[Is the sense of verticality vestibular?]

Misperception of body verticality in neurological disorders: A systematic review and meta-analysis

INTRODUCTION

The internal representation of verticality could be disturbed when a lesion in the central nervous system (CNS) affects the centers where information from the vestibular, visual, and/or somatosensory systems, increasing the risk of falling.

OBJECTIVE

The aim was to evaluate the vestibular and somatosensory contribution to the verticality pattern in patients with stroke and other neurological disorders.

METHODS

A literature search was performed in PubMed, Scopus, Web of Science, and CINAHL databases. Cross-sectional, case-control, and cohort studies comparing body verticality in patients with stroke or CNS diseases (CNSD) versus healthy controls were selected. Subjective postural vertical (SPV) in roll and pitch planes was used as the primary variable.

RESULTS

Ten studies reporting data from 390 subjects were included. The overall effect for CNSD patients showed a misperception of body verticality in roll (standardized mean difference [SMD] = 1.05; 95% confidence interval [CI] .84-1.25) and pitch planes (SMD = 1.03; 95% CI .51-1.55). In subgroup analyses, a high effect was observed in the perception of SPV both in roll and pitch planes in stroke (p = .002) and other CNSD (p < .001).

CONCLUSION

These findings suggest a potential misperception of SPV in patients with stroke and other neurological disturbances. Patients with CNSD could present an alteration of vestibular and somatosensory contribution to verticality construction, particularly stroke patients with pusher syndrome (PS), followed by those with PS combined with hemineglect.

Post-Traumatic Craniocervical Disorders From a Postural Control Perspective: A Narrative Review

Mild traumatic brain injury (mTBI) and whiplash injury (WI) may lead to long-term disabling consequences known as post-concussive syndrome (PCS) and whiplash-associated disorders (WADs). PCS and WAD patients commonly complain of conditions encompassing dizziness, vertigo, headache, neck pain, visual complaints, anxiety, and neurocognitive dysfunctions. A proper medical work-up is a priority in order to rule out any acute treatable consequences. However investigations may remain poorly conclusive. Gathered in the head and neck structures, the ocular sensorimotor, the vestibular, and the cervical proprioceptive systems, all involved in postural control, may be damaged by mTBI or WI. Their dysfunctions are associated with a wide range of functional disorders including symptoms reported by PCS and WAD patients. In addition, the stomatognathic system needs to be specifically assessed particularly when associated to WI. Evidence for considering the post-traumatic impairment of these systems in PCS and WAD-related symptoms is still lacking but seems promising. Furthermore, few studies have considered the assessment and/or treatment of these widely interconnected systems from a comprehensive perspective. We argue that further research focusing on consequences of mTBI and WI on the systems involved in the postural control are necessary in order to bring new perspective of treatment.

A perception bias of the gravitational vertical is confirmed in Adolescent Idiopathic Scoliosis

PURPOSE

Adolescent Idiopathic Scoliosis (AIS) is the most frequent spine deformity in adolescence. The cause of AIS remains unknown. Several studies show that AIS can be associated with a perception bias of gravitational vertical. In particularly, AIS patients with a right thoracic convexity exhibit deviation of the Subjective Postural Vertical. The origin of this disturbance could be located in trunk proprioceptive graciveptors. We wanted to verify this result with a population of lumbar and thoracolumbar AIS with left convexity.

METHODS

It was a multicenter, cross-sectional case-control study. Thirty adolescents with left lumbar or thoraco-lumbar AIS (age 14.3 ± 1.7 years; Cobb angle 27.6° ± 6.1°) and 30 controls matched for age (14.0 ± 1.5 years), were compared for Subjective Visual Vertical (SVV) measured in static and dynamic (optokinetic stimulation) conditions, and Subjective Postural Vertical (SPV).

RESULTS

For SVV, there was no difference in the two groups, for static and dynamic conditions. The SPV was significantly different between the two groups (p < 0.0001). The SPV was shifted to the left for most of the AIS patients (med - 2.4°[- 3.6; - 1.7]) compared with controls (med 0°[- 0.5; 1.7]). Adolescents with AIS perceived verticality with significant greater uncertainty in postural modality than controls (p = 0.017).

