Enhancing touch sensibility with sensory electrical stimulation and sensory retraining.

A large proportion of stroke survivors suffer from sensory loss, negatively impacting their independence, quality of life, and neurorehabilitation prognosis. Despite the high prevalence of somatosensory impairments, our understanding of somatosensory interventions such as sensory electrical stimulation (SES) in neurorehabilitation is limited. We aimed to study the effectiveness of SES combined with a sensory discrimination task in a well-controlled virtual environment in healthy participants, setting a foundation for its potential application in stroke rehabilitation. We employed electroencephalography (EEG) to gain a better understanding of the underlying neural mechanisms and dynamics associated with sensory training and SES. We conducted a single-session experiment with 26 healthy participants who explored a set of three visually identical virtual textures-haptically rendered by a robotic device and that differed in their spatial period-while physically guided by the robot to identify the odd texture. The experiment consisted of three phases: pre-intervention, intervention, and post-intervention. Half the participants received subthreshold whole-hand SES during the intervention, while the other half received sham stimulation. We evaluated changes in task performance-assessed by the probability of correct responses-before and after intervention and between groups. We also evaluated differences in the exploration behavior, e.g., scanning speed. EEG was employed to examine the effects of the intervention on brain activity, particularly in the alpha frequency band (8-13 Hz) associated with sensory processing. We found that participants in the SES group improved their task performance after intervention and their scanning speed during and after intervention, while the sham group did not improve their task performance. However, the differences in task performance improvements between groups only approached significance. Furthermore, we found that alpha power was sensitive to the effects of SES; participants in the stimulation group exhibited enhanced brain signals associated with improved touch sensitivity likely due to the effects of SES on the central nervous system, while the increase in alpha power for the sham group was less pronounced. Our findings suggest that SES enhances texture discrimination after training and has a positive effect on sensory-related brain areas. Further research involving brain-injured patients is needed to confirm the potential benefit of our solution in neurorehabilitation.

The challenge of measuring physiological parameters during motor imagery engagement in patients after a stroke.

Introduction: It is suggested that eye movement recordings could be used as an objective evaluation method of motor imagery (MI) engagement. Our investigation aimed to evaluate MI engagement in patients after stroke (PaS) compared with physical execution (PE) of a clinically relevant unilateral upper limb movement task of the patients' affected body side. Methods: In total, 21 PaS fulfilled the MI ability evaluation [Kinaesthetic and Visual Imagery Questionnaire (KVIQ-10), body rotation task (BRT), and mental chronometry task (MC)]. During the experiment, PaS moved a cup to distinct fields while wearing smart eyeglasses (SE) with electrooculography electrodes integrated into the nose pads and electrodes for conventional electrooculography (EOG). To verify MI engagement, heart rate (HR) and oxygen saturation (SpO2) were recorded, simultaneously with electroencephalography (EEG). Eye movements were recorded during MI, PE, and rest in two measurement sessions to compare the SE performance between conditions and SE's psychometric properties. Results: MI and PE correlation of SE signals varied between r = 0.12 and r = 0.76. Validity (cross-correlation with EOG signals) was calculated for MI (r = 0.53) and PE (r = 0.57). The SE showed moderate test-retest reliability (intraclass correlation coefficient) with r = 0.51 (95% CI 0.26-0.80) for MI and with r = 0.53 (95% CI 0.29 - 0.76) for PE. Event-related desynchronization and event-related synchronization changes of EEG showed a large variability. HR and SpO2 recordings showed similar values during MI and PE. The linear mixed model to examine HR and SpO2 between conditions (MI, PE, rest) revealed a significant difference in HR between rest and MI, and between rest and PE but not for SpO2. A Pearson correlation between MI ability assessments (KVIQ, BRT, MC) and physiological parameters showed no association between MI ability and HR and SpO2. Conclusion: The objective assessment of MI engagement in PaS remains challenging in clinical settings. However, HR was confirmed as a reliable parameter to assess MI engagement in PaS. Eye movements measured with the SE during MI did not resemble those during PE, which is presumably due to the demanding task. A re-evaluation with task adaptation is suggested.

Enhancing touch sensibility by sensory retraining in a sensory discrimination task via haptic rendering.

