A new modular neuroprosthesis suitable for hybrid FES-robot applications and tailored assistance

BACKGROUND

To overcome the application limitations of functional electrical stimulation (FES), such as fatigue or nonlinear muscle response, the combination of neuroprosthetic systems with robotic devices has been evaluated, resulting in hybrid systems that have promising potential. However, current technology shows a lack of flexibility to adapt to the needs of any application, context or individual. The main objective of this study is the development of a new modular neuroprosthetic system suitable for hybrid FES-robot applications to meet these needs.

METHODS

In this study, we conducted an analysis of the requirements for developing hybrid FES-robot systems and reviewed existing literature on similar systems. Building upon these insights, we developed a novel modular neuroprosthetic system tailored for hybrid applications. The system was specifically adapted for gait assistance, and a technological personalization process based on clinical criteria was devised. This process was used to generate different system configurations adjusted to four individuals with spinal cord injury or stroke. The effect of each system configuration on gait kinematic metrics was analyzed by using repeated measures ANOVA or Friedman's test.

RESULTS

A modular NP system has been developed that is distinguished by its flexibility, scalability and personalization capabilities. With excellent connection characteristics, it can be effectively integrated with robotic devices. Its 3D design facilitates fitting both as a stand-alone system and in combination with other robotic devices. In addition, it meets rigorous requirements for safe use by incorporating appropriate safety protocols, and features appropriate battery autonomy, weight and dimensions. Different technological configurations adapted to the needs of each patient were obtained, which demonstrated an impact on the kinematic gait pattern comparable to that of other devices reported in the literature.

CONCLUSIONS

The system met the identified technical requirements, showcasing advancements compared to systems reported in the literature. In addition, it demonstrated its versatility and capacity to be combined with robotic devices forming hybrids, adapting well to the gait application. Moreover, the personalization procedure proved to be useful in obtaining various system configurations tailored to the diverse needs of individuals.

Revolutionizing motor dysfunction treatment: A novel closed-loop electrical stimulator guided by multiple motor tasks with predictive control

Functional electrical stimulation (FES) has been demonstrated as a viable method for addressing motor dysfunction in individuals affected by stroke, spinal cord injury, and other etiologies. By eliciting muscle contractions to facilitate joint movements, FES plays a crucial role in fostering the restoration of motor function compromised nervous system. In response to the challenge of muscle fatigue associated with conventional FES protocols, a novel biofeedback electrical stimulator incorporating multi-motor tasks and predictive control algorithms has been developed to enable adaptive modulation of stimulation parameters. The study initially establishes a Hammerstein model for the stimulated muscle group, representing a time-varying relationship between the stimulation pulse width and the root mean square (RMS) of the surface electromyography (sEMG). An online parameter identification algorithm utilizing recursive least squares is employed to estimate the time-varying parameters of the Hammerstein model. Predictive control is then implemented through feedback corrections based on the comparison between predicted and actual outputs, guided by an optimization objective function. The integration of predictive control and roll optimization enables closed-loop control of muscle stimulation. The motor training tasks of elbow flexion and extension, wrist flexion and extension, and five-finger grasping were selected for experimental validation. The results indicate that the model parameters were accurately identified, with a RMS error of 3.83 % between actual and predicted values. Furthermore, the predictive control algorithm, based on the motor tasks, effectively adjusted the stimulus parameters to ensure that the stimulated muscle groups can achieve the desired sEMG characteristic trajectory. The biofeedback electrical stimulator that was developed has the potential to assist patients experiencing motor dysfunction in achieving the appropriate joint movements. This research provides a foundation for a novel intelligent electrical stimulation model.