CONCLUSION

Our study confirms a significant directional bias in the orientation of SPV in left lumbar or thoraco-lumbar AIS. This confirmation paves the way to a new physiopathological model focused on trunk proprioception.

LEVEL OF EVIDENCE

III.

Twenty-four-hour variation of vestibular function in young and elderly adults

Animal and human studies demonstrate anatomical and functional links between the vestibular nuclei and the circadian timing system. This promotes the hypothesis of a circadian rhythm of vestibular function. The objective of this study was to evaluate the vestibular function through the vestibulo-ocular reflex using a rotatory chair at different times of the day to assess circadian rhythmicity of vestibular function. Two identical studies evaluating temporal variation of the vestibulo-ocular reflex (VOR) were performed, the first in young adults (age: 22.4 ± 1.5 y), and the second in older adults (70.7 ± 4.7 y). The slow phase velocity and time constant of the VOR were evaluated in six separate test sessions, i.e., 02:00, 06:00, 10:00, 14:00, 18:00, and 22:00 h. In both studies, markers of circadian rhythmicity (temperature, fatigue, and sleepiness) displayed expected usual temporal variation. In young adults, the time constant of the VOR showed variation throughout the day (p < .005), being maximum 12:25 h (06:00 h test session) before the acrophase of temperature circadian rhythm. In older adults, the slow phase velocity and time constant also displayed temporal variation (p < .05). Maximum values were recorded at 10:35 h (06:00 h test session) before the acrophase of temperature circadian rhythm. The present study demonstrates that vestibular function is not constant throughout the day. The implication of the temporal variation in vestibular system in equilibrium potentially exposes the elderly, in particular, to differential risk during the 24 h of losing balance and falling.

New Mobile Device to Measure Verticality Perception: Results in Young Subjects with Headaches

The subjective visual vertical (SVV) test has been frequently used to measure vestibular contribution to the perception of verticality. Recently, mobile devices have been used to efficiently perform this measurement. The aim of this study was to analyze the perception of verticality in subjects with migraines and headaches. A cross-sectional study was conducted that included 28 patients with migraine, 74 with tension-type headache (TTH), and 93 healthy subjects. The SVV test was used through a new virtual reality system. The mean absolute error (MAE) of degrees deviation was also measured to qualify subjects as positive when it was greater than 2.5°. No differences in the prevalence of misperception in verticality was found among healthy subjects (31.18%), migraineurs (21.43%), or those with TTH (33.78%) (p = 0.480). The MAE was not significantly different between the three groups (migraine = 1.36°, TTH = 1.61°, and healthy = 1.68°) (F = 1.097, p = 0.336, and η2 = 0.011). The perception of verticality could not be explained by any variable usually related to headaches. No significant differences exist in the vestibular contribution to the perception of verticality between patients with headaches and healthy subjects. New tests measuring visual and somatosensory contribution should be used to analyze the link between the perception of verticality and headaches.

Subjective visual vertical in patients with Usher syndrome

BACKGROUND

Verticality, or more precisely the ability to perceive spatial orientation with regard to gravity, is based on the integration of visual, vestibular and somesthetic information.

OBJECTIVE

The purpose of the present study was to compare the subjective visual vertical (SVV) in patients with Usher (type I and type II) with visual or vestibular impairment, and in healthy participants, in order to explore the importance of the visual and vestibular functions on the vertical’s perception.

METHODS

We evaluated the SVV using a wall housing which projects on the opposite wall a red-light line of about 2 meters, obtained by laser cannon. The evaluation was carried out under two tilt conditions: clockwise and counter-clockwise randomly performed five times in each direction. The response to the SVV task was quantified by the mean of the absolute values of the SVV.

RESULTS

Responses to the SVV were significantly less accurate in patients with Usher with respect to healthy participants while it was similar for the two groups of patients with Usher.

CONCLUSIONS

We hypothesize that visual inputs play a very important role in the perception of verticality and that the symmetrical bilateral vestibular deficit in Usher type I does not have a strong impact in perception of verticality.

