Noise-enhanced vibrotactile sensitivity in older adults, patients with stroke, and patients with diabetic neuropathy

Getting LOST: A conceptual framework for supporting and enhancing spatial navigation in aging

Spatial navigation is more difficult and effortful for older than younger individuals, a shift which occurs for a variety of neurological, physical, and cognitive reasons associated with aging. Despite a large body of evidence documenting age-related deficits in spatial navigation, comparatively less research addresses how to facilitate more effective navigation behavior for older adults. Since navigation challenges arise for a variety of reasons in old age, a one-size-fits-all solution is unlikely to work. Here, we introduce a framework for the variety of spatial navigation challenges faced in aging, which we call LOST-Location, Orientation, Spatial mapping, and Transit. The LOST framework builds on evidence from the cognitive neuroscience of spatial navigation, which reveals distinct components underpinning human wayfinding. We evaluate research on navigational aids-devices and depictions-which help people find their way around; and we reflect on how navigation aids solve (or fail to solve) specific wayfinding difficulties faced by older adults. In summary, we emphasize a bespoke approach to improving spatial navigation in aging, which focuses on tailoring navigation solutions to specific navigation challenges. Our hope is that by providing precise support to older navigators, navigation opportunities can facilitate independence and exploration, while minimizing the danger of becoming lost. We conclude by delineating critical knowledge gaps in how to improve older adults' spatial navigation capacities that the novel LOST framework could guide to address. This article is categorized under: Psychology > Development and Aging Neuroscience > Cognition Neuroscience > Behavior.

Decrease in current perception thresholds of A-beta fibers by subthreshold noise stimulation using transcutaneous electrical nerve stimulation

Developing effective supplements and rehabilitation of the impaired tactile and proprioception sensation is a significant challenge. One potential method for improving these sensations in clinical practice is using stochastic resonance with white noise. While transcutaneous electrical nerve stimulation (TENS) is a simple method, the effect of subthreshold noise stimulation via TENS on sensory nerve thresholds is currently unknown. This study aimed to investigate whether subthreshold TENS can alter afferent nerve thresholds. The electric current perception thresholds (CPT) of A-beta, A-delta, and C fibers were assessed in 21 healthy volunteers during both subthreshold TENS and control conditions. Subthreshold TENS was found to have lower CPT values compared to the control condition for A-beta fibers. No significant differences were observed between subthreshold TENS and control for A-delta and C fibers. Our findings indicated that subthreshold TENS might selectively enhance the function of A-beta fibers.

Influence of vibrotactile random noise on the smoothness of the grasp movement in patients with chemotherapy-induced peripheral neuropathy

Patients with chemotherapy-induced peripheral neuropathy (CIPN) often suffer from sensorimotor dysfunction of the distal portion of the extremities (e.g., loss of somatosensory sensation, numbness/tingling, difficulty typing on a keyboard, or difficulty buttoning/unbuttoning a shirt). The present study aimed to reveal the effects of subthreshold vibrotactile random noise stimulation on sensorimotor dysfunction in CIPN patients without exacerbating symptoms. Twenty-five patients with CIPN and 28 age-matched healthy adults participated in this study. To reveal the effects of subthreshold vibrotactile random noise stimulation on sensorimotor function, participants were asked to perform a tactile detection task and a grasp movement task during random noise stimulation delivered to the volar and dorsal wrist. We set three intensity conditions of the vibrotactile random noise: 0, 60, and 120% of the sensory threshold (Noise 0%, Noise 60%, and Noise 120% conditions). In the tactile detection task, a Semmes-Weinstein monofilament was applied to the volar surface of the tip of the index finger using standard testing measures. In the grasp movement task, the distance between the thumb and index finger was recorded while the participant attempted to grasp a target object, and the smoothness of the grasp movement was quantified by calculating normalized jerk in each experimental condition. The experimental data were compared using two-way repeated-measures analyses of variance with two factors: experimental condition (Noise 0, 60, 120%) × group (Healthy controls, CIPN patients). The tactile detection threshold and the smoothness of the grasp movement were only improved in the Noise 60% condition without exacerbating numbness/tingling in CIPN patients and healthy controls. The current study suggested that the development of treatment devices using stochastic resonance can improve sensorimotor function for CIPN patients.

The Effect of Subliminal Electrical Noise Stimulation on Plantar Vibration Sensitivity in Persons with Diabetes Mellitus

Subliminal electrical noise (SEN) enhances sensitivity in healthy individuals of various ages. Diabetes and its neurodegenerative profile, such as marked decreases in foot sensitivity, highlights the potential benefits of SEN in such populations. Accordingly, this study aimed to investigate the effect of SEN on vibration sensitivity in diabetes. Vibration perception thresholds (VPT) and corresponding VPT variations (coefficient of variation, CoV) of two experimental groups with diabetes mellitus were determined using a customized vibration exciter (30 and 200 Hz). Plantar measurements were taken at the metatarsal area with and without SEN stimulation. Wilcoxon signed-rank and t tests were used to test for differences in VPT and CoV within frequencies, between the conditions with and without SEN. We found no statistically significant effects of SEN on VPT and CoV (p > 0.05). CoV showed descriptively lower mean variations of 4 and 7% for VPT in experiment 1. SEN did not demonstrate improvements in VPT in diabetic individuals. Interestingly, taking into account the most severely affected (neuropathy severity) individuals, SEN seems to positively influence vibratory perception. However, the descriptively reduced variations in experiment 1 indicate that participants felt more consistently. It is possible that the effect of SEN on thick, myelinated Aβ-fibers is only marginally present.

A Therapeutic Vibrating Insole Device for Postural Instability in Older People with Type 2 Diabetes: A Randomized Control Study

INTRODUCTION

Frail older people with diabetes often present with or develop walking impairments, in part due to lower-limb sensory-motor neuropathy. Several studies suggest a possible improvement of balance control using somatosensory stimulation. We undertook a novel randomized control trial, the aim of which was to observe whether use of this device for 1 month improves walking speed as measured in the 10-m fast walking speed test standardized to body size at month 1 (M1) (FWS). Secondary outcomes were the differences between intervention (VS) and control (C) in the 10-m normal walking speed test, step length, short physical performance battery, timed up and go test, and posturographic measures.

METHODS

Subjects were aged ≥ 70 years and had had type 2 diabetes for at least 2 years. The intervention (VS) at home consisted of 22-min daily vibrating sequences with noise intensity set at 90% of the tactile threshold for each foot. The same device was used in group C but noise was set to 0. Compliance was retrieved from the device.

RESULTS

Among 56 subjects, 27 were in the VS group and 29 in the C group; 35 subjects were frail, 15 were prefrail ,and 6 were non-frail. Bilateral neuropathy was present in 17 subjects. More than half of sessions were done in 36 subjects with no discernible difference according to intervention. At M1 there were no discernible differences in FWS between the groups [VS: 0.96 (0.53) cm s-1 cm-1, C: 0.94 (0.47) cm s-1 cm-1]. There were also no discernible differences in other outcomes, irrespective of the presence of bilateral neuropathy.

CONCLUSION

In a cohort of frail, prefrail, or non-frail older subjects with diabetes, a 1-month intervention using a vibrating insole device did not alter measures of walking speed and related measures. Larger studies with longer term and different stimulation protocols are required to test this hypothesis more fully.

Concomitant sensory stimulation during therapy to enhance hand functional recovery post stroke

Background

Post-stroke hand impairment is prevalent and persistent even after a full course of rehabilitation. Hand diminishes stroke survivors’ abilities for activities of daily living and independence. One way to improve treatment efficacy is to augment therapy with peripheral sensory stimulation. Recently, a novel sensory stimulation, TheraBracelet, has been developed in which imperceptible vibration is applied during task practice through a wrist-worn device. The objective of this trial is to determine if combining TheraBracelet with hand task practice is superior to hand task practice alone.

