The vestibular cortex. Its locations, functions, and disorders

Puddles, parties, and professors: linking word categorization to neural patterns of visuospatial coding

Behavioral evidence suggests that during word processing people spontaneously map object, valence, and power information to locations in vertical space. Specifically, whereas "overhead" (e.g., attic), positive (e.g., party), and powerful nouns (e.g., professor) are associated with "up," "underfoot" (e.g., carpet), negative (e.g., accident), and powerless nouns (e.g., assistant) are associated with "down." What has yet to be elucidated, however, is the precise nature of these effects. To explore this issue, an fMRI experiment was undertaken, during which participants were required to categorize the position in which geometrical shapes appeared on a computer screen (i.e., upper or lower part of the display). In addition, they also judged a series of words with regard to location (i.e., up vs. down), valence (i.e., good vs. bad), and power (i.e., powerful vs. powerless). Using multivoxel pattern analysis, it was found that classifiers that successfully distinguished between the positions of shapes in subregions of the inferior parietal lobe also provided discriminatory information to separate location and valence, but not power word judgments. Correlational analyses further revealed that, for location words, pattern transfer was more successful the stronger was participants' propensity to use visual imagery. These findings indicate that visual coding and conceptual processing can elicit common representations of verticality but that divergent mechanisms may support the reported effects.

The thalamocortical vestibular system in animals and humans

The vestibular system provides the brain with sensory signals about three-dimensional head rotations and translations. These signals are important for postural and oculomotor control, as well as for spatial and bodily perception and cognition, and they are subtended by pathways running from the vestibular nuclei to the thalamus, cerebellum and the "vestibular cortex." The present review summarizes current knowledge on the anatomy of the thalamocortical vestibular system and discusses data from electrophysiology and neuroanatomy in animals by comparing them with data from neuroimagery and neurology in humans. Multiple thalamic nuclei are involved in vestibular processing, including the ventroposterior complex, the ventroanterior-ventrolateral complex, the intralaminar nuclei and the posterior nuclear group (medial and lateral geniculate nuclei, pulvinar). These nuclei contain multisensory neurons that process and relay vestibular, proprioceptive and visual signals to the vestibular cortex. In non-human primates, the parieto-insular vestibular cortex (PIVC) has been proposed as the core vestibular region. Yet, vestibular responses have also been recorded in the somatosensory cortex (area 2v, 3av), intraparietal sulcus, posterior parietal cortex (area 7), area MST, frontal cortex, cingulum and hippocampus. We analyze the location of the corresponding regions in humans, and especially the human PIVC, by reviewing neuroimaging and clinical work. The widespread vestibular projections to the multimodal human PIVC, somatosensory cortex, area MST, intraparietal sulcus and hippocampus explain the large influence of vestibular signals on self-motion perception, spatial navigation, internal models of gravity, one's body perception and bodily self-consciousness.

Non-sensory inputs to angular path integration

Non-sensory (cognitive) inputs can play a powerful role in monitoring one's self-motion. Previously, we showed that access to spatial memory dramatically increases response precision in an angular self-motion updating task [1]. Here, we examined whether spatial memory also enhances a particular type of self-motion updating - angular path integration. "Angular path integration" refers to the ability to maintain an estimate of self-location after a rotational displacement by integrating internally-generated (idiothetic) self-motion signals over time. It was hypothesized that remembered spatial frameworks derived from vision and spatial language should facilitate angular path integration by decreasing the uncertainty of self-location estimates. To test this we implemented a whole-body rotation paradigm with passive, non-visual body rotations (ranging 40 degrees -140 degrees ) administered about the yaw axis. Prior to the rotations, visual previews (Experiment 1) and verbal descriptions (Experiment 2) of the surrounding environment were given to participants. Perceived angular displacement was assessed by open-loop pointing to the origin (0 degrees ). We found that within-subject response precision significantly increased when participants were provided a spatial context prior to whole-body rotations. The present study goes beyond our previous findings by first establishing that memory of the environment enhances the processing of idiothetic self-motion signals. Moreover, we show that knowledge of one's immediate environment, whether gained from direct visual perception or from indirect experience (i.e., spatial language), facilitates the integration of incoming self-motion signals.

Mechanisms of sustained high firing rates in two classes of vestibular nucleus neurons: differential contributions of resurgent Na, Kv3, and BK currents

To fire at high rates, neurons express ionic currents that work together to minimize refractory periods by ensuring that sodium channels are available for activation shortly after each action potential. Vestibular nucleus neurons operate around high baseline firing rates and encode information with bidirectional modulation of firing rates up to several hundred Hz. To determine the mechanisms that enable these neurons to sustain firing at high rates, ionic currents were measured during firing by using the action potential clamp technique in vestibular nucleus neurons acutely dissociated from transgenic mice. Although neurons from the YFP-16 line fire at rates higher than those from the GIN line, both classes of neurons express Kv3 and BK currents as well as both transient and resurgent Na currents. In the fastest firing neurons, Kv3 currents dominated repolarization at all firing rates and minimized Na channel inactivation by rapidly transitioning Na channels from the open to the closed state. In slower firing neurons, BK currents dominated repolarization at the highest firing rates and sodium channel availability was protected by a resurgent blocking mechanism. Quantitative differences in Kv3 current density across neurons and qualitative differences in immunohistochemically detected expression of Kv3 subunits could account for the difference in firing range within and across cell classes. These results demonstrate how divergent firing properties of two neuronal populations arise through the interplay of at least three ionic currents.

Structural and functional plasticity of the hippocampal formation in professional dancers and slackliners

The acquisition of special skills can induce plastic changes in the human hippocampus, a finding demonstrated in expert navigators (Maguire et al. (2000) Proc Natl Acad Sci USA 97:4,398-403). Conversely, patients with acquired chronic bilateral vestibular loss develop atrophy of the hippocampus, which is associated with impaired spatial memory (Brandt et al. (2005) Brain 128:2,732-741). This suggests that spatial memory relies on vestibular input. In this study 21 professional dancers and slackliners were examined to assess whether balance training with extensive vestibulo-visual stimulation is associated with altered hippocampal formation volumes or spatial memory. Gray matter voxel-based morphometry showed smaller volumes in the anterior hippocampal formation and in parts of the parieto-insular vestibular cortex of the trained subjects but larger volumes in the posterior hippocampal formation and the lingual and fusiform gyri bilaterally. The local volumes in the right anterior hippocampal formation correlated negatively and those in the right posterior hippocampal formation positively with the amount of time spent training ballet/ice dancing or slacklining at the time of the study. There were no differences in general memory or in spatial memory as assessed by the virtual Morris water task. Trained subjects performed significantly better on a hippocampal formation-dependent task of nonspatial memory (transverse patterning). The smaller anterior hippocampal formation volumes of the trained subjects may be the result of a long-term suppression of destabilizing vestibular input. This is supported by the associated volume loss in the parieto-insular vestibular cortex. The larger volumes in the posterior hippocampal formation of the trained subjects might result from their increased utilization of visual cues for balance. This is supported by the concomitant larger volumes in visual areas like the lingual and fusiform gyri. Our findings indicate that there is a spatial separation of vestibular and visual processes in the human hippocampus.

