Frequency-Domain sEMG Classification Using a Single Sensor.

Working towards the development of robust motion recognition systems for assistive technology control, the widespread approach has been to use a plethora of, often times, multi-modal sensors. In this paper, we develop single-sensor motion recognition systems. Utilising the peripheral nature of surface electromyography (sEMG) data acquisition, we optimise the information extracted from sEMG sensors. This allows the reduction in sEMG sensors or provision of contingencies in a system with redundancies. In particular, we process the sEMG readings captured at the trapezius descendens and platysma muscles. We demonstrate that sEMG readings captured at one muscle contain distinct information on movements or contractions of other agonists. We used the trapezius and platysma muscle sEMG data captured in able-bodied participants and participants with tetraplegia to classify shoulder movements and platysma contractions using white-box supervised learning algorithms. Using the trapezius sensor, shoulder raise is classified with an accuracy of 99%. Implementing subject-specific multi-class classification, shoulder raise, shoulder forward and shoulder backward are classified with a 94% accuracy amongst object raise and shoulder raise-and-hold data in able bodied adults. A three-way classification of the platysma sensor data captured with participants with tetraplegia achieves a 95% accuracy on platysma contraction and shoulder raise detection.

Electrophysiological Mapping During Brain Tumor Surgery: Recording Cortical Potentials Evoked Locally, Subcortically and Remotely by Electrical Stimulation to Assess the Brain Connectivity On-line.

Direct electrical stimulation (DES) is used to perform functional brain mapping during awake surgery and in epileptic patients. DES may be coupled with the measurement of Evoked Potentials (EP) to study the conductive and integrative properties of activated neural ensembles and probe the spatiotemporal dynamics of short- and long-range networks. However, its electrophysiological effects remain by far unknown. We recorded ECoG signals on two patients undergoing awake brain surgery and measured EP on functional sites after cortical stimulations and were the firsts to record three different types of EP on the same patients. Using low-intensity (1-3 mA) to evoke electrogenesis we observed that: (i) "true" remote EPs are attenuated in amplitude and delayed in time due to the divergence of white matter pathways; (ii) "false" remote EPs are attenuated but not delayed: as they originate from the same electrical source; (iii) Singular but reproducible positive components in the EP can be generated when the DES is applied in the temporal lobe or the premotor cortex; and (iv) rare EP can be triggered when the DES is applied subcortically: these can be either negative, or surprisingly, positive. We proposed different activation and electrophysiological propagation mechanisms following DES, based on the nature of activated neural elements and discussed important methodological pitfalls when measuring EP in the brain. Altogether, these results pave the way to map the connectivity in real-time between the DES and the recording sites; to characterize the local electrophysiological states and to link electrophysiology and function. In the future, and in practice, this technique could be used to perform electrophysiological mapping in order to link (non)-functional to electrophysiological responses with DES and could be used to guide the surgical act itself.

Patterns of axono-cortical evoked potentials: an electrophysiological signature unique to each white matter functional site?

BACKGROUND: Brain-to-brain evoked potentials constitute a new methodology that could help to understand the network-level correlates of electrical stimulation applied for brain mapping during tumor resection. In this paper, we aimed to describe the characteristics of axono-cortical evoked potentials recorded from distinct, but in the same patient, behaviorally eloquent white matter sites. METHODS: We report the intraoperative white matter mapping and axono-cortical evoked potentials recordings observed in a patient operated on under awake condition of a diffuse low-grade glioma in the left middle frontal gyrus. Out of the eight behaviorally eloquent sites identified with 60-Hz electrical stimulation, five were probed with single electrical pulses (delivered at 1 Hz), while recording evoked potentials on two electrodes, covering the inferior frontal gyrus and the precentral gyrus, respectively. Postoperative diffusion-weighted MRI was used to reconstruct the tractograms passing through each of the five stimulated sites. RESULTS: Each stimulated site generated an ACEP on at least one of the recorded electrode contacts. The whole pattern-i.e., the specific contacts with ACEPs and their waveform-was distinct for each of the five stimulated sites. CONCLUSIONS: We found that the patterns of ACEPs provided unique electrophysiological signatures for each of the five white matter functional sites. Our results could ultimately provide neurosurgeons with a new tool of intraoperative electrophysiologically based functional guidance.

