Subjective Visual Vertical Tilt Research Articles

Complete ocular tilt reaction with subjective visual vertical tilt in a patient with a medial prefrontal cortex lesion: a case report

A 61-year-old male patient undergoing chemotherapy for esophageal cancer presented with symptoms of rightward tilting while both sitting and walking. A neurological examination revealed a head tilt, skew deviation with hypertrophy of the left eye, and a rightward shift in his gait. No spontaneous nystagmus was observed, and the vestibulo-ocular reflex was normal. Magnetic resonance imaging of the head revealed a suspected metastatic lesion in the right medial prefrontal cortex. Following the initiation of levetiracetam treatment, the patient demonstrated marked improvement, with the resolution of both head tilt and skew deviation within 1 month. Traditionally, the ocular tilt reaction has been attributed to unilateral or asymmetric dysfunction of the graviceptive pathways extending from the utricle to the upper midbrain lesions. However, this case highlights the potential involvement of the prefrontal cortex in the ocular tilt reaction. Further research is warranted on the role of the prefrontal cortex within the vestibular system.

Contraversive Ocular Tilt Reaction, Body Lateropulsion and Gaze-Evoked Nystagmus After Inferior Cerebellar Peduncle and Dentate Nucleus Stroke

Contraversive Ocular Tilt Reaction, Body Lateropulsion and Gaze-Evoked Nystagmus After Inferior Cerebellar Peduncle and Dentate Nucleus Stroke

Static Subjective Visual Vertical (SVV) in Patients with Vestibular Migraine.

Vestibular migraine (VM) is one of the common causes of episodic dizziness, but it is underdiagnosed and poorly understood. Previous research suggests that otolith reflex pathway performance is often impaired in this patient group, leading to altered perception of roll plane stimuli. Clinically, this perception can be measured with subjective visual vertical (SVV) testing. The aim of this study is to compare static SVV performance (absolute mean SVV tilt, variance) in a cohort of patients diagnosed with VM to results obtained from clinically derived normative data. Retrospective case review. Ninety-four consecutive patients between 18 and 65 years of age diagnosed with VM were included in this comparison to clinically derived normative data. Retrospective chart review was completed. Demographic data, symptom report, and vestibular laboratory results were documented. SVV performance was documented in terms of absolute mean SVV tilt and response variance. Abnormal mean SVV tilt was described in 54% (n = 51) of patients with VM. Including abnormal response variance increased those identified with abnormal presentation to 67% (n = 63). Laboratory findings were insignificant for semicircular canal function, but of those with abnormal ocular vestibular myogenic potential results (n = 30), 77% (n = 23) demonstrated both abnormal SVV and utriculo-ocular reflex performance. There were no associations noted for SVV performance and demographic or other self-report variables. Absolute mean SVV tilt and response variance are often abnormal in patients diagnosed with VM. These findings support theories suggesting atypical intralabyrinthine integration within the vestibular nuclei and cerebellar nodular pathways.

Cochlear implant surgery and perioperative dizziness is associated with utricular hyperfunction.

Dizziness is a common perioperative complication after cochlear implantation (CI). To date, the exact cause behind this phenomenon remains unclear. There is recent evidence to suggest that otolith function, specifically utricular, may be affected shortly after CI surgery, however whether these changes are related to patient symptoms has not yet been investigated. To determine whether CI surgery and perioperative dizziness is associated with changes in utricular function. We performed an observational study on patients undergoing routine CI surgery. Utricular function was assessed using the Subjective Visual Vertical (SVV), and perioperative dizziness was determined using a questionnaire. The study followed patients before surgery and then again 1-day, 1-week and 6-weeks after implantation. Forty-one adult CI recipients participated in the study. The SVV deviated away from the operated ear by an average of 2.17° a day after implantation, 0.889° 1 week and -0.25° 6 weeks after surgery. Dizziness contributed to a tilt of 0.5° away from the implanted ear. These deviations were statistically significant. CI surgery causes utricular hyperfunction in the operated ear that resolves over 6 weeks. SVV tilts were greater in participants experiencing dizziness, suggesting that utricular hyperfunction may contribute to the dizziness.