Evidence for modulation of opioidergic activity in central vestibular processing: A [(18)F] diprenorphine PET study

Animal and functional imaging studies had identified cortical structures such as the parieto-insular vestibular cortex, the retro-insular cortex, or the anterior cingulate cortex belonging to a vestibular cortical network. Basic animal studies revealed that endorphins might be important transmitters involved in cerebral vestibular processing. The aim of the present study was therefore to analyse whether the opioid system is involved in vestibular neurotransmission of humans or not. Changes in opioid receptor availability during caloric air stimulation of the right ear were studied with [(18)F] Fluoroethyl-diprenorphine ([(18)F]FEDPN) PET scans in 10 right-handed healthy volunteers and compared to a control condition. Decrease in receptor availability to [(18)F]FEDPN during vestibular stimulation in comparison to the control condition was significant at the right posterior insular cortex and the postcentral region indicating more endogenous opioidergic binding in these regions during stimulation. These data give evidence that the opioidergic system plays a role in the right hemispheric dominance of the vestibular cortical system in right-handers.

Macaque parieto-insular vestibular cortex: responses to self-motion and optic flow

The parieto-insular vestibular cortex (PIVC) is thought to contain an important representation of vestibular information. Here we describe responses of macaque PIVC neurons to three-dimensional (3D) vestibular and optic flow stimulation. We found robust vestibular responses to both translational and rotational stimuli in the retroinsular (Ri) and adjacent secondary somatosensory (S2) cortices. PIVC neurons did not respond to optic flow stimulation, and vestibular responses were similar in darkness and during visual fixation. Cells in the upper bank and tip of the lateral sulcus (Ri and S2) responded to sinusoidal vestibular stimuli with modulation at the first harmonic frequency and were directionally tuned. Cells in the lower bank of the lateral sulcus (mostly Ri) often modulated at the second harmonic frequency and showed either bimodal spatial tuning or no tuning at all. All directions of 3D motion were represented in PIVC, with direction preferences distributed approximately uniformly for translation, but showing a preference for roll rotation. Spatiotemporal profiles of responses to translation revealed that half of PIVC cells followed the linear velocity profile of the stimulus, one-quarter carried signals related to linear acceleration (in the form of two peaks of direction selectivity separated in time), and a few neurons followed the derivative of linear acceleration (jerk). In contrast, mainly velocity-coding cells were found in response to rotation. Thus, PIVC comprises a large functional region in macaque areas Ri and S2, with robust responses to 3D rotation and translation, but is unlikely to play a significant role in visual/vestibular integration for self-motion perception.

Headache-associated dizziness in a headache population: Prevalence and impact

Headache is an underestimated burden on general health and social functioning. Accompanying symptoms of headache episodes might influence this impact. In a survey in a headache population in Luxembourg on the social and emotional impact of headaches, accompanying symptoms of headache episodes were evaluated. In 1909 participants with episodic (<15 days per month) headaches (77.1% women), visual symptoms (52.4%) and dizziness (51.1%) were frequent accompanying symptoms of headache episodes. Visual symptoms and dizziness were each independently associated with migraine in both genders and independently associated with greater headache-related disability (scored on the Migraine Disability Scale [MIDAS]), more severe depression, and higher disability as measured by the disease-independent World Health Organization Disability Assessment Schedule (WHODAS). We found that dizziness is a frequent accompanying symptom of headache, particularly in migraine. The presence of dizziness was found to have an exacerbating impact on disability and depression associated with headaches. The effect of dizziness was comparable in magnitude and independent from the presence of visual symptoms.

How vestibular stimulation interacts with illusory hand ownership

Artificial stimulation of the peripheral vestibular system has been shown to improve ownership of body parts in neurological patients, suggesting vestibular contributions to bodily self-consciousness. Here, we investigated whether galvanic vestibular stimulation (GVS) interferes with the mechanisms underlying ownership, touch, and the localization of one's own hand in healthy participants by using the "rubber hand illusion" paradigm. Our results show that left anodal GVS increases illusory ownership of the fake hand and illusory location of touch. We propose that these changes are due to vestibular interference with spatial and/or temporal mechanisms of visual-tactile integration leading to an enhancement of visual capture. As only left anodal GVS lead to such changes, and based on neurological data on body part ownership, we suggest that this vestibular interference is mediated by the right temporo-parietal junction and the posterior insula.

Phase-linking and the perceived motion during off-vertical axis rotation

Human off-vertical axis rotation (OVAR) in the dark typically produces perceived motion about a cone, the amplitude of which changes as a function of frequency. This perception is commonly attributed to the fact that both the OVAR and the conical motion have a gravity vector that rotates about the subject. Little-known, however, is that this rotating-gravity explanation for perceived conical motion is inconsistent with basic observations about self-motion perception: (a) that the perceived vertical moves toward alignment with the gravito-inertial acceleration (GIA) and (b) that perceived translation arises from perceived linear acceleration, as derived from the portion of the GIA not associated with gravity. Mathematically proved in this article is the fact that during OVAR these properties imply mismatched phase of perceived tilt and translation, in contrast to the common perception of matched phases which correspond to conical motion with pivot at the bottom. This result demonstrates that an additional perceptual rule is required to explain perception in OVAR. This study investigates, both analytically and computationally, the phase relationship between tilt and translation at different stimulus rates-slow (45 degrees /s) and fast (180 degrees /s), and the three-dimensional shape of predicted perceived motion, under different sets of hypotheses about self-motion perception. We propose that for human motion perception, there is a phase-linking of tilt and translation movements to construct a perception of one's overall motion path. Alternative hypotheses to achieve the phase match were tested with three-dimensional computational models, comparing the output with published experimental reports. The best fit with experimental data was the hypothesis that the phase of perceived translation was linked to perceived tilt, while the perceived tilt was determined by the GIA. This hypothesis successfully predicted the bottom-pivot cone commonly reported and a reduced sense of tilt during fast OVAR. Similar considerations apply to the hilltop illusion often reported during horizontal linear oscillation. Known response properties of central neurons are consistent with this ability to phase-link translation with tilt. In addition, the competing "standard" model was mathematically proved to be unable to predict the bottom-pivot cone regardless of the values used for parameters in the model.