Methods

A double-blind randomized controlled trial will be used. Chronic stroke survivors will undergo a standardized hand task practice therapy program (3 days/week for 6 weeks) while wearing a device on the paretic wrist. The device will deliver TheraBracelet vibration for the treatment group and no vibration for the control group. The primary outcome is hand function measured by the Wolf Motor Function Test. Other outcomes include the Box and Block Test, Action Research Arm Test, upper extremity use in daily living, biomechanical measure of the sensorimotor grip control, and EEG-based neural communication.

Discussion

This research will determine clinical utility of TheraBracelet to guide future translation. The TheraBracelet stimulation is delivered via a wrist-worn device, does not interfere with hand motion, and can be easily integrated into clinical practice. Enhancing hand function should substantially increase stroke survivors' independence and quality of life and reduce caregiver burden.

Trial registration

NCT04569123. Registered on September 29, 2020

Subthreshold Vibration Influences Standing Balance but Has Unclear Impact on Somatosensation in Persons With Transtibial Amputations

Stochastic resonance has been successfully used to improve human movement when using subthreshold vibration. Recent work has shown promise in improving mobility in individuals with unilateral lower limb amputations. Furthering this work, we present an investigation of two different signal structures in the use of stochastic resonance to improve mobility in individuals with unilateral lower limb amputations. Cutaneous somatosensation and standing balance measures using spatial and temporal analysis were assessed. There were no differences in the somatosensation measures, but differences in the temporal characteristics of the standing measures were seen with the various vibration structures when compared to no vibration, one of which suggesting mass may play an important role in determining who may or may not benefit from this intervention. Stochastic resonance employed with subthreshold vibration influences mobility in individuals with unilateral amputations, but the full direction and extent of influence is yet to be understood.

Remote Subthreshold Stimulation Enhances Skin Sensitivity in the Lower Extremity

Foot sole skin interfaces with the ground and contributes to successful balance. In situations with reduced sensitivity in the glabrous foot skin, stochastic resonance (SR) improves skin sensitivity by adding tactile noise. Some situations, however, involve an interface comprised of hairy skin, which has higher thresholds for sensitivity. For example, in lower extremity amputation the residual limb is comprised of hairy leg skin. The main objective of this study was to determine if SR improves skin sensitivity in hairy skin, and whether a specific intensity of noise is most effective. Secondary objectives were to compare the effect between locations, ages and modalities. In 60 healthy participants a vibrotactile (test) input was delivered at the lower extremity concurrently with a second, noisy stimulus applied more proximally. The presence of a remote SR effect was tested in 15 young participants using electrotactile noise at the calf. Secondary objectives were tested in separate groups of 15 subjects and differed by substituting for one of the three variables: vibrotactile noise, heel site, and with older participants. A forced-choice protocol was used to determine detection ability of the subthreshold vibration test input with varying noise levels applied simultaneously (0, 20, 40, 60, 80, and 100% of perceptual threshold). An SR effect was identified when increased detection of the input was obtained at any level of noise versus no noise. It was found that all four test groups demonstrated evidence of SR: 33–47% of individuals showed better detection of the input with added noise. The SR effect did not appear consistently at any specific noise level for any of the groups, and none of the variables showed a superior ability to evoke SR. Interestingly, in approximately 33% of cases, threshold values fluctuated throughout testing. While this work has provided evidence that SR can enhance the perception of a vibrotactile input in hairy skin, these data suggest that the ability to repeatably show an SR effect relies on maintaining a consistent threshold.

Auditory noise improves balance control by cross-modal stochastic resonance

It is known that enhanced somatosensory function leads to improved balance, and somatosensory function can be enhanced by the appropriate level of mechanical, visual, or auditory noise. In this study, we tested the potential benefit of an auditory noise on balance control. We first assessed static balance by measuring 10 times the duration of standing on the toes of one leg with closed eyes. For the 18 healthy adult participants, the median standing times ranged from 2.1 to 45.6 s, and the median of the distribution was 9.9 s. From the above, the participants were divided into two groups: lower (below 10 s, n = 9) and higher (above 10 s, n = 9) balance groups. We then investigated the effect on balance control of an auditory white noise emitted at the detection threshold. Each individual performed 20 trials. The auditory noise was applied in half the trials, while the remaining trials were conducted without noise. The order of the noise and no-noise trials was quasi-random. In the lower-balance group, the median standing time significantly increased during the noise trials (10.3 s) compared with the time in the no-noise controls (5.2 s). On the other hand, noise had no significant effect in the higher-balance group, presumably because of a ceiling effect. These findings suggest that static balance in the lower-balance participants can be improved by applying a weak noise through cross-modal stochastic resonance.

A Review of Hand-Arm Vibration Studies Conducted by US NIOSH since 2000

Studies on hand-transmitted vibration exposure, biodynamic responses, and biological effects were conducted by researchers at the Health Effects Laboratory Division (HELD) of the National Institute for Occupational Safety and Health (NIOSH) during the last 20 years. These studies are systematically reviewed in this report, along with the identification of areas where additional research is needed. The majority of the studies cover the following aspects: (i) the methods and techniques for measuring hand-transmitted vibration exposure; (ii) vibration biodynamics of the hand-arm system and the quantification of vibration exposure; (iii) biological effects of hand-transmitted vibration exposure; (iv) measurements of vibration-induced health effects; (iv) quantification of influencing biomechanical effects; and (v) intervention methods and technologies for controlling hand-transmitted vibration exposure. The major findings of the studies are summarized and discussed.

Vibrotactile sensitivity testing for occupational and disease-induce peripheral neuropathies

The International Standard Organization (ISO) standard 13091-1 describes methods and procedures for performing the vibrotactile perception threshold (VPT) testing to diagnose changes in tactile sensory function associated with occupational exposures. However, the VPT test also has been used in the diagnosis of peripheral neuropathies associated with a number of disorders. This review examines the VPT test, variations in procedures that have been used, as well as disorders and diseases in which this test has been reliable for the detection of sensory changes. Mechanisms potentially underlying the changes in VPTs are also discussed along with procedural and subject/patient factors that may affect the interpretation of test results. Based upon the review of the literature, there are also suggestions for where additional research might improve the administration of this test, depending upon the subject/patient population and interpretation of data.

Integrating Tactile Feedback Technologies Into Home-Based Telerehabilitation: Opportunities and Challenges in Light of COVID-19 Pandemic

The COVID-19 pandemic has highlighted the need for advancing the development and implementation of novel means for home-based telerehabilitation in order to enable remote assessment and training for individuals with disabling conditions in need of therapy. While somatosensory input is essential for motor function, to date, most telerehabilitation therapies and technologies focus on assessing and training motor impairments, while the somatosensorial aspect is largely neglected. The integration of tactile devices into home-based rehabilitation practice has the potential to enhance the recovery of sensorimotor impairments and to promote functional gains through practice in an enriched environment with augmented tactile feedback and haptic interactions. In the current review, we outline the clinical approaches for stimulating somatosensation in home-based telerehabilitation and review the existing technologies for conveying mechanical tactile feedback (i.e., vibration, stretch, pressure, and mid-air stimulations). We focus on tactile feedback technologies that can be integrated into home-based practice due to their relatively low cost, compact size, and lightweight. The advantages and opportunities, as well as the long-term challenges and gaps with regards to implementing these technologies into home-based telerehabilitation, are discussed.

Stochastic Resonance Reduces Sway and Gait Variability in Individuals With Unilateral Transtibial Amputation: A Pilot Study

Sub-threshold (imperceptible) vibration, applied to parts of the body, impacts how people move and perceive our world. Could this idea help someone who has lost part of their limb? Sub-threshold vibration was applied to the thigh of the affected limb of 20 people with unilateral transtibial amputation. Vibration conditions tested included two noise structures: pink and white. Center of pressure (COP) excursion (range and root-mean-square displacements) during quiet standing, and speed and spatial stride measures (mean and standard deviations of step length and width) during walking were assessed. Pink noise vibration decreased COP displacements in standing, and white noise vibration decreased sound limb step length standard deviation in walking. Sub-threshold vibration positively impacted aspects of both posture and gait; however, different noise structures had different effects. The current study represents foundational work in understanding the potential benefits of incorporating stochastic resonance as an intervention for individuals with amputation.