Role of subjective visual vertical in patients with posterior canal benign paroxysmal positional vertigo as a prognostic marker after canalith repositioning maneuver

ObjectiveTo study the potential role of subjective visual vertical (SVV) as a prognostic marker for canalith repositioning maneuver (CRM) in patients with posterior canal benign paroxysmal positional vertigo (PC-BPPV) for the Indian population. MethodsSVV was examined in 30 patients with PC-BPPV before and after canalith repositioning maneuver and after complete resolution of PC-BPPV. Study parameters included the mean of 10 angular tilt readings and direction of deviation, which were compared before and after CRM and following complete resolution of PC-BPPV. ResultsThe angle of SVV tilt was greater and deviated towards the affected ear before CRM in all patients, which decreased significantly shortly after CRM and continued to decrease after complete resolution of PC-BPPV (p < 0.0001). ConclusionsSVV can be used to test utricular dysfunction in PC-BPPV. The angle of tilt improves in response to CRM, which may be used as a prognostic marker in patients with PC-BPPV receiving CRM.

Reorganization of sensory networks after subcortical vestibular infarcts: A longitudinal symptom-related voxel-based morphometry study.

We aimed to delineate common principles of reorganization after infarcts of the subcortical vestibular circuitry related to the clinical symptomatology. Our hypothesis was that the recovery of specific symptoms is associated with changes in distinct regions within the core vestibular, somatosensory, and visual cortical and subcortical networks. We used voxel- and surface-based morphometry to investigate structural reorganization of subcortical and cortical brain areas in 42 patients with a unilateral, subcortical infarct with vestibular and ocular motor deficits in the acute phase. The patients received structural neuroimaging and clinical monitoring twice (acute phase and after 6months) to detect within-subject changes over time. In patients with vestibular signs such as tilts of the subjective visual vertical (SVV) and ocular torsion in the acute phase, significant volumetric increases in the superficial white matter around the parieto-opercular (retro-)insular vestibular cortex (PIVC) were found at follow-up. In patients with SVV tilts, spontaneous nystagmus, and rotatory vertigo in the acute phase, gray matter volume decreases were located in the cerebellum and the visual cortex bilaterally at follow-up. Patients with saccade pathology demonstrated volumetric decreases in cerebellar, thalamic, and cortical centers for ocular motor control. The findings support the role of the PIVC as the key hub for vestibular processing and reorganization. The volumetric decreases represent the reciprocal interaction of the vestibular, visual, and ocular motor systems during self-location and egomotion detection. A modulation in vestibular and ocular motor as well as visual networks was induced independently of the vestibular lesion site.

Factors Contributing to the Severity and Laterality of Pisa Syndrome in Parkinson's Disease.

Objective: Pisa syndrome (PS) is a disabling postural deformity in Parkinson’s disease (PD). We aimed to elucidate clinical factors determining the severity and laterality of PS in PD.Methods: In 54 PD patients with PS, we measured the clinical factors that are previously known to contribute to the occurrence of PS as follows: asymmetry of motor symptoms for the evaluation of asymmetric basal ganglia dysfunction, the degree and direction of subjective visual vertical (SVV) tilt for the misperception of body verticality, the canal paresis for unilateral peripheral vestibulopathy, and the tonic electromyographic (EMG) hyperactivity of paraspinal muscles for dystonia. Multivariable linear and logistic regression analyses were conducted to identify the clinical factors associated with the degree of truncal tilt, for the quantification of the severity of PS, and PS tilting to the less affected side, respectively.Results: The multivariable linear regression analyses revealed that the larger degree of SVV tilt (β = 0.29, SE = 0.10, p = 0.005), right-sided SVV tilt (β = 2.32, SE = 0.82, p = 0.007), and higher Hoehn and Yahr (HY) stage (β = 4.01, SE = 1.29, p = 0.003) significantly increased the severity of PS. In the multivariable logistic regression analyses, greater asymmetry of motor symptoms [odds ratio (OR) = 2.01, 95% CI = 1.34–3.49] was significantly associated with PS tilting to the less affected side, while right-sided SVV tilt (OR = 0.02, 95% CI = 0.001–0.21), unilateral canal paresis (OR = 0.06, 95% CI = 0.003–0.79), and higher HY stage (OR = 0.04, 95% CI = 0.002–0.46) were associated with PS tilting to the more affected side.Conclusion: Misperception of verticality, asymmetric basal ganglia dysfunction, unilateral peripheral vestibulopathy, and motor disability are the clinical factors associated with the severity and laterality of PS in patients with PD.