Processing of Targets in Smooth or Apparent Motion Along the Vertical in the Human Brain: An fMRI Study

Neural substrates for processing constant speed visual motion have been extensively studied. Less is known about the brain activity patterns when the target speed changes continuously, for instance under the influence of gravity. Using functional MRI (fMRI), here we compared brain responses to accelerating/decelerating targets with the responses to constant speed targets. The target could move along the vertical under gravity (1 g), under reversed gravity (−1 g), or at constant speed (0 g). In the first experiment, subjects observed targets moving in smooth motion and responded to a GO signal delivered at a random time after target arrival. As expected, we found that the timing of the motor responses did not depend significantly on the specific motion law. Therefore brain activity in the contrast between different motion laws was not related to motor timing responses. Average BOLD signals were significantly greater for 1 g targets than either 0 g or −1 g targets in a distributed network including bilateral insulae, left lingual gyrus, and brain stem. Moreover, in these regions, the mean activity decreased monotonically from 1 g to 0 g and to −1 g. In the second experiment, subjects intercepted 1 g, 0 g, and −1 g targets either in smooth motion (RM) or in long-range apparent motion (LAM). We found that the sites in the right insula and left lingual gyrus, which were selectively engaged by 1 g targets in the first experiment, were also significantly more active during 1 g trials than during −1 g trials both in RM and LAM. The activity in 0 g trials was again intermediate between that in 1 g trials and that in −1 g trials. Therefore in these regions the global activity modulation with the law of vertical motion appears to hold for both RM and LAM. Instead, a region in the inferior parietal lobule showed a preference for visual gravitational motion only in LAM but not RM.

Sensitivity of human visual and vestibular cortical regions to egomotion-compatible visual stimulation

The analysis and representation of visual cues to self-motion (egomotion) is primarily associated with cortical areas MST, VIP, and (recently) cingulate sulcus visual area (CSv). Various other areas, including visual areas V6 and V6A, and vestibular areas parietoinsular vestibular cortex (PIVC), putative area 2v (p2v), and 3aNv, are also potentially suited to processing egomotion (in some cases based on multisensory cues), but it is not known whether they are in fact involved in this process. In a functional magnetic resonance imaging (fMRI) experiment, we presented human participants with 2 types of random dot kinematograms. Both contained coherent motion but one simulated egomotion while the other did not. An area in the parieto-occipital sulcus that may correspond to V6, PIVC, and p2v were all differentially responsive to egomotion-compatible visual stimuli, suggesting that they may be involved in encoding egomotion. More generally, we show that the use of such stimuli provides a simple and reliable fMRI localizer for human PIVC and p2v, which hitherto required galvanic or caloric stimulation to be identified.

A vestibular sensation: probabilistic approaches to spatial perception

The vestibular system helps maintain equilibrium and clear vision through reflexes, but it also contributes to spatial perception. In recent years, research in the vestibular field has expanded to higher-level processing involving the cortex. Vestibular contributions to spatial cognition have been difficult to study because the circuits involved are inherently multisensory. Computational methods and the application of Bayes theorem are used to form hypotheses about how information from different sensory modalities is combined together with expectations based on past experience in order to obtain optimal estimates of cognitive variables like current spatial orientation. To test these hypotheses, neuronal populations are being recorded during active tasks in which subjects make decisions based on vestibular and visual or somatosensory information. This review highlights what is currently known about the role of vestibular information in these processes, the computations necessary to obtain the appropriate signals, and the benefits that have emerged thus far.

Roll-dependent modulation of the subjective visual vertical: contributions of head- and trunk-based signals

Precision and accuracy of the subjective visual vertical (SVV) modulate in the roll plane. At large roll angles, systematic SVV errors are biased toward the subject's body-longitudinal axis and SVV precision is decreased. To explain this, SVV models typically implement a bias signal, or a prior, in a head-fixed reference frame and assume the sensory input to be optimally tuned along the head-longitudinal axis. We tested the pattern of SVV adjustments both in terms of accuracy and precision in experiments in which the head and the trunk reference frames were not aligned. Twelve subjects were placed on a turntable with the head rolled about 28 degrees counterclockwise relative to the trunk by lateral tilt of the neck to dissociate the orientation of head- and trunk-fixed sensors relative to gravity. Subjects were brought to various positions (roll of head- or trunk-longitudinal axis relative to gravity: 0 degrees , +/-75 degrees ) and aligned an arrow with perceived vertical. Both accuracy and precision of the SVV were significantly (P < 0.05) better when the head-longitudinal axis was aligned with gravity. Comparing absolute SVV errors for clockwise and counterclockwise roll tilts, statistical analysis yielded no significant differences (P > 0.05) when referenced relative to head upright, but differed significantly (P < 0.001) when referenced relative to trunk upright. These findings indicate that the bias signal, which drives the SVV toward the subject's body-longitudinal axis, operates in a head-fixed reference frame. Further analysis of SVV precision supports the hypothesis that head-based graviceptive signals provide the predominant input for internal estimates of visual vertical.

Mal de debarquement

Mal de debarquement (MdD), the "sickness of disembarkment," occurs when habituation to background rhythmic movement becomes resistant to readaption to stable conditions and results in a phantom perception of self motion typically described as rocking, bobbing, or swaying. Although several studies have shown that brief periods of MdD are common in healthy individuals, this otherwise natural phenomenon can become persistent in some individuals and lead to severe balance problems. Increased recognition of MdD in a persistent pathological form occurred after the publication of a case series of six patients by Brown and Baloh in 1987. Over 20 years later, although more is known about the clinical syndrome of persistent MdD, little is known about what leads to this persistence. This review addresses the clinical features of MdD, the associated symptoms in the persistent form, theories on pathogenesis, experience with treatment, and future directions for research.

