A Novel EMG-driven Functional Electrical Stimulator for Post- Stroke Individuals to Practice Activities of Daily Living.

Prior research has demonstrated that hand function can be recovered in individuals with mild stroke through an intervention that is both 'intense' and 'functional'. However, in individuals with moderate to severe post stroke hand paresis, current evidence for an effective intervention to regain hand function is almost absent. A possible contributor to such poor recovery in these individuals may be the inability to intensively practice with the paretic hand during activities of daily living (ADLs). Many ADLs require use of the paretic arm and hand. Due to post-stroke abnormal muscle synergies, functional arm movements, such as lifting or reaching, often result in unwanted activity in the wrist/finger flexors. This makes voluntary hand opening more difficult. A possible solution to enable these individuals to practice with their paretic hand in a functional context is using devices to assist hand opening. Unfortunately, most of currently available hand rehabilitation devices do not sufficiently address hand opening with the appearance of abnormal muscle synergies. We, therefore, developed a synergy resistant, electromyographic (EMG)-driven electrical stimulation device that allows for $\mathbf {Re}$liable and $\mathbf {In}$tuitive control of the hand (ReIn-Hand) opening while using the paretic arm during lifting and reaching.

Estimating Voluntary Activation Of The Elbow And Wrist Muscles In Chronic Hemiparetic Stroke Using Twitch Interpolation Methodology.

One of the cardinal motor deficits that occurs after stroke is paresis, a decrease in the voluntary activation of muscles. Paresis leads to a decrease in voluntary joint strength, impacting stroke survivors' ability to perform activities of daily living (ADLs). Quantifying this decrease in voluntary activation is important when designing rehabilitation interventions to address movement impairments and restore the ability to perform ADLs. Twitch interpolation is an experimental technique developed to quantify muscle voluntary activation [1]. This method has been used widely across pathologies but often limited to assessment of the voluntary activation of the plantar flexors, given the ease of activating these muscles through stimulation of the tibial nerve [2]. The complex innervation of elbow and wrist musculature imposes practical difficulties when applying the twitch interpolation technique to these joints [1]. Therefore, only a few studies have used this technique to examine the pathological [3]-[5] upper extremity, with little quantitative data documenting the degree of paresis present in the upper limb after stroke. The goal of this study is to evaluate the feasibility of applying twitch interpolation to quantify voluntary activation of the elbow and wrist flexors and extensors in chronic stroke survivors.

Evaluation of Electroencephalography Source Localization Algorithms with Multiple Cortical Sources.

BACKGROUND: Source localization algorithms often show multiple active cortical areas as the source of electroencephalography (EEG). Yet, there is little data quantifying the accuracy of these results. In this paper, the performance of current source density source localization algorithms for the detection of multiple cortical sources of EEG data has been characterized. METHODS: EEG data were generated by simulating multiple cortical sources (2-4) with the same strength or two sources with relative strength ratios of 1:1 to 4:1, and adding noise. These data were used to reconstruct the cortical sources using current source density (CSD) algorithms: sLORETA, MNLS, and LORETA using a p-norm with p equal to 1, 1.5 and 2. Precision (percentage of the reconstructed activity corresponding to simulated activity) and Recall (percentage of the simulated sources reconstructed) of each of the CSD algorithms were calculated. RESULTS: While sLORETA has the best performance when only one source is present, when two or more sources are present LORETA with p equal to 1.5 performs better. When the relative strength of one of the sources is decreased, all algorithms have more difficulty reconstructing that source. However, LORETA 1.5 continues to outperform other algorithms. If only the strongest source is of interest sLORETA is recommended, while LORETA with p equal to 1.5 is recommended if two or more of the cortical sources are of interest. These results provide guidance for choosing a CSD algorithm to locate multiple cortical sources of EEG and for interpreting the results of these algorithms.

Properties of the motor unit action potential shape in proximal and distal muscles of the upper limb in healthy and post-stroke individuals.

Spectral analysis of surface electromyograms (sEMG) is often used to estimate central and peripheral characteristics of a motor unit (MU) population, such as average conduction velocity, proportion of muscle fiber types, and pattern of MU recruitment. This estimation is based on the assumption that the sEMG adequately reflects the frequency characteristics of the underlying MU action potentials (MUAP). However, sEMG has limitations in this respect, based on physiological and non-physiological factors that influence its frequency content. We present a method to examine characteristics of a MU population more reliably by assessing the distributions of frequency content and amplitude for a collection of individual MUAPs, identified using high-density sEMG decomposition. We demonstrate the use of this approach to examine how MU characteristics differ across muscles and in the post-stroke state by presenting preliminary data from deltoid (DELT), biceps (BIC), and finger flexor (FF) MU populations from 12 post-stroke individuals and 8 able-bodied controls. The results show differences in the magnitude and range of MUAP median frequencies across muscles in both groups. The group median values were higher in the stroke group for the DELT and FF and lower in the stroke group for the BIC. The range of frequencies was larger in the stroke group for all muscles. The distribution of MUAP RMS amplitude in both stroke and control groups had a substantially larger range in FF than in DELT and BIC. The group median values for the FF were twice as large in the stroke group. In addition, there were differences in the frequency and amplitude results between MUAP and global sEMG analyses. The implications of these findings and possible applications of the approach are discussed.

Development of a method to quantify inter-limb coupling in individuals with hemiparetic stroke.