Subthreshold Electrical Noise Applied to the Plantar Foot Enhances Lower-Limb Cutaneous Reflex Generation

Reflex responses generated by cutaneous mechanoreceptors of the plantar foot are important for the maintenance of balance during postural tasks and gait. With aging, reflex generation, particularly from fast adapting type I receptors, is reduced, which likely contributes to impaired postural stability in this population. Therefore, improving reflex generation from these receptors may serve as a tool to improve balance performance. A mechanism to enhance reflexes may lie in the phenomenon of stochastic resonance, whereby the addition of certain intensities and frequencies of noise stimuli improves the performance of a system. This study was conducted to determine whether tactile noise stimuli could improve cutaneous reflex generation. In 12 healthy young adults, we evoked cutaneous reflex responses using a 0–50 Hz Gaussian noise vibration applied to the plantar heel. Concurrently, we applied one of six subthreshold intensities of electrical tactile noise to the plantar heel [0%, 20%, 40%, 60%, 80% or 100% (threshold)] and were able to analyze data from 0%, 20% and 40% trials. Across participants, it was found that the addition of a 20% perceptual threshold (PT) noise resulted in enhanced reflex responses when analyzed in both the time and frequency domains. These data provide evidence that cutaneous reflex generation can be enhanced via a stochastic resonance effect and that 20% PT is the optimal intensity of noise to do so. Therefore, the addition of noise stimuli may be a valuable clinical intervention to improve reflex responses associated with postural balance in populations with impairments.

The potential influence of stochastic resonance vibrations on neuromuscular strategies and center of pressure sway during single-leg stance

BACKGROUND

Stochastic resonance vibrations are known to enhance balance in the elderly and patients with impaired plantar sensation. However, the underlying mechanisms of plantar vibrations on balance capacity are not well resolved. This study investigated the impact of stochastic resonance vibrations on activities of major extrinsic foot muscles and center of pressure sway in tactile inhibited subjects.

METHODS

Using a customized vibration insole, single-leg stance tests were performed in fourteen healthy subjects at control, ice-intervention-only (inhibited foot sensation) and ice-intervention plus vibration conditions. The sway parameters and the root mean square of electromyography of medial gastrocnemius, tibialis anterior, peroneus longus, and extensor digitorum longus were examined.

FINDINGS

The sway area in the ice-intervention-only condition was significantly increased compared with the control (P < .001). Following vibrations, the sway area, however, was significantly decreased. Regression analysis showed the activity levels of all extrinsic foot muscles were positively correlated with sway area when foot sensation was inhibited. In contrast, following vibrations, only that of the tibialis anterior muscle was positively correlated with sway area, indicative of a muscle control strategy similar to the control condition.

INTERPRETATION

The study showed that stochastic resonance vibrations could effectively reduce body sway in the healthy subjects with inhibited foot sensation. The effects seemed to be associated with improved muscle activities in particular to the tibialis anterior muscle. It suggested that vibration insole may be used as a means to affect neuromuscular strategies to enhance balance control in people with diminished plantar sensations.

Effects of vibro-medical insoles with and without vibrations on balance control in diabetic patients with mild-to-moderate peripheral neuropathy

The purpose of this study was to investigate the effects of a total-contact insole with and without subthreshold mechanical random noise on the balance control in diabetic patients with mild-to-moderate peripheral neuropathy. Twenty diabetic patients with mild-to-moderate neuropathy was recruited to this study. A total-contact insole was prototyped and vibratory motors were embedded into it. The parameters of the center of pressure (amplitude, velocity, and phase plane portrait) were analyzed after 30-minute walks with the shoe only, the shoe with vibro-medical insole with and without vibrations in eyes open and closed condition. The center of pressure amplitude, velocity, and phase plane portrait in the anterior-posterior and medio-lateral directions were significantly decreased using a vibro-medical insole without vibration in the eyes open condition (p < 0.05), as compared to the shoe, and with vibro- medical insole with vibration in both eyes open and closed conditions (p < 0.05) compared to the shoe. A significant drop was observed in the center of pressure amplitude, velocity and phase plane portrait parameters when the vibro-medical insole with vibration was used compared to vibro- medical insole without vibration in eyes closed condition (p < 0.05). The use of vibro-medical insoles was found to improve the patient's balance control, as compared to the shoe. In the eyes closed condition, an improvement in the balance control was observed only with vibro-medical insole with vibration rather than vibro-medical insole without vibration or the shoe. Current finding suggest that a combination of the total-contact insole with vibration may improve the balance control remarkably in diabetic patients with mild-to-moderate neuropathy.

A Tactile Virtual Reality for the Study of Active Somatosensation

Natural exploration of textures involves active sensing, i.e., voluntary movements of tactile sensors (e.g., human fingertips or rodent whiskers) across a target surface. Somatosensory input during moving tactile sensors varies according to both the movement and the surface texture. Combining motor and sensory information, the brain is capable of extracting textural features of the explored surface. Despite the ecological relevance of active sensing, psychophysical studies on active touch are largely missing. One reason for the lack of informative studies investigating active touch is the considerable challenge of assembling an appropriate experimental setup. A possible solution might be in the realm of virtual tactile reality that provides tactile finger stimulation depending on the position of the hand and the simulated texture of a target surface. In addition to rigorous behavioral studies, the investigation of the neuronal mechanisms of active tactile sensing in humans is highly warranted, requiring neurophysiological experiments using electroencephalography (EEG), magnetoencephalography (MEG) and/or functional magnetic resonance imaging (fMRI). However, current neuroimaging techniques impose specific requirements on the tactile stimulus delivery equipment in terms of compatibility with the neurophysiological methods being used. Here, we present a user-friendly, MEG compatible, tactile virtual reality simulator. The simulator consists of a piezo-electric tactile stimulator capable of independently protruding 16 plastic pistons of 1 mm diameter arranged in a 4 × 4 matrix. The stimulator delivers a spatial pattern of tactile stimuli to the tip of a finger depending on the position of the finger moving across a 2-dimensional plane. In order to demonstrate the functionality of the tactile virtual reality, we determined participants’ detection thresholds in active and passive touch conditions. Thresholds in both conditions were higher than reported in the literature. It could well be that the processing of the piston-related stimulation was masked by the sensory input generated by placing the finger on the scanning probe. More so, the thresholds for both the active and passive tasks did not differ significantly. In further studies, the noise introduced by the stimulator in neuromagnetic recordings was quantified and somatosensory evoked fields for active and passive touch were recorded. Due to the compatibility of the stimulator with neuroimaging techniques such as MEG, and based on the feasibility to record somatosensory-related neuromagnetic brain activity the apparatus has immense potential for the exploration of the neural underpinnings of active tactile perception.

Vibrotactile Feedback for Improving Standing Balance

Maintaining balance standing upright is an active process that complements the stabilizing properties of muscle stiffness with feedback control driven by independent sensory channels: proprioceptive, visual, and vestibular. Considering that the contribution of these channels is additive, we investigated to what extent providing an additional channel, based on vibrotactile stimulation, may improve balance control. This study focused only on healthy young participants for evaluating the effects of different encoding methods and the importance of the informational content. We built a device that provides a vibrotactile feedback using two vibration motors placed on the anterior and posterior part of the body, at the L5 level. The vibration was synchronized with an accelerometric measurement encoding a combination of the position and acceleration of the body center of mass in the anterior-posterior direction. The goal was to investigate the efficacy of the information encoded by this feedback in modifying postural patterns, comparing, in particular, two different encoding methods: vibration always on and vibration with a dead zone, i.e., silent in a region around the natural stance posture. We also studied if after the exposure, the participants modified their normal oscillation patterns, i.e., if there were after effects. Finally, we investigated if these effects depended on the informational content of the feedback, introducing trials with vibration unrelated to the actual postural oscillations (sham feedback). Twenty-four participants were asked to stand still with their eyes closed, alternating trials with and without vibrotactile feedback: nine were tested with vibration always on and sham feedback, fifteen with dead zone feedback. The results show that synchronized vibrotactile feedback reduces significantly the sway amplitude while increasing the frequency in anterior-posterior and medial-lateral directions. The two encoding methods had no different effects of reducing the amount of postural sway during exposure to vibration, however only the dead-zone feedback led to short-term after effects. The presence of sham vibration, instead, increased the sway amplitude, highlighting the importance of the encoded information.

