Vestibular Information Research Articles

Body ownership shapes self-orientation perception

Self-orientation perception is a necessary ability for everyday life that heavily depends on visual and vestibular information. To perceive the orientation of oneself with respect to the external environment would seem to first require that one has a clear sense of one’s own body (‘sense of body ownership’). However, the experimental evidence for this is sparse. Therefore, the aim of the present study was to investigate how the sense of body ownership affects perceived self-orientation. We combined a self-orientation illusion – where the visual scene, i.e., a fully furnished room, was rotated slowly around the roll axis – with a full-body ownership illusion paradigm – where the ownership of a stranger’s body seen from the first-person perspective in the center of the scene was manipulated by synchronous (illusion) or asynchronous (control) visual-tactile stimulation. Participants were asked to judge the appearance of shaded disk stimuli (a shape-from-shading test), which are perceived as three-dimensional (3D) spheres; this perception depends on perceived self-orientation. Illusory body ownership influenced self-orientation as reported subjectively in questionnaires and as evident from the objective shape-from-shading test data. Thus, body ownership determines self-orientation perception, presumably by boosting the weighting of visual cues over the gravitational forces detected by the vestibular system.

Putting proprioception for balance to the test: Contrasting and combining sway referencing and tendon vibration

BackgroundPostural control relies on sensory information from visual, vestibular and proprioceptive channels, with proprioception being the key sensory modality in this task. Two well-established ways of manipulating proprioceptive information in postural control are tendon vibration and sway referencing. The aim of the present study was to assess postural adaptation when inaccurate proprioceptive information is introduced using tendon vibration and sway referencing in isolation and combination. MethodsSeventeen young adults were asked to stand, without vision, for 2 min on a fixed surface (baseline) immediately followed by 3 min of bilateral Achilles tendon vibration, sway reference, or combined presentation of the two manipulations (adaptation) and finally 3 min of standing on a fixed surface (aftereffect). ResultsDuring adaptation, vibration showed the lowest sway variability, followed by sway reference and the combined condition. Spectral analyses focusing on the dominant frequencies in this task (0–0.4 Hz) showed that in the first half of adaptation sway amplitude was greater when the two manipulations were combined compared with each manipulation alone. However, in the second half differences between sway reference and the combined condition disappeared but differences between vibration and the other two conditions increased. ConclusionWe interpret these findings primarily as due to a prolonged attenuation in effects of vibration over the course of the adaptation phase and we offer two explanations for this phenomenon. One is a decline in neurotransmitter release from the group Ia terminals and the other is sensory reweighting which down-weights proprioception and up-weights the accurate, vestibular information.

Stimulation or lesion of the medial vestibular nucleus increases the number of choline acetyltransferase-positive efferent vestibular neurons in the brainstem.

The vestibular center of the brainstem contains afferent and efferent vestibular neurons, which play an important role in information perception, processing, and sensory integration. Vestibular efferent neurons (VENs) can receive changes in vestibular afferent information and regulate peripheral vestibular function; however, it remains unclear how VENs change after vestibular afferent information increases or weakens. In this study, we used animal models with altered vestibular afferent information by electrically stimulating or destroying the vestibular medial nucleus (MVe). We confirmed the location of VENs in the brainstem by injecting five adult male Wistar rats in the vestibular region with a retrograde tracer. Following this, the MVe was stimulated electrically for 30 min in 20 naive rats. Rats were anesthetized and euthanized 1, 3, 6, and 12 h after stimulation. The MVe was electrolytically lesioned in another group (n=20); then, the rats were anesthetized and euthanized 1, 3, 5, and 7 days after lesioning. VENs were clearly identified dorsolateral to the genu of the facial nerve (g7) in coronal brainstem sections using choline acetyltransferase (ChAT) staining. The number of ChAT-positive VENs dorsolateral to g7 increased significantly on both sides compared with the control group 3 and 6 h after electrical stimulation. The number of ChAT-positive VENs dorsolateral to g7 was significantly greater on both sides compared with controls 3 and 5 days after electrolytic lesion. In summary, we found that the number of ChAT-positive VENs was significantly increased following a change in the excitability of MVe neurons. This suggests that VENs can respond to changes in afferent vestibular information and feedback, and regulate the peripheral vestibule. In addition, this shows that acetylcholine is an important neurotransmitter that plays an important role in the perception and fine regulation of the vestibular system.