Simulation of FES on the forearm with muscle-specific activation resolution

Introduction

Functional electrical stimulation (FES) is an established method of supporting neurological rehabilitation. However, particularly on the forearm, it still cannot elicit selective muscle activations that form the basis of complex hand movements. Current research approaches in the context of selective muscle activation often attempt to enable targeted stimulation by increasing the number of electrodes and combining them in electrode arrays. In order to determine the best stimulation positions and settings, manual or semi-automated algorithms are used. This approach is limited due to experimental limitations. The supportive use of simulation studies is well-established, but existing simulation models are not suitable for analyses of selective muscle activation due to missing or arbitrarily arranged innervation zones.

Methods

This study introduces a new modeling method to design a person-specific digital twin that enables the prediction of muscle activations during FES on the forearm. The designed individual model consists of three parts: an anatomically based 3D volume conductor, a muscle-specific nerve fiber arrangement in various regions of interest (ROIs), and a standard nerve model. All processes were embedded in scripts or macros to enable automated changes to the model and the simulation setup.

Results

The experimental evaluation of simulated strength-duration diagrams showed good coincidence. The relative differences of the simulated amplitudes to the mean amplitude of the four experiments were in the same range as the inter-experimental differences, with mean values between 0.005 and 0.045. Based on these results, muscle-specific activation thresholds were determined and integrated into the simulation process. With this modification, simulated force-intensity curves showed good agreement with additionally measured curves.

Discussion

The results show that the model is suitable for simulating realistic muscle-specific activations. Since complex hand movements are physiologically composed of individual, selective muscle activations, it can be assumed that the model is also suitable for simulating these movements. Therefore, this study presents a new and very promising approach for developing new applications and products in the context of the rehabilitation of sensorimotor disorders.

A 14-Bit, 12 V-to-100 V Voltage Compliance Electrical Stimulator with Redundant Digital Calibration

Electrical stimulation is an important technique for modulating the functions of the nervous system through electrical stimulus. To implement a more competitive prototype that can tackle the domain-specific difficulties of existing electrical stimulators, three key techniques are proposed in this work. Firstly, a load-adaptive power saving technique called over-voltage detection is implemented to automatically adjust the supply voltage. Secondly, redundant digital calibration (RDC) is proposed to improve current accuracy and ensure safety during long-term electrical stimulation without costing too much circuit area and power. Thirdly, a flexible waveform generator is designed to provide arbitrary stimulus waveforms for particular applications. Measurement results show the stimulator can adjust the supply voltage from 12 V to 100 V automatically, and the measured effective resolution of the stimulation current reaches 14 bits in a full range of 6.5 mA. Without applying charge balancing techniques, the average mismatch between the cathodic and anodic current pulses in biphasic stimulus is 0.0427%. The proposed electrical stimulator can generate arbitrary stimulus waveforms, including sine, triangle, rectangle, etc., and it is supposed to be competitive for implantable and wearable devices.

Automated calibration of somatosensory stimulation using reinforcement learning

BACKGROUND

The identification of the electrical stimulation parameters for neuromodulation is a subject-specific and time-consuming procedure that presently mostly relies on the expertise of the user (e.g., clinician, experimenter, bioengineer). Since the parameters of stimulation change over time (due to displacement of electrodes, skin status, etc.), patients undergo recurrent, long calibration sessions, along with visits to the clinics, which are inefficient and expensive. To address this issue, we developed an automatized calibration system based on reinforcement learning (RL) allowing for accurate and efficient identification of the peripheral nerve stimulation parameters for somatosensory neuroprostheses.

METHODS

We developed an RL algorithm to automatically select neurostimulation parameters for restoring sensory feedback with transcutaneous electrical nerve stimulation (TENS). First, the algorithm was trained offline on a dataset comprising 49 subjects. Then, the neurostimulation was then integrated with a graphical user interface (GUI) to create an intuitive AI-based mapping platform enabling the user to autonomously perform the sensation characterization procedure. We assessed the algorithm against the performance of both experienced and naïve and of a brute force algorithm (BFA), on 15 nerves from five subjects. Then, we validated the AI-based platform on six neuropathic nerves affected by distal sensory loss.