Shoes with active insoles mitigate declines in balance after fatigue

Fatigue can induce postural instability and even lead to falls. However, most current methods to delay or reduce fatigue require long preparatory time, or large and expensive equipment. We propose a convenient method to alleviate postural instability due to fatigue. We paid attention to that fatigue and aging share similar neurophysiological deterioration of sensory-motor function. Considering that stochastic resonance via sub-sensory mechanical vibration increases postural stability in the elderly, we propose that sub-sensory insole vibration reduces the negative effect of fatigue on postural control. We performed experiments with 21 young and healthy adult participants, and demonstrated that insole vibration compensates for the loss of balance ability due to fatigue. The sub-sensory insole vibration restored both the area of center of pressure and the complexity of the time series of the motor output after fatigue to the pre-fatigue levels. The insole units generating the vibration were completely concealed in shoes and controlled by a smart phone. This compact implementation contrasts with the cumbersome procedure of current solutions to fatigue-induced postural instability.

Mechanical Noise Improves the Vibration Perception Threshold of the Foot in People With Diabetic Neuropathy

BACKGROUND

Mechanical noise may improve somatosensation at the dorsal side of the foot, but the effect at the plantar side of the foot, the side most at risk for foot ulceration, is unknown. Moreover, techniques used in research so far have several problems that limit applicability in daily practice. Piezoelectric actuators may provide mechanical noise with better clinical applicability. We assessed the effects of piezoelectric actuators generating mechanical noise on the vibration perception threshold (VPT) at the plantar side of the foot in people with diabetic neuropathy.

METHODS

Double-blind within-subjects design in a controlled laboratory setting including participants with diabetic neuropathy (N = 40; 18 male; mean age 69.6 years; mean duration of diabetes 14.1 years; mean BMI 30.5). VPT was measured at three plantar foot locations with and without mechanical noise applied via piezoelectric actuators.

RESULTS

Mechanical noise improved VPT at metatarsophalangeal joint (MTP) 1 (left 39.3V vs 43.5V; right 39.0 vs 42.6 V), MTP5 (left 37.5V vs 41.7V; right 34.5V vs 40.8V) and the heel (left 40.0V vs 44.0V; right 39.3V vs 41.0V), all P < .001.

CONCLUSIONS

Mechanical noise improves VPT at the plantar side of the foot in people with diabetic neuropathy. This is an important step for further development of insoles using mechanical noise that may have the potential to improve VPT and decrease the risk of foot ulceration.

The Effect of Daily Use of Plantar Mechanical Stimulation Through Micro-Mobile Foot Compression Device Installed in Shoe Insoles on Vibration Perception, Gait, and Balance in People With Diabetic Peripheral Neuropathy

OBJECTIVE

People with diabetic peripheral neuropathy (DPN) have impaired gait and balance performance. The aim of this study is to investigate therapeutic effectiveness of mechanical stimulation through a wearable foot compression device equipped in a shoe insole on vibration perception, balance control and gait performance in people with DPN.

METHODS

Using a single-arm 4-week intervention study design, we examined effectiveness of daily use of shoes equipped with the foot compression device (Footbeat™, AVEX, Grand Junction, CO, USA) on improving vibration perception threshold (VPT_max), skin perfusion pressure (SPP), ankle brachial index (ABI), lower extremities edema (circumferences in the calf and ankle), and motor performance (postural sway with eyes open and closed conditions, and gait performance during normal, dual-task and fast walking). Thirty people with type 2 diabetes and symptoms of PN completed the experimental protocol.

RESULTS

Improvements in VPT_max (before = 27.4 V, after = 23.3 V, P = .007, d = 0.33, where d denotes effect size), center-of-mass sway in the mediolateral direction with both eyes open and closed conditions (before = 0.94 cm, after = 0.76 cm, P = .020, d = 0.47; before = 1.10 cm, after = 0.83 cm, P = .033, d = 0.66, respectively), and stride velocity for normal walking, dual-task walking and fast walking tasks (before = 0.87 m/s, after = 0.96 m/s, P = .017, d = 0.41; before = 0.75 m/s, after = 0.91 m/s, P = .001, d = 0.77; before = 1.10 m/s, after = 1.20 m/s, P = .043, d = 0.33, respectively) were found post treatment. There was no significant improvement in SPP, ABI, and circumferences in the calf and ankle.

CONCLUSIONS

Our findings suggest the wearable foot compression device may be effective for reducing neuropathic symptoms and enhancing motor performances in people with DPN.

Velocity controlled pattern writing: An application of stochastic resonance

In the present work, the concept of stochastic resonance is employed for pattern fabrication. In particular, the interplay of noise amplitudes and intrinsic system time scales is investigated. This interplay enabled us to obtain preordained patterns. Experiments were performed galvanostatically in a two electrode electrochemical cell onto a n-type Si substrate using a coherent wavelength laser source of 5 mW intensity. A focused laser beam was swept along the silicon substrate unidirectionally by moving the electrochemical cell at different velocities. By systematic tuning of the velocity, we have observed a unimodal variation in the contrast of the pattern. This indicates the occurrence of the stochastic resonance phenomena. Corresponding numerical simulations, performed on a spatial array of diffusively coupled FitzHugh-Nagumo oscillators in the presence of external noise, reveal good agreement with the experimental observations.

Subthreshold Vibrotactile Noise Stimulation Immediately Improves Manual Dexterity in a Child With Developmental Coordination Disorder: A Single-Case Study

Developmental coordination disorder (DCD) is the most common childhood movement disorder. It is characterized by clumsiness of fine and gross motor skills in developing children. Children with DCD have low ability to effectively use tactile information for movements, instead relying on visual information. In addition, children with DCD have deficits in visuo-motor temporal integration, which is important in motor control. These traits subsequently lead to clumsiness of movements. Conversely, however, imperceptible vibrotactile noise stimulation (at 60%-intensity of the sensory threshold) to the wrist provides stochastic resonance (SR) phenomenon to the body, improving the sensory and motor systems. However, the effects of SR have not yet been validated in children with DCD. Thus, we conducted a single case study of a 10-year-old boy with a diagnosis of DCD to investigate the effect of SR on visual dependence, visuo-motor temporal integration, and manual dexterity. SR was provided by vibrotactile noise stimulation (at an intensity of 60% of the sensory threshold) to the wrist. Changes in manual dexterity (during the SR on- and off-conditions) were measured using the manual dexterity test of the Movement Assessment Battery for Children-2nd edition. The point of subjective equality measured by visual or tactile temporal order judgment task served as a quantitative indicator reflecting specific sensory dependence. The delay detection threshold and steepness of delay detection probability curve, which were measured using the delayed visual feedback detection task, were used as quantitative indicators of visuo-motor temporal integration. The results demonstrated alleviated visual dependence and improved visuo-motor temporal integration during the SR on-conditions rather than the SR off-conditions. Most importantly, manual dexterity during the SR on-conditions was significantly improved compared to that during the SR off-conditions. Thus, the present results highlighted that SR could contribute to improving poor movement in children with DCD. However, since this was a single case study, a future interventional study with a large sample size is needed to determine the effectiveness of SR for children with DCD.

