Oscillatory neural responses evoked by natural vestibular stimuli in humans

Electrophysiological markers of vestibular-mediated self-motion perception - A pilot study

Peripheral vestibular activation results in multi-level responses, from brainstem-mediated reflexes (e.g. vestibular ocular reflex - VOR) to perception of self-motion. While VOR responses indicate preserved vestibular peripheral and brainstem functioning, there are no automated measures of vestibular perception of self-motion - important since some patients with brain disconnection syndromes manifest a vestibular agnosia (intact VOR but impaired self-motion perception). Electroencephalography ('EEG') - may provide a surrogate marker of vestibular perception of self-motion. A related objective is obtaining an EEG marker of vestibular sensory signal processing, distinct from vestibular-motion perception. We performed a pilot study comparing EEG responses in the dark when healthy participants sat in a vibrationless computer-controlled motorised rotating chair moving at near threshold of self-motion perception, versus a second situation in which subjects sat in the chair at rest in the dark who could be induced (or not) into falsely perceiving self-motion. In both conditions subjects could perceive self-motion perception, but in the second there was no bottom-up reflex-brainstem activation. Time-frequency analyses showed: (i) alpha frequency band activity is linked to vestibular sensory-signal activation; and (ii) theta band activity is a marker of vestibular-mediated self-motion perception. Consistent with emerging animal data, our findings support the role of theta activity in the processing of self-motion perception.

Modulation of Visually Induced Self-motion Illusions by α Transcranial Electric Stimulation over the Superior Parietal Cortex

The growing popularity of virtual reality systems has led to a renewed interest in understanding the neurophysiological correlates of the illusion of self-motion (vection), a phenomenon that can be both intentionally induced or avoided in such systems, depending on the application. Recent research has highlighted the modulation of α power oscillations over the superior parietal cortex during vection, suggesting the occurrence of inhibitory mechanisms in the sensorimotor and vestibular functional networks to resolve the inherent visuo-vestibular conflict. The present study aims to further explore this relationship and investigate whether neuromodulating these waves could causally affect the quality of vection. In a crossover design, 22 healthy volunteers received high amplitude and focused α-tACS (transcranial alternating current stimulation) over the superior parietal cortex while experiencing visually induced vection triggered by optokinetic stimulation. The tACS was tuned to each participant's individual α peak frequency, with θ-tACS and sham stimulation serving as controls. Overall, participants experienced better quality vection during α-tACS compared with control θ-tACS and sham stimulations, as quantified by the intensity of vection. The observed neuromodulation supports a causal relationship between parietal α oscillations and visually induced self-motion illusions, with their entrainment triggering overinhibition of the conflict within the sensorimotor and vestibular functional networks. These results confirm the potential of noninvasive brain stimulation for modulating visuo-vestibular conflicts, which could help to enhance the sense of presence in virtual reality environments.

Modification of cortical electrical activity in stroke survivors with abnormal subjective visual vertical: An eLORETA study

Objectives

Balance impairment is among the main complications of stroke. The gravity-based subjective vertical (SV) is considered an important reference for upright posture and navigation affected by stroke. The correlation between injury location and pathological perception of verticality remains controversial. This study aimed to evaluate the cortico-cortical network of vertical perception among patients with the right hemisphere stroke and abnormal visual-vertical perception compared with healthy individuals.

Materials and methods

This observational cross-sectional study included 40 patients with the right hemisphere stroke and 35 healthy participants. All patients had abnormal visual-vertical perception. The EEG connectivity analysis was conducted through the exact low-resolution brain electromagnetic tomography analysis (eLORETA).

Results

Stroke survivors manifested a power spectral density that reduced within the beta-2 frequency band in the left hemisphere and increased within the beta-3 frequency band in the right hemisphere compared with controls (p < 0.01). The lagged-phase synchronization was increased within alpha-1, beta-2, and beta-3 bands and decreased in stroke survivors compared with controls in the vestibular network involved in visual-vertical perception (p < 0.01).

Conclusion

The results of this study demonstrated variations in the function and functional connectivity of cortical areas involved in the visual-vertical perception that are mainly located in the vestibular cortex.

