A Pilot Study to Measure Upper Extremity H-reflexes Following Neuromuscular Electrical Stimulation Therapy after Stroke

Upper extremity (UE) hemiparesis persists after stroke, limiting hand function. Neuromuscular electrical stimulation (NMES) is an effective intervention to improve UE recovery, although the underlying mechanisms are not fully understood. Our objective was to establish a reliable protocol to measure UE agonist–antagonist forearm monosynaptic reflexes in a pilot study to determine if NMES improves wrist function after stroke. We established the between-day reliability of the H-reflex in the extensor carpi radialis longus (ECRL) and flexor carpi radialis (FCR) musculature for individuals with prior stroke (n = 18). The same-day generation of ECRL/FCR H-reflex recruitment curves was well tolerated, regardless of age or UE spasticity. The between-day reliability of the ECRL H-reflex was enhanced above FCR, similar to healthy subjects [20], with the Hmax the most reliable parameter quantified in both muscles. H-reflex and functional measures following NMES show the potential for NMES-induced increases in ECRL Hmax, but confirmation requires a larger clinical study. Our initial results support the safe, easy, and efficacious use of in-home NMES, and establish a potential method to measure UE monosynaptic reflexes after stroke

Swallowing Neurorehabilitation: From the Research Laboratory to Routine Clinical Application

This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/The recent application of neurostimulation techniques to enhance the understanding of swallowing neural plasticity has expanded the focus of rehabilitation research from manipulation of swallowing biomechanics to manipulation of underlying neural systems. Neuromodulatory strategies that promote the brain's ability to reorganize its neural connections have been shown to hold promising potential to aid the recovery of impaired swallowing function. These techniques include those applied to the brain through the intact skull, such as transcranial magnetic stimulation or transcranial direct current stimulation, or those applied to the sensorimotor system in the periphery, such as neuromuscular electrical stimulation. Recent research has demonstrated that each of these techniques, either by themselves or in combination with these and other treatments, can, under certain circumstances, modify the excitability of motor representations of muscles involved in swallowing. In some studies, experimentally induced plastic changes have been shown to have functional relevance for swallowing biomechanics. However, the transition of novel, neuromodulatory brain stimulation techniques from the research laboratory to routine clinical practice is accompanied by a number of ethical, organizational, and clinical implications that impact professions concerned with the treatment of swallowing rehabilitation. In this article, we provide a brief overview of the neuromodulatory strategies that may hold potential to aid the recovery of swallowing function, and raise a number of issues that we believe the clinical professions involved in the rehabilitation of swallowing disorders must confront as these novel brain stimulation techniques emerge into clinical practice

The role of somatosensory feedback for brain-machine interfaces applications

Brain-machine interfaces (BMI) based on motor imagery (MI) have emerged as a promising approach to enhance motor skills and restore motor functions. However, the efficacy and efficiency of BMI systems remain limited. The current lack of usability can be explained by the fact that significant efforts have been dedicated to improve decoding efficiency and accuracy, but BMI studies have generally ignored the user-training component of BMI operation. It has been suggested that somatosensory feedback would be more suitable than standard visual feedback to train subjects to control a BMI. In this thesis, a novel feedback modality has been explored to improve BMI usability, namely sensory-threshold neuromuscular electrical stimulation (St-NMES). St-NMES delivers transcutaneous electrical stimulation that depolarizes sensory and motor axons without eliciting any muscular contraction. In order to assess the effect of this new feedback modality on BMI skill learning this thesis is composed of four experiments. In a first experiment, the effect of St-NMES on MI performance was investigated. Twelve healthy subjects participated in a cross-over design experiment comparing St-NMES with visual feedback. Offline analyses showed that St-NMES not only enhanced MI brain patterns, but also improved classification accuracy. Importantly, St-NMES alone did not induce detectable artefacts. In a second experiment, physiological impact of online BMI training on corticospinal tract (CST) plasticity was studied according to the feedback modality âeither St-NMES or visual feedback. Ten healthy participants were enrolled in a cross-over design experiment testing both BMI systems. Results showed that BMI based on St-NMES significantly enhanced CST excitability compared to BMI based on visual feedback. Moreover, BMI system based on St-NMES was significantly more robust and accurate over days. A third experiment further explored the parallelism between BMI learning based on St-NMES feedback and natural motor learning, putting particular attention on the underlying physiology of the process. Apart from analyzing the evolution of BMI performance, we also examined changes in CST excitability and modulation of intracortical inhibition in the early learning phase (after one BMI session) as well as later learning stage (after 2 weeks training). Ten healthy participants were trained to control a BMI based on St-NMES feedback. Results showed that subjects improved their BMI control with practice, what might be explained by the adaptation of the central nervous system over time. Finally, the last experiment explored the feasibility of BMI-St-NMES for upper limb rehabilitation after stroke. A chronic stroke patient with a severe motor disability was trained with BMI-St-NMES over 3 weeks. After training, upper-limb motor function improved, reaching clinical relevance. Based on our previous observations, we believe that BMI-St-NMES training enhanced CST projections leading to motor recovery. As a conclusion, this thesis showcases that a contingent activation of central nervous system with somatosensory stimulation through BMI-St-NMES is a promising solution to enhance BMI control and to induce cortico and corticospinal changes. This new BMI modality could become a future opportunity for several fields of research including mental training assistive scenarios as well as motor rehabilitation of patients with lesions within central nervous system