New Stimulation Device to Drive Multiple Transverse Intrafascicular Electrodes and Achieve Highly Selective and Rich Neural Responses.

Peripheral Nerve Stimulation (PNS) is a promising approach in functional restoration following neural impairments. Although it proves to be advantageous in the number of implantation sites provided compared with intramuscular or epimysial stimulation and the fact that it does not require daily placement, as is the case with surface electrodes, the further advancement of PNS paradigms is hampered by the limitation of spatial selectivity due to the current spread and variations of nerve physiology. New electrode designs such as the Transverse Intrafascicular Multichannel Electrode (TIME) were proposed to resolve this issue, but their use was limited by a lack of innovative multichannel stimulation devices. In this study, we introduce a new portable multichannel stimulator-called STIMEP-and implement different stimulation protocols in rats to test its versatility and unveil the potential of its combined use with TIME electrodes in rehabilitation protocols. We developed and tested various stimulation paradigms in a single fascicle and thereafter implanted two TIMEs. We also tested its stimulation using two different waveforms. The results highlighted the versatility of this new stimulation device and advocated for the parameterizing of a hyperpolarizing phase before depolarization as well as the use of small pulse widths when stimulating with multiple electrodes.

Six-Month Assessment of a Hand Prosthesis with Intraneural Tactile Feedback.

OBJECTIVE: Hand amputation is a highly disabling event, which significantly affects quality of life. An effective hand replacement can be achieved if the user, in addition to motor functions, is provided with the sensations that are naturally perceived while grasping and moving. Intraneural peripheral electrodes have shown promising results toward the restoration of the sense of touch. However, the long-term usability and clinical relevance of intraneural sensory feedback have not yet been clearly demonstrated. METHODS: To this aim, we performed a 6-month clinical study with 3 transradial amputees who received implants of transverse intrafascicular multichannel electrodes (TIMEs) in their median and ulnar nerves. After calibration, electrical stimulation was delivered through the TIMEs connected to artificial sensors in the digits of a prosthesis to generate sensory feedback, which was then used by the subjects while performing different grasping tasks. RESULTS: All subjects, notwithstanding their important clinical differences, reported stimulation-induced sensations from the phantom hand for the whole duration of the trial. They also successfully integrated the sensory feedback into their motor control strategies while performing experimental tests simulating tasks of real life (with and without the support of vision). Finally, they reported a decrement of their phantom limb pain and a general improvement in mood state. INTERPRETATION: The promising results achieved with all subjects show the feasibility of the use of intraneural stimulation in clinical settings. ANN NEUROL 2019;85:137-154.

Attenuation and Delay of Remote Potentials Evoked by Direct Electrical Stimulation During Brain Surgery.

Direct electrical stimulation (DES) is used to perform functional brain mapping during awake surgery but its electrophysiological effects remain by far unknown. DES may be coupled with the measurement of evoked potentials (EPs) to study the conductive and integrative properties of activated neural ensembles and probe the spatiotemporal dynamics of short- and long-range networks. We recorded ECoG signals on two patients undergoing awake brain surgery and measured EPs on functional sites after cortical stimulations, using combinations of stimulation parameters. EPs were similar in shape but delayed in time and attenuated in amplitude when elicited from a different gyrus or remotely from the recording site. We were able to trigger remote EPs using low stimulation intensities. We propose different activation and electrophysiological propagation mechanisms following DES based on activated neural elements.

Selective neural electrical stimulation restores hand and forearm movements in individuals with complete tetraplegia.