Frequency-Dependent Reduction of Cybersickness in Virtual Reality by Transcranial Oscillatory Stimulation of the Vestibular Cortex

Virtual reality (VR) applications are pervasive of everyday life, as in working, medical, and entertainment scenarios. There is yet no solution to cybersickness (CS), a disabling vestibular syndrome with nausea, dizziness, and general discomfort that most of VR users undergo, which results from an integration mismatch among visual, proprioceptive, and vestibular information. In a double-blind, controlled trial, we propose an innovative treatment for CS, consisting of online oscillatory imperceptible neuromodulation with transcranial alternating current stimulation (tACS) at 10 Hz, biophysically modelled to reach the vestibular cortex bilaterally. tACS significantly reduced CS nausea in 37 healthy subjects during a VR rollercoaster experience. The effect was frequency-dependent and placebo-insensitive. Subjective benefits were paralleled by galvanic skin response modulation in 25 subjects, addressing neurovegetative activity. Besides confirming the role of transcranially delivered oscillations in physiologically tuning the vestibular system function (and dysfunction), results open a new way to facilitate the use of VR in different scenarios and possibly to help treating also other vestibular dysfunctions.

Vestibular loss disrupts visual reactivity in the alpha EEG rhythm

The alpha rhythm is a dominant electroencephalographic oscillation relevant to sensory-motor and cognitive function. Alpha oscillations are reactive, being for example enhanced by eye closure, and suppressed following eye opening. The determinants of inter-individual variability in reactivity in the alpha rhythm (e.g. changes with amplitude following eye closure) are not fully understood despite the physiological and clinical applicability of this phenomenon, as indicated by the fact that ageing and neurodegeneration reduce reactivity. Strong interactions between visual and vestibular systems raise the theoretical possibility that the vestibular system plays a role in alpha reactivity. To test this hypothesis, we applied electroencephalography in sitting and standing postures in 15 participants with reduced vestibular function (bilateral vestibulopathy, median age = 70 years, interquartile range = 51-77 years) and 15 age-matched controls. We found participants with reduced vestibular function showed less enhancement of alpha electroencephalography power on eye closure in frontoparietal areas, compared to controls. In participants with reduced vestibular function, video head impulse test gain - as a measure of residual vestibulo-ocular reflex function - correlated with reactivity in alpha power across most of the head. Greater reliance on visual input for spatial orientation ('visual dependence', measured with the rod-and-disc test) correlated with less alpha enhancement on eye closure only in participants with reduced vestibular function, and this was partially moderated by video head impulse test gain. Our results demonstrate for the first time that vestibular function influences alpha reactivity. The results are partly explained by the lack of ascending peripheral vestibular input but also by central reorganisation of processing relevant to visuo-vestibular judgements.

Vestibular mapping of the naturalistic head-centered motion spectrum

BACKGROUND

Naturalistic head accelerations can be used to elicit vestibular evoked potentials (VestEPs). These potentials allow for analysis of cortical vestibular processing and its multi-sensory integration with a high temporal resolution.

METHODS

We report the results of two experiments in which we compared the differential VestEPs elicited by randomized translations, rotations, and tilts in healthy subjects on a motion platform.

RESULTS

An event-related potential (ERP) analysis revealed that established VestEPs were verifiable in all three acceleration domains (translations, rotations, tilts). A further analysis of the VestEPs showed a significant correlation between rotation axes (yaw, pitch, roll) and the amplitude of the evoked potentials. We found increased amplitudes for rotations in the roll compared to the pitch and yaw plane. A distributed source localization analysis showed that the activity in the cingulate sulcus visual (CSv) area best explained direction-dependent amplitude modulations of the VestEPs, but that the same cortical network (posterior insular cortex, CSv) is involved in processing vestibular information, regardless of the motion direction.

CONCLUSION

The results provide evidence for an anisotropic, direction-dependent processing of vestibular input by cortical structures. The data also suggest that area CSv plays an integral role in ego-motion perception and interpretation of spatial features such as acceleration direction and intensity.

