A new approach of inducing proprioceptive illusion by transcutaneous electrical stimulation

A session of transcutaneous electrical nerve stimulation changes the input-output function of motoneurons and alters the sense of force

Transcutaneous electrical nerve stimulation (TENS) is commonly used in research and clinical settings for pain management and augmenting somatosensory inputs for motor recovery. Besides its functional effect, TENS acutely alters kinesthesia and force steadiness. However, the short-term impact following a session of TENS on proprioception and motor unit behavior is unknown. We evaluated the effect of a session of TENS on the senses of force, joint position, touch, and discharge activity of motor units. Fifteen healthy participants underwent two experiments, each with two visits randomly administering TENS or sham-TENS. The sense of force (experiment 1) and position (experiment 2) were evaluated through matching trials by pinching a dial and rotating their wrist (ulnar deviation). Isometric pinch contractions were performed before and after the session of TENS or sham-TENS, in which electromyographic (EMG) signals were recorded from the first dorsal interosseus (FDI) and abductor pollicis brevis (APB). Results showed that TENS acutely altered the senses of force, position, and touch, but only the sense of force remained altered following TENS. Motor unit discharge rates increased in both FDI and APB muscles for the same force output following TENS. A positive correlation was also observed between changes in motor unit discharge rates and changes in errors in force perception. These findings suggest that a session of TENS may have short-term effects on the input/output function of motoneurons (5-10 min in this study), which in turn may alter the sense of force. However, the precise timeline for these short-term aftereffects is unknown.NEW & NOTEWORTHY It is often assumed that transcutaneous electrical nerve stimulation (TENS) has a transient effect on proprioception and motor control. We found that position, force, and touch perception were altered during TENS. However, the sense of force remained altered following TENS. As the discharge rate of motor units also increased in first dorsal interosseus (FDI) and abductor pollicis brevis (APB) muscles for the same force output following TENS, we suggest that their input-output function was altered, potentially causing a sustained decrease in performance in force-matching tasks.

Effects of Proprioceptive Attenuation with Noisy Tendon Electrical Stimulation on Adaptation to Beyond-Real Interaction

Virtual reality (VR) enables beyond-real interactions (BRI) that transcend physical constraints, offering effective user experiences like extending a hand to grasp distant objects. However, adapting to novel mappings of BRI often reduces performance and the sense of embodiment. To address this, we propose using noisy tendon electrical stimulation (n-TES) to decrease proprioceptive precision. Previous studies have suggested that attenuating proprioceptive precision is crucial for sensory-motor adaptations. Thus, we hypothesize that n-TES, which has been shown to reduce proprioceptive precision and induce visual-dependent perception in VR, can enhance user adaptation to BRI. We conducted a user study using go-go interaction, a BRI technique for interacting with distant objects, to assess the effects of n-TES. Given the individual variability in n-TES response, participants first underwent a proprioceptive precision test to determine the optimal stimulation intensity to lower the proprioceptive precision from 5 levels $(\sigma=0.25-125\text{mA})$. Reaching tasks using a 2x2 within-participants design evaluated the effects of go-go interaction and n-TES on performance, subjective task load, and embodiment. Results from 24 participants showed that go-go interaction increased reaching time and task load while decreasing the sense of embodiment. Contrary to our hypothesis, n-TES did not significantly mitigate most of these negative effects of go-go interaction, except that perceived agency was higher with n-TES during go-go interaction. The limited effectiveness of n-TES may be due to participants' habituation or sensory adaptation during the tasks. Future research should consider the adaptation process to BRI and investigate different BRI scenarios.

Physiotherapy management focusing on proprioceptive impairment in a patient with gait and balance impairments following stroke: A case report

BACKGROUND

Proprioceptive impairment contributes to gait and balance impairments in patients with stroke. Diagnosis functional impairments and evaluation treatment efficacy require quantitative proprioception assessment. However, proprioception assessment has remained limited to ordinal scale measurement, with a lack of ratio scale measurements.

PURPOSE

This case report describes a physiotherapy management program focusing on proprioceptive impairment in patients with stroke using quantitative tests such as Threshold to Detect Passive Motion (TDPM) and Joint Position Sense (JPS).

CASE DESCRIPTION

A63-year-old male patient with an acute pontine lacunar infarction was admitted to our hospital. His muscle strength, selective movement, and trunk activity were preserved. However, the Berg Balance Scale (BBS) and Gait Assessment andIntervention Tool (GAIT) score were 42 and 9 points, observing balance impairment and the buckling knee pattern with hip ataxia during gait. Based on these, TDPM and JPS using image capture were performed. In physiotherapeuticdiagnosis, proprioceptive impairments in the hip and knee joints were the primary functional impairments related to balance and gait. To address these proprioceptive impairments, a 13-day treatment protocol incorporating transcutaneous electrical nerve stimulation (intensity: sensory threshold, frequency: 100 Hz) targeting the quadriceps femoris was performed.