A common motor deficit in individuals post-stroke is altered interlimb coupling. Efforts at one extremity can cause involuntary muscle activity and movement at a different extremity. An important step in understanding interlimb coupling and developing effective treatment strategies is to have an accurate quantification of the motor behavior. This paper outlines the development of an approach to measure interlimb coupling between the upper and lower extremity. Isometric and EMG based approaches were explored before determining that the use of a haptic robotic system was ideal to quantify altered interlimb coupling. This is a novel engineering approach that can measure biomechanical parameters while avoiding confounding factors. Preliminary evidence shows that lower extremity efforts cause involuntary movement in the upper extremity in stereotypical flexion and extension patterns.

Assessment of the contralesional corticospinal tract in early-onset pediatric hemiplegia: Preliminary findings.

While pediatric hemiplegia results from a unilateral lesion, the immature state of the brain at the time of injury increases the likelihood of observing changes in the non-lesioned hemisphere as well. The purpose of this preliminary study was to use diffusion tensor imaging to evaluate the contralesional corticospinal tracts in individuals with early-onset pediatric hemiplegia. Twelve individuals with pediatric hemiplegia and ten age-matched controls underwent diffusion tensor imaging (DTI). Corticospinal projections were reconstructed using probabilistic tractography for both the lesioned and contralesional side in pediatric hemiplegia as well as the dominant and non-dominant sides in control subjects. The contralesional tract was found to have decreased white matter integrity relative to control subjects. Compared to controls, the contralesional tract also showed increased tract volume. The increase in volume suggests the presence of ipsilateral corticospinal projections from the contralesional hemisphere that are maintained during development to control the paretic extremities. Decreases in integrity may be explained by diffuse damage or incomplete maturation. The findings of this study support the notion of bilateral motor involvement in pediatric hemiplegia, and the need to address bilateral neural changes as well as motor deficits in this population.

Increased shoulder abduction loads decreases volitional finger extension in individuals with chronic stroke: Preliminary findings.

The ability to open the paretic hand is greatly affected after a stroke. The loss of especially finger extension has been previously reported during isolated finger movements. However, activities of daily life require the combination of reaching and grasping which will require shoulder abduction. Shoulder abductor activity will result in concurrent elbow, wrist and finger flexion which is also referred to as the flexion synergy. Therefore as part of this study the effect of of shoulder abduction (SABD) loading on volitional finger extension in individuals with chronic stroke is investigated. We expect to observe that shoulder abduction loading will further decrease the already impaired volitional finger extension in individuals with chronic stroke. A total of four moderately impaired individuals with chronic stroke and three age-matched able-bodied subjects participated in this study. Finger extension was recorded during hand open while subjects kept their arm extended at the end of a reach. The preliminary data showed that the maximal volitional finger extension was significantly decreased by increasing the SABD loads in individuals with chronic stroke, but not in age-matched able-bodied subjects.

Pilot study to test effectiveness of video game on reaching performance in stroke.

Robotic systems currently used in upper-limb rehabilitation following stroke rely on some form of visual feedback as part of the intervention program. We evaluated the effect of a video game environment (air hockey) on reaching in stroke with various levels of arm support. We used the Arm Coordination Training 3D system to provide variable arm support and to control the hockey stick. We instructed seven subjects to reach to one of three targets covering the workspace of the impaired arm during the reaching task and to reach as far as possible while playing the video game. The results from this study showed that across subjects, support levels, and targets, the reaching distances achieved with the reaching task were greater than those covered with the video game. This held even after further restricting the mapped workspace of the arm to the area most affected by the flexion synergy (effectively forcing subjects to fight the synergy to reach the hockey puck). The results from this study highlight the importance of designing video games that include specific reaching targets in the workspace compromised by the expression of the flexion synergy. Such video games would also adapt the target location online as a subject's success rate increases.

The ACT-4D: a novel rehabilitation robot for the quantification of upper limb motor impairments following brain injury.

Rehabilitation robots and other controlled diagnostic devices are useful tools to objectively quantify debilitating, post-stroke impairments. The goal of this paper is to describe the design of the ACT-4D rehabilitation robot which can quantify arm impairments during functional movement. The robot can instantly switch between a compliant mode that minimizes impedance of voluntary movement, and a stiff mode that applies controlled position/speed perturbations to the elbow (up to 75 Nm or 450 deg/s at 4500 deg/s(2)). It has a limited range of movement of the shoulder and elbow, which is further reduced when a damper is needed to enhance the positional stiffness of the base robot. In recent experiments, the ACT-4D has been used successfully for the quantification of elbow impairments.

Wrist and Finger Torque Sensor for the quantification of upper limb motor impairments following brain injury.

This paper details the design of the Wrist and Finger Torque Sensing module (WFTS): a lightweight, portable device that measures isometric wrist and finger flexion and extension joint torques. The WFTS can be used in combination with rehabilitation robots such as the ACT-3D, with isometric measurement stations, or as a stand-alone device. Because many robotic devices are limited in that they involve the hand in isolation, the WFTS is designed to investigate abnormal joint torque coupling at the paretic wrist and fingers in individuals with adult-onset stroke or childhood hemiplegia during 3D arm movements or isometric generation of shoulder and elbow torques. In short, the versatility of the WFTS allows for a variety of applications.

Muscle focus: a new biomechanical-based index on the selectivity of EMG activity and its application in quantifying the muscle coactivation patterns during isometric torque generation at the elbow and shoulder.

Electromyographic (EMG) recordings are widely used in the study of sensorimotor and neuromuscular systems, more specifically, in the measurement of the muscle activation patterns during isometric torque generation at the elbow and shoulder. In this paper, we introduce a new biomechanics based index of muscle focus. This new index quantifies the degree of selectivity in muscle activation during a shoulder/elbow motor task with a scalar. The muscle focus takes into account both muscle co-activation and muscle co-contraction (which is a special case of co-activation caused by activation of agonist and antagonist muscles about a single joint).