BACKGROUND: We hypothesized that a selective neural electrical stimulation of radial and median nerves enables the activation of functional movements in the paralyzed hand of individuals with tetraplegia. Compared to previous approaches for which up to 12 muscles were targeted through individual muscular stimulations, we focused on minimizing the number of implanted electrodes however providing almost all the needed and useful hand movements for subjects with complete tetraplegia. METHODS: We performed acute experiments during scheduled surgeries of the upper limb with eligible subjects. We scanned a set of multicontact neural stimulation cuff electrode configurations, pre-computed through modeling simulations. We reported the obtained isolated and functional movements that were considered useful for the subject (different grasping movements). RESULTS: In eight subjects, we demonstrated that selective stimulation based on multicontact cuff electrodes and optimized current spreading over the active contacts provided isolated, compound, functional and strong movements; most importantly 3 out of 4 had isolated fingers or thumb flexion, one patient performed a Key Grip, another one the Power and Hook Grips, and the 2 last all the 3 Grips. Several configurations were needed to target different areas within the nerve to obtain all the envisioned movements. We further confirmed that the upper limb nerves have muscle specific fascicles, which makes it possible to activate isolated movements. CONCLUSIONS: The future goal is to provide patients with functional restoration of object grasping and releasing with a minimally invasive solution: only two cuff electrodes above the elbow. Ethics Committee / ANSM clearance prior to the beginning of the study (inclusion period 2016-2018): CPP Sud Méditerranée, #ID-RCB:2014-A01752-45, first acceptance 10th of February 2015, amended 12th of January 2016. TRIAL REGISTRATION: (www.clinicaltrials.gov): #NCT03721861, Retrospectively registered on 26th of October 2018.

Respiratory Monitoring Based on Tracheal Sounds: Continuous Time-Frequency Processing of the Phonospirogram Combined with Phonocardiogram-Derived Respiration.

Patients with central respiratory paralysis can benefit from diaphragm pacing to restore respiratory function. However, it would be important to develop a continuous respiratory monitoring method to alert on apnea occurrence, in order to improve the efficiency and safety of the pacing system. In this study, we present a preliminary validation of an acoustic apnea detection method on healthy subjects data. Thirteen healthy participants performed one session of two 2-min recordings, including a voluntary respiratory pause. The recordings were post-processed by combining temporal and frequency detection domains, and a new method was proposed-Phonocardiogram-Derived Respiration (PDR). The detection results were compared to synchronized pneumotachograph, electrocardiogram (ECG), and abdominal strap (plethysmograph) signals. The proposed method reached an apnea detection rate of 92.3%, with 99.36% specificity, 85.27% sensitivity, and 91.49% accuracy. PDR method showed a good correlation of 0.77 with ECG-Derived Respiration (EDR). The comparison of R-R intervals and S-S intervals also indicated a good correlation of 0.89. The performance of this respiratory detection algorithm meets the minimal requirements to make it usable in a real situation. Noises from the participant by speaking or from the environment had little influence on the detection result, as well as body position. The high correlation between PDR and EDR indicates the feasibility of monitoring respiration with PDR.

Assisted Grasping in Individuals with Tetraplegia: Improving Control through Residual Muscle Contraction and Movement.

Individuals who sustained a spinal cord injury often lose important motor skills, and cannot perform basic daily living activities. Several assistive technologies, including robotic assistance and functional electrical stimulation, have been developed to restore lost functions. However, designing reliable interfaces to control assistive devices for individuals with C4-C8 complete tetraplegia remains challenging. Although with limited grasping ability, they can often control upper arm movements via residual muscle contraction. In this article, we explore the feasibility of drawing upon these residual functions to pilot two devices, a robotic hand and an electrical stimulator. We studied two modalities, supra-lesional electromyography (EMG), and upper arm inertial sensors (IMU). We interpreted the muscle activity or arm movements of subjects with tetraplegia attempting to control the opening/closing of a robotic hand, and the extension/flexion of their own contralateral hand muscles activated by electrical stimulation. Two groups were recruited: eight subjects issued EMG-based commands; nine other subjects issued IMU-based commands. For each participant, we selected at least two muscles or gestures detectable by our algorithms. Despite little training, all participants could control the robot's gestures or electrical stimulation of their own arm via muscle contraction or limb motion.

Impact of direct epispinal stimulation on bladder and bowel functions in pigs: A feasibility study.