Virtual reality and the role of the prefrontal cortex in adults and children

In this review, the neural underpinnings of the experience of presence are outlined. Firstly, it is shown that presence is associated with activation of a distributed network, which includes the dorsal and ventral visual stream, the parietal cortex, the premotor cortex, mesial temporal areas, the brainstem and the thalamus. Secondly, the dorsolateral prefrontal cortex (DLPFC) is identified as a key node of the network as it modulates the activity of the network and the associated experience of presence. Thirdly, children lack the strong modulatory influence of the DLPFC on the network due to their unmatured frontal cortex. Fourthly, it is shown that presence-related measures are influenced by manipulating the activation in the DLPFC using transcranial direct current stimulation (tDCS) while participants are exposed to the virtual roller coaster ride. Finally, the findings are discussed in the context of current models explaining the experience of presence, the rubber hand illusion, and out-of-body experiences.

Perceived timing of vestibular stimulation relative to touch, light and sound

Different senses have different processing times. Here we measured the perceived timing of galvanic vestibular stimulation (GVS) relative to tactile, visual and auditory stimuli. Simple reaction times for perceived head movement (438 +/- 49 ms) were significantly longer than to touches (245 +/- 14 ms), lights (220 +/- 13 ms), or sounds (197 +/- 13 ms). Temporal order and simultaneity judgments both indicated that GVS had to occur about 160 ms before other stimuli to be perceived as simultaneous with them. This lead was significantly less than the relative timing predicted by reaction time differences compatible with an incomplete tendency to compensate for differences in processing times.

The vestibular component in out-of-body experiences: a computational approach

Neurological evidence suggests that disturbed vestibular processing may play a key role in triggering out-of-body experiences (OBEs). Little is known about the brain mechanisms during such pathological conditions, despite recent experimental evidence that the scientific study of such experiences may facilitate the development of neurobiological models of a crucial aspect of self-consciousness: embodied self-location. Here we apply Bayesian modeling to vestibular processing and show that OBEs and the reported illusory changes of self-location and translation can be explained as the result of a mislead Bayesian inference, in the sense that ambiguous bottom-up signals from the vestibular otholiths in the supine body position are integrated with a top-down prior for the upright body position, which we measure during natural head movements. Our findings have relevance for self-location and translation under normal conditions and suggest novel ways to induce and study experimentally both aspects of bodily self-consciousness in healthy subjects.

Vestibular syndrome: a change in internal spatial representation

The vestibular system contributes to a wide range of functions from reflexes to spatial representation. This paper reviews behavioral, perceptive, and cognitive data that highlight the role of changes in internal spatial representation on the vestibular syndrome. Firstly, we review how visual vertical perception and postural orientation depend on multiple reference frames and multisensory integration and how reference frames are selected according to the status of the peripheral vestibular system (i.e., unilateral or bilateral hyporeflexia), the environmental constraints (i.e., sensory cues), and the postural constraints (i.e., balance control). We show how changes in reference frames are able to modify vestibular lesion-induced postural and locomotor deficits and propose that fast changes in reference frame may be considered as fast-adaptive processes after vestibular loss. Secondly, we review data dealing with the influence of vestibular loss on higher levels of internal representation sustaining spatial orientation and navigation. Particular emphasis is placed on spatial performance according to task complexity (i.e., the required level of spatial knowledge) and to the sensory cues available to define the position and orientation within the environment (i.e., real navigation in darkness or visual virtual navigation without any actual self-motion). We suggest that vestibular signals are necessary for other sensory cues to be properly integrated and that vestibular cues are involved in extrapersonal space representation. In this respect, vestibular-induced changes would be based on a dynamic mental representation of space that is continuously updated and that supports fast-adaptive processes.

[Chronic dizziness in elderly people: its clinical characteristics and magneto-encephalographic findings]

Many elderly people complain dizziness which may continue occasionally for months or years. According to epidemiological studies, 25-29% of subjects with more than 60 years of age have the experience of dizziness. Dizziness occurs most commonly during head positional changes or walking. Clinical studies have indicated that causes of dizziness are nonspecific and multi-factorial; cerebrovascular diseases, cervical spondylosis, depressive state, poor vision, orthostatic hypotension, whiplash injury, or low cerebrospinal fluid syndrome may play a role in the development of dizziness. Patients with dizziness commonly have neck/shoulder pain, insomnia, left-right imbalance of visual acuity, scoliosis, white matter lesions on head MRI. Little, however, has yet been known as to how these symptoms and radiological findings are related to mechanisms of dizziness. During the last several years, we performed cerebral functional studies using auditory-evoked magneto-encephalography (MEG) in elderly people with chronic dizziness. Two types of functional abnormalities were found in dizziness patients. One is a rotational abnormality of MEG signals at the temporal cortex (Type A) which can be detected by current arrow mapping analysis. This abnormality is similar to that detected by non-evoked MEG in temporal lobe epilepsy patients. In patients with Type A abnormality, administration of anticonvulsants brought about dramatic improvement of dizziness in association with disappearance of rotational abnormalities. The other is abnormal prolongation of interhemispheric neural conduction time (INCT) between the left and right temporal cortices (Type B) which can be estimated from the difference of left and right N100 m peak latencies. The INCT was found to be prolonged correlating with the grade of white matter lesions on MRI. The INCT also seems to be prolonged by lack of sleep. Patients with Type B abnormality commonly have the asymmetry of body, such as left-right imbalance of visual acuity, left-right neck pain, or remarkable scoliosis, in association with insomnia and/or depressive state. According to the study of Penfield, dizziness or vertigo is manifested by stimulation of upper temporal cortex and lower parietal cortex. Mechanisms of dizziness can be hypothecated on the basis of MEG findings as follows: Presumably, there are head-position recognizing (HPR) centers in the left and right cerebral hemispheres. The HPR centers may correspond to the vestibular cortex or the combined system of vestibular, visual and somatosensory cortices. The HPR centers in two hemispheres are receiving head-position signals from vestibular, visual and somatosensory corices and are readjusting the dissociation of information which may exist between each other through rapid interhemispheric neural conduction. In patients with Type A abnormality, dizziness may be caused by abnormal neuronal excitements in left or right HPR center. In patients with Type B abnormalities, dizziness may be caused by the combined factors, one the abnormal prolongation of INCT between left and right HPR centers and the other the large dissociation of head position signals between the left and right HPR centers due to the body asymmetry, such as scoliosis or left-right neck pain imbalance.