Electroencephalographic response to transient adaptation of vestibular perception

Abstract

When given a series of sinusoidal oscillations in which the two hemicycles have equal amplitude but asymmetric velocity, healthy subjects lose perception of the slower hemicycle (SHC), reporting a drift towards the faster hemicycle (FHC). This response is not reflected in the vestibular–ocular reflex, suggesting that the adaptation is of higher order. This study aimed to define EEG correlates of this adaptive response. Twenty‐five subjects underwent a series of symmetric or asymmetric oscillations and reported their perceived head orientation at the end using landmarks in the testing room; this was converted into total position error (TPE). Thirty‐two channel EEG was recorded before, during and after adaptation. Spectral power and coherence were calculated for the alpha, beta, delta and theta frequency bands. Linear mixed models were used to determine a region‐by‐condition effect of the adaptation. TPE was significantly greater in the asymmetric condition and reported error was always in the direction of the FHC. Regardless of condition, alpha desynchronised in response to stimulation, then rebounded back toward baseline values. This pattern was accelerated and attenuated in the prefrontal and occipital regions, respectively, in the asymmetric condition. Functional connectivity networks were identified in the beta and delta frequency bands; these networks, primarily comprising frontoparietal connections, were more coherent during asymmetric stimulation. These findings suggest that the temporary vestibulo‐perceptual ‘neglect’ induced by asymmetric vestibular stimulation may be mediated by alpha rhythms and frontoparietal attentional networks. The results presented further our understanding of brain rhythms and cortical networks involved in vestibular perception and adaptation.

Key points

Whole‐body asymmetric sinusoidal oscillations, which consist of hemicycles with equal amplitude but differing velocities, can induce transient ‘neglect’ of the slower hemicycle in the vestibular perception of healthy subjects.

In this study, we aimed to elucidate EEG correlates of this ‘neglect’, thereby identifying a cortical role in vestibular perception and adaptation.

We identified a desynchronisation–resynchronisation response in the alpha frequency band (8–14 Hz) that was accelerated in the prefrontal region and attenuated in the occipital region when exposed to asymmetric, as compared to symmetric, rotations.

We additionally identified functional connectivity networks in the beta (14–30 Hz) and delta (1–4 Hz) frequency bands consisting primarily of frontoparietal connections.

These results suggest a prominent role of alpha rhythms and frontoparietal attentional networks in vestibular perception and adaptation.

Electroencephalography Microstate Alterations in Otogenic Vertigo: A Potential Disease Marker

Objectives

A huge population, especially the elderly, suffers from otogenic vertigo. However, the multi-modal vestibular network changes, secondary to periphery vestibular dysfunction, have not been fully elucidated. We aim to identify potential microstate electroencephalography (EEG) signatures for otogenic vertigo in this study.

Materials and Methods

Patients with recurrent otogenic vertigo and age-matched healthy adults were recruited. We performed 256-channel EEG recording of all participants at resting state. Neuropsychological questionnaires and vestibular function tests were taken as a measurement of patients’ symptoms and severity. We clustered microstates into four classes (A, B, C, and D) and identified their dynamic and syntax alterations of them. These features were further fed into a support vector machine (SVM) classifier to identify microstate signatures for vertigo.

Results

We compared 40 patients to 45 healthy adults, finding an increase in the duration of Microstate A, and both the occurrence and time coverage of Microstate D. The coverage and occurrence of Microstate C decreased significantly, and the probabilities of non-random transitions between Microstate A and D, as well as Microstate B and C, also changed. To distinguish the patients, the SVM classifier, which is built based on these features, got a balanced accuracy of 0.79 with a sensitivity of 0.78 and a specificity of 0.8.

Conclusion

There are several temporal dynamic alterations of EEG microstates in patients with otogenic vertigo, especially in Microstate D, reflecting the underlying process of visual-vestibular reorganization and attention redistribution. This neurophysiological signature of microstates could be used to identify patients with vertigo in the future.

Resting-State Electroencephalography and P300 Evidence: Age-Related Vestibular Loss as a Risk Factor Contributes to Cognitive Decline

Background:

In recent years, there have been several meaningful advances in the understanding of the cognitive effects of vestibular loss. However, there has not yet been an investigation exploring the early biomarkers of preclinical cognitive decline in individuals with age-related vestibular loss.