A Therapeutic Insole Device for Postural Stability in Older People With Type 2 Diabetes. A Feasibility Study (SENSOLE Part I)

The application of a stochastic mechanical noise has been shown to improve plantar touch sensitivity in patients with diabetic neuropathy and balance control. The present work aimed to test the feasibility of a specially designed vibrating device on gait and posture in older patients with type 2 diabetes with special interest on potential side effect (sensation of needles or tingling, dizziness or falls) before further investigations. For this, gait and balance tests were performed in 29 older out and in-patients (mean age 84 years, Barthel index ≥ 60/100) immediately before and after a 19 min plantar vibrating sequence, as well as 15 min after. These tests included posturographic measurements under eyes closed and static conditions and clinical gait tests (Short Physical Performance Battery and Timed-Up and Go tests). The results showed that no side effect was measured immediately, 15 min and up to 30 days after the vibration sequence. Besides, postural and clinical gait tests showed global positive effects at immediate and 15 min follow-up. Further investigation are now necessary to determine whether a daily stimulation sequence for a given time would lead to long-term positive effects on daily living (NCT01654341; https://clinicaltrials.gov/ct2/show/NCT01654341).

Investigation on the effect of noisy galvanic vestibular stimulation on fine motor skills during a visuomotor task in healthy participants

Noisy galvanic vestibular stimulation (nGVS) has been shown to improve dynamic walking stability, affect postural responses, enhance balance in healthy subjects, and influence motor performance in individuals with Parkinson’s disease. Although the studies to fully characterize the effect of nGVS are still ongoing, stochastic resonance theory which states that the addition of noisy signal may enhance a weak sensory input signals transmission in a non-linear system may provide a possible explanation for the observed positive effects of nGVS. This study explores the effect of nGVS on fine tracking behavior in healthy subjects. Ten healthy participants performed a computer-based visuomotor task by controlling an object with a joystick to follow an amplitude-modulated signal path while simultaneously receiving a sham or pink noise nGVS. The stimulation was generated to have a zero-mean, linearly detrended 1/f-type power spectrum, Gaussian distribution within 0.1–10 Hz range, and a standard deviation (SD) set to 90% based on each participant’s cutaneous threshold value. Results show that simultaneous nGVS delivery statistically improved the tracking performance with a decreased root-mean-squared error of 5.71±6.20% (mean±SD), a decreased time delay of 11.88±9.66% (mean±SD), and an increased signal-to-noise ratio of 2.93% (median, interquartile range (IQR) 3.31%). This study showed evidence that nGVS may be beneficial in improving sensorimotor performance during a fine motor tracking task requiring fine wrist movement in healthy subjects. Further research with a more comprehensive subset of tasks is required to fully characterize the effects of nGVS on fine motor skills.

Effect of stochastic resonance on proprioception and kinesthesia in anterior cruciate ligament reconstructed patients

Low amplitude mechanical noise vibration has been shown to improve somatosensory acuity in various clinical groups with comparable deficiencies through a phenomenon known as Stochastic Resonance (SR). This technology showed promising outcomes in improving somatosensory acuity in other clinical patients (e.g., Parkinson's disease and osteoarthritis). Some degree of chronic somatosensory deficiency in the knee has been reported following anterior cruciate ligament (ACL) reconstruction surgery. In this study, the effect of the SR phenomenon on improving knee somatosensory acuity (proprioception and kinesthesia) in female ACL reconstructed (ACLR) participants (n = 19) was tested at three months post-surgery, and the results were compared to healthy controls (n = 28). Proprioception was quantified by the measure of joint position sense (JPS) and kinesthesia with the threshold to detection of passive movement (TDPM). The results based on the statistical analysis demonstrated an overall difference between the somatosensory acuity in the ACLR limb compared to healthy controls (p = 0.007). A larger TDPM was observed in the ACLR limb compared to the healthy controls (p = 0.002). However, the JPS between the ACLR and healthy limbs were not statistically significantly different (p = 0.365). SR significantly improved JPS (p = 0.006) while the effect was more pronounced in the ACLR cohort. The effect on the TDPM did not reach statistical significance (p = 0.681) in either group. In conclusion, deficient kinesthesia in the ACLR limb was observed at three months post-surgery. Also, the positive effects of SR on somatosensory acuity in the ACL reconstructed group warrant further investigation into the use of this phenomenon to improve proprioception in ACLR and healthy groups.

Stochastic resonance improves visuomotor temporal integration in healthy young adults

Mechanical and electrical noise stimulation to the body is known to improve the sensorimotor system. This improvement is related to stochastic resonance (SR), a phenomenon described as a "noise benefit" to various sensory and motor systems. The current study investigated the influence of SR on visuomotor temporal integration and hand motor function under delayed visual feedback in healthy young adults. The purpose of this study was to measure the usefulness of SR as a neurorehabilitation device for disorders of visuomotor temporal integration. Thirty healthy volunteers underwent detection tasks and hand motor function tests under delayed visual feedback, with or without SR. Of the 30 participants, 15 carried out the tasks under delayed visual feedback in the order of SR on-condition, off-condition, off-condition, and on-condition. The remaining 15 participants conducted the experimental tasks in the order of SR off-condition, on-condition, on-condition, and off-condition. Comparisons of the delay detection threshold (DDT), steepness of the delay detection probability curves, box and block test (BBT) scores, and nine-hole peg test (NHPT) scores between the SR on- and off-conditions were performed. The DDT under the SR on-condition was significantly shortened compared with the SR off-condition. There was no significant difference between the SR on- and off-conditions for the steepness of the delay detection probability curves, BBT scores, and NHPT scores. SR improved visuomotor temporal integration in healthy young adults, and may therefore improve movement disorders in patients with impaired visuomotor temporal integration. However, because the current results showed that SR did not improve hand motor function under delayed visual feedback, it may not improve motor function when a large distortion of visuomotor temporal integration is present. Further studies are required considering several limitations of the current study, and future clinical trials are necessary to verify the effects of motor training using SR for the treatment of visuomotor temporal integration disorders.

The effects of vibro-medical insole on sensation and plantar pressure distribution in diabetic patients with mild-to-moderate peripheral neuropathy

BACKGROUND

The first aim of this study was to determine the effect of a vibro-medical insole on pressure sensation and the second was to measure the effects of a vibro-medical insole with and without random noise on plantar pressure distribution in diabetic patients with mild-to-moderate peripheral neuropathy.

METHODS

Twenty patients with mild-to-moderate diabetic neuropathy were recruited in the clinical trial pre-test, post-test study. A medical insole was made for each participant and a vibratory system was inserted into it. Pressure sensation was evaluated before and after the 30-min walk using the vibro-medical insole with added random noise by Semmes-Weinstein Monofilaments. Peak pressure data was measured before and after 30-min walking with a vibro-medical insole with and without random noise by the Pedar-x system.

FINDINGS

Pressure sensations showed improvement after 30-min walking with the vibro-medical insole with added random noise at the heel, metatarsophalangeal heads and hallux of both feet in all participants (p < 0.05). Peak pressure decreased significantly in the heel, MTP_2,3, MTP_4,5 and hallux (p < 0.05) and increased in midfoot (p < 0.05) using the vibro-medical insole with and without random noise compared to the shoe only condition. Only the peak pressure of the heel region decreased using the vibro-medical insole with random noise compared to without random noise (p = 0.006).

INTERPRETATION

Thirty minute walking with a vibro-medical insole seems to improve pressure sensation and alter peak pressure in diabetic patients with mild-to-moderate peripheral neuropathy. This work suggests that vibro-medical insoles can be used for daily living activities and possibly decreases the risk of ulceration in diabetic neuropathy patients.

Subliminal electrical and mechanical stimulation does not improve foot sensitivity in healthy elderly subjects

OBJECTIVE

Deterioration of cutaneous perception may be one reason for the increased rate of falling in the elderly. The stochastic resonance phenomenon may compensate this loss of information by improving the capability to detect and transfer weak signals. In the present study, we hypothesize that subliminal electrical and mechanical noise applied to the sole of the foot of healthy elderly subjects improves vibration perception thresholds (VPT).