Vestibular impairments in episodic ataxia type 2.

Episodic ataxia type 2 (EA2) can present diverse ocular motor abnormalities, but few studies have systematically evaluated vestibular function during the interictal periods. This study aimed to determine vestibular impairments in patients with EA2 during the interictal periods. We recruited 17 patients with genetically confirmed EA2 (10 men, age range = 16-85years, median = 32years). We systematically evaluated the vestibular function by measuring the semicircular canals (SCCs) function with bithermal caloric tests, rotatory chair test, and video head impulse test (vHIT), and the otolith function with subjective visual vertical (SVV) tilt and variability, and cervical and ocular vestibular-evoked myogenic potentials (VEMPs). Patients with EA2 commonly showed abnormal VOR responses at least for one SCC with high-acceleration, high-frequency head impulses (14/16, 88%), and impaired visual-vestibular interaction (7/12, 58%). In response to low acceleration and frequency stimuli, the VOR gains were generally normal. The majority of EA2 patients had impairments in at least one of the otolith function tests (13/16, 81%): SVV tilt or variability (7/14, 50%), oVEMP (8/15, 53%), and cVEMP (4/16, 25%). Vestibular impairments are common in EA2 even during the interictal periods. Selective decrease in the VOR responses during higher acceleration stimuli along with impaired visual-vestibular interaction and otolith function suggests degeneration of the vestibulocerebellum or vestibular nuclei.

Impaired Subjective Visual Vertical and Increased Visual Dependence in Older Adults With Falls.

Aging affects the vestibular system and may disturb the perception of verticality and lead to increased visual dependence (VD). Studies have identified that abnormal upright perception influences the risk of falling. The aim of our study was to evaluate subjective visual vertical (SVV) and VD using a mobile virtual reality-based system for SVV assessment (VIRVEST) in older adults with falls and evaluate its relationship with clinical balance assessment tools, dizziness, mental state, and depression level. This study included 37 adults >65 years who experienced falls and 40 non-faller age-matched controls. Three tests were performed using the VIRVEST system: a static SVV, dynamic SVV with clockwise and counter-clockwise background stimulus motion. VD was calculated as the mean of absolute values of the rod tilt from each trial of dynamic SVV minus the mean static SVV rod tilt. Older adults who experienced falls manifested significantly larger biases in static SVV (p = 0.012), dynamic SVV (p < 0.001), and VD (p = 0.014) than controls. The increase in static SVV (odds ratio = 1.365, p = 0.023), dynamic SVV (odds ratio = 1.623, p < 0.001) and VD (odds ratio = 1.460, p = 0.010) tilt by one degree significantly related to falls risk in the faller group. Fallers who had a high risk of falling according to the Tinetti test exhibited significantly higher tilts of dynamic SVV than those who had a low or medium risk (p = 0.037). In the faller group, the increase of the dynamic SVV tilt by one degree was significantly related to falls risk according to the Tinetti test (odds ratio = 1.356, p = 0.049). SVV errors, particularly with the dynamic SVV test (i.e., greater VD) were associated with an increased risk of falling in the faller group. The VIRVEST system may be applicable in clinical settings for SVV testing and predicting falls in older adults.

