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

Subjective Visual Vertical test with the 3D virtual reality system: effective factors and cybersickness

BACKGROUND

3D Virtual Reality (VR) offers new opportunities in vestibular science. It also presents new challenges and problems.

AIMS/OBJECTIVES

The study aimed to evaluate the effective factors in the 3D VR Subjective Visual Vertical (SVV) test and the impact of cybersickness on the test results.

MATERIAL AND METHODS

The effect of the foam surface, head position in the yaw axis, moving background, and arm position holding the controller was tested. Cybersickness was evaluated using the Simulator Sickness Questionnaire (SSQ).

RESULTS

The head position and controller holding style significantly affected the results. The foam surface and the moving background did not have a significant effect. Although 61.4% of the patients fell into the bad category according to the symptoms of the SSQ score, cybersickness did not significantly affect the SVV results.

CONCLUSIONS AND SIGNIFICANCE

In 3D VR SVV, additional factors should be considered: the headset's weight, head position, and how we hold the controller. The A-effect emerged when the head was 45 degrees turned on the yaw axis. A significant shift was detected in the test, with the arm holding the controller at 90 degrees. Most subjects felt cybersickness at a considerable level. Cybersickness should always be taken into account in VR when planning new applications.

Gravity perception disturbance in patients with unilateral Meniere disease

Objective

To investigate gravity perception disturbance (GPD) in patients with Meniere disease (MD), we classified GPD type based on the results of the head-tilt perception gain (HTPG) and the head-upright subjective visual vertical (HU-SVV) evaluated by the head-tilt SVV (HT-SVV) test in patients with unilateral MD.

Methods

We conducted the HT-SVV test on 115 patients with unilateral MD and 115 healthy controls. Among the 115 patients, the period from the first vertigo episode to the examination (PFVE) was known for 91 patients.

Results

The HT-SVV test classified 60.9% and 39.1% of patients with unilateral MD as GPD and non-GPD, respectively. GPD was classified according to HTPG/HU-SVV combinations as follows: Type A GPD (21.7%, normal HTPG/abnormal HU-SVV), Type B GPD (23.5%, abnormal HTPG/normal HU-SVV), and Type C GPD (15.7%, abnormal HTPG/abnormal HU-SVV). As the PFVE became longer, patients with non-GPD and Type A GPD decreased; however, those with Types B and C GPD increased.

Conclusion

This study provides novel information on unilateral MD from the perspective of gravity perception by classifying GPD based on the results of the HT-SVV test. This study's findings suggest that overcompensation for vestibular dysfunction in patients with unilateral MD exhibited by large HTPG abnormalities may be strongly associated with persistent postural-perceptual dizziness.

Level of Evidence

3b.

Does plantar skin abrasion affect cutaneous mechanosensation?

In humans, plantar cutaneous mechanoreceptors provide critical input signals for postural control during walking and running. Because these receptors are located within the dermis, the mechanical properties of the overlying epidermis likely affect the transmission of external stimuli. Epidermal layers are highly adaptable and can form hard and thick protective calluses, but their effects on plantar sensitivity are currently disputed. Some research has shown no effect of epidermal properties on sensitivity to vibrations, whereas other research suggests that vibration and touch sensitivity diminishes with a thicker and harder epidermis. To address this conflict, we conducted an intervention study where 26 participants underwent a callus abrasion while an age-matched control group (n = 16) received no treatment. Skin hardness and thickness as well as vibration perception thresholds and touch sensitivity thresholds were collected before and after the intervention. The Callus abrasion significantly decreased skin properties. The intervention group exhibited no change in vibration sensitivity but had significantly better touch sensitivity. We argue that touch sensitivity was impeded by calluses because hard skin disperses the monofilament's standardized pressure used to stimulate the mechanoreceptors over a larger area, decreasing indentation depth and therefore stimulus intensity. However, vibration sensitivity was unaffected because the vibrating probe was adjusted to reach specific indentation depths, and thus stimulus intensity was not affected by skin properties. Since objects underfoot necessarily indent plantar skin during weight-bearing, calluses should not affect mechanosensation during standing, walking, or running.