The posterior cingulate cortex and planum temporale/parietal operculum are activated by coherent visual motion

The posterior cingulate cortex (PCC) is involved in higher order sensory and sensory-motor integration while the planum temporale/parietal operculum (PT/PO) junction takes part in auditory motion and vestibular processing. Both regions are activated during different types of visual stimulation. Here, we describe the response characteristics of the PCC and PT/PO to basic types of visual motion stimuli of different complexity (complex and simple coherent as well as incoherent motion). Functional magnetic resonance imaging (fMRI) was performed in 10 healthy subjects at 3 Tesla, whereby different moving dot stimuli (vertical, horizontal, rotational, radial, and random) were contrasted against a static dot pattern. All motion stimuli activated a distributed cortical network, including previously described motion-sensitive striate and extrastriate visual areas. Bilateral activations in the dorsal region of the PCC (dPCC) were evoked using coherent motion stimuli, irrespective of motion direction (vertical, horizontal, rotational, radial) with increasing activity and with higher complexity of the stimulus. In contrast, the PT/PO responded equally well to all of the different coherent motion types. Incoherent (random) motion yielded significantly less activation both in the dPCC and in the PT/PO area. These results suggest that the dPCC and the PT/PO take part in the processing of basic types of visual motion. However, in dPCC a possible effect of attentional modulation resulting in the higher activity evoked by the complex stimuli should also be considered. Further studies are warranted to incorporate these regions into the current model of the cortical motion processing network.

Retention of habituation of vestibulo-ocular reflex and sensation of rotation in humans

In humans, habituation of vestibulo-ocular reflex (VOR) by repeated caloric or rotational stimulation has been well documented. However, less attention has been directed to the effect of habituation on the sensation of self-rotation and little is known about the retention duration of vestibular habituation. To investigate these characteristics, subjects were exposed to ten sessions of angular velocity steps in yaw, with a chair rotating either alternatively in both CW and CCW directions (bidirectional protocol) or always in the same direction (unidirectional protocol), i.e., CW or CCW. The retention of habituation of VOR and sensation of rotation induced by both protocols was studied for a period up to 8 months following the end of the habituation protocols. There was a progressive decline in the VOR peak slow phase velocity and time constant throughout the sessions during both protocols. These parameters then followed an exponential recovery with a time constant of about 1 month. The duration of the sensation of rotation also habituated during repeated angular velocity steps, but it was shorter for both directions of stimulation, including after the unidirectional protocol. Sinusoidal VOR gain was not affected by vestibular habituation to velocity steps, but sinusoidal VOR phase showed an increase in phase lead at 0.02 and 0.04 Hz, which also returned to baseline values within about 1 month. We conclude that vestibular habituation is a long-lasting phenomenon. These results may be helpful for designing and scheduling the protocols for drug studies using crossover design, rehabilitation of balance disorder patients, and for the application of intermittent artificial gravity during space missions.

Functional brain imaging of peripheral and central vestibular disorders

This review summarizes our current knowledge of multisensory vestibular structures and their functions in humans. Most of it derives from brain activation studies with PET and fMRI conducted over the last decade. The patterns of activations and deactivations during caloric and galvanic vestibular stimulations in healthy subjects have been compared with those in patients with acute and chronic peripheral and central vestibular disorders. Major findings are the following: (1) In patients with vestibular neuritis the central vestibular system exhibits a spontaneous visual-vestibular activation-deactivation pattern similar to that described in healthy volunteers during unilateral vestibular stimulation. In the acute stage of the disease regional cerebral glucose metabolism (rCGM) increases in the multisensory vestibular cortical and subcortical areas, but simultaneously it significantly decreases in the visual and somatosensory cortex areas. (2) In patients with bilateral vestibular failure the activation-deactivation pattern during vestibular caloric stimulation shows a decrease of activations and deactivations. (3) Patients with lesions of the vestibular nuclei due to Wallenberg's syndrome show no activation or significantly reduced activation in the contralateral hemisphere during caloric irrigation of the ear ipsilateral to the lesioned side, but the activation pattern in the ipsilateral hemisphere appears 'normal'. These findings indicate that there are bilateral ascending vestibular pathways from the vestibular nuclei to the vestibular cortex areas, and the contralateral tract crossing them is predominantly affected. (4) Patients with posterolateral thalamic infarctions exhibit significantly reduced activation of the multisensory vestibular cortex in the ipsilateral hemisphere, if the ear ipsilateral to the thalamic lesion is stimulated. Activation of similar areas in the contralateral hemisphere is also diminished but to a lesser extent. These data demonstrate the functional importance of the posterolateral thalamus as a vestibular gatekeeper. (5) In patients with vestibulocerebellar lesions due to a bilateral floccular deficiency, which causes downbeat nystagmus (DBN), PET scans reveal that rCGM is reduced in the region of the cerebellar tonsil and flocculus/paraflocculus bilaterally. Treatment with 4-aminopyridine lessens this hypometabolism and significantly improves DBN. These findings support the hypothesis that the (para-) flocculus and tonsil play a crucial role in DBN. Although we can now for the first time attribute particular activations and deactivations to functional deficits in distinct vestibular disorders, the complex puzzle of the various multisensory and sensorimotor functions of the phylogenetically ancient vestibular system is only slowly being unraveled.

A source analysis of short-latency vestibular evoked potentials produced by air- and bone-conducted sound

OBJECTIVE

To map short-latency vestibular evoked potentials (VsEPs) using air- (AC) and bone-conducted (BC) sound and to perform source analysis to determine their origin.

METHODS

Ten normal volunteers, chosen to have low-normal thresholds for acoustic vestibular activation, participated. In the first part, the subjects' individual thresholds for vestibular activation (V(T)) were established using vestibular evoked myogenic potentials (VEMPs) recorded from the sternocleidomastoid muscles. AC sound was delivered with headphones and BC sound with a commercial B71 bone vibrator. In the second part, VsEPs were recorded using Ag/AgCl scalp electrodes in a 10-20 montage supplemented by infra-ocular, mastoid and cerebellar electrodes. Stimuli were 2ms pips, consisting of a single cycle of 500 Hz, presented at +18 dB re V(T) ("vestibular" condition) and -3 dB re V(T) (control condition).

RESULTS

Following the control stimulus, auditory mid-latency responses (MLRs) were observed. In the vestibular condition, two dominant groups of non-MLR potentials of presumed vestibular origin appeared (vestibular evoked potentials, or VsEPs), which consisted of a P10-N17 complex maximal at Pz, and an N15-P21 complex maximal at Fpz. Large potentials were also recorded from the infra-ocular electrodes at similar latencies. Source analysis indicated that the two complexes were largely accounted for by a combination of ocular vestibular evoked myogenic potentials (OVEMPs) and sub-cortical sources (possibly vestibular cerebellum), with a smaller contribution from anterior cortical and other myogenic sources.