Different time course of compensation of subjective visual vertical and ocular torsion after acute unilateral vestibular lesion

PurposeTime course of the recovery of otolithic dis-function caused by superior vestibular neuritis has been examined in fifteen patients.MethodsThe subjective visual vertical (SVV) and the ocular cyclotorsion (OT) have been measured four times after the acute episode up to 1 yearResultsIn most of the patients the SVV tilt returned to control values within few months (3–6 months) after the acute episode, while OT remained out of normal range in almost all patients a year later.ConclusionThe abnormal OT observed after 1 year from the acute episode of vestibular neuritis, suggests that the otolithic receptors remained altered for several months and the OT may be a good indicator of the entity of the residual peripheral otolithic lesion. Moreover, the dissociation between the SVV tilt recovery and that of OT supports the issue that the two signs of the otolithic disfunction are only partially linked each other with centrally or peripherally distinct re-balancing circuits.

Young and Older Adults Differ in Integration of Sensory Cues for Vertical Perception.

Introduction The subjective visual vertical (SVV) measures the perception of a person's spatial orientation relative to gravity. Weighted central integration of vestibular, visual, and proprioceptive inputs is essential for SVV perception. Without any visual references and minimal proprioceptive contribution, the static SVV reflects balance of the otolith organs. Normal aging is associated with bilateral and progressive decline in otolith organ function, but age-dependent effects on SVV are inconclusive. Studies on sensory reweighting for visual vertical and multisensory integration strategies reveal age-dependent differences, but most studies have included elderly participants in comparison to younger adults. The aim of this study was to compare young adults with older adults, an age group younger than the elderly. Methods Thirty-three young and 28 older adults (50–65 years old) adjusted a tilted line accurately to their perceived vertical. The rod's final position from true vertical was recorded as tilt error in degrees. For otolithic balance, visual vertical was recorded in the dark without any visual references. The rod and frame task (RFT) with tilted disorienting visual frames was used for creating visuovestibular conflict. We adopted Nyborg's analysis method to derive the rod and frame effect (RFE) and trial-to-trial variability measures. Rod alignment times were also analyzed. Results There was no age difference in signed tilts of SVV without visual reference. There was an age effect on RFE and on overall trial-to-trial variability of rod tilt, with older adults displaying larger frame effects and greater variability in rod tilts. Alignment times were longer in the tilted-frame conditions for both groups and in the older adults compared to their younger counterparts. The association between tilt accuracy and tilt precision was significant for older adults only during visuovestibular conflict, revealing an increase in RFE with an increase in tilt variability. Correlation of σSVV, which represents vestibular input precision, with RFE yielded exactly the same contribution of σSVV to the variance in RFE for both age groups. Conclusions Older adults have balanced otolithic input in an upright position. Increased reliance on visual cues may begin at ages younger than what is considered elderly. Increased alignment times for older adults may create a broader time window for integration of relevant and irrelevant sensory information, thus enhancing their multisensory integration. In parallel with the elderly, older adults may differ from young adults in their integration of sensory cues for visual vertical perception.

Decreased grey matter in the postural control network is associated with lateral flexion of the trunk in Parkinson’s disease