Effect of a neuromuscular electrical stimulation muscle strength training intervention on muscle force and mass, physical health and quality of life in people with spinal cord injury

Spinal cord injury (SCI) leads to significant deficits in muscle strength and mass, impacting negatively on physical health and quality of life (QoL). Physical rehabilitation techniques for people with SCI rely on constant updates and the accumulation of evidence regarding the efficacy of available and/or new physical interventions. Neuromuscular electrical stimulation (NMES) is already commonly used to activate skeletal muscles and subsequently reverse muscle atrophy, however NMES as a high-intensity “strength training” intervention appears to be a particularly promising technique for increasing muscle strength and mass and to subsequently improve physical health and quality of life (QoL) in people with SCI. Nonetheless, there are many factors limiting the use of standard NMES protocols, and further evidence pertaining to the use of high-intensity NMES strength training in clinical populations is warranted. The primary aim of the research described in this thesis was to examine the effects of NMES as a high-intensity muscle strength training intervention, specifically using wide-pulse width (1000 μs), low-to-moderate frequency (30 Hz) NMES combined with tendon vibration, on muscle strength and mass, physical health, symptoms of spasticity and QoL in people with SCI. This thesis includes two cross-sectional studies examining the effects of patellar tendon vibration (55 Hz, 7 mm amplitude) superimposed onto wide-pulse width (1000 μs) NMES (e.g. 30 Hz over 2 s) on the peak muscular (knee extensor) force and total impulse elicited by, and rate of recovery from, the intervention in healthy subjects (Study 1) and in people with chronic SCI (Study 2). The results of Study 1 revealed that superimposing tendon vibration onto wide-pulse width NMES leads to an increase in the muscle work performed before fatigue in only some individuals (i.e. positive responders, 50% of individuals in the current study), but decreases it in others (i.e. negative responders). However, it tends to reduce the voluntary force loss that was consistently experienced after a training session using high-intensity NMES, and may thus allow for additional exercise or rehabilitation work to be performed without ongoing voluntary muscle fatigue in healthy people. The results of Study 2 also identified positive and negative responders to tendon vibration in people with SCI, however the responses were less clear and a defined effect of tendon vibration superimposed onto NMES was not discerned. In Study 3, a 12-week (twice-weekly) high-intensity NMES strength training intervention was implemented in people with chronic SCI; based on results of Study 2, high-force contractions were evoked by NMES without superimposed tendon vibration. A significant increase in muscle mass (45%) and strength (tetanic evoked force; 31.8%), amelioration of spasticity symptoms, and improvement in some aspects of physical health and QoL were observed. Therefore, the use of high-intensity NMES strength training appears to be an effective rehabilitation tool to increase muscle force and mass, ameliorate symptoms of spasticity and improve physical and mental health outcomes in people with SCI

Increased Corticomuscular Coherence and Brain Activation Immediately After Short-Term Neuromuscular Electrical Stimulation