RESULTS

Our automatized approach demonstrated the ability to find the optimal values of neurostimulation achieving reliable and comfortable elicited sensations. When compared to alternatives, RL outperformed the naïve and BFA, significantly decreasing the time for mapping and the number of delivered stimulation trains, while improving the overall quality. Furthermore, the RL algorithm showed performance comparable to trained experimenters. Finally, we exploited it successfully for eliciting sensory feedback in neuropathic patients.

CONCLUSIONS

Our findings demonstrated that the AI-based platform based on a RL algorithm can automatically and efficiently calibrate parameters for somatosensory nerve stimulation. This holds promise to avoid experts' employment in similar scenarios, thanks to the merging between AI and neurotech. Our RL algorithm has the potential to be used in other neuromodulation fields requiring a mapping process of the stimulation parameters.

TRIAL REGISTRATION

ClinicalTrial.gov (Identifier: NCT04217005).

Effects on hemodynamic enhancement and discomfort of a new textile electrode integrated in a sock during calf neuromuscular electrical stimulation

PURPOSE

To compare fixed transverse textile electrodes (TTE) knitted into a sock versus motor point placed standard gel electrodes (MPE) on peak venous velocity (PVV) and discomfort, during calf neuromuscular electrical stimulation (calf-NMES).

METHODS

Ten healthy participants received calf-NMES with increasing intensity until plantar flexion (measurement level I = ML I), and an additional mean 4 mA intensity (ML II), utilizing TTE and MPE. PVV was measured with Doppler ultrasound in the popliteal and femoral veins at baseline, ML I and II. Discomfort was assessed with a numerical rating scale (NRS, 0-10). Significance was set to p < 0.05.

RESULTS

TTE and MPE both induced significant increases in PVV from baseline to ML I and significantly higher increases to ML II, in both the popliteal and femoral veins (all p < 0.001). The popliteal increases of PVV from baseline to both ML I and II were significantly higher with TTE versus MPE (p < 0.05). The femoral increases of PVV from baseline to both ML I and II were not significantly different between TTE and MPE. TTE versus MPE resulted at ML I in higher mA and NRS (p < 0.001), and at ML II in higher mA (p = 0.005) while NRS was not significantly different.

CONCLUSION

TTE integrated in a sock produces intensity-dependent increases of popliteal and femoral hemodynamics comparable to MPE, but results in more discomfort at plantar flexion due to higher current required. TTE exhibits in the popliteal vein higher increases of PVV compared to MPE.

TRIAL REGISTRATION

Trial_ID: ISRCTN49260430. Date: 11/01/2022. Retrospectively registered.

Neuromuscular electrical stimulation in garments optimized for compliance

PURPOSE

Physical inactivity is associated with muscle atrophy and venous thromboembolism, which may be prevented by neuromuscular electrical stimulation (NMES). This study aimed to investigate the effect on discomfort, current amplitude and energy consumption when varying the frequency and phase duration of low-intensity NMES (LI-NMES) via a sock with knitting-integrated transverse textile electrodes (TTE).

METHODS

On eleven healthy participants (four females), calf-NMES via a TTE sock was applied with increasing intensity (mA) until ankle-plantar flexion at which point outcomes were compared when testing frequencies 1, 3, 10 and 36 Hz and phase durations 75, 150, 200, 300 and 400 µs. Discomfort was assessed with a numerical rating scale (NRS, 0-10) and energy consumption was calculated and expressed in milli-Joule (mJ). Significance set to p ≤ 0.05.

RESULTS

1 Hz yielded a median (inter-quartile range) NRS of 2.4 (1.0-3.4), significantly lower than both 3 Hz with NRS 2.8 (1.8-4.2), and 10 Hz with NRS 3.4 (1.4-5.4) (both p ≤ .014). Each increase in tested frequency resulted in significantly higher energy consumption, e.g. 0.6 mJ (0.5-0.8) for 1 Hz vs 14.9 mJ (12.3-21.2) for 36 Hz (p = .003). Longer phase durations had no significant effect on discomfort despite generally requiring significantly lower current amplitudes. Phase durations 150, 200 and 400 µs required significantly lower energy consumption compared to 75 µs (all p ≤ .037).

