of their ongoing spatial position. There is a failure of dynamic path integration of the semicircular canal signals, such as occurs in weightless conditions.

Toward Predicting Motion Sickness Using Virtual Reality and a Moving Platform Assessing Brain, Muscles, and Heart Signals

Motion sickness (MS) and postural control (PC) conditions are common complaints among those who passively travel. Many theories explaining a probable cause for MS have been proposed but the most prominent is the sensory conflict theory, stating that a mismatch between vestibular and visual signals causes MS. Few measurements have been made to understand and quantify the interplay between muscle activation, brain activity, and heart behavior during this condition. We introduce here a novel multimetric system called BioVRSea based on virtual reality (VR), a mechanical platform and several biomedical sensors to study the physiology associated with MS and seasickness. This study reports the results from 28 individuals: the subjects stand on the platform wearing VR goggles, a 64-channel EEG dry-electrode cap, two EMG sensors on the gastrocnemius muscles, and a sensor on the chest that captures the heart rate (HR). The virtual environment shows a boat surrounded by waves whose frequency and amplitude are synchronized with the platform movement. Three measurement protocols are performed by each subject, after each of which they answer the Motion Sickness Susceptibility Questionnaire. Nineteen parameters are extracted from the biomedical sensors (5 from EEG, 12 from EMG and, 2 from HR) and 13 from the questionnaire. Eight binary indexes are computed to quantify the symptoms combining all of them in the Motion Sickness Index (I _MS ). These parameters create the MS database composed of 83 measurements. All indexes undergo univariate statistical analysis, with EMG parameters being most significant, in contrast to EEG parameters. Machine learning (ML) gives good results in the classification of the binary indexes, finding random forest to be the best algorithm (accuracy of 74.7 for I _MS ). The feature importance analysis showed that muscle parameters are the most relevant, and for EEG analysis, beta wave results were the most important. The present work serves as the first step in identifying the key physiological factors that differentiate those who suffer from MS from those who do not using the novel BioVRSea system. Coupled with ML, BioVRSea is of value in the evaluation of PC disruptions, which are among the most disturbing and costly health conditions affecting humans.

The Scientific Contributions of Bernard Cohen (1929-2019)

Throughout Bernard Cohen's active career at Mount Sinai that lasted over a half century, he was involved in research on vestibular control of the oculomotor, body postural, and autonomic systems in animals and humans, contributing to our understanding of such maladies as motion sickness, mal de débarquement syndrome, and orthostatic syncope. This review is an attempt to trace and connect Cohen's varied research interests and his approaches to them. His influence was vast. His scientific contributions will continue to drive research directions for many years to come.

Evaluation of the vestibular system with video head impulse test in pregnant women with hyperemesis gravidarum

AIM

We aimed to evaluate the semicircular canal functions of the vestibular system in pregnant women with hyperemesis gravidarum.

METHODS

This is a prospective case-control study. Among pregnant women in their first trimester (<14. gestational weeks) who presented to our outpatient clinic, 36 patients diagnosed with hyperemesis gravidarum defined as persistent nausea and vomiting requiring intravenous hydration or loss of at least 5% of prepregnancy weight and 34 healthy pregnant without nausea and vomiting were included. Otorhinolaryngologic examination and video head impulse test (vHIT) was performed to all patients. Vestibular-ocular reflex (VOR) gain and gain asymmetry were assessed between groups.

RESULTS

The VOR gains in each semicircular canal did not differ between hyperemesis and control groups. Using a VOR gain cut-off value of 0.8, the groups were compared in terms of the frequency of low values. In the hyperemesis group, abnormally low gain values of left anterior canal were more frequently observed than in the control group (32 [88.9%], 22 [64.7%], respectively, P = 0.01). In left anterior-right posterior (LARP) plane VOR gain asymmetry was higher in hyperemesis group (13.5 [1.0-71.0], 6.0 [0.0-35.0], P = 0.001). No significant gain asymmetry was detected between the groups in the other planes.

CONCLUSION

Semicircular canal functions were not abnormal globally in women with hyperemesis gravidarum. However, higher LARP plane asymmetry and low LA gain in women with hyperemesis suggests need for further research to clarify functional role of vestibular system on hyperemesis gravidarum.

Challenges to the central nervous system during human spaceflight missions to Mars

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.

Velocity storage: its multiple roles

Our research described in this article was motivated by the puzzling finding of the Skylab M131 experiments: head movements made while rotating that are nauseogenic and disorienting on Earth are innocuous in a weightless, 0-g environment. We describe a series of parabolic flight experiments that directly addressed this puzzle and discovered the gravity-dependent responses to semicircular canal stimulation, consistent with the principles of velocity storage. We describe a line of research that started in a different direction, investigating dynamic balancing, but ended up pointing to the gravity dependence of angular velocity-to-position integration of semicircular canal signals. Together, these lines of research and the theoretical framework of velocity storage provide an answer to at least part of the M131 puzzle. We also describe recently discovered neural circuits by which active, dynamic vestibular, multisensory, and motor signals are interpreted as either appropriate for action and orientation or as conflicts evoking motion sickness and disorientation.

Motion sickness: an overview

Background

Motion sickness is a common phenomenon that affects almost everybody at some point in their lifetime. Clinicians should be familiar with the proper management of this condition.

Objective

To provide an update on the current understanding of the pathophysiology and management of motion sickness.

Methods

A PubMed search was performed with Clinical Queries using the key term ‘motion sickness.’ The search strategy included meta-analyses, randomized controlled trials, clinical trials, observational studies, and reviews. The search was restricted to English literature. The information retrieved from the earlier search was used in the compilation of the present article.

Results

Motion sickness is typically triggered by low-frequency vertical, lateral, angular, rotary motion, or virtual stimulator motion, to which an individual has not adapted. Sine qua non for developing motion sickness is when the brain receives conflicting information from different sensors about real body movements or virtual environment. The principal sensors are the eyes, the vestibular apparatus, and proprioceptive receptors. The conflicting information is judged in relation to a pattern of expected associations formed under normal or experienced conditions stored in the brain. Motion sickness typically presents with malaise, anorexia, nausea, yawning, sighing, increased salivation, burping, headache, blurred vision, non-vertiginous dizziness, drowsiness, spatial disorientation, difficulty concentrating, and sometimes vomiting. Simple behavioral and environmental modifications can be effective in the prevention of motion sickness. Medications that are effective in the prophylaxis and/or treatment of motion sickness include anticholinergics, antihistamines, and sympathomimetics.

Conclusion

In most cases, motion sickness can be prevented by behavioral and environmental modifications (avoidance, habituation, and minimization of motion stimuli). Pharmacotherapy should be considered in the prevention and/or treatment of more severe motion sickness and for patients who do not respond to conservative measures. Medications are most effective when combined with behavioral and environmental modifications. Drugs that are effective in the prophylaxis and/or treatment of motion sickness include anticholinergic agents and antihistamines.