BackgroundDisruption of central networks, particularly of those responsible for integrating multimodal afferents in a spatial reference frame, were proposed in the pathophysiology of lateral trunk flexion in Parkinson’s disease (PD). Knowledge about the underlying neuroanatomical structures is limited. ObjectiveTo investigate if decreased focal grey matter (GM) is associated with trunk flexion to the side and if the revealed GM clusters correlate with a disturbed perception of verticality in PD. Methods37 PD patients with and without lateral trunk flexion were recruited. Standardized photos were taken from each patient and trunk orientation was measured by a blinded rater. Voxel-based morphometry (VBM) was used to detect associated clusters of decreased GM. The subjective visual vertical (SVV) was assessed as a marker for perception of verticality and SVV estimates were correlated with GM clusters. ResultsVBM revealed clusters of decreased GM in the right posterior parietal cortex and in the right thalamus were associated with lateral trunk flexion. The SVV correlated with the extent of trunk flexion, and the side of the SVV tilt correlated with the side of trunk flexion. GM values from the thalamus correlated with the SVV estimates. ConclusionsWe report an association between neurodegenerative changes within the posterior parietal cortex and the thalamus and lateral trunk flexion in PD. These brain structures are part of a network proposed to be engaged in postural control and spatial self-perception. Disturbed perception of verticality points to a shifted egocentric spatial reference as an important pathophysiological feature.

Isolated Dizziness with Subjective Visual Vertical Tilt in Acute Infarction of Temporo-Parieto-Occipital Junction

Pathological tilts of the subjective visual vertical (SVV) in the roll plane are most sensitive and frequent clinical vestibular signs of unilateral lesions extending from the labyrinths via the brainstem and thalamus to the cortex. SVV deviations in cortical lesion are usually related with the parietoinsular vestibular cortex or superior temporal gyrus. We report isolated dizziness with contralesional SVV tilt with a focal infarction restricted to the right temporo-parieto-occipital junction. Key Words: Visual perception, Stroke, Dizziness

Vestibular disorders in roll plane from brainstem to cortex

The aim is to review current knowledge of the perception of verticality, its normal function and disorders. This is based on an integrative graviceptive input from the vertical semicircular canals and the otolith organs. The focus is particularly on human psychophysics, neurophysiological and imaging data on vestibular disorders in the roll plane. The signs and symptoms are head tilt, vertical divergence of the eyes (skew deviation), ocular torsion, and tilts of subjective visual vertical (SVV) adjustments, all of which represent the so-called ocular tilt reaction (OTR). Furthermore, these signs will be related to mathematical modeling of specific vestibular cell functions for orientation in space in rodents and in patients. Pathological tilts of the SVV in the roll plane are most sensitive and frequent clinical vestibular signs of unilateral lesions extending from the labyrinths via the brainstem and thalamus to the parieto-insular vestibular cortex [[1]Brandt T. Dieterich M. The dizzy patient: Don’t forget disorders of the central vestibular system.Nat. Rev. Neurol. 2017 Jun; 13: 352-362https://doi.org/10.1038/nrneurol.2017.58Google Scholar]. Due to crossings of ascending graviceptive fibers, peripheral vestibular and pontomedullary lesions cause ipsilateral tilts of the SVV; ponto-mesencephalic lesions cause contralateral tilts. In contrast, SVV tilts, which are measured in unilateral vestibular lesions at thalamic and cortical levels, have two different characteristic features: (i) they may be ipsi- or contralateral, and (ii) they are smaller than those found in lower brainstem or peripheral lesions. Motor signs such as head tilt and body lateropulsion, i.e. components of OTR, are typical for vestibular lesions of the peripheral vestibular organ and the pontomedullary brainstem (vestibular nucleus). They are less frequent in midbrain lesions (interstitial nucleus of Cajal) and rare in cortical lesions. Vestibular function in the roll plane and its disorders can be mathematically modeled by an attractor model of the function of angular head velocity cells and head direction cells [[2]Glasauer S. Dieterich M. Brandt T. Neuronal network-based mathematical modelling of perceived verticality in acute unilateral vestibular lesions: from nerve to thalamus and cortex.J. Neurol. 2018 May 29; https://doi.org/10.1007/s00415-018-8909-5Google Scholar]. Conclusion: Clinical determinations of the SVV are easy and reliable. They indicate acute unilateral vestibular dysfunctions, the causative lesion of which extends from labyrinth to cortex. Together with additional ocular motor or brainstem signs they allow precise topographical diagnosis of side and level.