OUTCOMES

The patient was discharged after achieving independent ambulation and improvement in BBS (56 points) and GAIT (2 points) scores, exceeding the minimum clinically important difference. Recovery of proprioceptive impairment corresponded withimproved balance and gait ability.

CONCLUSION

Quantitatively evaluating proprioceptive impairments may provide novel rehabilitation for patients with stroke who have proprioceptive impairments and contribute to clinical decision-making.

Electrotactile proprioception training improves finger control accuracy and potential mechanism is proprioceptive recalibration

This study presents a novel training technique, visual + electrotactile proprioception training (visual + EP training), which provides additional proprioceptive information via tactile channel during motor training to enhance the training effectiveness. In this study, electrotactile proprioception delivers finger aperture distance information in real-time, by mapping frequency of electrical stimulation to finger aperture distance. To test the effect of visual + EP training, twenty-four healthy subjects participated in the experiment of matching finger aperture distance with distance displayed on screen. Subjects were divided to three groups: the first group received visual training and the other two groups received visual + EP training with or without a post-training test with electrotactile proprioception. Finger aperture control error was measured before and after the training (baseline, 15-min post, 24-h post). Experimental data suggest that both training methods decreased finger aperture control error at 15-min post-training. However, at 24-h post-training, the training effect was fully retained only for the subjects who received visual + EP training, while it washed out for the subjects with visual training. Distribution analyses based on Bayesian inference suggest that the most likely mechanism of this long-term retention is proprioceptive recalibration. Such applications of artificially administered sense have the potential to improve motor control accuracy in a variety of applications.

Spinal Orthosis in Adolescent Idiopathic Scoliosis: An Overview of the Braces Provided by the National Health Service in Italy

Adolescent idiopathic scoliosis (AIS) is a lateral, rotated curvature of the spine. It is a 3-dimensional deformity that arises in otherwise healthy children at or around puberty. AIS is the most common form of scoliosis in the pediatric population. The etiology is multifactorial, including genetic and environmental factors. The incidence is roughly equal between males and females, while there is a higher risk of progression in females. Guidelines for AIS treatment identify three levels of treatment: observation, physiotherapy scoliosis-specific exercises, and braces. In this paper, we carried out a review of the scientific literature about the indication and success rates of the braces provided for free by the National Health Service in Italy (SSN). Despite a general consensus on the efficacy of rigid bracing treatment and its use in AIS, an important heterogeneity about the treatment is present in the scientific literature, demonstrating a high degree of variability. The overall success rate of the braces provided by the SSN is high, suggesting an important therapeutic role in the treatment of AIS. Robust guidelines are needed to ensure uniform and effective treatments.

Optimizing Movement Performance with Altered Sensation: An Examination of Multisensory Inputs

Two experiments were conducted to assess the impact of induced paresthesia on movement parameters of goal-directed aiming movements to determine how visual and auditory feedback may enhance performance when somatosensory feedback is disrupted. In both experiments, neurotypical adults performed the goal-directed aiming task in four conditions: (i) paresthesia-full vision; (ii) paresthesia-no vision; (iii) no paresthesia-full vision; (iv) no paresthesia-no vision. Targets appeared on a computer screen, vision was obscured using visual occlusion spectacles, and paresthesia was induced with a constant current stimulator. The first and last 20% of trials (early and late performance) were compared to assess adaptability to altered somatosensory input. Experiment 2 added an auditory tone that confirmed successful target acquisitions. When compared to early performance in the no-paresthesia and no-vision conditions, induced paresthesia and no vision led to significantly larger endpoint error toward the body midline in both early and late performance. This finding reveals the importance of proprioceptive input for movement accuracy in the absence of visual feedback. The kinematic results indicated that vision could not fully compensate for the disrupted proprioceptive input when participants experienced induced paresthesia. However, when auditory feedback confirmed successful aiming movements in Experiment 2, participants were able to improve their endpoint variability when experiencing induced paresthesia through changes in movement preparation.

Limb loading enhances skill transfer between augmented and physical reality tasks during limb loss rehabilitation

BACKGROUND

Virtual and augmented reality (AR) have become popular modalities for training myoelectric prosthesis control with upper-limb amputees. While some systems have shown moderate success, it is unclear how well the complex motor skills learned in an AR simulation transfer to completing the same tasks in physical reality. Limb loading is a possible dimension of motor skill execution that is absent in current AR solutions that may help to increase skill transfer between the virtual and physical domains.