Stroke survivors are commonly affected by somatosensory impairment, hampering their ability to interpret somatosensory information. Somatosensory information has been shown to critically support movement execution in healthy individuals and stroke survivors. Despite the detrimental effect of somatosensory impairments on performing activities of daily living, somatosensory training-in stark contrast to motor training-does not represent standard care in neurorehabilitation. Reasons for the neglected somatosensory treatment are the lack of high-quality research demonstrating the benefits of somatosensory interventions on stroke recovery, the unavailability of reliable quantitative assessments of sensorimotor deficits, and the labor-intensive nature of somatosensory training that relies on therapists guiding the hands of patients with motor impairments. To address this clinical need, we developed a virtual reality-based robotic texture discrimination task to assess and train touch sensibility. Our system incorporates the possibility to robotically guide the participants' hands during texture exploration (i.e., passive touch) and no-guided free texture exploration (i.e., active touch). We ran a 3-day experiment with thirty-six healthy participants who were asked to discriminate the odd texture among three visually identical textures -haptically rendered with the robotic device- following the method of constant stimuli. All participants trained with the passive and active conditions in randomized order on different days. We investigated the reliability of our system using the Intraclass Correlation Coefficient (ICC). We also evaluated the enhancement of participants' touch sensibility via somatosensory retraining and compared whether this enhancement differed between training with active vs. passive conditions. Our results showed that participants significantly improved their task performance after training. Moreover, we found that training effects were not significantly different between active and passive conditions, yet, passive exploration seemed to increase participants' perceived competence. The reliability of our system ranged from poor (in active condition) to moderate and good (in passive condition), probably due to the dependence of the ICC on the between-subject variability, which in a healthy population is usually small. Together, our virtual reality-based robotic haptic system may be a key asset for evaluating and retraining sensory loss with minimal supervision, especially for brain-injured patients who require guidance to move their hands.

Design of an isokinetic knee dynamometer for evaluation of functional electrical stimulation strategies.

BACKGROUND: The limitations of functional electrical stimulation (FES) cycling directly affect the health benefits acquired from this technology and prevents its' full potential to be realised. Experiments should be done on a test bed which can isolate and focus only on one muscle group, namely the quadriceps. The aim of this work was to design and develop an isokinetic robotic leg extension/flexion dynamometer which can mimic knee joint motion during actual cycling to be used for evaluation of novel functional electrical stimulation strategies. Although the main motivation for development of the dynamometer was for application in FES studies, it has the potential to be used for various different muscle physiology studies. METHODS: A feedback control system with integrated electrical stimulation for isokinetic knee joint torque measurement has been developed and tested for safety and functionality. The leg extension/flexion device was modified and equipped with a DC motor drive system to imitate isokinetic knee joint motion during cycling when the hip joint remains fixed. Real-time bi-directional effective torque on the lever arm was measured by a magnetostrictive torque sensor and a load cell. Closed-loop motor control system was also designed to mimic the cyclical motion at desired angular velocity. RESULTS: A functional model of the robotic dynamometer was developed and evaluated. The dynamometer is capable of simulating the knee angle during cycling at a cadence of up to 70 rpm with range of motion of 72∘. The magnetostrictive torque sensor can measure torque values up to 75 Nm. The lever arm can be adjusted and the target knee angle was controlled with RMSE tracking error of less than 2.1∘ in tests with and without a test person, and with and without muscle stimulation. CONCLUSIONS: The isokinetic knee joint torque measurement system was designed and validated in this work, and subsequently used to develop and evaluate novel muscle activation strategies. This is important for fundamental research on effective stimulation patterns and novel activation strategies. This will, in turn, enhance the efficiency of FES cycling exercise and has the potential to improve the health-beneficial effects.

The road to Cybathlon 2016 - Functional electrical stimulation cycling Team IRPT/SPZ.

Functional electrical stimulation (FES) provides a good possibility to activate paralysed muscles and it has been shown to elicit substantial physiological and health benefits. For successful application of FES, a perfect symbiosis of the bike and the pilot has to be achieved. The road to the Cybathlon 2016 describes the different pieces needed for FES cycling in spinal cord injury. The systematic optimisation of the stimulation parameters and the Cybatrike, and sophisticated training contributed to the team's success as the fastest surface-electrode team in the competition.

Effect of Stochastic Modulation of Inter-Pulse Interval During Stimulated Isokinetic Leg Extension.

Recumbent cycling exercise achieved by functional electrical stimulation (FES) of the paralyzed leg muscles is effective for cardiopulmonary and musculoskeletal conditioning after spinal cord injury, but its full potential has not yet been realized. Mechanical power output and efficiency is very low and endurance is limited due to early onset of muscle fatigue. The aim of this work was to compare stochastic modulation of the inter-pulse interval (IPI) to constant-frequency stimulation during an isokinetic leg extension task similar to FES-cycling. Seven able-bodied subjects participated: both quadriceps muscles were stimulated (n = 14) with two activation patterns (P1-constant frequency, P2-stochastic IPI). There was significantly higher power output with P2 during the first 30 s (p = 0.0092), the last 30 s (p = 0.018) and overall (p = 0.0057), but there was no overall effect on fatiguability when stimulation frequency was randomly modulated.