Multisensory Influences on Driver Steering During Curve Navigation.

The effects of inertial (vestibular and somatosensory) information on driver steering during curve navigation were investigated, using an electric four-wheel mobility vehicle outfitted with a steering wheel and a portable virtual reality system. When driving, multiple sources of perceptual information are available. Researchers have focused on visual information, which plays a critical role in steering control. However, it is not yet well established how inertial information might contribute. I biased inertial cues by varying visual/inertial gains (doubled, halved, reversed), as drivers negotiated curving paths, and measured steering accuracy and efficiency. I also assessed whether being exposed to inertial biases had an impact on postbias steering by comparing pre- and posttest session performance measures. Doubling or halving inertial cues had little effect on steering performance. Inertial information only disrupted steering when it was reversed with respect to visual information. Over time, the influence of this extreme inertial bias was reduced though not eliminated. Postbias curve navigation performance was not impacted, likely because participants had learned to disregard, rather than integrate, biased inertial cues. Results suggest that biased inertial information has little influence on curve navigation performance when visual information is available. Though inertial cues may be important for open-loop steering, when visual cues are unavailable, their role in closed-loop steering seems less influential. This has implications for driving simulation and suggests that inertial discrepancies due to limitations in motion-cuing capabilities may not be all that problematic for the simulation of closed-loop curve steering tasks.

Balancing presynaptic release and endocytic membrane retrieval at hair cell ribbon synapses.

The timely and reliable processing of auditory and vestibular information within the inner ear requires highly sophisticated sensory transduction pathways. On a cellular level, these demands are met by hair cells, which respond to sound waves - or alterations in body positioning - by releasing glutamate-filled synaptic vesicles (SVs) from their presynaptic active zones with unprecedented speed and exquisite temporal fidelity, thereby initiating the auditory and vestibular pathways. In order to achieve this, hair cells have developed anatomical and molecular specializations, such as the characteristic and name-giving 'synaptic ribbons' - presynaptically anchored dense bodies that tether SVs prior to release - as well as other unique or unconventional synaptic proteins. The tightly orchestrated interplay between these molecular components enables not only ultrafast exocytosis, but similarly rapid and efficient compensatory endocytosis. So far, the knowledge of how endocytosis operates at hair cell ribbon synapses is limited. In this Review, we summarize recent advances in our understanding of the SV cycle and molecular anatomy of hair cell ribbon synapses, with a focus on cochlear inner hair cells.

Assessment of vestibular function in elderly patients.

Individuals over the age of 60 are at an increased risk of falls, even if they do not have an isolated dysfunction of the vestibular system. The aim of this article is to review the various vestibular testing currently available and its usefulness in determining the presence of vestibular dysfunction in the elderly population. The primary vestibular tests to be reviewed include: balance function testing, vestibular evoked myogenic potentials (VEMPs), and video head impulse testing (vHIT). Balance function testing is important as it evaluates the integration of vestibular information along with sensory and visual information, which may also be impaired. VEMP testing provides a small diagnostic yield as most elderly patients have absent or reduced responses. vHIT gain is reduced in this population, but will still be within the normal range for individuals with normal balance function. The combination of various vestibular tests provides complimentary information instead of redundant information on the patient's balance function. Each test evaluates various aspects of the vestibular system which are all needed to determine stable balance in the elderly population.

