Do the organs of the labyrinth differentially influence the sympathetic and parasympathetic systems?

Vestibular CCK signaling drives motion sickness-like behavior in mice

Travel can induce motion sickness (MS) in susceptible individuals. MS is an evolutionary conserved mechanism caused by mismatches between motion-related sensory information and past visual and motion memory, triggering a malaise accompanied by hypolocomotion, hypothermia, hypophagia, and nausea. Vestibular nuclei (VN) are critical for the processing of movement input from the inner ear. Motion-induced activation of VN neurons recapitulates MS-related signs. However, the genetic identity of VN neurons mediating MS-related autonomic and aversive responses remains unknown. Here, we identify a central role of cholecystokinin (CCK)-expressing VN neurons in motion-induced malaise. Moreover, we show that CCK VN inputs onto the parabrachial nucleus activate Calca-expressing neurons and are sufficient to establish avoidance to novel food, which is prevented by CCK-A receptor antagonism. These observations provide greater insight into the neurobiological regulation of MS by identifying the neural substrates of MS and providing potential targets for treatment.

Effect of Visually Induced Motion Sickness from Head-Mounted Display on Cardiac Activity

Head-mounted display (HMD) virtual reality devices can facilitate positive experiences such as co-presence and deep immersion; however, motion sickness (MS) due to these experiences hinders the development of the VR industry. This paper proposes a method for assessing MS caused by watching VR content on an HMD using cardiac features. Twenty-eight undergraduate volunteers participated in the experiment by watching VR content on a 2D screen and HMD for 12 min each, and their electrocardiogram signals were measured. Cardiac features were statistically analyzed using analysis of covariance (ANCOVA). The proposed model for classifying MS was implemented in various classifiers using significant cardiac features. The results of ANCOVA reveal a significant difference between 2D and VR viewing conditions, and the correlation coefficients between the subjective ratings and cardiac features have significant results in the range of -0.377 to -0.711 (for SDNN, pNN50, and ln HF) and 0.653 to 0.677 (for ln VLF and ln VLF/ln HF ratio). Among the MS classification models, the linear support vector machine achieves the highest average accuracy of 91.1% (10-fold cross validation) and has a significant permutation test outcome. The proposed method can contribute to quantifying MS and establishing viewer-friendly VR by determining its qualities.

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.

Effect of economically friendly acustimulation approach against cybersickness in video-watching tasks using consumer virtual reality devices

BACKGROUND

Consumer virtual reality (VR) devices are becoming more prevalent in the market, but cybersickness induced by VR devices limits their potential application and promotion. Acustimulation has been found effective in reducing cybersickness symptoms. However, in previous forms, the more effective way of acustimulation is either intrusive or electrical which is hard to be applied to daily VR use.

PURPOSE

In this study, we aimed to find a both simple and more effective acustimulation approach, acupressure plus acupaste (AcP+) to reducing the adverse effects caused by cybersickness from VR applications.

METHOD

In this study, we set three conditions: acupressure plus acupaste (AcP+) (main condition of interest), acupressure with fake acupaste (AcP), and a no acustimulation condition (NoAcP). In AcP and AcP + conditions, we applied acupressure or acupressure with true acupaste on P6 point before conducting video-watching tasks using VR headsets, while in NoAcP condition, participants received no special treatment before video-watching tasks. We used questionnaires to measure symptoms of cybersickness and compared the results between these 3 conditions, especially between acupressure plus acupaste (AcP+) and acupressure (AcP) to examine the effect of AcP+, and compared AcP and AcP+ with NoAcP to confirm the effect of acustimulation.

RESULT

Participants reported significant fewer symptoms of cybersickness nausea feelings in both acustimulation methods, compared with NoAcP; and AcP+ was more effective than AcP against cybersickness on visual oculomotor aspect, and facilitated cybersickness recovery.

IMPLICATION

It would be promising to develop acupressure equipment and apply stimulation before VR application to reduce cybersickness.