Neuromuscular Electrical Stimulation (NMES) is commonly used in motor rehabilitation for stroke patients. It has been verified that NMES can improve muscle strength and activate the brain, but the studies on how NMES affects the corticomuscular connection are limited. Some studies found an increased corticomuscular coherence (CMC) after a long-term NMES. However, it is still unknown about CMC during NMES, as relatively pure EMG is very difficult to obtain with the contamination of NMES current pulses. In order to approach the condition during NMES, we designed an experiment with short-term NMES and immediately captured data within 100 s. The repetition of wrist flexion was used to realize static muscle contractions for CMC calculation and dynamic contractions for event-related desynchronization (ERD). The result of 13 healthy participants showed that maximal values (p = 0.0020) and areas (p = 0.0098) of CMC and beta ERD were significantly increased immediately after NMES. It was concluded that a short-term NMES can still reinforce corticomuscular functional connection and brain activation related to motor task. This study verified the immediate strengthen of corticomuscular changes after NMES, which was expected to be the basis of long-term neural plasticity induced by NMES

Vibration-induced extra torque during electrically-evoked contractions of the human calf muscles

<p>Abstract</p> <p>Background</p> <p>High-frequency trains of electrical stimulation applied over the lower limb muscles can generate forces higher than would be expected from a peripheral mechanism (i.e. by direct activation of motor axons). This phenomenon is presumably originated within the central nervous system by synaptic input from Ia afferents to motoneurons and is consistent with the development of plateau potentials. The first objective of this work was to investigate if vibration (sinusoidal or random) applied to the Achilles tendon is also able to generate large magnitude extra torques in the triceps surae muscle group. The second objective was to verify if the extra torques that were found were accompanied by increases in motoneuron excitability.</p> <p>Methods</p> <p>Subjects (n = 6) were seated on a chair and the right foot was strapped to a pedal attached to a torque meter. The isometric ankle torque was measured in response to different patterns of coupled electrical (20-Hz, rectangular 1-ms pulses) and mechanical stimuli (either 100-Hz sinusoid or gaussian white noise) applied to the triceps surae muscle group. In an additional investigation, M_maxand F-waves were elicited at different times before or after the vibratory stimulation.</p> <p>Results</p> <p>The vibratory bursts could generate substantial self-sustained extra torques, either with or without the background 20-Hz electrical stimulation applied simultaneously with the vibration. The extra torque generation was accompanied by increased motoneuron excitability, since an increase in the peak-to-peak amplitude of soleus F waves was observed. The delivery of electrical stimulation following the vibration was essential to keep the maintained extra torques and increased F-waves.</p> <p>Conclusions</p> <p>These results show that vibratory stimuli applied with a background electrical stimulation generate considerable force levels (up to about 50% MVC) due to the spinal recruitment of motoneurons. The association of vibration and electrical stimulation could be beneficial for many therapeutic interventions and vibration-based exercise programs. The command for the vibration-induced extra torques presumably activates spinal motoneurons following the size principle, which is a desirable feature for stimulation paradigms.</p

The role of noise in sensorimotor control

Goal-directed arm movements show stereotypical trajectories, despite the infinite possible ways to reach a given end point. This thesis examines the hypothesis that this stereotypy arises because movements are optimised to reduce the consequences of signal-dependent noise on the motor command. Both experimental and modelling studies demonstrate that signal-dependent noise arises from the normal behaviour of the muscle and motor neuron pool, and has a particular distribution across muscles of different sizes. Specifically, noise decreases in a systematic fashion with increasing muscle strength and motor unit number. Simulations of obstacle avoidance performance in the presence of signal-dependent noise demonstrate that the optimal trajectory for reaching the target accurately and without collision matches the observed trajectories. Isometric force generation is also shown to have systematic changes in variability with posture, which can be explained by the presence of signal-dependent noise in the muscles of the arm. These results confirm the tested hypothesis and imply that consideration of the statistics of action is crucial to human movement planning. To investigate the importance of feedback in the motor system, the impact of static position on motor excitability was examined using transcranial magnetic stimulation and systematic changes in motor evoked potentials were observed. Force generated at the wrist following stimulation was analysed in terms of different possible movement representations, and the differences between force fields arising from stimulation over the cervical spinal cord and from stimulation over primary motor cortex are determined. These results demonstrate the structured influence of proprioceptive feedback on the human motor system. All the experiments are discussed in relation to current theories describing the control of human movements and the impact of noise in the motor system