Targeting head movements in humans: Compensation for disturbance from simultaneous body rotations

Vestibular information plays an important role in spatially oriented motor control and perception. With regard to reorienting head movements, little is known of (1) how vestibular mechanisms compensate for disturbances from concurrent passive trunk rotations (e.g. in a veering vehicle), and (2) whether and how this disturbance compensation is related to the perception of body orientation in space. We here address these two questions in a single experiment.Six healthy subjects (Ss) seated on a turning chair in darkness performed two tasks. (1) Head pointing: Ss made swift head movements in darkness towards the angular position in space of a previously shown visual target. These movements were disturbed by concurrent rotations of the chair, and hence the trunk, which were driven by scaled down versions of the Ss’ own head-on-trunk rotations. Although unaware of the disturbance, Ss adjusted their head movements so as to attenuate its effect on head-in-space (HS) position by about 45%. (2) Visual straight ahead (VSA): Using a light pointer, Ss indicated their VSA before each head-pointing trial and tried to reproduce it after the trial. In all Ss, VSA accounted for the disturbing trunk rotation, although to individually varying degrees. No correlation could be detected between VSA reproduction and motor performance, neither within nor across subjects. A vestibular loss subject who performed the same two tasks made no compensatory movements during head pointing and did not account for the disturbance of his HS position during VSA reproduction.Three concepts of vestibular information processing for head movement control were explored with regard to their compatibility with the head-pointing results: (1) Conventional negative feedback, (2) Interaction with an efference copy, and (3) Interaction with neck proprioceptive information. Theoretical analyses and model simulations indicated that all three concepts can explain the observed disturbance compensation. However, they differ in terms of control stability in the presence of feedback time delays, with (3) being best and (1) worst. The different concepts might correspond to fast simple and slower complex compensation mechanisms, respectively, and possibly complement each other during natural behaviours. VSA reproduction may be based on analogous processing principles, but appears to involve different neural circuitries.

Prediction during self-motion: the primate cerebellum selectively encodes unexpected vestibular information

Prediction during self-motion: the primate cerebellum selectively encodes unexpected vestibular information

Vestibular and Oculomotor Function in Children with Cerebral Palsy: A Scoping Review.

Cerebral palsy (CP) is a nonprogressive permanent brain injury that causes an impairment of movement and posture. This scoping review aimed to answer the following questions: (1) "What is the status of oculomotor function in children with CP?" (2) "What is the status of vestibular function (i.e., gaze stability, perception of vertical, vestibular-related balance abilities) in children with CP?" Using Arksey's and O'Malley's five-stage framework, we searched six online databases for relevant articles. The inclusion criteria were: (1) participants of the studies included individuals with CP; (2) a primary outcome in the studies was measurement of oculomotor, vestibular, and/or balance; (3) studies were published within the past 20 years; and (4) the participants in the studies were between 0 and 21 years of age. Twenty-one articles were found that described impairments in oculomotor function ( n = 9), vestibular function ( n = 1), and oculomotor and vestibular integration ( n = 11) in children with CP. The evidence suggests that children with CP may have altered saccadic and smooth pursuit eye movements, abnormal saccular function, poor eye-hand coordination, and abnormal use of vestibular information for balance. Future studies should explore peripheral and central vestibular function using reliable and valid methods for this population. This scoping review demonstrated a paucity of rigorous and objective research to describe the status of oculomotor and vestibular function in children with CP. However, preliminary studies suggest that more research is warranted.

Visual-Vestibular Interaction for Postural Control During Sit-to-Stand: Effects of Aging.

During sit-to-stand (STS), the vestibular system is highly stimulated in response to linear acceleration of the head and may play an important role, in addition to vision, for postural control. We examined the effects of aging on visual-vestibular interaction for postural control during STS in 15 young (22.5 ± 1.1years) and 15 older (73.9 ± 5.3years) participants. Vestibular information was manipulated using galvanic vestibular stimulation. Vision conditions involved normal (eyes open), suboptimal (blurring goggles), and no (eyes closed) vision. Older participants had significantly greater mediolateral peak-to-peak trunk roll (p = .025) and center of mass displacements (p < .001) than young participants. However, despite having greater mediolateral instability, older participants utilized similar strategies as young participants to overcome sensory perturbations during STS. Overall visual inputs were more dominantly used for mediolateral trunk control during STS than vestibular inputs.