Vestibular loss as a contributor to Alzheimer's disease

Alzheimer's disease is a complex disorder whose etiology is still controversial. It is proposed that vestibular loss may contribute to the onset of Alzheimer's disease, which initially involves degeneration of cholinergic systems in the posterior parietal-temporal, medial-temporal, and posterior-cingulate regions. A major projection to this system emanates from the semicircular canals of the vestibular labyrinth, with vestibular damage leading to severe degeneration of the medial-temporal region. The vestibular loss hypothesis is further supported by the vestibular symptoms found in Alzheimer's patients as well as in various diseases that are major risk factors for Alzheimer's disease.

Vestibular Stimulation for ADHD: randomized controlled trial of Comprehensive Motion Apparatus

OBJECTIVE

This research evaluates effects of vestibular stimulation by Comprehensive Motion Apparatus (CMA) in ADHD.

METHOD

Children ages 6 to 12 (48 boys, 5 girls) with ADHD were randomized to thrice-weekly 30-min treatments for 12 weeks with CMA, stimulating otoliths and semicircular canals, or a single-blind control of equal duration and intensity, each treatment followed by a 20-min typing tutorial.

RESULTS

In intent-to-treat analysis (n = 50), primary outcome improved significantly in both groups (p = .0001, d = 1.09 to 1.30), but treatment difference not significant (p = .7). Control children regressed by follow-up (difference p = .034, d = 0.65), but overall difference was not significant (p = .13, d = .47). No measure showed significant treatment differences at treatment end, but one did at follow-up. Children with IQ-achievement discrepancy > or = 1 SD showed significantly more CMA advantage on three measures.

CONCLUSION

This study illustrates the importance of a credible control condition of equal duration and intensity in trials of novel treatments. CMA treatment cannot be recommended for combined-type ADHD without learning disorder.

Effect of dimenhydrinate on autonomic activity in humans

The purpose of this study was to examine the effect of dimenhydrinate on resting muscle sympathetic nerve activity (MSNA), the vestibulosympathetic reflex, and the baroreflexes. Sixteen subjects participated in two double-blinded studies that measured mean arterial pressure (MAP), heart rate (HR), and MSNA responses before and after oral administration of dimenhydrinate (100 mg) or a placebo. In study one, 3 min of head-down rotation (HDR) was performed to engage the otolith organs. Dimenhydrinate (n = 10) did not alter resting MSNA, MAP, or HR. HDR increased MSNA before (Delta5 +/- 1 bursts/min; P < 0.01) and after (Delta4 +/- 1 bursts/min; P < 0.01) drug administration, but these responses were not different from the placebo (n = 6). In study two, 4 min of lower body negative pressure (LBNP) at -30 mmHg was performed. During the third min of LBNP, HDR was performed. MSNA increased during the first 2 min of LBNP before (Delta13 +/- 2 bursts/min; P < 0.01) and after (Delta14 +/- 2 bursts/min; P < 0.01) dimenhydrinate. HDR combined with LBNP increased MSNA further during the third min of LBNP (Delta18 +/- 2 bursts/min before and Delta17 +/- 2 bursts/min after dimenhydrinate; P < 0.01). These responses were not significantly different from the placebo. In contrast, HR responses to LBNP during the dimenhydrinate trial were increased when compared to all other trials (Delta5 +/- 1 beats/min; P < 0.01). These results indicate that dimenhydrinate augments heart rate responses to baroreceptor unloading, but does not alter resting MSNA, the sympathetic baroreflexes, or the vestibulosympathetic reflex.

Autonomic responses during motion sickness induced by virtual reality

OBJECTIVE

To examine the development of subjective symptoms and heart rate variability (HRV) during motion sickness induced by virtual reality (VR).

METHODS

Subjects were 10 healthy young volunteers. During VR immersion, subjects were immersed in a visual-vestibular conflict produced by VR. The levels of the subjective symptoms were assessed by Graybiel's and Hamilton's criteria. HRV was determined by measuring microvascular blood flow or electrocardiogram.

RESULTS

Subjective symptoms evaluated by Graybiel's and Hamilton's criteria were gradually worsened during VR. Power spectrum analysis of HRV demonstrated a gradual increase in the low frequency but no change in the high frequency during VR. In this study, individual subjective symptoms were not correlated with the individual result of power spectrum analysis.

