Effects of neck muscle vibration on subjective visual vertical: comparative analysis with effects on nystagmus

Comparing the impact of the method of adjustment and forced-choice methodologies on subjective visual vertical bias and variability

BACKGROUND

Previous research suggested that the method of adjustment and forced choice variants of the subjective visual vertical (SVV) produce comparable estimates of both bias and variability. However, variants of the SVV that utilize a method of adjustment procedure are known to be heavily influenced by task parameters, including the stimulus rotation speed, which was not accounted for in previous SVV research comparing the method of adjustment to forced-choice.

OBJECTIVE

The aim of the present study was to determine if (1) the SVV with a forced-choice procedure produces both bias and variability estimates that are comparable to those obtained using a method of adjustment procedure, (2) to see if rotation speed impacts the comparability of estimates and (3) quantify correlations between the estimates produced by different procedures.

METHODS

Participants completed a variant of the SVV which utilized a forced-choice procedure as well as two variants of the SVV using a method of adjustment procedure with two different rotation speeds (6°/s and 12°/s).

RESULTS

We found that the bias estimates were similar across all three conditions tested and that the variability estimates were greater in the SVV variants that utilized a method of adjustment procedure. This difference was more pronounced when the rotation speed was slower (6°/s).

CONCLUSIONS

The results of this study suggest that forced-choice and method of adjustment methodologies yield similar bias estimates and different variability estimates. Given these results, we recommend utilizing forced-choice procedures unless (a) forced-choice is not feasible or (b) response variability is unimportant. We also recommend that clinicians consider the SVV methods when interpreting a patient's test results, especially for variability metrics.

[Clinical application progress of subjective visual vertical test]

Subjective visual vertical test is considered as an effective technique to evaluate otolith organ function and central pathway of gravity perception. This test is non-invasive, easy to operate and has little stimulation. At present, there are few such studies in China. This paper reviews the concept, measurement principle and method, influencing factors, application, advantages and disadvantages of subjective visual vertical test.

The effects of neck muscle vibration on postural orientation and spatial perception: A systematic review

BACKGROUND

Neck muscle vibration (NMV) is increasingly used for its modulation of body orientation and spatial perception, but its mechanisms of action are still not well known.

OBJECTIVES

To describe the effects of NMV on postural orientation and spatial perception, in both healthy people and patients with disturbed balance potentially related to distorted body orientation perception.

METHODS

Following the PRISMA guidelines, a systematic search was performed using the databases MEDLINE, EMBASE, Cochrane library and PEDrO with the key words ((Postural balance) OR (Spatial reference)) AND (Neck muscle vibration) for articles published through to July 2016.

RESULTS

A total of 67 articles were assessed; these exhibited wide heterogeneity and generally poor quality methodology. In healthy subjects, under bilateral NMV, the body tilts in the anterior direction (Level of Evidence LoE II). Under unilateral NMV, the visual environment moves towards the side opposite the vibration (LoE II) and the subject's experience of "straight ahead" is shifted towards the side of the vibration (LoE II). NMV also modulates both spatial and postural bias between stroke and vestibular patients.

DISCUSSION

NMV modulates both spatial and postural bias and could thus be proposed as a tool in rehabilitative therapy. However, due to the heterogeneity of published data and the various significant shortfalls highlighted, current research does not allow clear guidelines to be proposed.

[Pilot study: Determination of the subjective trunk vertical in upright head position]

BACKGROUND

Consensus has been established that the subjective vertical (SV) is a result of multimodal sensory integration. In order to be able to calculate the vestibulocervical sensory competence for the SV, the isolated subjective trunk vertical axis (STV) was measured under conditions of vertical head fixation.

MATERIALS AND METHODS

Young, healthy volunteers (n = 49) were compared to older, healthy volunteers (n = 50) on a three-dimensionally deflectable (tilt, torsion, pitch) trunk excursion chair in which the volunteer's head remains in an upright position. Another young, healthy group was divided into a placebo (n = 27) and a monophasic cervical transcutaneous electrical nerve stimulation (C-TENS; n = 22) group to examine verticality perception.

RESULTS

In the STV after trunk pitch, age was a significant variable (p = 0.021). The older, healthy group of subjects missed the physical vertical by an average of 1.8° more than the younger group. Only the placebo group showed an average improvement in STV of 4.3° after torsion.

CONCLUSION

Apart from the macular organs the vestibulocervical sensory afference is involved in finding the trunk vertical. A difference in age to the disadvantage of the older healthy subjects was observed, as well as a lack of learning success after applied C‑TENS. The presented pilot study was able to confirm that a correct vertical trunk sensation is caused by vestibulocervical sensory afference in upright head position.