Analysis of the subjective postural vertical on diagonal plane in elderly subjects and left hemiparetic patients after stroke

The subjective postural vertical (SPV) in healthy subjects is robustly maintained by integrating somatosensory and vestibular information, and extremely correct on frontal and sagittal plane. It is well-known that brain injury patients indicate disturbance of SPV on frontal or sagittal plane. On the other hand, stroke patients frequently fall paretic side and backward, but SPV on diagonal plane in normal subjects and stroke patients is unclear. The purpose of present study was to clarify the difference of SPV on diagonal plane between elderly subjects and stroke patients. The subjects comprised 14 elderly subjects (control group) and 10 left hemiparetic patients (LHP group). All subjects provided their written informed consent to take part in the study. SPV was measured using an electrical vertical board (EVB). The subjects sat on the EVB and were moved in the opposite direction from the left-backward or right-forward. The tilt of the seat when the subject feels and judges vertical position was recorded with a digital inclinometer. The mean (tilt direction) and standard deviation (variability) of eight trials were calculated. A true vertical position was considered 0°, diagonally backward and diagonally forward was treated as negative and positive, respectively. The values of SPV were compared between groups using the unpaired t-test ( P < 0.05). There was no difference between control group (66.8 ± 9.2 years [mean ± SD]) and LHP groups (67.5 ± 10.8 years) in age. In tilt direction, LHP group (−2.5 ± 0.7°) demonstrated significant tilt backward to the left than control group (−1.3 ± 1.4°). Variability was significantly higher in LHP (5.4 ± 2.0°) than control (2.5 ± 0.9°). In stroke patients, tilt direction deviated to the diagonally backward and the judgement of verticality was unstable. These results suggest a possibility to explain the tilt of sitting posture and the difficulty of transfer movement in stroke patients.

Influence of hearing on vestibulospinal control in healthy subjects.

Balance control is based on multisensory interaction. In addition to vestibular, proprioceptive and visual information, it seems that auditory input also plays an important role. The aim of the study was to investigate the effect of hearing on vestibulospinal coordination and to obtain deeper knowledge about mechanisms of audiovestibular interaction. In normal hearing, healthy subjects who performed the Unterberger (Fukuda) stepping test with and without frontal presentation of noise, the distance of displacement, the angle of displacement and the angle of rotation were measured by means of ultrasound based cranio-corpo-graphy (CCG). Additionally, subjective estimation of the effect of auditory input was compared to objective test results. In the noise condition, there was asignificant improvement in the distance of displacement (mean with noise 66.9 cm± 33.5 standard deviation, SD, mean without noise 77.0 cm±32.7 SD, p< 0.001) and in the angle of rotation (mean with noise 14.2°± 10.1 SD, mean without noise 28.3°± 20.2 SD, p< 0.001), while no difference was found within the conditions regarding the angle of displacement (mean with noise 29.1°± 33.5 SD, mean without noise 30.0°± 34.0 SD, p= 0.641). Side-specific analysis revealed apositive correlation between angle of displacement and angle of rotation in the condition without noise (Spearman r = 0.441, p< 0.001). The rate of agreement between subjective estimation of noise influence and objective test results ranged between only 43% and 63%, depending on the question and endpoint. Hearing had aclearly beneficial effect of auditory inputs on vestibulospinal coordination, especially for distance of displacement and angle of rotation.

Falling backward whilst bending forward: An apparent contradiction resolved in one case of Parkinson disease