Objective:

We aim to explore the “early biomarkers” of preclinical cognitive decline based on altered cortical activity (resting-state electroencephalography (EEG) and P300) with a multichannel EEG system in individuals with age-related vestibular loss.

Method:

This is a case-control study. A total of 21 patients with age-related vestibular loss (66.50±5.79 years, 13 [62% ] females), 19 patients with cognitive decline (68.42±5.82 years, 13 [68% ] females), and 21 age- and sex-matched healthy controls were recruited. All participants underwent a comprehensive battery of neuropsychological tests, audio-vestibular evaluations, resting-state EEG and P300 recordings.

Results:

Significant visuo-spatial, executive, and attention hypofunction were observed in the age-related vestibular group, reflected by decreased subscale scores. Reduced gamma functional connectivity between the right cuneus (Brodmann area 19, BA19) and the left superior parietal gyrus (BA7) was observed in both the age-related vestibular group and the cognitive impairment group. Smaller P300 amplitudes were observed in the age-related vestibular group (1.43±3.69μV) and cognitive impairment group (1.15±4.24μV) than in the healthy control group (3.97±2.38μV).

Conclusion:

Decreased P300 amplitude and functional connectivity between the right BA19 and the left BA7 were “early biomarkers” observed in individuals with age-related vestibular loss; these biomarkers may contribute to visuospatial, executive, and attention hypofunction.

On the Dynamics of Spatial Updating

Most of our knowledge on the human neural bases of spatial updating comes from functional magnetic resonance imaging (fMRI) studies in which recumbent participants moved in virtual environments. As a result, little is known about the dynamic of spatial updating during real body motion. Here, we exploited the high temporal resolution of electroencephalography (EEG) to investigate the dynamics of cortical activation in a spatial updating task where participants had to remember their initial orientation while they were passively rotated about their vertical axis in the dark. After the rotations, the participants pointed toward their initial orientation. We contrasted the EEG signals with those recorded in a control condition in which participants had no cognitive task to perform during body rotations. We found that the amplitude of the P₁N₁ complex of the rotation-evoked potential (RotEPs) (recorded over the vertex) was significantly greater in the Updating task. The analyses of the cortical current in the source space revealed that the main significant task-related cortical activities started during the N₁P₂ interval (136–303 ms after rotation onset). They were essentially localized in the temporal and frontal (supplementary motor complex, dorsolateral prefrontal cortex, anterior prefrontal cortex) regions. During this time-window, the right superior posterior parietal cortex (PPC) also showed significant task-related activities. The increased activation of the PPC became bilateral over the P₂N₂ component (303–470 ms after rotation onset). In this late interval, the cuneus and precuneus started to show significant task-related activities. Together, the present results are consistent with the general scheme that the first task-related cortical activities during spatial updating are related to the encoding of spatial goals and to the storing of spatial information in working memory. These activities would precede those involved in higher order processes also relevant for updating body orientation during rotations linked to the egocentric and visual representations of the environment.

Enhancement of capability for motor imagery using vestibular imbalance stimulation during brain computer interface

Objective.Motor imagery (MI), based on the theory of mirror neurons and neuroplasticity, can promote motor cortical activation in neurorehabilitation. The strategy of MI based on brain-computer interface (BCI) has been used in rehabilitation training and daily assistance for patients with hemiplegia in recent years. However, it is difficult to maintain the consistency and timeliness of receiving external stimulation to neural activation in most subjects owing to the high variability of electroencephalogram (EEG) representation across trials/subjects. Moreover, in practical application, MI-BCI cannot highly activate the motor cortex and provide stable interaction owing to the weakness of the EEG feature and lack of an effective mode of activation.Approach.In this study, a novel hybrid BCI paradigm based on MI and vestibular stimulation motor imagery (VSMI) was proposed to enhance the capability of feature response for MI. Twelve subjects participated in a group of controlled experiments containing VSMI and MI. Three indicators, namely, activation degree, timeliness, and classification accuracy, were adopted to evaluate the performance of the task.Main results.Vestibular stimulation could significantly strengthen the suppression ofαandβbands of contralateral brain regions during MI, that is, enhance the activation degree of the motor cortex (p< 0.01). Compared with MI, the timeliness of EEG feature-response achieved obvious improvements in VSMI experiments. Moreover, the averaged classification accuracy of VSMI and MI was 80.56% and 69.38%, respectively.Significance.The experimental results indicate that specific vestibular activity contributes to the oscillations of the motor cortex and has a positive effect on spontaneous imagery, which provides a novel MI paradigm and enables the preliminary exploration of sensorimotor integration of MI.

