Head position-based electrotactile tongue biofeedback affects postural responses to Achilles tendon vibration in humans

Vibration-induced postural reactions: a scoping review on parameters and populations studied

Objective

Mechanical vibration is an effective way for externally activating Ia primary endings of the muscle spindles and skin mechanoreceptors. Despite its popularity in proprioception and postural control studies, there is still no review covering the wide variety of vibration parameters or locations used in studies. The main purpose of this scoping review was thus to give an overview of general vibration parameters and to identify, if available, the rationale for justifying methodological choices concerning vibration parameters.

Methods

Three databases (Pubmed, CINHAL, and SPORTDiscus) were searched from inception to July 2022. Included articles were to focus on the study of muscle spindles and skin mechanoreceptors vibration in humans and assess postural control. Following inclusion, data regarding demographic information, populations, vibration parameters and rationale were extracted and summarized.

Results

One hundred forty-seven articles were included, mostly targeting lower extremities (n = 137) and adults (n = 126). The parameters used varied widely but were most often around 80 Hz, at an amplitude of 1 mm for 10-20 s. Regarding rationales, nearly 50% of the studies did not include any, whereas those including one mainly cited the same two studies, without elaborating specifically on the parameter's choice.

Conclusion

This scoping review provided a comprehensive description of the population recruited and parameters used for vibration protocols in current studies with humans. Despite many studies, there remain important gaps of knowledge that needs to be filled, especially for vibration amplitude and duration parameters in various populations.

Trunk velocity-dependent Light Touch reduces postural sway during standing

Light Touch (LT) has been shown to reduce postural sway in a wide range of populations. While LT is believed to provide additional sensory information for balance modulation, the nature of this information and its specific effect on balance are yet unclear. In order to better understand LT and to potentially harness its advantages for a practical balance aid, we investigated the effect of LT as provided by a haptic robot. Postural sway during standing balance was reduced when the LT force (~ 1 N) applied to the high back area was dependent on the trunk velocity. Additional information on trunk position, provided through orthogonal vibrations, further reduced the sway position-metric of balance but did not further improve the velocity-metric of balance. Our results suggest that limited and noisy information on trunk velocity encoded in LT is sufficient to influence standing balance.

Changes in gait and plantar foot loading upon using vibrotactile wearable biofeedback system in patients with stroke

BACKGROUND

Patients with stroke walk with excessive foot inversion at the affected side, which may disturb their balance and gait.

OBJECTIVES

This study aimed to investigate the effects of instant biofeedback of plantar force at the medial and lateral forefoot regions on gait and plantar foot loading in patients with stroke.

METHODS

A total of eight patients with hemiplegic stroke, who had flexible rearfoot varus deformity at the affected side, participated in this study. A vibrotactile biofeedback system was developed and evaluated. It analyzed forces at the medial and lateral forefeet, and instantly provided vibration clues when the plantar force at medial forefoot was less than a threshold. Each subject's three-dimensional gait parameters and plantar-pressure distribution during walking were measured under two experimental conditions (sequence randomized): with and without the device turned on (Trial-registration number: ChiCTR-IPB-15006530 and HKCTR-1853).

RESULTS

Providing biofeedback significantly reduced the foot inversion and increased the mid-stance foot-floor contact area and medial midfoot plantar pressure of the affected limb, bringing the values of these parameters closer to those of the unaffected side. The biofeedback also significantly reduced the unaffected side's excessive knee flexion and hip abduction.

CONCLUSIONS

There were signs of improved foot loading characteristics and gait upon provision of instant vibrotactile biofeedback of plantar force. The positive results of this study further support the development of wearable biofeedback devices for improving gait of patients with stroke.