CONCLUSIONS

Both the N15 and P10 potentials appear to receive an ocular myogenic contribution but both appear also to receive a contribution from other central structures.

SIGNIFICANCE

The P10 and N15 complexes appear to represent the activity of otolith-dependent projections.

Sympathetic arousal to a vestibular stressor in high and low hostile men

The aim of the present experiment was to extend the literature on hostility and a cerebral systems based model of sympathetic arousal to a vestibular-based stress. Several authors have concluded that autonomic stress reactivity in high hostile individuals must be interpersonally based, whereas healthy vestibular system functioning does not depend on interpersonal features. Utilizing a vestibular activation paradigm, skin conductance levels of 15 high hostile and 15 low hostile men were recorded after brief passive rotation about the vertical neuroaxis. It was expected that hostile individuals would exhibit higher skin conductance levels after rotation compared with low hostile individuals. The results confirmed expectations of heightened sympathetic tone among high hostiles subsequent to vestibular stress. Overall, the findings are interpreted to support a cerebral model of frontal region capacity limitation for regulation of vestibular stress that is independent of psychosocial mechanisms.

Central processes amplify and transform anisotropies of the visual system in a test of visual-haptic coordination

The CNS may use multimodal reference frames to combine proprioceptive, visual, and gravitational information. Indeed, spatial information could be encoded simultaneously with respect to egocentric and allocentric references such as the body axis and gravity, respectively. It has further been proposed that gravity might serve to align reference frames between different sensory modalities. We performed a series of experiments in which human subjects matched the orientation of a visual stimulus to a visual reference (visual-visual), a haptic stimulus to a haptic reference (haptic-haptic), or a visual stimulus to a haptic reference (visual-haptic). These tests were performed in a normal upright posture, with the body tilted with respect to gravity, and in the weightless environment of Earth orbit. We found systematic patterns of errors in the matching of stimulus orientations. For an upright posture on Earth, a classic oblique effect appeared in the visual-visual comparison, which was then amplified in the haptic-visual task. Leftward or rightward whole-body tilt on Earth abolished both of these effects, yet each persisted in the absence of gravity. Leftward and rightward tilt also produced asymmetric biases in the visual-haptic but not in the visual-visual or haptic-haptic responses. These results illustrate how spatial anisotropy can be molded by sensorimotor transformations in the CNS. Furthermore, the results indicate that gravity plays a significant, but nonessential role in defining the reference frames for these tasks. These results provide insight into how the nervous system processes spatial information between different sensory modalities.

Supraspinal locomotor control in quadrupeds and humans

Locomotion in humans and other vertebrates is based on spinal pattern generators, which are regulated by supraspinal control. Most of our knowledge about the hierarchical network of supraspinal locomotion centres derives from animal experiments, mainly in the cat. Here we summarize evidence that the supraspinal network of quadrupeds is conserved in humans despite their transition to bipedalism. By use of mental imagery of locomotion in fMRI we found (1), locomotion modulates sensory systems and is itself modulated by sensory signals. During automated locomotion in healthy subjects cortical sensory inhibition occurs in vestibular and somatosensory areas; this inhibition is cancelled in the congenitally blind; (2), we delineated separate and distinct areas in the brainstem and cerebellum which are remarkably similar to the feline locomotor network. The activations found here include homologues to the pacemakers for gait initiation and speed regulation in the interfastigial cerebellum and bilateral midbrain tegmentum (cerebellar and mesencephalic locomotor regions), their descending target regions in the pontine reticular formation, and the rhythm generators in the cerebellar vermis and paravermal cerebellar cortex. This conservation of the basic organization of supraspinal locomotor control during vertebrate phylogeny opens new perspectives for both, the diagnosis and treatment of common gait disorders. It is conceivable that electrical stimulation of locomotor brain stem centres may initiate and improve gait in selected patients suffering from Parkinson's disease or progressive supranuclear palsy.

Shared computational mechanism for tilt compensation accounts for biased verticality percepts in motion and pattern vision

To determine the direction of object motion in external space, the brain must combine retinal motion signals and information about the orientation of the eyes in space. We assessed the accuracy of this process in eight laterally tilted subjects who aligned the motion direction of a random-dot pattern (30% coherence, moving at 6 degrees /s) with their perceived direction of gravity (motion vertical) in otherwise complete darkness. For comparison, we also tested the ability to align an adjustable visual line (12 degrees diameter) to the direction of gravity (line vertical). For small head tilts (<40 degrees ), systematic errors in either task were almost negligible. In contrast, tilts >60 degrees revealed a pattern of large systematic errors (often >30 degrees ) that was virtually identical in both tasks. Regression analysis confirmed that mean errors in the two tasks were closely related, with slopes close to 1.0 and correlations >0.89. Control experiments ruled out that motion settings were based on processing of individual single-dot paths. We conclude that the conversion of both motion direction and line orientation on the retina into a spatial frame of reference involves a shared computational strategy. Simulations with two spatial-orientation models suggest that the pattern of systematic errors may be the downside of an optimal strategy for dealing with imperfections in the tilt signal that is implemented before the reference-frame transformation.

The use of tDCS and CVS as methods of non-invasive brain stimulation

Transcranial direct current stimulation (tDCS) and caloric vestibular stimulation (CVS) are safe methods for selectively modulating cortical excitability and activation, respectively, which have recently received increased interest regarding possible clinical applications. tDCS involves the application of low currents to the scalp via cathodal and anodal electrodes and has been shown to affect a range of motor, somatosensory, visual, affective and cognitive functions. Therapeutic effects have been demonstrated in clinical trials of tDCS for a variety of conditions including tinnitus, post-stroke motor deficits, fibromyalgia, depression, epilepsy and Parkinson's disease. Its effects can be modulated by combination with pharmacological treatment and it may influence the efficacy of other neurostimulatory techniques such as transcranial magnetic stimulation. CVS involves irrigating the auditory canal with cold water which induces a temperature gradient across the semicircular canals of the vestibular apparatus. This has been shown in functional brain-imaging studies to result in activation in several contralateral cortical and subcortical brain regions. CVS has also been shown to have effects on a wide range of visual and cognitive phenomena, as well as on post-stroke conditions, mania and chronic pain states. Both these techniques have been shown to modulate a range of brain functions, and display potential as clinical treatments. Importantly, they are both inexpensive relative to other brain stimulation techniques such as electroconvulsive therapy (ECT) and transcranial magnetic stimulation (TMS).