Vestibular-Evoked Cerebral Potentials

The human vestibular cortex has mostly been approached using functional magnetic resonance imaging and positron emission tomography combined with artificial stimulation of the vestibular receptors or nerve. Few studies have used electroencephalography and benefited from its high temporal resolution to describe the spatiotemporal dynamics of vestibular information processing from the first milliseconds following vestibular stimulation. Evoked potentials (EPs) are largely used to describe neural processing of other sensory signals, but they remain poorly developed and standardized in vestibular neuroscience and neuro-otology. Yet, vestibular EPs of brainstem, cerebellar, and cortical origin have been reported as early as the 1960s. This review article summarizes and compares results from studies that have used a large range of vestibular stimulation, including natural vestibular stimulation on rotating chairs and motion platforms, as well as artificial vestibular stimulation (e.g., sounds, impulsive acceleration stimulation, galvanic stimulation). These studies identified vestibular EPs with short latency (<20 ms), middle latency (from 20 to 50 ms), and late latency (>50 ms). Analysis of the generators (source analysis) of these responses offers new insights into the neuroimaging of the vestibular system. Generators were consistently found in the parieto-insular and temporo-parietal junction-the core of the vestibular cortex-as well as in the prefrontal and frontal areas, superior parietal, and temporal areas. We discuss the relevance of vestibular EPs for basic research and clinical neuroscience and highlight their limitations.

The role of delta and theta oscillations during ego-motion in healthy adult volunteers

The successful cortical processing of multisensory input typically requires the integration of data represented in different reference systems to perform many fundamental tasks, such as bipedal locomotion. Animal studies have provided insights into the integration processes performed by the neocortex and have identified region specific tuning curves for different reference frames during ego-motion. Yet, there remains almost no data on this topic in humans.

In this study, an experiment originally performed in animal research with the aim to identify brain regions modulated by the position of the head and eyes relative to a translational ego-motion was adapted for humans. Subjects sitting on a motion platform were accelerated along a translational pathway with either eyes and head aligned or a 20° yaw-plane offset relative to the motion direction while EEG was recorded.

Using a distributed source localization approach, it was found that activity in area PFm, a part of Brodmann area 40, was modulated by the congruency of translational motion direction, eye, and head position. In addition, an asymmetry between the hemispheres in the opercular-insular region was observed during the cortical processing of the vestibular input. A frequency specific analysis revealed that low-frequency oscillations in the delta- and theta-band are modulated by vestibular stimulation. Source-localization estimated that the observed low-frequency oscillations are generated by vestibular core-regions, such as the parieto-opercular region and frontal areas like the mid-orbital gyrus and the medial frontal gyrus.

Symptoms of depersonalisation/derealisation disorder as measured by brain electrical activity: A systematic review

Depersonalisation/derealisation disorder (DPD) refers to frequent and persistent detachment from bodily self and disengagement from the outside world. As a dissociative disorder, DPD affects 1-2 % of the population, but takes 7-12 years on average to be accurately diagnosed. In this systematic review, we comprehensively describe research targeting the neural correlates of core DPD symptoms, covering publications between 1992 and 2020 that have used electrophysiological techniques. The aim was to investigate the diagnostic potential of these relatively inexpensive and convenient neuroimaging tools. We review the EEG power spectrum, components of the event-related potential (ERP), as well as vestibular and heartbeat evoked potentials as likely electrophysiological biomarkers to study DPD symptoms. We argue that acute anxiety- or trauma-related impairments in the integration of interoceptive and exteroceptive signals play a key role in the formation of DPD symptoms, and that future research needs analysis methods that can take this integration into account. We suggest tools for prospective studies of electrophysiological DPD biomarkers, which are urgently needed to fully develop their diagnostic potential.