AIMS: This study assesses the potential of epispinal (subdural) stimulation application in the treatment of urinary and bowel neurological disorders. Acute experiments were performed on a large animal model - the domestic pig - to develop a new methodology facilitating future results and technology transfers to human. METHODS: After rectal and bladder catheterization, four Landrace pigs (45-50 kg) underwent spinal cord surgery - that is, lumbosacral incision, laminectomy [L4-S4], dural opening and microsurgical arachnoid dissection. Three successive electrical stimulation sessions were carried out: 1) nerve roots stimulation, 2) epispinal stimulation with a matrix electrode, 3) epispinal stimulation with a small diameter needle electrode. Changes in rectal and bladder pressures were monitored throughout the various procedures to identify spinal areas inducing responses while evaluating the influence of electrode contacts size in the measured responses amplitudes. RESULTS: An interesting area was identified in the upper portion of the spinal myelomeres (ie, spinal cord segment delimited by two successive pairs of spinal roots) directly adjoining root with best pressures (either rectal or vesical). Significant responses (up to 40 cmH2 O) were also obtained with a needle electrode. Furthermore, bowel evacuation was triggered in one of the animals. Despite the use of smaller electrode contacts, no detrusor or rectum selective responses were observed in none of the sessions. CONCLUSION: This study showed, for the first time, that epispinal stimulation causes significant detrusor and rectal responses in pigs and allows considering further studies with the objective of treating urinary and rectal disorders in spinal cord injury patients.

Alterations of EEG rhythms during motor preparation following awake brain surgery.

Slow-growing, infiltrative brain tumours may modify the electrophysiological balance between the two hemispheres. To determine whether and how asymmetry of EEG rhythms during motor preparation might occur following "awake brain surgery" for this type of tumour, we recorded electroencephalograms during a simple visuo-manual reaction time paradigm performed by the patients between 3 and 12 months after surgery and compared them to a control group of 8 healthy subjects. Frequency analyses revealed imbalances between the injured and healthy hemispheres. More particularly, we observed a power increase in the δ frequency band near the lesion site and a power increase in the α and ß frequency bands. Interestingly, these alterations seem to decrease for the two patients whose surgery were anterior to 9 months, independently of the size of the lesion. Reaction times did not reflect this pattern as they were clearly not inversely related to the anteriority of the surgery. Electrophysiology suggests here different processes of recovery compared to behavioral data and brings further insights for the understanding of EEG rhythms that should not be systematically confounded or assimilated with cognitive performances. EEG monitoring is rare for these patients, especially after awake brain surgery, however it is important.

Real-time estimation of FES-induced joint torque with evoked EMG : Application to spinal cord injured patients.

BACKGROUND: Functional electrical stimulation (FES) is a neuroprosthetic technique for restoring lost motor function of spinal cord injured (SCI) patients and motor-impaired subjects by delivering short electrical pulses to their paralyzed muscles or motor nerves. FES induces action potentials respectively on muscles or nerves so that muscle activity can be characterized by the synchronous recruitment of motor units with its compound electromyography (EMG) signal is called M-wave. The recorded evoked EMG (eEMG) can be employed to predict the resultant joint torque, and modeling of FES-induced joint torque based on eEMG is an essential step to provide necessary prediction of the expected muscle response before achieving accurate joint torque control by FES. METHODS: Previous works on FES-induced torque tracking issues were mainly based on offline analysis. However, toward personalized clinical rehabilitation applications, real-time FES systems are essentially required considering the subject-specific muscle responses against electrical stimulation. This paper proposes a wireless portable stimulator used for estimating/predicting joint torque based on real time processing of eEMG. Kalman filter and recurrent neural network (RNN) are embedded into the real-time FES system for identification and estimation. RESULTS: Prediction results on 3 able-bodied subjects and 3 SCI patients demonstrate promising performances. As estimators, both Kalman filter and RNN approaches show clinically feasible results on estimation/prediction of joint torque with eEMG signals only, moreover RNN requires less computational requirement. CONCLUSION: The proposed real-time FES system establishes a platform for estimating and assessing the mechanical output, the electromyographic recordings and associated models. It will contribute to open a new modality for personalized portable neuroprosthetic control toward consolidated personal healthcare for motor-impaired patients.

A new method for muscle fatigue assessment: Online model identification techniques.

INTRODUCTION: The purpose of this study was to propose a method that allows extraction of the current muscle state under electrically induced fatigue. METHODS: The triceps surae muscle of 5 subjects paralyzed by spinal cord injury was fatigued by intermittent electrical stimulation (5 × 5 trains at 30 Hz). Classical fatigue indices representing muscle contractile properties [peak twitch (Pt) and half-relaxation time (HRT)] were assessed before and after each 5-train series and were used to identify 2 relevant parameters (Fm , Ur ) of a previously developed mathematical model using the Sigma-Point Kalman Filter. RESULTS: Pt declined significantly during the protocol, whereas HRT remained unchanged. Identification of the model parameters with experimental data yielded a model-based fatigue assessment that gave a more stable evaluation of fatigue than classical parameters. CONCLUSIONS: This work reinforces clinical research by providing a tool that clinicians can use to monitor fatigue development during stimulation.