Effects of tibialis anterior vibration on postural control when exposed to support surface translations

The sensory re-weighting theory suggests unreliable inputs may be down-weighted to favor more reliable sensory information and thus maintain proper postural control. This study investigated the effects of tibialis anterior (TA) vibration on center of pressure (COP) motion in healthy individuals exposed to support surface translations to further explore the concept of sensory re-weighting. Twenty healthy young adults stood with eyes closed and arms across their chest while exposed to randomized blocks of five trials. Each trial lasted 8 s, with TA vibration either on or off. After 2 s, a sudden backward or forward translation occurred. Anterior-posterior (A/P) COP data were evaluated during the preparatory (first 2 s), perturbation (next 3 s), and recovery (last 3 s) phases to assess the effect of vibration on perturbation response features. The knowledge of an impending perturbation resulted in reduced anterior COP motion with TA vibration in the preparatory phase relative to the magnitude of anterior motion typically observed during TA vibration. During the perturbation phase, vibration did not influence COP motion. However, during the recovery phase vibration induced greater anterior COP motion than during trials without vibration. The fact that TA vibration produced differing effects on COP motion depending upon the phase of the perturbation response may suggest that the immediate context during which postural control is being regulated affects A/P COP responses to TA vibration. This indicates that proprioceptive information is likely continuously re-weighted according to the context in order to maintain effective postural control.

Quantified self and human movement: a review on the clinical impact of wearable sensing and feedback for gait analysis and intervention

The proliferation of miniaturized electronics has fueled a shift toward wearable sensors and feedback devices for the mass population. Quantified self and other similar movements involving wearable systems have gained recent interest. However, it is unclear what the clinical impact of these enabling technologies is on human gait. The purpose of this review is to assess clinical applications of wearable sensing and feedback for human gait and to identify areas of future research. Four electronic databases were searched to find articles employing wearable sensing or feedback for movements of the foot, ankle, shank, thigh, hip, pelvis, and trunk during gait. We retrieved 76 articles that met the inclusion criteria and identified four common clinical applications: (1) identifying movement disorders, (2) assessing surgical outcomes, (3) improving walking stability, and (4) reducing joint loading. Characteristics of knee and trunk motion were the most frequent gait parameters for both wearable sensing and wearable feedback. Most articles performed testing on healthy subjects, and the most prevalent patient populations were osteoarthritis, vestibular loss, Parkinson's disease, and post-stroke hemiplegia. The most widely used wearable sensors were inertial measurement units (accelerometer and gyroscope packaged together) and goniometers. Haptic (touch) and auditory were the most common feedback sensations. This review highlights the current state of the literature and demonstrates substantial potential clinical benefits of wearable sensing and feedback. Future research should focus on wearable sensing and feedback in patient populations, in natural human environments outside the laboratory such as at home or work, and on continuous, long-term monitoring and intervention.

Sensory Substitution for Balance Control Using a Vestibular-to-Tactile Device

Postural control is essential for most activities of daily living. The impairment of this function can be extremely disabling. This work was stimulated by the testimony of a bilateral partial foot amputee who describes his difficulty in maintaining balance while washing his hair in the shower. We postulated that if the postural control system could not rely on accurate and reliable somatosensory inputs from the foot and ankle, as is probably the case following bilateral foot amputation due to the loss of the foot afferents and efferents, the weight of visual and vestibular cues would increase. We therefore assessed if a vestibular-to-tactile sensory substitution device could compensate for this impairment. Two separate experiments were conducted. Experiment 1: The effect of a vestibular-to-tongue tactile biofeedback balance system on the postural stability of this amputee was tested (on a force platform) and compared with a non-amputated, matched control group. The results showed that use of the biofeedback reduced centre of foot (CoP) displacement in all subjects but more spectacularly in the amputee. Experiment 2: The effect of the biofeedback was tested in 16 young healthy adults following a protocol of ankle muscle fatigue (known to alter ankle neuromuscular function and to perturb the control of bipedal posture). The results showed a significant decrease in CoP displacement compared with the control, non-biofeedback condition and a significantly greater effect of the biofeedback in the fatigue than the non-fatigue condition. Taken together, the results of these two studies suggest that an individual with double partial foot amputation was able to improve his balance control thanks to the use of a vestibular-to-tongue tactile biofeedback balance system and that young healthy individuals were able to take advantage of it to reduce the postural destabilisation induced by plantar-flexor muscle fatigue. Further studies are however necessary to confirm this in larger numbers of impaired persons as well as to assess the effectiveness in dynamic situations.

