Vestibular rehabilitation with electrotactile vestibular substitution: early effects

Long-term effects of electrotactile sensory substitution therapy on balance disorders

This clinical research investigated whether a new type of rehabilitation therapy involving the use of a vestibular substitution tongue device (VSTD) is effective for severe balance disorders caused by unilateral vestibular loss. Sixteen patients with postural imbalances because of unilateral vestibular loss underwent training with VSTD. The VSTD transmits information on the head position to the brain through the tongue as substitutes for the lost vestibular information. The device's electrode array was placed on the tongue and participants were trained to maintain a centered body position by ensuring the electrical signals in the center of their tongue. All participants completed 10 min training sessions 2-3 times per day for 8 weeks. Functional gait assessments and the dizziness handicap inventory were, respectively, used to the evaluate participants' dynamic gait function and their severity of balance problems before and after the training period. All examined parameters improved after the 8-week training period. These changes were maintained for up to 2 years after the termination of the training program. Short-term training with VSTD had beneficial carry-over effects. VSTD training might represent a useful rehabilitation therapy in individuals with persistent balance disorders and might lead to long-term improvements in their balance performance and ability to perform daily and social activities.

Improving training for sensory augmentation using the science of expertise

Sensory substitution and augmentation devices (SSADs) allow users to perceive information about their environment that is usually beyond their sensory capabilities. Despite an extensive history, SSADs are arguably not used to their fullest, both as assistive technology for people with sensory impairment or as research tools in the psychology and neuroscience of sensory perception. Studies of the non-use of other assistive technologies suggest one factor is the balance of benefits gained against the costs incurred. We argue that improving the learning experience would improve this balance, suggest three ways in which it can be improved by leveraging existing cognitive science findings on expertise and skill development, and acknowledge limitations and relevant concerns. We encourage the systematic evaluation of learning programs, and suggest that a more effective learning process for SSADs could reduce the barrier to uptake and allow users to reach higher levels of overall capacity.

Interaction between Vestibular Compensation Mechanisms and Vestibular Rehabilitation Therapy: 10 Recommendations for Optimal Functional Recovery

This review questions the relationships between the plastic events responsible for the recovery of vestibular function after a unilateral vestibular loss (vestibular compensation), which has been well described in animal models in the last decades, and the vestibular rehabilitation (VR) therapy elaborated on a more empirical basis for vestibular loss patients. The main objective is not to propose a catalog of results but to provide clinicians with an understandable view on when and how to perform VR therapy, and why VR may benefit from basic knowledge and may influence the recovery process. With this perspective, 10 major recommendations are proposed as ways to identify an optimal functional recovery. Among them are the crucial role of active and early VR therapy, coincidental with a post-lesion sensitive period for neuronal network remodeling, the instructive role that VR therapy may play in this functional reorganization, the need for progression in the VR therapy protocol, which is based mainly on adaptation processes, the necessity to take into account the sensorimotor, cognitive, and emotional profile of the patient to propose individual or "à la carte" VR therapies, and the importance of motivational and ecologic contexts. More than 10 general principles are very likely, but these principles seem crucial for the fast recovery of vestibular loss patients to ensure good quality of life.

Gentamicin-induced bilateral vestibulopathy in rabbits: vestibular dysfunction and histopathology

OBJECTIVES/HYPOTHESIS

Bilateral vestibulopathy (BV) is a mostly persistent and disabling disorder causing dizziness, oscillopsia, and imbalance during locomotion. The animal model is a prerequisite for experimental investigation on prevention and treatment of this disorder. The aim of this study was to determine the vestibular dysfunction and histopathology in rabbits with gentamicin-induced BV.

STUDY DESIGN

Prospective animal study in rabbits.

METHODS

We performed intratympanic gentamicin (ITGM) injections in 12 Lionhead rabbits. The injection was applied to each ear with a 3-day interval. The control group received injections of 0.9% normal saline. The animals were subjected to sinusoidal harmonic accelerations and open field tests for evaluation of the vestibular function before and after the procedures. We also determined histologic changes in the vestibular labyrinth 30 days after the first injection.

RESULTS

One day after unilateral ITGM injection, the rabbits mostly showed ipsiversive head tilt, contralesional spontaneous nystagmus, ipsiversive circling behavior, and decreased gain of the vestibulo-ocular reflex (VOR) during ipsiversive rotation. The second injection to the contralateral ear improved the head tilt but induced marked reduction in the activities and the VOR gains in both directions. These changes persisted until the histologic study confirmed the loss of the hair and supporting cells, diminished nerve fibers, and thinning of the sensory epithelium of the cristae ampullaris and otolith organs in the ITGM group 1 month later.

CONCLUSIONS

ITGM injection securely induced BV in rabbits without side effects such as nephrotoxicity. This rabbit model may be utilized for experiments on the prevention and treatment of BV.