METHODS

We implemented an immersive AR environment where individuals could operate a myoelectric virtual prosthesis to accomplish a variety of object relocation manipulations. Intact limb participants were separated into three groups, the load control (CG_LD; [Formula: see text]), the AR control (CG_AR; [Formula: see text]), and the experimental group (EG; [Formula: see text]). Both the CG_AR and EG completed a 5-session prosthesis training protocol in AR while the CG_LD performed simple muscle training. The EG attempted manipulations in AR while undergoing limb loading. The CG_AR attempted the same manipulations without loading. All participants performed the same manipulations in physical reality while operating a real prosthesis pre- and post-training. The main outcome measure was the change in the number of manipulations completed during the physical reality assessments (i.e. completion rate). Secondary outcomes included movement kinematics and visuomotor behavior.

RESULTS

The EG experienced a greater increase in completion rate post-training than both the CG_AR and CG_LD. This performance increase was accompanied by a shorter motor learning phase, the EG's performance saturating in less sessions of AR training than the CG_AR.

CONCLUSION

The results demonstrated that limb loading plays an important role in transferring complex motor skills learned in virtual spaces to their physical reality analogs. While participants who did not receive limb loading were able to receive some functional benefit from AR training, participants who received the loading experienced a greater positive change in motor performance with their performance saturating in fewer training sessions.

I Can Step Clearly Now, the TENS Is On: Transcutaneous Electric Nerve Stimulation Decreases Sensorimotor Uncertainty during Stepping Movements

Transcutaneous electric nerve stimulation (TENS) is a method of electrical stimulation that elicits activity in sensory nerves and leads to improvements in the clinical metrics of mobility. However, the underlying perceptual mechanisms leading to this improvement are unknown. The aim of this study was to apply a Bayesian inference model to understand how TENS impacts sensorimotor uncertainty during full body stepping movements. Thirty healthy adults visited the lab on two occasions and completed a motor learning protocol in virtual reality (VR) on both visits. Participants were randomly assigned to one of three groups: TENS on first visit only (TN), TENS on second visit only (NT), or a control group where TENS was not applied on either visit (NN). Using methods of Bayesian inference, we calculated the amount of uncertainty in the participants' center of mass (CoM) position estimates on each visit. We found that groups TN and NT decreased the amount of uncertainty in the CoM position estimates in their second visit while group NN showed no difference. The least amount of uncertainty was seen in the TN group. These results suggest that TENS reduces the amount of uncertainty in sensory information, which may be a cause for the observed benefits with TENS.

Electro-prosthetic E-skin Successfully Delivers Elbow Joint Angle Information by Electro-prosthetic Proprioception (EPP)

Neurotraumas and neurological diseases often result in compromised proprioceptive feedback, which plays a critical role in motor control by delivering real-time position information. Electro-prosthetic proprioception (EPP) using frequency-modulated electrotactile feedback is a promising solution, as it can deliver proprioceptive information such as a joint angle via tactile channel. Prior works demonstrated that EPP successfully delivered distance information between the end effector and the target object. In this study, we implemented the electronic skin (E-skin) monitoring the elbow joint angle and delivering it to the nervous system via tactile channel. We also demonstrated that EPP improved both accuracy and precision of the elbow joint angle control. The gyroscope measuring the elbow joint angle and electrodes delivering electrotactile feedback were integrated together as a skin using thin silicon coating and polyurethane film. We call this novel E-skin, monitoring and delivering joint angle information, as an electro-prosthetic E-skin. Elbow joint angle matching test with two healthy human subjects showed that the EPP, via electro-prosthetic E-skin, enhanced 101.7% accuracy and 63.8% precision in elbow joint angle control. Clinical Relevance-Presented electro-prosthetic E-skin will address the compromised proprioceptive feedback by delivering joint angle information by electro-prosthetic proprioception (EPP) via tactile channel. This novel E-skin will open up a new path to assist and rehabilitative motor control problems after neurotraumas and neurological diseases.

EXPRESS: Testing links between pain-related biases in visual attention and recognition memory: An eye-tracking study based on an impending pain paradigm

Although separate lines of research have evaluated pain-related biases in attention or memory, laboratory studies examining links between attention and memory for pain-related information have received little consideration. In this eye-tracking experiment, we assessed relations between pain-related attention biases (ABs) and recognition memory biases (MBs) among 122 pain-free adults randomly assigned to impending pain (n = 59) versus impending touch (n = 63) conditions wherein offsets of trials that included pain images were followed by subsequent possibly painful and non-painful somatosensory stimulation, respectively. Gaze biases of participants were assessed during presentations of pain-neutral (P-N) and happy-neutral (H-N) face image pairs within these conditions. Subsequently, condition differences in recognition accuracy for previously-viewed versus novel pained and happy face images were examined. Overall gaze durations were significantly longer for pain (versus neutral) faces that signaled impending pain than impending non-painful touch, particularly among the less resilient in the former condition. Impending pain cohorts also exhibited comparatively better recognition accuracy for both pained and happy face images. Finally, longer gaze durations on pain faces that signaled potential pain, but not potential touch, were related to more accurate recognition of previously-viewed pain faces. In sum, pain cues that signal potential personal discomfort maintain visual attention more fully and are subsequently recognized more accuracy than are pain cues that signal non-painful touch stimulation.