Perception of Verticality and Vestibular Disorders of Balance and Falls.

Objective: To review current knowledge of the perception of verticality, its normal function and disorders. This is based on an integrative graviceptive input from the vertical semicircular canals and the otolith organs.Methods: The special focus is on human psychophysics, neurophysiological and imaging data on the adjustments of subjective visual vertical (SVV) and the subjective postural vertical. Furthermore, examples of mathematical modeling of specific vestibular cell functions for orientation in space in rodents and in patients are briefly presented.Results: Pathological tilts of the SVV in the roll plane are most sensitive and frequent clinical vestibular signs of unilateral lesions extending from the labyrinths via the brainstem and thalamus to the parieto-insular vestibular cortex. Due to crossings of ascending graviceptive fibers, peripheral vestibular and pontomedullary lesions cause ipsilateral tilts of the SVV; ponto-mesencephalic lesions cause contralateral tilts. In contrast, SVV tilts, which are measured in unilateral vestibular lesions at thalamic and cortical levels, have two different characteristic features: (i) they may be ipsi- or contralateral, and (ii) they are smaller than those found in lower brainstem or peripheral lesions. Motor signs such as head tilt and body lateropulsion, components of ocular tilt reaction, are typical for vestibular lesions of the peripheral vestibular organ and the pontomedullary brainstem (vestibular nucleus). They are less frequent in midbrain lesions (interstitial nucleus of Cajal) and rare in cortical lesions. Isolated body lateropulsion is chiefly found in caudal lateral medullary brainstem lesions. Vestibular function in the roll plane and its disorders can be mathematically modeled by an attractor model of angular head velocity cell and head direction cell function. Disorders manifesting with misperception of the body vertical are the pusher syndrome, the progressive supranuclear palsy, or the normal pressure hydrocephalus; they may affect roll and/or pitch plane.Conclusion: Clinical determinations of the SVV are easy and reliable. They indicate acute unilateral vestibular dysfunctions, the causative lesion of which extends from labyrinth to cortex. They allow precise topographical diagnosis of side and level in unilateral brainstem or peripheral vestibular disorders. SVV tilts may coincide with or differ from the perception of body vertical, e.g., in isolated body lateropulsion.

Subjective visual vertical in posterior canal benign paroxysmal positional vertigo patients before and after Canalith repositioning maneuvers

Background: The subjective visual vertical (SVV) is a measure of otolith-mediated verticality perception. The aim of this study was to test otolith function using the SVV in patients with posterior canal (PC) benign paroxysmal positional vertigo (BPPV) before and after Epley’s Canalith repositioning maneuver (CRM).Methodology: This study included 20 PC BPPV patients and 20 healthy control subjects. SVV was tested using special equipment, at the time of BPPV diagnosis, then after CRM, and then 1 week after the resolution of vertigo and nystagmus. SVV was determined from clockwise (CW) and counter-clockwise (CCW) directions. The absolute average and the conventional numerical average was calculated.Results: Using the conventional method, there was no statistically significant difference between BPPV and their controls regarding either the CW or the CCW-SVV or the average slope. There was no statistically significant difference between CW and CCW-SVV in the patients. There was no statistically significant difference in the mean SVV values or the distribution of normal and abnormal results or the distribution of the SVV tilt between both-sided BPPV. Using the absolute average, SVV tilt was significantly higher in the patients than the controls. The preset angle affected the result. The mean SVV was significantly lower after resolution of BPPV than before treatment.Conclusion: Absolute SVV average was more accurate than numerical SVV average. There was a reduction of the SVV tilt after the CRM in BPPV patients. So, the SVV test can be used as a prognostic test for BPPV improvement after treatment.

Ocular Tilt Reaction in Compensated Vestibular Schwannoma

Ocular Tilt Reaction in Compensated Vestibular Schwannoma

Relationship of visual dependence to age, balance, attention, and vertigo.