CONCLUSION

LI-NMES applied via a TTE sock produces a relevant plantar flexion of the ankle with the best comfort and lowest energy consumption using 1 Hz and phase durations 150, 200 or 400 µs.

Design and fast-fabrication of a system for functional electrical stimulation in upper limb of people with tetraplegia

STUDY DESIGN

Proof of concept.

OBJECTIVES

Standard Functional Electrical Stimulation (FES) systems can enhance motor learning in people with tetraplegia and are widely delivered by self-adhesive electrodes. Their limitations are dexterity, specific knowledge to place the electrodes on muscles, need to fix electrodes when they lose the gel layer, and time. We designed a new FES system, using an existing protocol of drinking-like movements, to the upper limb of a person with tetraplegia C5 that fits in any anthropometry and can be easily produced. Furthermore, we tested the system to assess its effectiveness and users' perception during FES rehabilitation.

SETTING

São Carlos, SP, Brazil.

METHODS

A shell was designed with parametric design and fast-fabrication methods, and a stimulation unit and a smartphone application were developed. Questionnaires assessed the perceptions of a patient and a physiotherapist, about the usability of the new system in relation to standard FES. Kinematic data of drinking-like movements were collected from the patient wearing both systems and compared with data from an aged-matched control subject.

RESULTS

The results are a personalized shell and an intuitive FES system, overcoming the limitations of standard FES. The new system suggested better wrist-flexion control shown by the mean angles (-18.93°), then the other system (-59.35°), and compared with the control (-10.97°).

CONCLUSIONS

Fast-fabrication with parametric design offers a promising alternative for personalizing FES systems, with potential for home use. Further studies are required including randomized clinical trials.

Textile Electrodes: Influence of Electrode Construction and Pressure on Stimulation Performance in Neuromuscular Electrical Stimulation (NMES)

The major reason for preventable hospital death is venous thromboembolism (VTE). Non-pharmacological treatment options include electrical stimulation or compression therapy to improve blood flow in the extremities. Textile electrodes offer potential to replace bulky devices commonly used in this field, thereby improving the user compliance. In this work, the performance of dry and wet knitted electrodes in combination with pressure application to the electrode was evaluated in neuromuscular electrical stimulation (NMES). A motor point stimulation on the calf was performed on nine healthy subjects to induce a plantarflexion and the required stimulation intensity as well as the perceived pain were assessed. The performance of the different electrode constructions was compared and the influence of the pressure application was analysed. The results show that wet textile electrodes (0.9 % saline solution) perform significantly better than dry electrodes. However, opportunities were found for improving the performance of dry textile electrodes by using an uneven surface topography in combination with an intermediate to high pressure application to the electrode (> 20 mmHg), e.g. by using a compression stocking. Moreover, the smaller of the two tested electrode areas (16 cm²; 32 cm²) appears to be favourable in terms of stimulation comfort and efficiency.

FITFES: A Wearable Myoelectrically Controlled Functional Electrical Stimulator Designed Using a User-Centered Approach

Myoelectrically Controlled Functional Electrical Stimulation (MeCFES) has proven to be a useful tool in the rehabilitation of the hemiplegic arm. This paper reports the steps involved in the development of a wearable MeCFES device (FITFES) through a user-centered design. We defined the minimal viable features and functionalities requirements for the device design from a questionnaire-based survey among physiotherapists with experience in functional electrical stimulation. The result was a necklace layout that poses minimal hindrance to task-oriented movement therapy, the context in which it is aimed to be used. FITFES is battery-powered and embeds a standard low power Bluetooth module, enabling wireless control by using PC/Mobile devices vendor specific built-in libraries. It is designed to deliver a biphasic, charge-balanced stimulation current pulses of up to 113 mA with a maximum differential voltage of 300 V. The power consumption for typical clinical usage is 320 mW at 20mA stimulation current and of less than [Formula: see text] in sleep mode, thus ensuring an estimated full day of FITFES therapy on a battery charge. We conclude that a multidisciplinary user-centered approach can be successfully applied to the design of a clinically and ergonomically viable prototype of a wearable myoelectrically controlled functional electrical stimulator to be used in rehabilitation.