Palatal Electrotactile Display Outperforms Visual Display in Tongue Motor learning

Incomplete tongue motor control is a common yet challenging issue among individuals with neurotraumas and neurological disorders. In development of the training protocols, multiple sensory modalities including visual, auditory, and tactile feedback have been employed. However, the effectiveness of each sensory modality in tongue motor learning is still in question. The object of this study was to test the effectiveness of visual and electrotactile assistance on tongue motor learning, respectively. Eight healthy subjects performed the tongue pointing task, in which they were visually instructed to touch the target on the palate by their tongue tip as accurately as possible. Each subject wore a custom-made dental retainer with 12 electrodes distributed over the palatal area. For visual training, 3×4 LED array on the computer screen, corresponding to the electrode layout, was turned on with different colors according to the tongue contact. For electrotactile training, electrical stimulation was applied to the tongue with frequencies depending on the distance between the tongue contact and the target, along with a small protrusion on the retainer as an indicator of the target. One baseline session, one training session, and three post-training sessions were conducted over four-day duration. Experimental result showed that the error was decreased after both visual and electrotactile trainings, from 3.56±0.11 (Mean±STE) to 1.27±0.16, and from 3.97±0.11 to 0.53±0.19, respectively. The result also showed that electrotactile training leads to stronger retention than visual training, as the improvement was retained as 62.68±1.81% after electrotactile training and 36.59±2.24% after visual training, at 3-day post training.

Contribution of Cervical Proprioception, Vision, and Vestibular Feedback on Reducing Dynamic Head–Trunk Orientation Error in the Yaw Direction

The contribution of cervical proprioception, vision, and vestibular feedback to the dynamic head–trunk orientation error in the yaw direction was investigated to further the understanding over the mechanism of coordination among different sensory modalities for dynamic head–trunk orientation. To test the contribution of each sensory modality, individually and together, to dynamic head–trunk orientation, 10 healthy human subjects participated in the extended cervical joint position error test, measuring the ability of repositioning the head back to the reference orientation after 45° yaw rotation of head or trunk. The error between initial and returned angles was measured. The test was repeated under eight different conditions of sensory feedback, with or without each of three sensory modalities. Each subject completed 64 trials (8 per condition) in a random order for fair comparison. No change was found in bias when one of the three modalities was missing, while variance was largest at the lack of dynamic cervical proprioception. When two of the three modalities were missing (i.e., one of the three modalities was present), both bias and variance were minimum at the presence of cervical proprioception. Additionally, both visual and vestibular feedback was redundant (i.e., no further improvement in both bias and variance), if the other one (visual or vestibular feedback) was present with dynamic cervical proprioception. In sum, the experimental results suggest that dynamic cervical proprioception is the most significant sensory modality for reducing the dynamic head–trunk orientation error in the yaw direction.

Forehead Tactile Hallucination Is Augmented by the Perceived Risk and Accompanies Increase of Forehead Tactile Sensitivity

Tactile hallucinations frequently occur after mental illnesses and neurodegenerative diseases like Alzheimer’s and Parkinson’s disease. Despite their common occurrence, there are several complicating factors that make it difficult to elucidate the tactile hallucinations. The forehead tactile hallucination, evoked by the physical object approaching to the forehead, can be easily and consistently evoked in healthy-bodied subjects, and therefore it would help with investigating the mechanism of tactile hallucinations. In this pilot study, we investigated the principles of the forehead tactile hallucination with eight healthy subjects. We designed the experimental setup to test the effect of sharpness and speed of objects approaching towards the forehead on the forehead tactile hallucination, in both a physical and virtual experimental setting. The forehead tactile hallucination was successfully evoked by virtual object as well as physical object, approaching the forehead. The forehead tactile hallucination was increased by the increase of sharpness and speed of the approaching object. The forehead tactile hallucination also increased the tactile sensitivity on the forehead. The forehead tactile hallucination can be solely evoked by visual feedback and augmented by the increased perceived risk. The forehead tactile hallucination also increases tactile sensitivity. These experimental results may enhance the understanding of the foundational mechanisms of tactile hallucinations.