Future trends in brain aging research: Visuo-cognitive functions at stake during mobility and spatial navigation

Aging leads to a complex pattern of structural and functional changes, gradually affecting sensorimotor, perceptual, and cognitive processes. These multiscale changes can hinder older adults' interaction with their environment, progressively reducing their autonomy in performing tasks relevant to everyday life. Autonomy loss can further be aggravated by the onset and progression of neurodegenerative disorders (e.g., age-related macular degeneration at the sensory input level; and Alzheimer's disease at the cognitive level). In this context, spatial cognition offers a representative case of high-level brain function that involves multimodal sensory processing, postural control, locomotion, spatial orientation, and wayfinding capabilities. Hence, studying spatial behavior and its neural bases can help identify early markers of pathogenic age-related processes. Until now, the neural correlates of spatial cognition have mostly been studied in static conditions thereby disregarding perceptual (other than visual) and motor aspects of natural navigation. In this review, we first demonstrate how visuo-motor integration and the allocation of cognitive resources during locomotion lie at the heart of real-world spatial navigation. Second, we present how technological advances such as immersive virtual reality and mobile neuroimaging solutions can enable researchers to explore the interplay between perception and action. Finally, we argue that the future of brain aging research in spatial navigation demands a widespread shift toward the use of naturalistic, ecologically valid experimental paradigms to address the challenges of mobility and autonomy decline across the lifespan.

Results of subjective visual vertical tests in patients with vertigo/dizziness

OBJECTIVE

We previously established the head-tilt subjective visual vertical (HT-SVV) test to evaluate head-tilt perception gain (HTPG) in addition to the original head-upright SVV (HU-SVV) test (Wada-Y et al.: Laryngoscope Investig Otolaryngol, 2020). In this study, we aimed to investigate the HU-SVV and HT-SVV abnormality rates among patients with vertigo/dizziness.

METHODS

Between July 2014 and December 2020, 357 patients were hospitalized for examining the HU-SVV and HT-SVV at our vertigo/dizziness center. Among these patients, 120 had Meniere's disease (MD), 99 had unilateral vestibular disease (UVD), 76 had benign paroxysmal positional vertigo (BPPV), 14 had vestibular migraine (VM), 13 had orthostatic dysfunction (OD), 12 had bilateral vestibular disease (BVD), 12 had central dizziness (CD), 7 had vestibular schwannoma (VS), and 4 had psychogenic dizziness (PD). We determined the reference values of the absolute HU-SVV (<2.5°) and HTPG (0.80-1.25) for the sitting position and used these for calculating the HU-SVV and HT-SVV abnormality rates in each type of vertigo/dizziness.

RESULTS

Among the 357 patients, 111 had abnormal HU-SVV results (31.1%), 132 had abnormal HT-SVV results (37.0%), and 185 had abnormal HU-SVV and/or HT-SVV results (51.8%). The modified HT-SVV test in combination with the original HU-SVV test could detect gravity perception disturbance in patients with vertigo/dizziness significantly better than the original test alone (chi-square: p=0.00019). The HU-SVV, HT-SVV, and HU-SVV and/or HT-SVV abnormality rates were significantly higher in patients with peripheral vestibular diseases, i.e., MD, UVD, BPPV, and BVD than in those with other types of vertigo/dizziness, i.e., VM, OD, CD, VS, and PD (chi-square: p=0.010, p=0.020, and p=0.0025, respectively).

CONCLUSION

These findings suggest that the combined HT-SVV and HU-SVV test could be a powerful neuro-otologic examination for detecting pathologies in the vestibular otolithic pathway.

Does somatosensory feedback from the plantar foot sole contribute to verticality perception?