Reactive Exercises with Interactive Objects: Interim Analysis of a Randomized Trial on Task-Driven NMES Grasp Rehabilitation for Subacute and Early Chronic Stroke Patients

Enriched environments and tools are believed to promote grasp rehabilitation after stroke. We designed S2, an interactive grasp rehabilitation system consisting of smart objects, custom orthoses for selective grasp constraining, and an electrode array system for forearm NMES. Motor improvements and perceived usability of a new enriched upper limb training system for sub-acute stroke patients was assessed in this interim analysis. Inclusion criteria: sub-acute stroke patients with MMSE>20, ipsilesional MI>80%, and contralesional MI<80%. Effects of 30-min therapy supplements, conventional vs. S2 prototype, are compared through a parallel two-arms dose-matched open-label trial, lasting 27 sessions. Clinical centres: Asklepios Neurologische Klinik Falkenstein, Königstein im Taunus, Germany, and Clinica Villa Beretta, Costa Masnaga, Italy. Assessment scales: ARAT, System Usability, and Technology Acceptance. Methodology: 26 participants were block randomized, allocated to the study (control N=12, experimental N=14) and underwent the training protocol. Among them, 11 participants with ARAT score at inclusion below 35, n = 6 in the experimental group, and n = 5 in the control group were analysed. Results: participants in the enriched treatment group displayed a larger improvement in the ARAT scale (+14.9 pts, pval=0.0494). Perceived usability differed between clinics. No adverse effect was observed in relation to the treatments. Trial status: closed. Conclusions: The S2 system, developed according to shared clinical directives, was tested in a clinical proof of concept. Variations of ARAT scores confirm the feasibility of clinical investigation for hand rehabilitation after stroke.

A Robotic System with EMG-Triggered Functional Eletrical Stimulation for Restoring Arm Functions in Stroke Survivors

BACKGROUND

Robotic systems combined with Functional Electrical Stimulation (FES) showed promising results on upper-limb motor recovery after stroke, but adequately-sized randomized controlled trials (RCTs) are still missing.

OBJECTIVE

To evaluate whether arm training supported by RETRAINER, a passive exoskeleton integrated with electromyograph-triggered functional electrical stimulation, is superior to advanced conventional therapy (ACT) of equal intensity in the recovery of arm functions, dexterity, strength, activities of daily living, and quality of life after stroke.

METHODS

A single-blind RCT recruiting 72 patients was conducted. Patients, randomly allocated to 2 groups, were trained for 9 weeks, 3 times per week: the experimental group performed task-oriented exercises assisted by RETRAINER for 30 minutes plus ACT (60 minutes), whereas the control group performed only ACT (90 minutes). Patients were assessed before, soon after, and 1 month after the end of the intervention. Outcome measures were as follows: Action Research Arm Test (ARAT), Motricity Index, Motor Activity Log, Box and Blocks Test (BBT), Stroke Specific Quality of Life Scale (SSQoL), and Muscle Research Council.

RESULTS

All outcomes but SSQoL significantly improved over time in both groups (P < .001); a significant interaction effect in favor of the experimental group was found for ARAT and BBT. ARAT showed a between-group change of 11.5 points (P = .010) at the end of the intervention, which increased to 13.6 points 1 month after. Patients considered RETRAINER moderately usable (System Usability Score of 61.5 ± 22.8).

CONCLUSIONS

Hybrid robotic systems, allowing to perform personalized, intensive, and task-oriented training, with an enriched sensory feedback, was superior to ACT in improving arm functions and dexterity after stroke.