METHODS

VPTs of 99 healthy elderly subjects were measured at 30 Hz at the heel and first metatarsal head (MET I). Participants were randomly assigned to one of five groups: vibration (Vi-G), current (Cu-G), control (Co-G), placebo-vibration (Pl-Vi), and placebo-current (Pl-Cu). Vi-G and Cu-G were stimulated using 90% (subliminal) of their individual perception thresholds for five minutes in a standing position. Co-G received no stimulation. The placebo groups were treated with mock stimulation. VPTs were measured twice before the intervention (baseline (BASE) and pre-measurement (PRE)), and once after the intervention (post-measurement (POST)).

RESULTS

Significant differences were found between measurement conditions comparing BASE and POST, and PRE and POST. VPTs between groups within each measurement condition showed no significant differences. Vi-G was the only group that showed significantly higher VPTs in POST compared to BASE and PRE, which contradicts previous studies.

CONCLUSION

We analyzed increased VPTs after subliminal mechanical stimulation. The pressure load of standing for five minutes combined with subliminal stimulation may have shifted the initial level of mechanoreceptor sensitivity, which may lead to a deterioration of the VPT. The subliminal electrical stimulation had no effect on VPT.

SIGNIFICANCE

Based on our results, we cannot confirm positive effects of subliminal electrical or mechanical stimulation on the sole of the foot.

Children with moderate to severe cerebral palsy may not benefit from stochastic vibration when developing independent sitting

PURPOSE

Determine sitting postural control changes for children with cerebral palsy (CP), using a perceptual-motor intervention and the same intervention plus stochastic vibration through the sitting surface.

METHODS

Two groups of children with moderate or severe CP participated in the 12 week interventions. The primary outcome measure was center of pressure data from which linear and nonlinear variables were extracted and the gross motor function measure (GMFM).

RESULTS

There were no significant main effects of intervention or time or an interaction. Both treatment groups increased the Lyapunov exponent values in the medial-lateral direction three months after the start of treatment as well as their GMFM scores in comparison with baseline.

CONCLUSIONS

The stochastic vibration did not seem to advance the development of sitting postural control in children between the ages of 2 and 6 years. However, perceptual-motor intervention was found beneficial in advancing sitting behavior.

Intrinsic stochastic resonance via set-point variation

In the present paper, the possibility of invoking stochastic resonance (SR, periodic and aperiodic) by regulating the operating value of an appropriate parameter is explored. The operating values of these parameters are defined as the set point of the system throughout the present paper. Brusselator, a mathematical model [I. Prigogine and R. Lefever, J. Chem. Phys. 48, 1695 (1968)JCPSA60021-960610.1063/1.1668896] of nonlinear chemical reactions, is used for this purpose. We consider the effect of intrinsic noise in the Brusselator due to the Markovian nature of the chemical reactions. The stochastic time evolution is studied using the Gillespie algorithm [D. T. Gillespie, J. Comput. Phys. 22, 403 (1976)JCTPAH0021-999110.1016/0021-9991(76)90041-3], which is an exact stochastic simulation algorithm. We analyze the dependence of the resonance point on both the strength of the intrinsic noise as well as the distance from the bifurcation point. Subsequently, the phenomena of SR is explored using both periodic and aperiodic stimulus. It was found that, for a given system size, in both cases, SR is achieved by variation of the set point. Set-point variation can be achieved by regulating either the source concentration or the rate constants. Resonance is observed in both cases. However, this resonance occurs at different values of the set point, even with a fixed system size. This is clearly seen in the set-point versus system-size plane, where the resonance line has different slopes for the two scenarios. Our semianalytic treatment points to the fact that for a given system size intrinsic noise is affected differently for different methods involving the variation of the set point. This is explained by writing the corresponding chemical Langevin equation and comparing the various intrinsic noise sources.

Effects of White Noise Achilles Tendon Vibration on Quiet Standing and Active Postural Positioning

Applying white noise vibration to the ankle tendons has previously been used to improve passive movement detection and alter postural control, likely by enhancing proprioceptive feedback. The aim of the present study was to determine if similar methods focused on the ankle plantarflexors affect the performance of both quiet standing and an active postural positioning task, in which participants may be more reliant on proprioceptive feedback from actively contracting muscles. Twenty young, healthy participants performed quiet standing trials and active postural positioning trials designed to encourage reliance on plantarflexor proprioception. Performance under normal conditions with no vibration was compared to performance with 8 levels of vibration amplitude applied to the bilateral Achilles tendons. Vibration amplitude was set either as a percentage of sensory threshold (n = 10) or by root-mean-square (RMS) amplitude (n = 10). No vibration amplitude had a significant effect on quiet standing. In contrast, accuracy of the active postural positioning task was significantly (P = .001) improved by vibration with an RMS amplitude of 30 μm. Setting vibration amplitude based on sensory threshold did not significantly affect postural positioning accuracy. The present results demonstrate that appropriate amplitude tendon vibration may hold promise for enhancing the use of proprioceptive feedback during functional active movement.

Efficacy of Stochastic Vestibular Stimulation to Improve Locomotor Performance During Adaptation to Visuomotor and Somatosensory Distortion

Astronauts exposed to microgravity face sensorimotor challenges affecting balance control when readapting to Earth's gravity upon return from spaceflight. Small amounts of electrical noise applied to the vestibular system have been shown to improve balance control during standing and walking under discordant sensory conditions in healthy subjects, likely by enhancing information transfer through the phenomenon of stochastic resonance. The purpose of this study was to test the hypothesis that imperceptible levels of stochastic vestibular stimulation (SVS) could improve short-term adaptation to a locomotor task in a novel sensory discordant environment. Healthy subjects (14 males, 10 females, age = 28.7 ± 5.3 years, height = 167.2 ± 9.6 cm, weight = 71.0 ± 12.8 kg) were tested for perceptual thresholds to sinusoidal currents applied across the mastoids. Subjects were then randomly and blindly assigned to an SVS group receiving a 0–30 Hz Gaussian white noise electrical stimulus at 50% of their perceptual threshold (stim) or a control group receiving zero stimulation during Functional Mobility Tests (FMTs), nine trials of which were done under conditions of visual discordance (wearing up/down vision reversing goggles). Time to complete the course (TCC) was used to test the effect of SVS between the two groups across the trials. Adaptation rates from the normalized TCCs were also compared utilizing exponent values of power fit trendline equations. A one-tailed independent-samples t-test indicated these adaptation rates were significantly faster in the stim group (n = 12) than the control (n = 12) group [t_(16.18) = 2.00, p = 0.031]. When a secondary analysis was performed comparing “responders” (subjects who showed faster adaptation rates) of the stim (n = 7) group to the control group (n = 12), independent-samples t-tests revealed significantly faster trial times for the last five trials with goggles in the stim group “responders” than the controls. The data suggests that SVS may be capable of improving short-term adaptation to a locomotion task done under sensory discordance in a group of responsive subjects.

The effect of flat and textured insoles on the balance of primary care elderly people: a randomized controlled clinical trial

BACKGROUND

Aging is associated with reduced postural stability and increased fall risk. Foot orthoses have been reported as an adjuvant intervention to improve balance by stimulating foot plantar mechanical receptors and thus increasing somatosensory input.

PURPOSE

The aim of this study is to evaluate the effect of flat and textured insoles on the balance of primary care elderly people.

DESIGN

Prospective, parallel, randomized, and single-blind trial.

METHODS

A total of 100 subjects from a primary care unit, aged ≥65 years, were randomly assigned to intervention groups with flat insoles (n=33), textured insoles (n=33), or control group (n=34) without insoles. The Berg Balance Scale and the Timed Up and Go test were assessed at baseline and after 4 weeks.

RESULTS

Improvements in the Berg Balance Scale and the Timed Up and Go test were noted only in intervention groups with insoles but not in control group. No significant difference was found between flat and textured insoles. Minor adverse effects were noted only in the group with textured insoles.

CONCLUSION

The results suggest that foot orthoses (both flat and textured insoles) are effective in improving balance in primary care elderly people. They may represent a low-cost and high-availability adjuvant strategy to improve balance and prevent falls in this population.