We present a documented observation showing the existence of a biased representation of verticality in PD, resulting in a severe retropulsion and recurrent falls, and a camptocormia likely compensatory. A specific rehabilitation led to a spectacular result. A 68-year-old patient with Parkinson's disease fall backward 3 times a day. He presented an important camptocormia. There were no spinal muscular amyotrophy neither spinal canal stenosis on the lumbar tomography. The Postural vertical (PV) was tilted backward at −9° (normal for this age = −1.1° ± 1.4°). Our interpretation was that retropulsion was due to a backward tilt of the internal model of verticality, which led to recurrent falls. Camptocormia was mainly compensatory. The patient underwent an intensive rehabilitation program of 15 days including: erectus spinae muscles strengthening, realization of postural exercises thanks to mirror. A modulation of the internal model of verticality was undertaken on the basis of theoretical arguments (synthesis of graviceptive vestibular and somatosensory information) and on experimental studies: 30° forward tilted posture on a tilt table, bodyweight support walking, vibration of tibialis anterior's tendons. PV measurements before and after these technics confirmed the relevance of this approach. After 2 weeks the results were spectacular ( Table 1 ): posture spontaneously more upright (35 mm gain in C7 position), attenuated retropulsion (objectively assessed using the BDS), and normalization of PV = 0.1°. At discharge the patient was instructed to daily perform the exercises taught. Reviewed at M2 and M6, he was very satisfied with a dramatic reduction of fall frequency and the feeling to stand better. This observation brings a new insight about the nature of some postural disorders in PD, and suggests the interest of a novel rehabilitation dedicated to the sense of upright.

Robotic evaluation of fall risk in older people: Results on trunk parameters in static and dynamic balance conditions by hunova robot

Maintaining balance depends on the integration of sensory, proprioceptive and vestibular information to appropriately adjust movements responses to different postural conditions. hunova is a new robotic device developed and validated to perform functional evaluation and sensorimotor rehabilitation of lower limbs and trunk in static and dynamic environments. Aim of this study was to evaluate balance parameters in older subjects with different risk of fall. One hundred subjects aged ≥ 65 years (mean age 77.17 ± 6.49 SD years) were enrolled. According to the number of falls in the last 12 months, participants were allocated to low, medium or high-risk of fall. Balance was evaluated by hunova in static, unstable and perturbating conditions, in both standing/seated positions and with open/closed eyes. Parameters were: sway area (SA), path length (PL), range of oscillations in anterior-posterior (OAP) and mediolateral directions (OML) in both platform and trunk oscillations. Statistical analysis was carried out by means of Kruskal–Wallis test on medians and Spearman correlation test. Older fallers had higher trunk PL both in unstable [fallers, median (IQR): 32.5 (23.35) vs. non-faller 43.79 (29.21) (deg), P < 0.01] and moving [fallers 35.94 (22.12) vs. non-faller 45.27 (31.29) (deg), P < 0.05] platform in standing with open eyes condition. Trunk SA and OML were significantly different in subjects with different fall risk classes in perturbating conditions when seated with closed eyes. Trunk parameters in unstable and perturbating conditions showed also a strong and significative correlation with age ( P < 0.01). Hunova robot was able to detect physiological components involved in balance maintenance in older subjects with different fall risk. This evaluation could be crucial to prevent falls and to plan rehabilitation programs in older subjects at different risk of falls.

Influence of hearing on vestibulospinal control in healthy subjects. German version

Balance control is based on multisensory interaction. In addition to vestibular, proprioceptive and visual information, it seems that auditory input also plays an important role. The aim of the study was to investigate the effect of hearing on vestibulospinal coordination and to obtain deeper knowledge about mechanisms of audiovestibular interaction. In normal hearing, healthy subjects who performed the Unterberger (Fukuda) stepping test with and without frontal presentation of noise, the distance of displacement, the angle of displacement and the angle of rotation were measured by means of ultrasound based cranio-corpo-graphy (CCG). Additionally, subjective estimation of the effect of auditory input was compared to objective test results. In the noise condition, there was asignificant improvement in the distance of displacement (mean with noise 66.9 cm ± 33.5 standard deviation, SD, mean without noise 77.0 cm ± 32.7 SD, p < 0.001) and in the angle of rotation (mean with noise 14.2° ± 10.1 SD, mean without noise 28.3° ± 20.2 SD, p < 0.001), while no difference was found within the conditions regarding the angle of displacement (mean with noise 29.1° ± 33.5 SD, mean without noise 30.0° ± 34.0 SD, p = 0.641). Side-specific analysis revealed apositive correlation between angle of displacement and angle of rotation in the condition without noise (Spearman r = 0.441, p < 0.001). The rate of agreement between subjective estimation of noise influence and objective test results ranged between only 43% and 63%, depending on the question and endpoint. Hearing had aclearly beneficial effect of auditory inputs on vestibulospinal coordination, especially for distance of displacement and angle of rotation.