Textile Electrodes: Influence of Knitting Construction and Pressure on the Contact Impedance

Textile electrodes, also called textrodes, for biosignal monitoring as well as electrostimulation are central for the emerging research field of smart textiles. However, so far, only the general suitability of textrodes for those areas was investigated, while the influencing parameters on the contact impedance related to the electrode construction and external factors remain rather unknown. Therefore, in this work, six different knitted electrodes, applied both wet and dry, were compared regarding the influence of specific knitting construction parameters on the three-electrode contact impedance measured on a human forearm. Additionally, the influence of applying pressure was investigated in a two-electrode setup using a water-based agar dummy. Further, simulation of an equivalent circuit was used for quantitative evaluation. Indications were found that the preferred electrode construction to achieve the lowest contact impedance includes a square shaped electrode, knitted with a high yarn density and, in the case of dry electrodes, an uneven surface topography consisting of loops, while in wet condition a smooth surface is favorable. Wet electrodes are showing a greatly reduced contact impedance and are therefore to be preferred over dry ones; however, opportunities are seen for improving the electrode performance of dry electrodes by applying pressure to the system, thereby avoiding disadvantages of wet electrodes with fluid administration, drying-out of the electrolyte, and discomfort arising from a "wet feeling".

Advanced Neurotechnologies for the Restoration of Motor Function

Stroke is one of the leading causes of long-term disability. Advanced technological solutions ("neurotechnologies") exploiting robotic systems and electrodes that stimulate the nervous system can increase the efficacy of stroke rehabilitation. Recent studies on these approaches have shown promising results. However, a paradigm shift in the development of new approaches must be made to significantly improve the clinical outcomes of neurotechnologies compared with those of traditional therapies. An "evolutionary" change can occur only by understanding in great detail the basic mechanisms of natural stroke recovery and technology-assisted neurorehabilitation. In this review, we first describe the results achieved by existing neurotechnologies and highlight their current limitations. In parallel, we summarize the data available on the mechanisms of recovery from electrophysiological, behavioral, and anatomical studies in humans and rodent models. Finally, we propose new approaches for the effective use of neurotechnologies in stroke survivors, as well as in people with other neurological disorders.

Multichannel Nerve Stimulation for Diverse Activation of Finger Flexors

OBJECTIVE

Neuromuscular electrical stimulation (NMES) is a common approach to restore muscle strength of individuals with a neurological injury but restoring hand dexterity is still a challenge. This study sought to quantify the diversity of finger movements elicited by a multichannel nerve stimulation technique.

METHODS

A 2 × 8 stimulation grid, placed on the upper arm along the ulnar and median nerves, was used to activate different finger flexors by automatically switching between randomized bipolar electrodes. The forces from each individual finger as well as the high-density electromyogram (HDEMG) of the intrinsic and extrinsic flexors were recorded. The elicited finger forces were categorized using hierarchical clustering, and the 2D correlation of the spatial patterns of muscle activation was also calculated.

RESULTS

A wide range of movement patterns were identified, including multi-finger and single-digit movements. Additionally, a number of electrode pairs elicited similar finger movements. The muscle activation patterns showed similar and distinct spatial patterns, signifying activation redundancy.

CONCLUSION

These results revealed the diversity of elicitable finger movements and muscle activations. The system redundancy can be explored to compensate for system instability due to fatigue or electrode shift. The outcomes can also enable the development of an automatic calibration of the stimulation.

User-centered practicability analysis of two identification strategies in electrode arrays for FES induced hand motion in early stroke rehabilitation

BACKGROUND

Surface electrode arrays have become popular in the application of functional electrical stimulation (FES) on the forearm. Arrays consist of multiple, small elements, which can be activated separately or in groups, forming virtual electrodes (VEs). As technology progress yields rising numbers of possible elements, an effective search strategy for suitable VEs in electrode arrays is of increasing importance. Current methods can be time-consuming, lack user integration, and miss an evaluation regarding clinical acceptance and practicability.