Dose postural control improve following application of transcutaneous electrical nerve stimulation in diabetic peripheral neuropathic patients? A randomized placebo control trial

BACKGROUND

peripheral neuropathy is the most common problem of diabetes. Neuropathy leads to lower extremity somatosensory deficits and postural instability in these patients. However, there are not sufficient evidences for improving postural control in these patients.

AIM

To investigate the effects of transcutaneous electrical nerve stimulation (TENS) on postural control in patients with diabetic neuropathy.

METHODS

Twenty eighth patients with diabetic neuropathy (40-55 Y/O) participated in this RCT study. Fourteen patients in case group received TENS and sham TENS was used for control group. Force plate platform was used to extract sway velocity and COP displacement parameters for postural control evaluation.

RESULTS

The mean sway velocity and center of pressure displacement along the mediolateral and anteroposterior axes were not significantly different between two groups after TENS application (p>0.05).

CONCLUSION

Application of 5min high frequency TENS on the knee joint could not improve postural control in patients with diabetic neuropathy.

Spatially coincident vibrotactile noise improves subthreshold stimulus detection

Stochastic Resonance (SR) is a phenomenon, mainly present in nonlinear detection systems, in which the addition of certain amount of noise, called optimal noise, has proven to enhance detection performance of subthreshold stimuli. When added noise is present only during the stimulus, an additional enhancement can be reached. This phenomenon was called time Coincidence Enhanced Stochastic Resonance (CESR). The aim of this study was to study the effect of spatially distributed vibrotactile noise in subthreshold stimuli detection. The correct response rates from two different stimuli conditions were compared, using four tactile stimulator systems to excite four different spatial locations on the fingertip. Under two different conditions, the stimuli were present in only one randomly chosen stimulator. For the first condition, all stimulators contain optimal noise level. In the second condition, the optimal noise was present only at the stimulator with the stimulus. SR threshold principle should not produce different correct response rates between the two conditions, since in both cases the noise enables the subthreshold stimulus to go above threshold. The stimulus signal used was a rectangular displacement controlled pulse that lasted 300ms within a 1.5s attention interval, applied to the exploratory zone of the index finger of 13 human subjects. For all subjects it was found that detection rates were better (p<0.0003) when noise was spatially coincident with the stimulus, compared to the condition in which noise was present simultaneously in all the stimulators. According to our literature review this is the first report of SR being influenced by the spatial location of the noise. These results were not found previously reported, so represent the discovery of a new phenomenon. We call this phenomenon Spatial-Coincidence-Enhanced Stochastic Resonance (SCESR). As results show, the optimal noise level is dependent on the relative position between stimulus and noise.

A random-perturbation therapy in chronic non-specific low-back pain patients: a randomised controlled trial

The purpose of the study was to assess the effectiveness of a specific rehabilitation therapy for chronic non-specific low-back pain patients, based on a random/irregular functional perturbation training induced by force disturbances to the spine. Forty patients (20 controls and 20 in the perturbation-based group) finished the whole experimental design. A random-perturbation exercise, which included variable and unpredictable disturbances, was implemented in the therapy of the perturbation-based group (13 weeks, two times per week and 1.5 h per session). The participants of the control group did not receive any specific training. Low-back pain, muscle strength, and neuromuscular control of spine stability were investigated before and after the therapy using the visual analog scale, maximal isometric and isokinetic contractions, nonlinear time series analysis, and by determining the stiffness and damping of the trunk after sudden perturbations. The perturbation-based therapy reduced patient's low-back pain (35%), increased muscle strength (15-22%), and trunk stiffness (13%), while no significant changes were observed in the control group. It can be concluded that the proposed therapy has the potential to enhance trunk muscle capability as well as sensory information processing within the motor system during sudden loading and, as a consequence, improve the stabilization of the trunk.

Low-power transcutaneous current stimulator for wearable applications

BACKGROUND

Peripheral neuropathic desensitization associated with aging, diabetes, alcoholism and HIV/AIDS, affects tens of millions of people worldwide, and there is little or no treatment available to improve sensory function. Recent studies that apply imperceptible continuous vibration or electrical stimulation have shown promise in improving sensitivity in both diseased and healthy participants. This class of interventions only has an effect during application, necessitating the design of a wearable device for everyday use. We present a circuit that allows for a low-power, low-cost and small form factor implementation of a current stimulator for the continuous application of subthreshold currents.

RESULTS

This circuit acts as a voltage-to-current converter and has been tested to drive + 1 to - 1 mA into a 60 k[Formula: see text] load from DC to 1 kHz. Driving a 60 k[Formula: see text] load with a 2 mA peak-to-peak 1 kHz sinusoid, the circuit draws less than 21 mA from a 9 V source. The minimum operating current of the circuit is less than 12 mA. Voltage compliance is ± 60 V with just 1.02 mA drawn by the high voltage current drive circuitry. The circuit was implemented as a compact 46 mm × 21 mm two-layer PCB highlighting its potential for use in a body-worn device.

CONCLUSIONS

No design to the best of our knowledge presents comparably low quiescent power with such high voltage compliance. This makes the design uniquely appropriate for low-power transcutaneous current stimulation in wearable applications. Further development of driving and instrumentation circuitry is recommended.

An alternate protocol to achieve stochastic and deterministic resonances

Periodic and Aperiodic Stochastic Resonance (SR) and Deterministic Resonance (DR) are studied in this paper. To check for the ubiquitousness of the phenomena, two unrelated systems, namely, FitzHugh-Nagumo and a particle in a bistable potential well, are studied. Instead of the conventional scenario of noise amplitude (in the case of SR) or chaotic signal amplitude (in the case of DR) variation, a tunable system parameter ("a" in the case of FitzHugh-Nagumo model and the damping coefficient "j" in the bistable model) is regulated. The operating values of these parameters are defined as the "setpoint" of the system throughout the present work. Our results indicate that there exists an optimal value of the setpoint for which maximum information transfer between the input and the output signals takes place. This information transfer from the input sub-threshold signal to the output dynamics is quantified by the normalised cross-correlation coefficient ( |CCC|). |CCC| as a function of the setpoint exhibits a unimodal variation which is characteristic of SR (or DR). Furthermore, |CCC| is computed for a grid of noise (or chaotic signal) amplitude and setpoint values. The heat map of |CCC| over this grid yields the presence of a resonance region in the noise-setpoint plane for which the maximum enhancement of the input sub-threshold signal is observed. This resonance region could be possibly used to explain how organisms maintain their signal detection efficacy with fluctuating amounts of noise present in their environment. Interestingly, the method of regulating the setpoint without changing the noise amplitude was not able to induce Coherence Resonance (CR). A possible, qualitative reasoning for this is provided.

The clinical and biomechanical effects of subthreshold random noise on the plantar surface of the foot in diabetic patients and elder people: A systematic review

BACKGROUND

Central nervous system receives information from foot mechanoreceptors in order to control balance and perform movement tasks. Subthreshold random noise seems to improve sensitivity of the cutaneous mechanoreceptor.

OBJECTIVES

The purpose of this study was to systematically review published evidence conducted to evaluate the clinical and biomechanical effects of subthreshold random noise on the plantar surface of the foot in diabetic patients and elder people.

STUDY DESIGN

Systematic review.

METHODS

A literature search was performed in PubMed, Scopus, ScienceDirect, Web of Knowledge, CINAHL, and EMBASE databases based on population, intervention, comparison, outcomes, and study method. Quality of studies was assessed using the methodological quality assessment tool, using Physiotherapy Evidence Database scale.

RESULTS

In all, 11 studies were selected for final evaluation based on inclusion criteria. Five studies evaluated the effects of subthreshold random noise in diabetic patients and six in elder people. In seven studies, biomechanical (balance and gait parameters) effects and in four studies clinical (pressure and vibration sensations) effects of subthreshold random noise were investigated. All reviewed studies were scored fair (2) to good (9) quality in terms of methodological quality assessment using Physiotherapy Evidence Database scale.