The Reliance on Vestibular Information During Standing Balance Control Decreases With Severity of Vestibular Dysfunction.

The vestibular system is involved in gaze stabilization and standing balance control. However, it is unclear whether vestibular dysfunction affects both processes to a similar extent. Therefore, the objective of this study was to determine how the reliance on vestibular information during standing balance control is related to gaze stabilization deficits in patients with vestibular dysfunction. Eleven patients with vestibular dysfunction and twelve healthy subjects were included. Gaze stabilization deficits were established by spontaneous nystagmus examination, caloric test, rotational chair test, and head impulse test. Standing balance control was assessed by measuring the body sway (BS) responses to continuous support surface rotations of 0.5° and 1.0° peak-to-peak while subjects had their eyes closed. A balance control model was fitted on the measured BS responses to estimate balance control parameters, including the vestibular weight, which represents the reliance on vestibular information. Using multivariate analysis of variance, balance parameters were compared between patients with vestibular dysfunction and healthy subjects. Robust regression was used to investigate correlations between gaze stabilization and the vestibular weight. Our results showed that the vestibular weight was smaller in patients with vestibular dysfunction than in healthy subjects (F = 7.67, p = 0.011). The vestibular weight during 0.5° peak-to-peak support surface rotations decreased with increasing spontaneous nystagmus eye velocity (ρ = −0.82, p < 0.001). In addition, the vestibular weight during 0.5° and 1.0° peak-to-peak support surface rotations decreased with increasing ocular response bias during rotational chair testing (ρ = −0.72, p = 0.02 and ρ = −0.67, p = 0.04, respectively). These findings suggest that the reliance on vestibular information during standing balance control decreases with the severity of vestibular dysfunction. We conclude that particular gaze stabilization tests may be used to predict the effect of vestibular dysfunction on standing balance control.

Effect of sensory-motor latencies and active muscular stiffness on stability for an ankle-hip model of balance on a balance board

To achieve human upright posture (UP) and avoid falls, the central nervous system processes visual, vestibular, and proprioceptive information to activate the appropriate muscles to accelerate or decelerate the body’s center of mass. In this process, sensory-motor (SM) latencies and muscular deficits, even in healthy older adults, may cause falls. This condition is worse for people with chronic neuromuscular deficits (stroke survivors, patients with multiple sclerosis or Parkinson’s disease). One therapeutic approach is to recover or improve quiet UP by utilizing a balance board (BB) (a rotating surface with a tunable stiffness and time delay), where a patient attempts to maintain UP while task difficulty is manipulated. While BBs are commonly used, it is unclear how UP is maintained or how changes in system parameters such as SM latencies and BB time delay affect UP stability. To understand these questions, it is important that mathematical models be developed with enough degrees-of-freedom to capture the many responses evoked during the maintenance of UP on a BB. This paper presents an ankle-hip model of balance on a BB, which is used to study the combined effect of SM latencies and active muscular stiffness of the ankle and hip joints, and the BB stiffness and time delay on UP stability. The analysis predicts that people with proprioceptive, visual, vestibular loss, or increased SM latencies may show either leaning postures or larger body-sway. The results show that the BB time delay and the visual and vestibular feedback have the largest impact on UP stability.

Control of human gait stability through foot placement.