METHODS

Two array identification procedures with different levels of user integration-a semi-automatic and a fully automatic approach-are evaluated. The semi-automatic method allows health professionals to continuously modify VEs via a touchscreen while the stimulation intensities are automatically controlled to maintain sufficient wrist extension. The automatic approach evaluates stimulation responses of various VEs for different intensities using a cost function and joint-angles recordings. Both procedures are compared in a clinical setup with five sub-acute stroke patients with moderate hand disabilities. The task was to find suitable VEs in two arrays with 59 elements in total to generate hand opening and closing for a grasp-and-release task. Practicability and acceptance by patients and health professionals were investigated using questionnaires and interviews.

RESULTS

Both identification methods yield suitable VEs for hand opening and closing in patients who could tolerate the stimulation. However, the resulting VEs differed for both approaches. The average time for a complete search was 25% faster for the semi-automatic approach (semi-automatic: 7.3min, automatic: 10.5min). User acceptance was high for both methods, while no clear preference could be identified.

CONCLUSIONS

The semi-automatic approach should be preferred as the search strategy in arrays on the forearm. The observed faster search duration will further reduce when applying the system repeatedly on a patient as only small position adjustments for VEs are required. However, the setup time will significantly increase for generation of various grasp types and adaptation to different arm postures. We recommend different levels of user integration in FES systems such that the search strategy can be chosen based on the users' preferences and application scenario.

Variation of Finger Activation Patterns Post-stroke Through Non-invasive Nerve Stimulation

Purpose: A transcutaneous proximal nerve stimulation technique utilizing an electrode grid along the nerve bundles has previously shown flexible activation of multiple fingers. This case study aimed to further demonstrate the ability of this novel stimulation technique to induce various finger grasp patterns in a stroke survivor.

Methods: An individual with chronic hemiplegia and severe hand impairment was recruited. Electrical stimulation was delivered to different pairs of an electrode grid along the ulnar and median nerves to selectively activate different finger flexor muscles, with an automated electrode switching method. The resultant individual isometric flexion forces and forearm flexor high-density electromyography (HDEMG) were acquired to evaluate the finger activation patterns. A medium and low level of overall activation were chosen to gauge the available finger patterns for both the contralateral and paretic hands. All the flexion forces were then clustered to categorize the different types of grasp patterns.

Results: Both the contralateral and paretic sides demonstrated various force clusters including single and multi-finger activation patterns. The contralateral hand showed finger activation patterns mainly centered on median nerve activation of the index, middle, and ring fingers. The paretic hand exhibited fewer total activation patterns, but still showed activation of all four fingers in some combination.

Conclusion: Our results show that electrical stimulation at multiple positions along the proximal nerve bundles can elicit a select variety of finger activation patterns even in a stroke survivor with minimal hand function. This system could be further implemented for better rehabilitative training to help induce functional grasp patterns or to help regain muscle mass.

Technological Approaches for Neurorehabilitation: From Robotic Devices to Brain Stimulation and Beyond

Neurological diseases causing motor/cognitive impairments are among the most common causes of adult-onset disability. More than one billion of people are affected worldwide, and this number is expected to increase in upcoming years, because of the rapidly aging population. The frequent lack of complete recovery makes it desirable to develop novel neurorehabilitative treatments, suited to the patients, and better targeting the specific disability. To date, rehabilitation therapy can be aided by the technological support of robotic-based therapy, non-invasive brain stimulation, and neural interfaces. In this perspective, we will review the above methods by referring to the most recent advances in each field. Then, we propose and discuss current and future approaches based on the combination of the above. As pointed out in the recent literature, by combining traditional rehabilitation techniques with neuromodulation, biofeedback recordings and/or novel robotic and wearable assistive devices, several studies have proven it is possible to sensibly improve the amount of recovery with respect to traditional treatments. We will then discuss the possible applied research directions to maximize the outcome of a neurorehabilitation therapy, which should include the personalization of the therapy based on patient and clinician needs and preferences.