Subjective Visual Vertical in Idiopathic Bilateral Vestibular Hypofunction: Enhanced Role of Vision, Neck, and Body Proprioception

INTRODUCTION

We aimed to study the participation of proprioceptive and visual inputs in subjective visual vertical (SVV) in bilateral vestibular hypofunction and in normal subjects.

STUDY DESIGN

Prospective case-control study.

SETTING

Tertiary referral center.

MATERIALS AND METHODS

SVV (six replicates) was measured on a tiltable rehabilitation seat in 26 adult patients with idiopathic bilateral vestibular hypofunction (IBVH) and 33 adult controls. Subjects were asked to place vertically a 45 degrees-tilted red line on a screen (three replicates to left and three to right alternatively) using a remote control in total darkness and in seven body positions: vertical, head, and body left- and right-tilts to 12 and 24 degrees, and then body left- and right-tilt to 24 degrees with the head upright.

RESULTS

In the vertical position, SVV did not differ between IBVH and controls. Patients with IBVH were more sensitive to body tilt than controls (SVV: -8.1 ± 4.66 degrees for IBVH versus -0.2 ± 3.23 for control at 24 degrees body and head left-tilt, p < 0.0001, unpaired t test). The visual attraction effect defined by a deviation of the SVV to the side of the initial line presentation appeared to be higher in the IBVH than in controls suggesting higher visual dependence in IBVH. Placing the head upright while the body was still tilted significantly reduced this difference. Similar results were observed for the right-tilts.

CONCLUSION

Not only otolithic function but also visual plus body and neck proprioceptive entries participate in SVV. The influence of vision and proprioception appears to be enhanced in case of IBVH.

Perception of Upright: Multisensory Convergence and the Role of Temporo-Parietal Cortex

We inherently maintain a stable perception of the world despite frequent changes in the head, eye, and body positions. Such "orientation constancy" is a prerequisite for coherent spatial perception and sensorimotor planning. As a multimodal sensory reference, perception of upright represents neural processes that subserve orientation constancy through integration of sensory information encoding the eye, head, and body positions. Although perception of upright is distinct from perception of body orientation, they share similar neural substrates within the cerebral cortical networks involved in perception of spatial orientation. These cortical networks, mainly within the temporo-parietal junction, are crucial for multisensory processing and integration that generate sensory reference frames for coherent perception of self-position and extrapersonal space transformations. In this review, we focus on these neural mechanisms and discuss (i) neurobehavioral aspects of orientation constancy, (ii) sensory models that address the neurophysiology underlying perception of upright, and (iii) the current evidence for the role of cerebral cortex in perception of upright and orientation constancy, including findings from the neurological disorders that affect cortical function.

The Skull Vibration-Induced Nystagmus Test of Vestibular Function-A Review

A 100-Hz bone-conducted vibration applied to either mastoid induces instantaneously a predominantly horizontal nystagmus, with quick phases beating away from the affected side in patients with a unilateral vestibular loss (UVL). The same stimulus in healthy asymptomatic subjects has little or no effect. This is skull vibration-induced nystagmus (SVIN), and it is a useful, simple, non-invasive, robust indicator of asymmetry of vestibular function and the side of the vestibular loss. The nystagmus is precisely stimulus-locked: it starts with stimulation onset and stops at stimulation offset, with no post-stimulation reversal. It is sustained during long stimulus durations; it is reproducible; it beats in the same direction irrespective of which mastoid is stimulated; it shows little or no habituation; and it is permanent-even well-compensated UVL patients show SVIN. A SVIN is observed under Frenzel goggles or videonystagmoscopy and recorded under videonystagmography in absence of visual-fixation and strong sedative drugs. Stimulus frequency, location, and intensity modify the results, and a large variability in skull morphology between people can modify the stimulus. SVIN to 100 Hz mastoid stimulation is a robust response. We describe the optimum method of stimulation on the basis of the literature data and testing more than 18,500 patients. Recent neural evidence clarifies which vestibular receptors are stimulated, how they cause the nystagmus, and why the same vibration in patients with semicircular canal dehiscence (SCD) causes a nystagmus beating toward the affected ear. This review focuses not only on the optimal parameters of the stimulus and response of UVL and SCD patients but also shows how other vestibular dysfunctions affect SVIN. We conclude that the presence of SVIN is a useful indicator of the asymmetry of vestibular function between the two ears, but in order to identify which is the affected ear, other information and careful clinical judgment are needed.