During human walking, the centre of mass (CoM) is outside the base of support for most of the time, which poses a challenge to stabilizing the gait pattern. Nevertheless, most of us are able to walk without substantial problems. In this review, we aim to provide an integrative overview of how humans cope with an underactuated gait pattern. A central idea that emerges from the literature is that foot placement is crucial in maintaining a stable gait pattern. In this review, we explore this idea; we first describe mechanical models and concepts that have been used to predict how foot placement can be used to control gait stability. These concepts, such as for instance the extrapolated CoM concept, the foot placement estimator concept and the capture point concept, provide explicit predictions on where to place the foot relative to the body at each step, such that gait is stabilized. Next, we describe empirical findings on foot placement during human gait in unperturbed and perturbed conditions. We conclude that humans show behaviour that is largely in accordance with the aforementioned concepts, with foot placement being actively coordinated to body CoM kinematics during the preceding step. In this section, we also address the requirements for such control in terms of the sensory information and the motor strategies that can implement such control, as well as the parts of the central nervous system that may be involved. We show that visual, vestibular and proprioceptive information contribute to estimation of the state of the CoM. Foot placement is adjusted to variations in CoM state mainly by modulation of hip abductor muscle activity during the swing phase of gait, and this process appears to be under spinal and supraspinal, including cortical, control. We conclude with a description of how control of foot placement can be impaired in humans, using ageing as a primary example and with some reference to pathology, and we address alternative strategies available to stabilize gait, which include modulation of ankle moments in the stance leg and changes in body angular momentum, such as rapid trunk tilts. Finally, for future research, we believe that especially the integration of consideration of environmental constraints on foot placement with balance control deserves attention.

Modulation of Excitability in the Temporoparietal Junction Relieves Virtual Reality Sickness.

Virtual reality (VR) immersion often provokes subjective discomfort and postural instability, so called VR sickness. The neural mechanism of VR sickness is speculated to be related to visual-vestibular information mismatch and/or postural instability. However, the approaches proposed to relieve VR sickness through modulation of brain activity are poorly understood. Using transcranial direct current stimulation (tDCS), we aimed to investigate whether VR sickness could be relieved by the modulation of cortical excitability in the temporoparietal junction (TPJ), which is known to be involved in processing of both vestibular and visual information. Twenty healthy subjects received tDCS over right TPJ before VR immersion. The order of the three types of tDCS (anodal, cathodal, and sham) was counterbalanced across subjects. We evaluated the subjective symptoms, heart rate, and center of pressure at baseline, after tDCS, and after VR immersion. VR immersion using head-mounted displays provoked subjective discomfort and postural instability. However, anodal tDCS over right TPJ ameliorated subjective disorientation symptoms and postural instability induced by VR immersion compared with sham condition. The amelioration of VR sickness by anodal tDCS over the right TPJ might result from relief of the sensory conflict and/or facilitation of vestibular function. Our result not only has potential clinical implications for the neuromodulation approach of VR sickness but also implies a causal role of the TPJ in VR sickness.

Proprioceptive loss and the perception, control and learning of arm movements in humans: evidence from sensory neuronopathy

It is uncertain how vision and proprioception contribute to adaptation of voluntary arm movements. In normal participants, adaptation to imposed forces is possible with or without vision, suggesting that proprioception is sufficient; in participants with proprioceptive loss (PL), adaptation is possible with visual feedback, suggesting that proprioception is unnecessary. In experiment 1 adaptation to, and retention of, perturbing forces were evaluated in three chronically deafferented participants. They made rapid reaching movements to move a cursor toward a visual target, and a planar robot arm applied orthogonal velocity-dependent forces. Trial-by-trial error correction was observed in all participants. Such adaptation has been characterized with a dual-rate model: a fast process that learns quickly, but retains poorly and a slow process that learns slowly and retains well. Experiment 2 showed that the PL participants had large individual differences in learning and retention rates compared to normal controls. Experiment 3 tested participants’ perception of applied forces. With visual feedback, the PL participants could report the perturbation’s direction as well as controls; without visual feedback, thresholds were elevated. Experiment 4 showed, in healthy participants, that force direction could be estimated from head motion, at levels close to the no-vision threshold for the PL participants. Our results show that proprioceptive loss influences perception, motor control and adaptation but that proprioception from the moving limb is not essential for adaptation to, or detection of, force fields. The differences in learning and retention seen between the three deafferented participants suggest that they achieve these tasks in idiosyncratic ways after proprioceptive loss, possibly integrating visual and vestibular information with individual cognitive strategies.