Changes in the diurnal rhythms during a 45-day head-down bed rest

In spaceflight human circadian rhythms and sleep patterns are likely subject to change, which consequently disturbs human physiology, cognitive abilities and performance efficiency. However, the influence of microgravity on sleep and circadian clock as well as the underlying mechanisms remain largely unknown. Placing volunteers in a prone position, whereby their heads rest at an angle of -6° below horizontal, mimics the microgravity environment in orbital flight. Such positioning is termed head-down bed rest (HDBR). In this work, we analysed the influence of a 45-day HDBR on physiological diurnal rhythms. We examined urinary electrolyte and hormone excretion, and the results show a dramatic elevation of cortisol levels during HDBR and recovery. Increased diuresis, melatonin and testosterone were observed at certain periods during HDBR. In addition, we investigated the changes in urination and defecation frequencies and found that the rhythmicity of urinary frequency during lights-off during and after HDBR was higher than control. The grouped defecation frequency data exhibits rhythmicity before and during HDBR but not after HDBR. Together, these data demonstrate that HDBR can alter a number of physiological processes associated with diurnal rhythms.

Influence of sparkle and saccades on tongue electro-stimulation-based vision substitution of 2D vectors

Vision substitution by electro-stimulation has been studied since the 60s beginning with P. Bach-y-Rita. Camera pictures or movies encoded in gray levels are displayed using an electro-stimulation display device on the surface of a body part, such as the skin or the tongue. Medical-technical devices have been developed on this principle to compensate for sensory-motor disabilities such as blindness or loss of balance, or to guide specific actions, such as surgery. However, the electrical signals of stationary or moving slowly moving objects, displayed on a Tongue display unit (TDU), are quickly lost due to saturation of receptors undergoing electrostimulation. We propose to add random saccades or sparkle to the displayed visual scene to increase the quality of pattern recognition by the subjects. In the present experimental trimodal study (normal vision, TDU vision substitution, or both), we show that the presence of a moderate sparkle level enhances the perception of the direction of lines drawn on a TDU and reduces the response time.

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.

Effectiveness of a tongue-placed electrotactile biofeedback to improve ankle force sense following plantar-flexor muscles fatigue

To assess the effectiveness of a tongue-placed electrotactile biofeedback system to improve ankle force sense following plantar-flexor muscles fatigue, 11 young healthy adults were asked to perform an isometric contra-lateral force ankle-matching task in two experimental conditions of No fatigue and Fatigue of the plantar-flexor muscles and two conditions of No biofeedback and Biofeedback. The underlying principle of the biofeedback consisted of supplying subjects with supplementary information about the force developed by the plantar-flexor muscles through electrical stimulation of the tongue. Measures of the overall accuracy and the variability of the force ankle-matching performances were determined using the absolute error and the variable error, respectively. Results showed that (1) the Fatigue condition yielded increased absolute and variable errors relative to the No fatigue condition in the No biofeedback condition, whereas (2) no significant difference between the two No fatigue and Fatigue conditions was observed in the Biofeedback condition. These results suggest that subjects were able to integrate augmented sensory information delivered through electrotactile stimulation of the tongue to suppress the adverse effect of plantar-flexor muscles fatigue on ankle force sense.

Effectiveness of an electro-tactile vestibular substitution system in improving upright postural control in unilateral vestibular-defective patients

We investigated the effects of an electro-tactile vestibular substitution system (EVSS) on upright postural control in 12 unilateral vestibular-defective patients. The underlying principle of this system consists in supplying the user with additional information about his/her head orientation/motion with respect to gravitational vertical, normally provided by the vestibular system, through electro-tactile stimulation of his/her tongue. Subjects were asked to stand as immobile as possible with their eyes closed in two No-EVSS and EVSS conditions. Reduced centre-of-foot pressure displacements were observed in the EVSS relative to the No-EVSS condition. These results, demonstrating the effectiveness of the EVSS system in improving upright postural control in unilateral vestibular-defective patients, could have implications in clinical and rehabilitative areas.