CONCLUSION

These findings indicate that there was an increase in sympathetic nervous activity, but no change in parasympathetic nervous activity during motion sickness induced by VR. Given the large inter-individual variability and the reliability of subjective measures, it is not surprising that there is scarcely a relation between the subjective symptoms and the results of power spectrum analysis.

Alternative treatments for adults with attention-deficit hyperactivity disorder (ADHD)

A previous review of alternative treatments (Tx) of ADHD--those other than psychoactive medication and behavioral/psychosocial Tx--was supplemented with an additional literature search focused on adults with ADHD. Twenty-four alternative Tx were identified, ranging in scientific documentation from discrediting controlled studies through mere hypotheses to positive controlled double-blind clinical trials. Many of them are applicable only to a specific subgroup. Although oligoantigenic (few-foods) diets have convincing double-blind evidence of efficacy for a properly selected subgroup of children, they do not appear promising for adults. Enzyme-potentiated desensitization, relaxation/EMG biofeedback, and deleading also have controlled evidence of efficacy. Iron supplementation, magnesium supplementation, Chinese herbals, EEG biofeedback, massage, meditation, mirror feedback, channel-specific perceptual training, and vestibular stimulation all have promising prospective pilot data, many of these tests reasonably controlled. Single-vitamin megadosage has some intriguing pilot trial data. Zinc supplementation is hypothetically supported by systematic case-control data, but no systematic clinical trial. Laser acupuncture has promising unpublished pilot data and may be more applicable to adults than children. Essential fatty acid supplementation has promising systematic case-control data, but clinical trials are equivocal. RDA vitamin supplementation, non-Chinese herbals, homeopathic remedies, and antifungal therapy have no systematic data in ADHD. Megadose multivitamin combinations are probably ineffective for most patients and are possibly dangerous. Simple sugar restriction seems ineffective. Amino acid supplementation is mildly effective in the short term, but not beyond 2-3 months. Thyroid treatment is effective in the presence of documented thyroid abnormality. Some alternative Tx of ADHD are effective or probably effective, but mainly for certain patients. In some cases, they are the Tx of choice, and initial evaluation should consider the relevant etiologies. A few have failed to prove effective in controlled trials. Most need research to determine whether they are effective and/or to define the applicable subgroup. Some of them, although not safer than standard Tx, may be preferable for an etiologic subgroup.

Cardiovascular and Valsalva responses during parabolic flight

We investigated the integrated cardiovascular responses of 15 human subjects to the acute gravitational changes (micro- and hypergravity portions) of parabolic flight. Measurements were made with subjects quietly seated and while subjects performed controlled Valsalva maneuvers. During quiet, seated, parabolic flight, mean arterial pressure increased during the transition into microgravity but decreased as microgravity was sustained. The decrease in mean arterial pressure was accompanied by immediate reflexive increases in heart rate but by absent (or later-than-expected) reflexive increases in total vascular resistance. Mean arterial pressure responses in Valsalva phases IIl, III, and IV were accentuated in hypergravity relative to microgravity (P < 0.01, P < 0.01, and P < 0. 05, respectively), but accentuations differed qualitatively and quantitatively from those induced by a supine-to-seated postural change in 1 G. This study is the first systematic evaluation of temporal and Valsalva-related changes in cardiovascular parameters during parabolic flight. Results suggest that arterial baroreflex control of vascular resistance may be modified by alterations of cardiopulmonary, vestibular, and/or other receptor activity.

Effect of gravity on vestibular neural development

The timing, molecular basis, and morphophysiological and behavioral consequences of the interaction between external environment and the internal genetic pool that shapes the nervous system over a lifetime remain important questions in basic neuroscientific research. Space station offers the opportunity to study this interaction over several life cycles in a variety of organisms. This short review considers past work in altered gravity, particularly on the vestibular system, as the basis for proposing future research on space station, and discusses the equipment necessary to achieve goals. It is stressed that, in keeping with the international investment being made in this research endeavor, both the questions asked and the technologies to be developed should be bold. Advantage must be taken of this unique research environment to expand the frontiers of neuroscience.