Why cold water delays the onset of vestibular vertigo--an functional MRI study

The mechanism of vertigo is unclear. Generally, the peak time or the latency of blood oxygenation level dependent (BOLD) effect is about 6s. However, clinically, the latency of vertigo or nystagmus induced by caloric stimulations is much longer than 6s, commonly about 30s induced by water of 30 degrees C or 44 degrees C. We hypothesize that there is an inhibitive power or mechanism for the occurrence of vestibular vertigo, since it is an unpleasant feeling. The caloric test was performed in healthy volunteers during the BOLD fMRI scanning. The overlaid results of statistical parametric mapping (SPM) showed that three brain regions showed neural activation during vestibular dizziness while deactivation occurred in response to cold water simulation: (1) supplementary motor area (SMA); (2) middle temporal area/medial superior temporal area (MT/MST); (3) visual association area (BA19). The time course of the regions further demonstrated that the signal decreased during the cold-water stimulation and increased during the period of vertigo. We therefore further hypothesize that there may be two forces for the production of vertigo: inhibitory power (IP) and promotive power (PP). The delayed onset of vertigo was the result of the interaction between IP and PP. All of our findings, for the first time, suggested such an original mechanism of vertigo.

Experimental remission of unilateral spatial neglect

Over the past several decades a growing amount of research has focused on the possibility of transiently reducing left neglect signs in right brain-damaged patients by using vestibular and/or visuo-proprioceptive stimulations. Here we review seminal papers dealing with these visuo-vestibulo-proprioceptive stimulations in normal controls, right brain-damaged (RBD) patients, and animals. We discuss these data in terms of clinical implications but also with regards to theoretical frameworks commonly used to explain the unilateral neglect syndrome. We undermine the effect of these stimulations on the position of the egocentric reference and extend the notion that the positive effects of these stimulation techniques may stem from a reorientation of attention towards the neglected side of space or from a recalibration of sensori-motor correlations. We conclude this review with discussing the possible interaction between experimental rehabilitation, models of neglect and basic spatial cognition research.

Rapid relief of thalamic pain syndrome induced by vestibular caloric stimulation

Central post-stroke pain syndrome develops in a minority of patients following a stroke. The most usual causative lesion involves the lateral thalamus. The classic presentation is of severe, unrelenting pain that involves the entire contralateral half of the body. It is largely refractory to current treatments. We found that in two patients with this condition their pain was substantially improved by vestibular caloric stimulation, whereas placebo procedures had no effect. We proposed that this is because vestibular stimulation activates the posterior insula, which in turn inhibits the generation of pain in the anterior cingulate.

Spatial memory and hippocampal volume in humans with unilateral vestibular deafferentation

Patients with acquired chronic bilateral vestibular loss were recently found to have a significant impairment in spatial memory and navigation when tested with a virtual Morris water task. These deficits were associated with selective and bilateral atrophy of the hippocampus, which suggests that spatial memory and navigation also rely on vestibular input. In the present study 16 patients with unilateral vestibular deafferentation due to acoustic neurinoma were examined 5- to 13-yrs post-surgery. Volumetry of the hippocampus was performed in patients and age- and sex-matched healthy controls by manually tracing the structure and by an evaluator-independent voxel-based morphometry. Spatial memory and navigation were assessed with a virtual Morris water task. No significant deficits in spatial memory and navigation could be demonstrated in the patients with left vestibular failure, whereas patients with right vestibular loss showed a tendency to perform worse on the respective tests. Impairment was significant only for one computed measure (heading error). The subtle deficiencies with right vestibular loss are compatible with the recently described dominance of the right labyrinth and the vestibular cortex in the right hemisphere. Volumetry did not reveal any atrophy of the hippocampus in either patient group.

Can vestibular caloric stimulation be used to treat Dejerine–Roussy Syndrome?

Dejerine-Roussy Syndrome (thalamic pain syndrome) is characterised by the development of chronic, severe pain in the contralateral half of the body after a thalamic stroke. It is often largely refractory to treatment. In this paper we draw together a number of disparate pieces of knowledge to propose a novel therapy for this condition. There is already substantial evidence from neurological disease that the brain's left hemisphere serves to "smooth over" discrepancies in sensory input in order to impose order and maintain the existing view of the world around us. Conversely the right hemisphere acts on discrepant sensory input to cause a re-evaluation of one's world view. Based on this, it was proposed by Harris that pain is an organism's response to discrepancy. It is already known that cold water vestibular caloric irrigation of the ear leads to activation of a number of areas in the contralateral hemisphere - including the insular cortex. Indeed it is known that - presumably because it also activates the right parietal lobe - this technique can be used to treat anosognosia, somatoparaphrenia and neglect. In addition to being activated by vestibular stimulation, it has been shown that the posterior insula has a somatotopic map of the body for painful stimuli. We speculate that phylogenetically, close anatomical proximity between the pain and vestibular areas of the brain makes sense; as it would allow modulation of otherwise disabling chronic pain, when the organism makes a sudden movement to avoid a predator. Given Harris's theory we propose that post stroke thalamic pain may represent a pathological amplification of the thalamic posterior insular response to pain due to discrepant sensory input. Based on all the above we go on to hypothesise that cold vestibular caloric stimulation will be effective in treating Dejerine-Roussy Syndrome and we present provisional evidence from two patients which supports this conclusion. If our hypothesis is correct this will be the first time in clinical neurology that a chronic disorder, long considered refractory to treatment, is relieved by a simple non-invasive procedure.

Effect of gravity on human spontaneous 10-Hz electroencephalographic oscillations during the arrest reaction

Electroencephalographic oscillations at 10 Hz (alpha and mu rhythms) are the most prominent rhythms observed in awake, relaxed (eye-closed) subjects. These oscillations may be considered as a marker of cortical inactivity or an index of the active inhibition of the sensory information. Different cortical sources may participate in the 10-Hz oscillation and appear to be modulated by the sensory context and functional demands. In microgravity, the marked reduction in multimodal graviceptive inputs to cortical networks participating in the representation of space could be expected to affect the 10-Hz activity. The effect of microgravity on this basic oscillation has heretofore not been studied quantitatively. Because the alpha rhythm has a functional role in the regulation of network properties of the visual areas, we hypothesised that the absence of gravity would affect its strength. Here, we report the results of an experiment conducted over the course of 3 space flights, in which we quantified the power of the 10-Hz activity in relation to the arrest reaction (i.e., in 2 distinct physiological states: eyes open and eyes closed). We observed that the power of the spontaneous 10-Hz oscillation recorded in the eyes-closed state in the parieto-occipital (alpha rhythm) and sensorimotor areas (mu rhythm) increased in the absence of gravity. The suppression coefficient during the arrest reaction and the related spectral perturbations produced by eye-opening/closure state transition also increased in on orbit. These results are discussed in terms of current theories on the source and the importance of the alpha rhythm for cognitive function.