AIM OF THE STUDY

In upright standing, the human foot sole is the only point of contact with the ground conveying information about the pressure distribution under the feet. We examined how the altered somatosensory input from the plantar foot receptors, when standing on a soft surface, affects the subjective estimation of the earth vertical in different sensory contexts.

MATERIALS AND METHODS

Twelve (12) healthy young females (mean age: 21.8 ± 2.4 years) adjusted the orientation of a visual line (35 × 1.5 cm) representing the roll orientation of a hand-held (attached on a 24.9 × 4 cm cylinder) or head-attached electromagnetic tracking sensor (Nest of Birds, Ascension Technologies Inc., VT. USA, 60 Hz) under two visual conditions (eyes open, eyes closed) while standing on a soft or firm surface. The mean absolute (accuracy) and variable (precision) error in the verticality estimate was depicted in the sensor's roll deviation from the gravitational vertical.

RESULTS

The accuracy and the precision of the estimate decreased in the absence of vision, while standing on the soft surface and when the estimate was provided by an active hand rather than head rotation. The surface effect was significant only in the absence of vision and when the estimate was provided by the hand.

CONCLUSIONS

The contribution of the plantar foot mechanoreceptors to gravity perception is sensory context dependent. Perception of the earth vertical is more accurate when estimated by active head rotation due to the integration of the vestibular and neck proprioceptive afferents.

Effect of head roll-tilt on the subjective visual vertical in healthy participants: Towards better clinical measurement of gravity perception

OBJECTIVE

Gravity perception is an essential function for spatial orientation and postural stability; however, its assessment is not easy. We evaluated the head-tilt perception gain (HTPG, that is, mean perceptual gain [perceived/actual tilt angle] during left or right head roll-tilt conditions) and head-upright subjective visual vertical (SVV) using a simple method developed by us to investigate the characteristics of gravity perception in healthy participants.

METHODS

We measured the SVV and head roll-tilt angle during head roll-tilt within ±30° of vertical in the sitting and standing positions while the participant maintained an upright trunk (sitting, 434 participants; standing, 263 participants). We evaluated the head-upright SVV, HTPG, and laterality of the HTPG.

RESULTS

We determined the reference ranges of the absolute head-upright SVV (<2.5°), HTPG (0.80-1.25), and HTPG laterality (<10%) for the sitting position. The head-upright SVV and HTPG laterality were not influenced by sex or age. However, the HTPG was significantly greater in women than in men and in middle-aged (30-64 years) and elderly (65-88 years) participants than in young participants (18-29 years). The HTPG, but not the head-upright SVV or HTPG laterality, was significantly higher in the standing vs sitting position.

CONCLUSION

The HTPG is a novel parameter of gravity perception involving functions of the peripheral otolith and neck somatosensory systems to the central nervous system. The HTPG in healthy participants is influenced by age and sex in the sitting position and immediately increases after standing to reinforce the righting reflex for unstable posture, which was not seen in the head-upright SVV, previously considered the only parameter.

LEVEL OF EVIDENCE

4.

A gravity-based three-dimensional compass in the mouse brain

Gravity sensing provides a robust verticality signal for three-dimensional navigation. Head direction cells in the mammalian limbic system implement an allocentric neuronal compass. Here we show that head-direction cells in the rodent thalamus, retrosplenial cortex and cingulum fiber bundle are tuned to conjunctive combinations of azimuth and tilt, i.e. pitch or roll. Pitch and roll orientation tuning is anchored to gravity and independent of visual landmarks. When the head tilts, azimuth tuning is affixed to the head-horizontal plane, but also uses gravity to remain anchored to the allocentric bearings in the earth-horizontal plane. Collectively, these results demonstrate that a three-dimensional, gravity-based, neural compass is likely a ubiquitous property of mammalian species, including ground-dwelling animals.

Head direction neurons constitute the brain’s compass, and are classically known to indicate head orientation in the horizontal plane. Here, the authors show that head direction neurons form a three-dimensional compass that can also indicate head tilt, and anchors to gravity.