A mathematical model for incorporating biofeedback into human postural control

BACKGROUND

Biofeedback of body motion can serve as a balance aid and rehabilitation tool. To date, mathematical models considering the integration of biofeedback into postural control have represented this integration as a sensory addition and limited their application to a single degree-of-freedom representation of the body. This study has two objectives: 1) to develop a scalable method for incorporating biofeedback into postural control that is independent of the model's degrees of freedom, how it handles sensory integration, and the modeling of its postural controller; and 2) to validate this new model using multidirectional perturbation experimental results.

METHODS

Biofeedback was modeled as an additional torque to the postural controller torque. For validation, this biofeedback modeling approach was applied to a vibrotactile biofeedback device and incorporated into a two-link multibody model with full-state-feedback control that represents the dynamics of bipedal stance. Average response trajectories of body sway and center of pressure (COP) to multidirectional surface perturbations of subjects with vestibular deficits were used for model parameterization and validation in multiple perturbation directions and for multiple display resolutions. The quality of fit was quantified using average error and cross-correlation values.

RESULTS

The mean of the average errors across all tactor configurations and perturbations was 0.24° for body sway and 0.39 cm for COP. The mean of the cross-correlation value was 0.97 for both body sway and COP.

CONCLUSIONS

The biofeedback model developed in this study is capable of capturing experimental response trajectory shapes with low average errors and high cross-correlation values in both the anterior-posterior and medial-lateral directions for all perturbation directions and spatial resolution display configurations considered. The results validate that biofeedback can be modeled as an additional torque to the postural controller without a need for sensory reweighting. This novel approach is scalable and applicable to a wide range of movement conditions within the fields of balance and balance rehabilitation. The model confirms experimental results that increased display resolution does not necessarily lead to reduced body sway. To our knowledge, this is the first theoretical confirmation that a spatial display resolution of 180° can be as effective as a spatial resolution of 22.5°.

The tongue display unit (TDU) for electrotactile spatiotemporal pattern presentation

The Tongue Display Unit (TDU) is a 144-channel programmable pulse generator that delivers dc-balanced voltage pulses suitable for electrotactile (electrocutaneous) stimulation of the anterior-dorsal tongue, through a matrix of surface electrodes. This article reviews the theory of operation and a design overview of the TDU, as well as selected applications. These include sensory substitution, tactile information display and neurorehabilitation via induced neuroplasticity.

Electrical tongue stimulation normalizes activity within the motion-sensitive brain network in balance-impaired subjects as revealed by group independent component analysis

Multivariate analysis of functional magnetic resonance imaging (fMRI) data allows investigations into network behavior beyond simple activations of individual regions. We apply group independent component analysis to fMRI data collected in a previous study looking at the sustained neuromodulatory effects of electrical tongue stimulation in balance-impaired individuals. Twelve subjects with balance disorders viewed optic flow in an fMRI scanner before and after 5 days of electrical tongue stimulation. Nine healthy controls also viewed the visual stimuli but did not receive any stimulation. Multiple regression of the 47 estimated components found two that were modulated by the visual stimuli. Component 7, comprised primarily of the primary visual cortex (V1), responded to all visual stimuli and showed no difference in task-related activity between the healthy controls and the balance-impaired subjects before or after stimulation. Component 11 responded only to motion in the visual field and contained multiple cortical and subcortical regions involved in processing information pertinent to balance. Two-sample t-tests of the calculated signal change revealed that the task-related activity of this network is greater in balance-impaired subjects compared with controls before stimulation (p=0.02), but that this network hypersensitivity decreases after electrical tongue stimulation (p=0.001).

Vestibular substitution: comparative study

OBJECTIVE

To determine the efficacy of vestibular rehabilitation with the electrotactile vestibular substitution system, as a new treatment modality in patients with bilateral vestibular disorders.

STUDY DESIGN AND SETTINGS

Nineteen patients with bilateral, chronic, idiopathic vestibulopathy were studied prospectively. Patients were divided to two groups. Patients in the first group were rehabilitated with the electrotactile vestibular substitution system, while patients in the second group were treated with standard vestibular rehabilitation therapy. The sensory organisation test and dizziness handicap inventory were used to compare the pre- and post-training results of both rehabilitative treatments.

RESULTS

All group one patients in the standardised testing subset demonstrated improved results for both the composite sensory organisation test and for the functional transfer aspect of the dizziness handicap inventory, after five days' training with the electrotactile vestibular substitution system. In contrast, group two patients showed no significant improvement in their composite sensory organisation test or dizziness handicap inventory scores after eight weeks of therapy, compared with pre-treatment levels.

CONCLUSION

These preliminary results indicate the efficacy of the electrotactile vestibular substitution system in improving patients' symptoms of vestibulopathy, and constitute evidence of successful sensory substitution.