Two Neural Circuits to Point Towards Home Position After Passive Body Displacements

A challenge in motor control research is to understand the mechanisms underlying the transformation of sensory information into arm motor commands. Here, we investigated these transformation mechanisms for movements whose targets were defined by information issued from body rotations in the dark (i.e., idiothetic information). Immediately after being rotated, participants reproduced the amplitude of their perceived rotation using their arm (Experiment 1). The cortical activation during movement planning was analyzed using electroencephalography and source analyses. Task-related activities were found in regions of interest (ROIs) located in the prefrontal cortex (PFC), dorsal premotor cortex, dorsal region of the anterior cingulate cortex (ACC) and the sensorimotor cortex. Importantly, critical regions for the cognitive encoding of space did not show significant task-related activities. These results suggest that arm movements were planned using a sensorimotor-type of spatial representation. However, when a 8 s delay was introduced between body rotation and the arm movement (Experiment 2), we found that areas involved in the cognitive encoding of space [e.g., ventral premotor cortex (vPM), rostral ACC, inferior and superior posterior parietal cortex (PPC)] showed task-related activities. Overall, our results suggest that the use of a cognitive-type of representation for planning arm movement after body motion is necessary when relevant spatial information must be stored before triggering the movement.

Positron emission tomography visualized stimulation of the vestibular organ is localized in Heschl's gyrus

The existence of a human primary vestibular cortex is still debated. Current knowledge mainly derives from functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) acquisitions during artificial vestibular stimulation. This may be problematic as artificial vestibular stimulation entails coactivation of other sensory receptors. The use of fMRI is challenging as the strong magnetic field and loud noise during MRI may both stimulate the vestibular organ. This study aimed to characterize the cortical activity during natural stimulation of the human vestibular organ. Two fluorodeoxyglucose (FDG)-PET scans were obtained after natural vestibular stimulation in a self-propelled chair. Two types of stimuli were applied: (a) rotation (horizontal semicircular canal) and (b) linear sideways movement (utriculus). A comparable baseline FDG-PET scan was obtained after sitting motion-less in the chair. In both stimulation paradigms, significantly increased FDG uptake was measured bilaterally in the medial part of Heschl's gyrus, with some overlap into the posterior insula. This is the first neuroimaging study to visualize cortical processing of natural vestibular stimuli. FDG uptake was demonstrated in the medial-most part of Heschl's gyrus, normally associated with the primary auditory cortex. This anatomical localization seems plausible, considering that the labyrinth contains both the vestibular organ and the cochlea.

Shift in lateralization during illusory self-motion: EEG responses to visual flicker at 10 Hz and frequency-specific modulation by tACS

Self-motion perception is a key aspect of higher vestibular processing, suggested to rely upon hemispheric lateralization and alpha-band oscillations. The first aim of this study was to test for any lateralization in the EEG alpha band during the illusory sense of self-movement (vection) induced by large optic flow stimuli. Visual stimuli flickered at alpha frequency (approx. 10 Hz) in order to produce steady state visually evoked potentials (SSVEPs), a robust EEG measure which allows probing the frequency-specific response of the cortex. The first main result was that differential lateralization of the alpha SSVEP response was found during vection compared with a matched random motion control condition, supporting the idea of lateralization of visual-vestibular function. Additionally, this effect was frequency-specific, not evident with lower frequency SSVEPs. The second aim of this study was to test for a causal role of the right hemisphere in producing this lateralization effect and to explore the possibility of selectively modulating the SSVEP response. Transcranial alternating current stimulation (tACS) was applied over the right hemisphere simultaneously with SSVEP recording, using a novel artefact removal strategy for combined tACS-EEG. The second main result was that tACS enhanced SSVEP amplitudes, and the effect of tACS was not confined to the right hemisphere. Subsequent control experiments showed the effect of tACS requires the flicker frequency and tACS frequency to be closely matched and tACS to be of sufficient intensity. Combined tACS-SSVEPs are a promising method for future investigation into the role of neural oscillations and for optimizing tACS.