Identifying human parieto-insular vestibular cortex using fMRI and cytoarchitectonic mapping

The parieto-insular vestibular cortex (PIVC) plays a central role in the cortical vestibular network. Although this region was first defined and subsequently extensively studied in nonhuman primates, there is also ample evidence for a human analogue in the posterior parietal operculum. In this study, we functionally and anatomically characterize the putative human equivalent to macaque area PIVC by combining functional magnetic resonance imaging (fMRI) of the cortical response to galvanic vestibular stimulation (GVS) with probabilistic cytoarchitectonic maps of the human parietal operculum. Our fMRI data revealed a bilateral cortical response to GVS in posterior parieto-insular cortex. Based on the topographic similarity of these activations to primate area PIVC, we suggest that they constitute the functionally defined human equivalent to macaque area PIVC. The locations of these activations were then compared to the probabilistic cytoarchitectonic maps of the parietal operculum (Eickhoff et al. [2005a]: Cereb Cortex, in press; Eickhoff et al. [2005c]: Cereb Cortex, in press), whereby the functionally defined PIVC matched most closely the cytoarchitectonically defined area OP 2. This activation of OP 2 by vestibular stimulation and its cytoarchitectonic features, which are similar to other primary sensory areas, suggest that area OP 2 constitutes the human equivalent of macaque area PIVC.

Sex differences in mental rotation: Top–down versus bottom–up processing

Functional MRI during performance of a validated mental rotation task was used to assess a neurobiological basis for sex differences in visuospatial processing. Between-sex group analysis demonstrated greater activity in women than in men in dorsalmedial prefrontal and other high-order heteromodal association cortices, suggesting women performed mental rotation in an effortful, "top-down" fashion. In contrast, men activated primary sensory cortices as well as regions involved in implicit learning (basal ganglia) and mental imagery (precuneus), consistent with a more automatic, "bottom-up" strategy. Functional connectivity analysis in association with a measure of behavioral performance showed that, in men (but not women), accurate performance was associated with deactivation of parieto-insular vestibular cortex (PIVC) as part of a visual-vestibular network. Automatic evocation by men to a greater extent than women of this network during mental rotation may represent an effective, unconscious, bottom-up neural strategy which could reasonably account for men's traditional visuospatial performance advantage.

Depersonalisation/derealisation symptoms in vestibular disease

BACKGROUND

Depersonalisation is a subjective experience of unreality and detachment from the self often accompanied by derealisation; the experience of the external world appearing to be strange or unreal. Feelings of unreality can be evoked by disorienting vestibular stimulation.

OBJECTIVE

To identify the prevalence of depersonalisation/derealisation symptoms in patients with peripheral vestibular disease and experimentally to induce these symptoms by vestibular stimulation.

METHODS

121 healthy subjects and 50 patients with peripheral vestibular disease participated in the study. For comparison with the patients a subgroup of 50 age matched healthy subjects was delineated. All completed (1) an in-house health screening questionnaire; (2) the General Health Questionnaire (GHQ-12); (3) the 28-item depersonalisation/derealisation inventory of Cox and Swinson (2002). Experimental verification of "vestibular induced" depersonalisation/derealisation was assessed in 20 patients and 20 controls during caloric irrigation of the labyrinths.

RESULTS

The frequency and severity of symptoms in vestibular patients was significantly higher than in controls. In controls the most common experiences were of "déjà vu" and "difficulty in concentrating/attending". In contrast, apart from dizziness, patients most frequently reported derealisation symptoms of "feel as if walking on shifting ground", "body feels strange/not being in control of self", and "feel 'spacey' or 'spaced out'". Items permitted discrimination between healthy subjects and vestibular patients in 92% of the cases. Apart from dizziness, caloric stimulation induced depersonalisation/derealisation symptoms which healthy subjects denied ever experiencing before, while patients reported that the symptoms were similar to those encountered during their disease.

CONCLUSIONS

Depersonalisation/derealisation symptoms are both different in quality and more frequent under conditions of non-physiological vestibular stimulation. In vestibular disease, frequent experiences of derealisation may occur because distorted vestibular signals mismatch with the other sensory input to create an incoherent frame of spatial reference which makes the patient feel he or she is detached or separated from the world.

Asymmetrical perception of body rotation after unilateral injury to human vestibular cortex

Vestibular information plays a key role in many perceptual and cognitive functions, but surprisingly little is known about how vestibular signals are processed at the cortical level in humans. To address this issue, we tested the ability of two patients, with damage to key components of the vestibular network in either the left or right hemisphere, to perceive passive whole-body rotations (25-125 degrees) about the yaw axis. In both patients, the posterior insula, hippocampus, putamen, and thalamus were extensively damaged. The patients' responses were compared with those of nine age- and sex-matched neurologically intact participants. The body rotations were conducted without vision and the peak angular velocities ranged from 40 degrees to 90 degrees per second. Perceived rotation was assessed by open-loop manual pointing. The right hemisphere patient exhibited poor sensitivity for body rotations toward the contralesional (left) hemispace and generally underestimated the rotations. By contrast, his judgments of rotations toward the ipsilesional (right) hemispace greatly overestimated the physical rotation by 50-70 degrees for all tested magnitudes. The left hemisphere patient's responses were more appropriately scaled for both rotation directions, falling in the low-normal range. These findings suggest that there is some degree of hemispheric specialization in the cortical processing of dynamic head rotations in the yaw plane. In this view, right hemisphere structures play a dominant role, processing rotations in both directions, while left hemisphere structures process rotations only toward the contralesional hemispace.

Rotational vertigo associated with parietal cortical infarction

A 65-year-old woman experienced sudden positional vertigo with rightward, horizontal nystagmus that resolved within days. MRI revealed a left parietal lobe infarction involving the supramarginal gyrus. The patient experienced a transient recurrence of vertigo after 7 days but MRI failed to reveal the presence of any new lesions; furthermore, the patient's EEG was normal. We suggest that this patient's vertigo was due to her parietal cortical infarction.