Asymmetric interhemispheric excitability evidenced by event-related potential amplitude patterns after "wide-awake surgery" of brain tumours.

Slow-growing, infiltrative brain tumours may modify the electrophysiological balance between the two hemispheres. To determine whether and how asymmetry in interhemispheric excitability might occur following "wide-awake surgery" for this type of tumour, we recorded electroencephalograms during a simple visuo-manual reaction time paradigm performed by five patients between 3 and 12 months after surgery. Interhemispheric excitability asymmetries were computed by comparing the amplitudes of event-related potentials (ERPs) in the injured hemisphere to those in the healthy hemisphere. For the two patients with the smallest lesions (7.1 and 11.5 cm(3), respectively), increased excitability within the ipsilesional hemisphere was evidenced by characteristics increases in the ERP amplitude at several sites, with few occurrences in the contralesional hemisphere. For smaller lesions (and under certain experimental conditions), cortical excitability in the injured hemisphere may increase in order to maintain local compensation. In addition, we observed and increased excitability in the contralesional frontal homologue for one patient who underwent an extensive resection. Post-operative monitoring of interhemispheric asymmetries in ERP amplitudes is of value for determining task constraints inducing electrophysiological imbalance and guiding rehabilitation.

Implanted functional electrical stimulation: case report of a paraplegic patient with complete SCI after 9 years.

BACKGROUNDS: Experience of an implanted functional electrical stimulation neuroprosthesis (FES) associating 8-channel epimysial and 4-channel neural stimulations. The primary objective consisted in presenting clinical and technological experiences based on a 9-year follow-up of one patient implanted with this FES device. The secondary objective consisted in assessing resulting functional benefits. METHODS: One patient recruited in 1996 within the European Stand Up and Walk Project benefited from a 9-year follow-up with clinical and technological evaluations. RESULTS: The patient was still using the system nine years later making this a unique case, even when compared to other similar studies. The analysis of muscular response to FES underlined the great variability of stimulation thresholds evolution (-26% to +360%, mean +110%) and quality of the induced contraction. Three muscles out of five scored at least 4/5 on the Medical Research Council scale, all stimulated via neural pathways. The patient used the system once a week for 6 years, up to 2006, due to lack of use, the FES-induced muscular response worsened even though the implant was properly functioning, leading to significant decline in gait performances (best 3.45 m/s on 2.9 m), due to muscle fatigue and loss of muscle mass. CONCLUSION: Two major issues arise: first the importance of muscle fatigue, underlining the relevance of muscle strength training, and second technological hurdles raising up the question of neural vs. epimysial FES. This advanced technology proves the concept of restoring lower limb motor functions in patients with spinal cord injury. The main features of the stimulation device remain stable even after long periods of inactivity, yet there is a real need for close clinical and technological monitoring.

Voluntary EMG-to-force estimation with a multi-scale physiological muscle model.