Adaptation of balancing behaviour during continuous perturbations of stance. Supra-postural visual tasks and platform translation frequency modulate adaptation rate

When humans are administered continuous and predictable perturbations of stance, an adaptation period precedes the steady state of balancing behaviour. Little information is available on the modulation of adaptation by vision and perturbation frequency. Moreover, performance of supra-postural tasks may modulate adaptation in as yet unidentified ways. Our purpose was to identify differences in adaptation associated to distinct visual tasks and perturbation frequencies. Twenty non-disabled adult volunteers stood on a platform translating 10 cm in antero-posterior (AP) direction at low (LF, 0.18 Hz) and high frequency (HF, 0.56 Hz) with eyes open (EO) and closed (EC). Additional conditions were reading a text fixed to platform (EO-TP) and reading a text stationary on ground (EO-TG). Peak-to-peak (PP) displacement amplitude and AP position of head and pelvis markers were computed for each of 27 continuous perturbation cycles. The time constant and extent of head and pelvis adaptation and the cross-correlation coefficients between head and pelvis were compared across visual conditions and frequencies. Head and pelvis mean positions in space varied little across conditions and perturbation cycles but the mean head PP displacements changed over time. On average, at LF, the PP displacement of the head and pelvis increased progressively. Adaptation was rapid or ineffective with EO, but slower with EO-TG, EO-TP, EC. At HF, the head PP displacement amplitude decreased progressively with fast adaptation rates, while the pelvis adaptation was not apparent. The results show that visual tasks can modulate the adaptation rate, highlight the effect of the perturbation frequency on adaptation and provide evidence of priority assigned to pelvis stabilization over visual tasks at HF. The effects of perturbation frequency and optic flow and their interaction with other sensory inputs and cognitive tasks on the adaptation strategies should be investigated in impaired individuals and considered in the design of rehabilitation protocols.

Visual Verticality Perception in Spinal Diseases: A Systematic Review and Meta-Analysis

Patients diagnosed with traumatic or non-traumatic spinal pain and idiopathic scoliosis frequently suffer from imbalance. The evaluation of the perception of verticality by means of visual tests emerges as a quick and easy tool for clinical management of the balance disorders. Several studies have assessed the visual perception of verticality in spinal diseases obtaining controversial results. The aim of our study is to analyze the perception of visual verticality in subjects with several spinal diseases in comparison with healthy subjects. A meta-analysis was carried out. PubMed MEDLINE, Scopus, WoS, CINAHL, and SciELO databases were searched until January 2020. The standardized mean difference (SMD) was calculated to analyze differences between patients and healthy controls. Fifteen studies with a total of 2052 patients were included. In comparison with healthy subjects, a misperception of verticality was found in patients with spinal pain when the perception of the verticality was assessed with the rod and frame test (SMD = 0.339; 95% confidence interval (CI) = 0.181, 0.497; p < 0.001). It seems that the perception of visual verticality is not altered in patients with idiopathic scoliosis (p = 0.294). The present meta-analysis shows a misperception of visual verticality only in patients with spinal pain.

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.

Do Adolescents With Idiopathic Scoliosis Have an Erroneous Perception of the Gravitational Vertical?

STUDY DESIGN

Multicenter, case-control study.

OBJECTIVES

Demonstrate altered perception of verticality in AIS compared with matched controls.

SUMMARY OF BACKGROUND DATA

The cause of adolescent idiopathic scoliosis (AIS) remains to be found. AIS is associated with neurosensorial anomalies, in particular, altered control of orthostatic posture. During kinetic activity, the upright posture, in humans, is determined in reference to the gravitational vertical (GV). We hypothesized that in AIS, there is a discordance in the perception of the GV and the true GV. In AIS, the longitudinal axis of the body would thus be misoriented because of an erroneous perception of the GV.

METHODS

Thirty adolescents with right thoracic AIS (age 14.23 ± 1.75 years; Cobb angle 31.97°± 12.83°) and 30 controls matched for age (13.93 ± 1.85 years), body mass index, Tanner stage, and handedness were compared for subjective visual vertical (SVV) measured in static and dynamic (optokinetic stimulation) conditions, and subjective postural vertical (SPV).