Investigating the vestibular system using modern imaging techniques-A review on the available stimulation and imaging methods

The vestibular organs, located in the inner ear, sense linear and rotational acceleration of the head and its position relative to the gravitational field of the earth. These signals are essential for many fundamental skills such as the coordination of eye and head movements in the three-dimensional space or the bipedal locomotion of humans. Furthermore, the vestibular signals have been shown to contribute to higher cognitive functions such as navigation. As the main aim of the vestibular system is the sensation of motion it is a challenging system to be studied in combination with modern imaging methods. Over the last years various different methods were used for stimulating the vestibular system. These methods range from artificial approaches like galvanic or caloric vestibular stimulation to passive full body accelerations using hexapod motion platforms, or rotatory chairs. In the first section of this review we provide an overview over all methods used in vestibular stimulation in combination with imaging methods (fMRI, PET, E/MEG, fNIRS). The advantages and disadvantages of every method are discussed, and we summarize typical settings and parameters used in previous studies. In the second section the role of the four imaging techniques are discussed in the context of vestibular research and their potential strengths and interactions with the presented stimulation methods are outlined.

Transformation of vestibular signals for the decisions of hand choice during whole body motion

In daily life, we frequently reach toward objects while our body is in motion. We have recently shown that body accelerations influence the decision of which hand to use for the reach, possibly by modulating the body-centered computations of the expected reach costs. However, head orientation relative to the body was not manipulated, and hence it remains unclear whether vestibular signals contribute in their head-based sensory frame or in a transformed body-centered reference frame to these cost calculations. To test this, subjects performed a preferential reaching task to targets at various directions while they were sinusoidally translated along the lateral body axis, with their head either aligned with the body (straight ahead) or rotated 18° to the left. As a measure of hand preference, we determined the target direction that resulted in equiprobable right/left-hand choices. Results show that head orientation affects this balanced target angle when the body is stationary but does not further modulate hand preference when the body is in motion. Furthermore, reaction and movement times were larger for reaches to the balanced target angle, resembling a competitive selection process, and were modulated by head orientation when the body was stationary. During body translation, reaction and movement times depended on the phase of the motion, but this phase-dependent modulation had no interaction with head orientation. We conclude that the brain transforms vestibular signals to body-centered coordinates at the early stage of reach planning, when the decision of hand choice is computed. NEW & NOTEWORTHY The brain takes inertial acceleration into account in computing the anticipated biomechanical costs that guide hand selection during whole body motion. Whereas these costs are defined in a body-centered, muscle-based reference frame, the otoliths detect the inertial acceleration in head-centered coordinates. By systematically manipulating head position relative to the body, we show that the brain transforms otolith signals into body-centered coordinates at an early stage of reach planning, i.e., before the decision of hand choice is computed.

Dynamic Office Environments Improve Brain Activity and Attentional Performance Mediated by Increased Motor Activity

Current research demonstrates beneficial effects of physical activity on brain functions and cognitive performance. To date, less is known on the effects of gross motor movements that do not fall into the category of sports-related aerobic or anaerobic exercise. In previous studies, we found beneficial effects of dynamic working environments, i.e., environments that encourage movements during cognitive task performance, on cognitive performance and corresponding brain activity. Aim of the present study was to examine the effects of working in a dynamic and a static office environment on attentional and vigilance performance, and on the corresponding electroencephalographic (EEG) brain oscillatory patterns. In a 2-week intervention study, participants worked either in a dynamic or a static office. In each intervention group, 12 subjects performed attentional and vigilance tasks. Spontaneous EEG was measured from 19 electrodes continuosly before, during, and immediately after each experimental condition at the first, and at the last intervention session. Results showed differences in EEG brain activity in the dynamic compared to the static office at the beginning as well as at the end of the intervention. EEG theta power increased in the vigilance task in anterior regions, alpha power in central and parietal regions in the dynamic compared to the static office. Further, increases in beta activity in the attention and vigilance task were shown in frontal and central regions in the dynamic office. Gamma power increased in the attention task in frontal and central regions. After 2 weeks, effects on brain activity increased in the attentional and vigilance task in the dynamic office. Increased theta and alpha oscillations were obtained in anterior areas with higher activity in the beta band in anterior and central areas in the dynamic compared to the static office. EEG oscillatory patterns indicate beneficial effects of dynamic office environments on attentional and vigilance performance that are mediated by increased motor activity. We discuss the obtained patterns of EEG oscillations in terms of the close interrelations between the attentional and the motor system.