BACKGROUND: EMG-to-force estimation based on muscle models, for voluntary contraction has many applications in human motion analysis. The so-called Hill model is recognized as a standard model for this practical use. However, it is a phenomenological model whereby muscle activation, force-length and force-velocity properties are considered independently. Perreault reported Hill modeling errors were large for different firing frequencies, level of activation and speed of contraction. It may be due to the lack of coupling between activation and force-velocity properties. In this paper, we discuss EMG-force estimation with a multi-scale physiology based model, which has a link to underlying crossbridge dynamics. Differently from the Hill model, the proposed method provides dual dynamics of recruitment and calcium activation. METHODS: The ankle torque was measured for the plantar flexion along with EMG measurements of the medial gastrocnemius (GAS) and soleus (SOL). In addition to Hill representation of the passive elements, three models of the contractile parts have been compared. Using common EMG signals during isometric contraction in four able-bodied subjects, torque was estimated by the linear Hill model, the nonlinear Hill model and the multi-scale physiological model that refers to Huxley theory. The comparison was made in normalized scale versus the case in maximum voluntary contraction. RESULTS: The estimation results obtained with the multi-scale model showed the best performances both in fast-short and slow-long term contraction in randomized tests for all the four subjects. The RMS errors were improved with the nonlinear Hill model compared to linear Hill, however it showed limitations to account for the different speed of contractions. Average error was 16.9% with the linear Hill model, 9.3% with the modified Hill model. In contrast, the error in the multi-scale model was 6.1% while maintaining a uniform estimation performance in both fast and slow contractions schemes. CONCLUSIONS: We introduced a novel approach that allows EMG-force estimation based on a multi-scale physiology model integrating Hill approach for the passive elements and microscopic cross-bridge representations for the contractile element. The experimental evaluation highlights estimation improvements especially a larger range of contraction conditions with integration of the neural activation frequency property and force-velocity relationship through cross-bridge dynamics consideration.

A method based on wavelets to analyse overlapped and dependant M-Waves.

Implanted stimulation restores hand movement in patients with complete spinal cord injuries. However, assessing the response by surface evoked EMG recordings is challenging because the forearm muscles are small and overlapping. Moreover, M-waves are dependent because they are induced by a single stimulation paradigm. We hypothesized that the M-waves of each muscle has a specific time-frequency signature and we have developed a method to reconstruct the recruitment curves using the energy of this specific time-frequency signature. Orthogonal wavelets are used to analyze individual M-waves. As the selection of the wavelet family and the determination of the time-frequency signature were not trivial, the impact of these choices was evaluated. First, we were able to discriminate the 2 relevant M-waves related to the studied muscles thanks to their specific time-frequency representations. Second, the Meyer family, compared to the Daubechies 2 and 4 families, is the most robust choice against the uncertainty of the time-frequency region definition. Finally, the results are consistent with the semi-quantitative evaluation performed with the MRC scoring. The Meyer wavelet transform combined with the definition of a specific area of interest for each individual muscle allows us to quantitatively and objectively evaluate the evoked EMG in a robust manner.

Influence of the H-reflex on the selectivity of recruitment using multi-contact epineural stimulation of the median nerve in a participant with complete tetraplegia.

Multi-contact epineural electrical stimulation is a technique that can be used to restore grip movements in people with complete tetraplegia. However, neural stimulation can induce undesired H-reflex. This reflex is known to induce a global lower recruitment threshold together with a steepest recruitment curve leading to a degraded selective response. In this study, during stimulation of the median nerve using a multi-contact cuff electrode, a H-reflex response was observed for one muscle (the pronator teres i.e. PT) among the five recorded. As both M-wave and H-wave were separately recorded, we compared the changes of recruitment, recruitment order and se-lectivity with and without the H-reflex and found that blocking the reflex would have enhance the selectivity and increase the range of the intensity amplitude while providing a higher level of gripping force. Thus, blocking H-reflex is an important issue to further enhance epineural multicontact selective stimulation.

A Residual Movement Classification Based User Interface for Control of Assistive Devices by Persons With Complete Tetraplegia.

OBJECTIVE: Complete tetraplegia can deprive a person of hand function. Assistive technologies may improve autonomy but needs for ergonomic interfaces for the user to pilot these devices still persist. Despite the paralysis of their arms, people with tetraplegia may retain residual shoulder movements. In this work we explored these movements as a mean to control assistive devices. METHODS: We captured shoulder movement with a single inertial sensor and, by training a support vector machine based classifier, we decode such information into user intent. RESULTS: The setup and training process take only a few minutes and so the classifiers can be user specific. We tested the algorithm with 10 able body and 2 spinal cord injury participants. The average classification accuracy was 80% and 84%, respectively. CONCLUSION: The proposed algorithm is easy to set up, its operation is fully automated, and achieved results are on par with state-of-the-art systems. SIGNIFICANCE: Assistive devices for persons without hand function present limitations in their user interfaces. Our work presents a novel method to overcome some of these limitations by classifying user movement and decoding it into user intent, all with simple setup and training and no need for manual tuning. We demonstrate its feasibility with experiments with end users, including persons with complete tetraplegia without hand function.