RESULTS

There was no difference in the two groups, AIS and controls, for SVV. The SPV was significantly different between the two groups (p = .00023). The SPV was shifted to the right for most of the AIS patients (2.13°± 2.22°) compared with controls (-0.08°±1.40°). There was a significant correlation between SPV and clinical frontal tilt in the AIS patients.

CONCLUSION

Our findings demonstrate that patients with right thoracic AIS have an erroneous perception of the GV. In most AIS patients, SPV was shifted to the right, with no alteration of the SVV. AIS might be the consequence of a reoriented longitudinal body axis aligned with an erroneous vertical reference. The underlying mechanism might involve dysfunction of trunk graviceptors. The primary or secondary nature of this dysfunction remains an open question.

Plantar cutaneous afferents influence the perception of Subjective Visual Vertical in quiet stance

The estimation of Subjective Visual Vertical (SVV) involves the allocentric, gravitational and egocentric references, which are built by visual, vestibular and somatosensory afferents. Our goals were to assess the influence of plantar cutaneous afferents on the perception of SVV, and to see if there is a difference according to the efficiency of plantar cutaneous afferents. We recruited 48 young and healthy subjects and assessed their SVV and postural performances in quiet stance with a force platform, at 40 or 200 cm, in four ground conditions: on firm ground, on foam, with a bilateral, or with a unilateral 3 mm arch support. We also assessed the efficiency of our subjects' plantar afferents with the plantar quotient method and divided them in two groups: subjects with a normal use of plantar afferents and subjects with Plantar Exteroceptive Inefficiency (PEI). The results showed significant decreases in the counter clockwise SVV deviation only with the unilateral arch support, at near distance, and among the typically behaving subjects. We conclude that asymmetric foot cutaneous afferents are able to bias the egocentric vertical reference and hence influence the perception of SVV. This influence disappears among subjects with PEI, probably because of a distortion of the plantar signal.

Effect of sleep deprivation on diurnal variation of vertical perception and postural control

The aim of the study was to test the effect of total sleep deprivation on performance and time-of-day pattern of subjective visual vertical (SVV) and postural control. Nineteen healthy, young participants (4 women and 15 men 21.9 ± 1.2 yr) were engaged in two counterbalanced experimental sessions with or without total sleep deprivation. Oral temperature, Karolinska Sleepiness Scale, and visual analogic scale for fatigue, postural control, and SVV were randomly measured every 4 h, from 0600 to 2200. A linear mixed model was used to capture the effect of time of day and sleep condition as factors. A classical adjusted COSINOR function was then used to modelize this daily variation. After the control night of sleep, SVV as well as oral temperature, sleepiness, and fatigue showed significant time-of-day variation, contrasting with measures of postural control which remained stable across the day. After sleep deprivation, SVV showed no diurnal variation, but its mean deviation value increased by 29%. Postural control capability also decreased after sleep deprivation, with a higher center of pressure surface (+70.4%) and total length (+7.37%) but remained stable throughout the day. These results further confirm the negative effect of sleep loss on postural control capability. Even if a direct relationship cannot be confirmed, the disruption of SVV capacity after sleep deprivation could strongly play a role in postural control capacity changes. Sleep deprivation should be considered as a potent factor involved in balance loss and subsequent fall. NEW & NOTEWORTHY The topic of sleep deprivation and postural control is not understood, with discrepancy among results. This study described that postural control displays a stable level throughout the day and that sleep deprivation, even if it increases postural sway, does not affect this stable diurnal pattern. The modification of the perception of the vertical level after sleep deprivation could strongly play a role in the observed changes in postural control capacity.