Alterations in R-R variability associated with experimental motion sickness

Motion sickness is a complex integration of responses from multiple physiological systems. Whether the changes that occur during the time course of motion sickness are mediated by the sympathetic or parasympathetic systems is still controversial. The present study evaluates alterations in R-R variability during experimental motion sickness in motion sick and non-motion sick subjects. Ten motion sick subjects and 7 non-motion sick subjects participated in the study. Power spectrum analysis of R-R variation was conducted for all subjects 10 min before a brief vestibular disorientation test (BVDT), for 5-10 min of the test, and 10 min after the test. Subjects were also asked to report their symptoms during the test. The motion sick group showed a significant reduction in the power spectrum density of the R-R interval at the mid and high frequencies during the BVDT test period (BVDT), in comparison with the rest period (Rest). These changes probably indicate a decrease in parasympathetic activity during the time course of motion sickness. The non-motion sick group did not show significant differences at any of the frequencies during BVDT. Power spectrum analysis of the R-R interval provides an objective measure of the autonomic response to experimental motion sickness.

Response to vestibular stimulation of sympathetic outflow to muscle in humans

The objective of the present study was to determine the effect of vestibular stimulation on the sympathetic outflow to muscle in humans. Fourteen healthy volunteers were studied while in the supine position with electrocardiography, blood pressure monitoring and electro-oculography. The muscle sympathetic nerve activity (MSNA) was recorded directly from the bilateral tibial nerves by using microneurographic double recording technique. Caloric vestibular stimulation was loaded by alternate irrigation with 50 ml of cold (10 degrees C) water and 50 ml of hot (44 degrees C) water into the left and right external meatus. After cold water irrigation, two MSNA response peaks were elicited, respectively, before and after the maximum slow phase velocity (SPV) of nystagmus. The first peak of the MSNA enhancement was caused by non-specific factors because its time course coincided with that in cold pressor test with immersion of the subject's hand in ice/water (4 degrees C). Transient suppression of MSNA after cold water irrigation in the period of maximum SPV of nystagmus was observed by cross correlogram analysis between the SPV of the nystagmus and MSNA. After hot water irrigation, only one MSNA response peak was elicited after the period of strong nystagmus. The second peak of MSNA enhancement evoked by cold irrigation (379.4 +/- 221.8%, with the control value set as 100%, mean +/- SE) was significantly higher than that evoked by hot irrigation (243.0 +/- 14.5%). The degree of MSNA enhancement by either cold (the second peak) or hot stimulation was proportional to the maximum SPV of the nystagmus. There was no significant difference between the MSNA responses ipsilateral to and contralateral to the irrigated side. In conclusion, the caloric vestibular stimulation can influence the bilateral sympathetic outflow to muscle in humans. The degree of MSNA enhancement is proportional to the magnitude of vestibular excitement indicated by maximum slow phase velocity of the nystagmus.

GABAergic inhibitory response of locus coeruleus neurons to caloric vestibular stimulation in rats

We examined the effects of caloric vestibular stimulation on the neuronal activity of the locus coeruleus (LC) in urethane-anesthetized rats. The middle ear cavity was irrigated with hot (44 degrees C) or cold (30 degrees C) water through a polyethylene tube. Most neurons (hot water: 76%, 55/72; cold water: 90%, 19/21) exhibited suppression of neuronal discharge in response to caloric stimulation. The suppression of LC neuronal discharge following caloric stimulation occurred with a long latency (approximately 80 s), and lasted a long period of time (approximately 3 min). Neither caloric stimulation of the auricle, nor irrigation of the middle ear with water at 37 degrees C, nor caloric stimulation of the middle ear after labyrinthectomy inhibited LC neuronal discharge. The caloric stimulation-induced LC neuronal inhibition was significantly attenuated by the intravenous injection of picrotoxin and by the iontophoretic application of bicuculline methiodide. These findings indicate that the predominant effect of caloric vestibular stimulation on LC neuronal discharge is inhibitory, and that the caloric stimulation-induced LC neuronal inhibition is mediated by GABAA receptors located on the membrane of LC neurons. It is suggested that the suppressed activity of noradrenergic LC neurons is involved in the vestibulo-autonomic reflex.