CONCLUSION

The results indicated that subthreshold random noise improves balance and sensation in diabetic patients and elder people. Also gait variables can be improved in elder people with subthreshold random noise. However, further well-designed studies are needed.

CLINICAL RELEVANCE

The previous studies reported that subthreshold random noise may improve gait, balance, and sensation, but more studies are needed to evaluate the long-term effect of subthreshold random noise in shoe or insole for daily living tasks in diabetic patients and elder people.

Use of stochastic resonance methods for improving laparoscopic surgery performance

BACKGROUND

Vibrotactile feedback (VIB) has been utilized in previous research as sensory augmentation to improve performance during minimally invasive surgical tasks. Stochastic resonance (SR), introduced into the human control system as white noise at a subthreshold level, has shown promise to improve the sensitivity of tactile receptors resulting in performance enhancement for sensorimotor tasks. The purpose of this study was to determine whether SR could improve performance (accuracy, speed) in a simulated laparoscopic palpation task.

METHODS

Sixteen subjects performed a palpation task using a laparoscopic tool to detect the presence of tumors (compacted felt) embedded in simulated tissue samples (silicone gel) inside a laparoscopic trainer box. Subjects were randomly assigned to one of the four different conditions: (1) SR, (2) VIB, (3) VIB + SR, and (4) Control. The VIB and SR signals were administered via two separate haptic actuators attached to the subjects' dominant upper arms and forearms, respectively. All subjects were presented with 36 tissue samples with no sensory augmentation (Control) to establish baseline, followed by another 36 samples under one of the randomly assigned vibration conditions (SR, VIB, VIB + SR, or Control).

RESULTS

Results show a significantly larger improvement in tumor detection accuracy in the SR group compared to the VIB and Control groups. There was no difference in the time to task completion, indicating that there was no speed-accuracy trade-off.

CONCLUSIONS

The results have implications for the design of instruments and methods for increasing detection accuracy such as in palpation tasks. This technology could help surgeons better identify tumors located in healthy surrounding tissue.

Effect of imperceptible vibratory noise applied to wrist skin on fingertip touch evoked potentials - an EEG study

Random vibration applied to skin can change the sense of touch. Specifically, low amplitude white-noise vibration can improve fingertip touch perception. In fact, fingertip touch sensation can improve even when imperceptible random vibration is applied to other remote upper extremity areas such as wrist, dorsum of the hand, or forearm. As such, vibration can be used to manipulate sensory feedback and improve dexterity, particularly during neurological rehabilitation. Nonetheless, the neurological bases for remote vibration enhanced sensory feedback are yet poorly understood. This study examined how imperceptible random vibration applied to the wrist changes cortical activity for fingertip sensation. We measured somatosensory evoked potentials to assess peak-to-peak response to light touch of the index fingertip with applied wrist vibration versus without. We observed increased peak-to-peak somatosensory evoked potentials with wrist vibration, especially with increased amplitude of the later component for the somatosensory, motor, and premotor cortex with wrist vibration. These findings corroborate an enhanced cortical-level sensory response motivated by vibration. It is possible that the cortical modulation observed here is the result of the establishment of transient networks for improved perception.

Application of vibration to wrist and hand skin affects fingertip tactile sensation

A recent study showed that fingertip pads’ tactile sensation can improve by applying imperceptible white-noise vibration to the skin at the wrist or dorsum of the hand in stroke patients. This study further examined this behavior by investigating the effect of both imperceptible and perceptible white-noise vibration applied to different locations within the distal upper extremity on the fingertip pads’ tactile sensation in healthy adults. In 12 healthy adults, white-noise vibration was applied to one of four locations (dorsum hand by the second knuckle, thenar and hypothenar areas, and volar wrist) at one of four intensities (zero, 60%, 80%, and 120% of the sensory threshold for each vibration location), while the fingertip sensation, the smallest vibratory signal that could be perceived on the thumb and index fingertip pads, was assessed. Vibration intensities significantly affected the fingertip sensation (P < 0.01) in a similar manner for all four vibration locations. Specifically, vibration at 60% of the sensory threshold improved the thumb and index fingertip tactile sensation (P < 0.01), while vibration at 120% of the sensory threshold degraded the thumb and index fingertip tactile sensation (P < 0.01) and the 80% vibration did not significantly change the fingertip sensation (P > 0.01), all compared with the zero vibration condition. This effect with vibration intensity conforms to the stochastic resonance behavior. Nonspecificity to the vibration location suggests the white-noise vibration affects higher level neuronal processing for fingertip sensing. Further studies are needed to elucidate the neural pathways for distal upper extremity vibration to impact fingertip pad tactile sensation.

Investigating the role of vibrotactile noise in early response to perturbation

Timely reaction to perturbation is important in activities of daily living. Modulation of reaction time to and early recovery from perturbation via vibrotactile noise was investigated. It was hypothesized that subthreshold vibrotactile noise applied to the upper extremity can accelerate a person's reaction to and recovery from handle perturbation. This intervention was developed based on previous studies in which the earliest cue available for people to detect handle perturbation was somatosensation detecting changes in pressure on the hand whose sensitivity can improve with subthreshold vibrotactile noise. To induce a handle perturbation, a sudden upward load was applied to the handle that subjects were lightly grasping. Eighteen healthy subjects were instructed to stop the handle from moving up when they detected the perturbation. The muscle reaction time and handle stabilization time with and without vibrotactile noise were determined. The results showed that the muscle reaction time and handle stabilization time significantly decreased by 3 ms ( ) and 6 ms ( ), respectively, when vibrotactile noise was applied to the upper extremity, regardless of where the noise was applied among four different locations within the upper extremity ( p > 0.05). In conclusion, the application of subthreshold vibrotactile noise enhanced persons' muscle reaction time to handle perturbation and led to early recovery from the perturbation. Use of the vibrotactile noise may increase a person's ability to rapidly respond to perturbation of a grasped object in potentially dangerous situations such as holding onto ladder rungs from elevation or manipulating knives.

An MRI-compatible hand sensory vibrotactile system

Recently, the application of vibrotactile noise to the wrist or back of the hand has been shown to enhance fingertip tactile sensory perception (Enders et al 2013), supporting the potential for an assistive device worn at the wrist, that generates minute vibrations to help the elderly or patients with sensory deficit. However, knowledge regarding the detailed physiological mechanism behind this sensory improvement in the central nervous system, especially in the human brain, is limited, hindering progress in development and use of such assistive devices. To enable investigation of the impact of vibrotactile noise on sensorimotor brain activity in humans, a magnetic resonance imaging (MRI)-compatible vibrotactile system was developed to provide vibrotactile noise during an MRI of the brain. The vibrotactile system utilizes a remote (outside the MR room) signal amplifier which provides a voltage from -40 to +40 V to drive a 12 mm diameter piezoelectric vibrator (inside the MR room). It is portable and is found to be MRI-compatible which enables its use for neurologic investigation with MRI. The system was also found to induce an improvement in fingertip tactile sensation, consistent with the previous study.

Effect of remote sensory noise on hand function post stroke

Hand motor impairment persists after stroke. Sensory inputs may facilitate recovery of motor function. This pilot study tested the effectiveness of tactile sensory noise in improving hand motor function in chronic stroke survivors with tactile sensory deficits, using a repeated measures design. Sensory noise in the form of subthreshold, white noise, mechanical vibration was applied to the wrist skin during motor tasks. Hand dexterity assessed by the Nine Hole Peg Test and the Box and Block Test and pinch strength significantly improved when the sensory noise was turned on compared with when it was turned off in chronic stroke survivors. The subthreshold sensory noise to the wrist appears to induce improvements in hand motor function possibly via neuronal connections in the sensoriomotor cortex. The approach of applying concomitant, unperceivable mechanical vibration to the wrist during hand motor tasks is easily adoptable for clinic use as well as unsupervised home use. This pilot study suggests a potential for a wristband-type assistive device to complement hand rehabilitation for stroke survivors with sensorimotor deficit.