Internal model of gravity influences configural body processing

Human bodies are processed by a configural processing mechanism. Evidence supporting this claim is the body inversion effect, in which inversion impairs recognition of bodies more than other objects. Biomechanical configuration, as well as both visual and embodied expertise, has been demonstrated to play an important role in this effect. Nevertheless, the important factor of body inversion effect may also be linked to gravity orientation since gravity is one of the most fundamental constraints of our biology, behavior, and perception on Earth. The visual presentation of an inverted body in a typical body inversion paradigm turns the observed body upside down but also inverts the implicit direction of visual gravity in the scene. The orientation of visual gravity is then in conflict with the direction of actual gravity and may influence configural processing. To test this hypothesis, we dissociated the orientations of the body and of visual gravity by manipulating body posture. In a pretest we showed that it was possible to turn an avatar upside down (inversion relative to retinal coordinates) without inverting the orientation of visual gravity when the avatar stands on his/her hands. We compared the inversion effect in typical conditions (with gravity conflict when the avatar is upside down) to the inversion effect in conditions with no conflict between visual and physical gravity. The results of our experiment revealed that the inversion effect, as measured by both error rate and reaction time, was strongly reduced when there was no gravity conflict. Our results suggest that when an observed body is upside down (inversion relative to participants' retinal coordinates) but the orientation of visual gravity is not, configural processing of bodies might still be possible. In this paper, we discuss the implications of an internal model of gravity in the configural processing of observed bodies.

Maintaining Trunk and Head Upright Optimizes Visual Vertical Measurement After Stroke

Background. Visual vertical (VV) measurement provides information about spatial cognition and is now part of postural disorders assessment. Guidelines for clinical VV measurement after stroke remain to be established, especially regarding the orientation settings for patients who do not sit upright. Objectives. We analyzed the need to control body orientation while patients estimate the VV. Methods. VV orientation and variability were assessed in 20 controls and 36 subacute patients undergoing rehabilitation after a first hemisphere stroke, in 3 settings: body not maintained (trunk and head free), partially maintained (trunk maintained, head free), or maintained (trunk and head). VV was analyzed as a function of trunk and head tilt, also quantified. Results. Trunk and head orientations were independent. The ability to sit independently was affected by a tilted trunk. The setting had a strong effect on VV orientation and variability in patients with contralesional trunk tilt (n = 11; trunk orientation −18.4 ± 11.7°). The contralesional VV bias was severe and consistent under partially maintained (−8.4 ± 5.2°) and maintained (−7.8 ± 3.5°) settings, whereas various individual behaviors reduced the mean bias under the nonmaintained setting (−3.6 ± 9.3°, P < .05). VV variability was lower under the maintained (1.5 ± 0.2°) than nonmaintained (3.7 ± 0.4°, P < .001) and partially maintained (3.6 ± 0.2°, P < .001) settings. In contrast, setting had no effect in patients with satisfactory postural control in sitting. Conclusion. Subject setting improves VV measurement in stroke patients with postural disorders. Maintaining the trunk upright enhances the validity of VV orientation, and maintaining the head upright enhances the validity of within-subject variability. Measuring VV without any body maintaining is valid in patients with satisfactory balance abilities.

Neck proprioception shapes body orientation and perception of motion

This review article deals with some effects of neck muscle proprioception on human balance, gait trajectory, subjective straight-ahead (SSA), and self-motion perception. These effects are easily observed during neck muscle vibration, a strong stimulus for the spindle primary afferent fibers. We first remind the early findings on human balance, gait trajectory, SSA, induced by limb, and neck muscle vibration. Then, more recent findings on self-motion perception of vestibular origin are described. The use of a vestibular asymmetric yaw-rotation stimulus for emphasizing the proprioceptive modulation of motion perception from the neck is mentioned. In addition, an attempt has been made to conjointly discuss the effects of unilateral neck proprioception on motion perception, SSA, and walking trajectory. Neck vibration also induces persistent aftereffects on the SSA and on self-motion perception of vestibular origin. These perceptive effects depend on intensity, duration, side of the conditioning vibratory stimulation, and on muscle status. These effects can be maintained for hours when prolonged high-frequency vibration is superimposed on muscle contraction. Overall, this brief outline emphasizes the contribution of neck muscle inflow to the construction and fine-tuning of perception of body orientation and motion. Furthermore, it indicates that tonic neck-proprioceptive input may induce persistent influences on the subject's mental representation of space. These plastic changes might adapt motion sensitiveness to lasting or permanent head positional or motor changes.