Differential effects of vestibular processing on orienting exogenous and endogenous covert visual attention

Recent research highlights the overwhelming role of vestibular information for higher order cognition. Central to body perception, vestibular cues provide information about self-location in space, self-motion versus object motion, and modulate the perception of space. Surprisingly, however, little research has dealt with how vestibular information combines with other senses to orient one's attention in space. Here we used passive whole body rotations as exogenous (Experiment 1) or endogenous (Experiment 2) attentional cues and studied their effects on orienting visual attention in a classical Posner paradigm. We show that-when employed as an exogenous stimulus-rotation impacts attention orienting only immediately after vestibular stimulation onset. However, when acting as an endogenous stimulus, vestibular stimulation provides a robust benefit to target detection throughout the rotation profile. Our data also demonstrate that vestibular stimulation boosts attentional processing more generally, independent of rotation direction, associated with a general improvement in performance. These data provide evidence for distinct effects of vestibular processing on endogenous and exogenous attention as well as alertness that differ with respect to the temporal dynamics of the motion profile. These data reveal that attentional spatial processing and spatial body perception as manipulated through vestibular stimulation share important brain mechanisms.

The parieto-insular vestibular cortex in humans: more than a single area?

Here, we review the structure and function of a core region in the vestibular cortex of humans that is located in the midposterior Sylvian fissure and referred to as the parieto-insular vestibular cortex (PIVC). Previous studies have investigated PIVC by using vestibular or visual motion stimuli and have observed activations that were distributed across multiple anatomical structures, including the temporo-parietal junction, retroinsula, parietal operculum, and posterior insula. However, it has remained unclear whether all of these anatomical areas correspond to PIVC and whether PIVC responds to both vestibular and visual stimuli. Recent results suggest that the region that has been referred to as PIVC in previous studies consists of multiple areas with different anatomical correlates and different functional specializations. Specifically, a vestibular but not visual area is located in the parietal operculum, close to the posterior insula, and likely corresponds to the nonhuman primate PIVC, while a visual-vestibular area is located in the retroinsular cortex and is referred to, for historical reasons, as the posterior insular cortex area (PIC). In this article, we review the anatomy, connectivity, and function of PIVC and PIC and propose that the core of the human vestibular cortex consists of at least two separate areas, which we refer to together as PIVC+. We also review the organization in the nonhuman primate brain and show that there are parallels to the proposed organization in humans.

Role of Alpha-Band Oscillations in Spatial Updating across Whole Body Motion

When moving around in the world, we have to keep track of important locations in our surroundings. In this process, called spatial updating, we must estimate our body motion and correct representations of memorized spatial locations in accordance with this motion. While the behavioral characteristics of spatial updating across whole body motion have been studied in detail, its neural implementation lacks detailed study. Here we use electroencephalography (EEG) to distinguish various spectral components of this process. Subjects gazed at a central body-fixed point in otherwise complete darkness, while a target was briefly flashed, either left or right from this point. Subjects had to remember the location of this target as either moving along with the body or remaining fixed in the world while being translated sideways on a passive motion platform. After the motion, subjects had to indicate the remembered target location in the instructed reference frame using a mouse response. While the body motion, as detected by the vestibular system, should not affect the representation of body-fixed targets, it should interact with the representation of a world-centered target to update its location relative to the body. We show that the initial presentation of the visual target induced a reduction of alpha band power in contralateral parieto-occipital areas, which evolved to a sustained increase during the subsequent memory period. Motion of the body led to a reduction of alpha band power in central parietal areas extending to lateral parieto-temporal areas, irrespective of whether the targets had to be memorized relative to world or body. When updating a world-fixed target, its internal representation shifts hemispheres, only when subjects’ behavioral responses suggested an update across the body midline. Our results suggest that parietal cortex is involved in both self-motion estimation and the selective application of this motion information to maintaining target locations as fixed in the world or fixed to the body.