[Purpose] The aim of this study was to investigate the relationship of increased visual dependence to age, balance, attention, and vertigo. [Subjects and Methods] Twelve younger, 12 visually independent (VI) older and 12 visually dependent (VD) older adults were assessed for levels of visual dependence using Subjective Visual Vertical (SVV) tilt values, balance ability using the Clinical Test of Sensory Integration for Balance (CTSIB), and attentional requirements through the dual-task paradigm and experience of vertigo by completing the Situational Vertigo Questionnaire (SVQ). [Results] VD older adults had higher SVV tilt values, greater postural sway in a scenario where visual and proprioceptive inputs were simultaneously altered, similar dual-task cost and lower SVQ scores compared with younger and VI older adults. No difference was observed between the latter two. [Conclusion] Visual dependence may not necessarily increase with age but affect balance in a sensory condition involving visual-proprioceptive conflict. There is a non-significant trend for elevated visual dependence with increased attentional demands. Greater visual dependence is not accompanied by more frequent symptoms of vertigo in visually complex environments.

Altered processing of otolithic information in isolated lateral medullary infarction.

Ocular and cervical vestibular-evoked myogenic potentials (VEMPs) evaluate the function of otolithic pathways in central as well as peripheral vestibular disorders. This study aimed to determine the associations and dissociations of otolithic dysfunction in lateral medullary infarction (LMI), the most well-known disorder of central vestibulopathy. At the Dizziness Clinic of a referral-based University Hospital, 45 patients with isolated LMI (28 men, mean age = 55.6 ± 12.5) had evaluation of the ocular tilt reaction (OTR), tilt of the subjective visual vertical (SVV), and ocular and cervical VEMPs from Janurary 2011 to August 2015 during the acute phase, 1-11days from the symptom onset (median=2days). Almost all (42/45, 93%) patients showed at least one component of the OTR or SVV tilt that was invariably ipsiversive. In contrast, oVEMPs were abnormal only in 12 (27%) and cVEMPs in 13 (29%) patients. Only three patients showed abnormal results in all the tests of the OTR, SVV tilt, and ocular and cervical VEMPs. Abnormal oVEMPs were more common in patients with the OTR than those without (38 vs 6%, Pearson X 2 test, p=0.021). In contrast, abnormality of cVEMPs showed no correlation with the presence of OTR (28 vs 31%, Pearson X 2 test, p=0.795). In patients with LMI, ipsiversive OTR is invariable, but abnormalities of oVEMPs and cVEMPs were much less common and mostly dissociated even in the patients with abnormal results. This discrepancy in otolithic dysfunction suggests different anatomical substrates and/or dissimilar reciprocal modulation for processing of each otolithic signal in central vestibular structures located in the dorsolateral medulla.

Vestibular thalamus: Two distinct graviceptive pathways.

To determine whether there are distinct thalamic regions statistically associated with either contraversive or ipsiversive disturbance of verticality perception measured by subjective visual vertical (SVV). We used modern statistical lesion behavior mapping on a sample of 37 stroke patients with isolated thalamic lesions to clarify which thalamic regions are involved in graviceptive otolith processing and whether there are distinct regions associated with contraversive or ipsiversive SVV deviation. We found 2 distinct systems of graviceptive processing within the thalamus. Contraversive tilt of SVV was associated with lesions to the nuclei dorsomedialis, intralamellaris, centrales thalami, posterior thalami, ventrooralis internus, ventrointermedii, ventrocaudales and superior parts of the nuclei parafascicularis thalami. The regions associated with ipsiversive tilt of SVV were located in more inferior regions, involving structures such as the nuclei endymalis thalami, inferior parts of the nuclei parafascicularis thalami, and also small parts of the junction zone of the nuclei ruber tegmenti and brachium conjunctivum. Our data indicate that there are 2 anatomically distinct graviceptive signal processing mechanisms within the vestibular network in humans that lead, when damaged, to a vestibular tone imbalance either to the contraversive or to the ipsiversive side.