Direct and crossed effects of somatosensory stimulation on neuronal excitability and motor performance in humans

Sensory Stimulation and Robot-Assisted Arm Training after Stroke: A Randomized Controlled Trial

BACKGROUND AND PURPOSE

Functional recovery after stroke is often limited, despite various treatment methods such as robot-assisted therapy. Repetitive sensory stimulation (RSS) might be a promising add-on therapy that is thought to directly drive plasticity processes. First positive effects on sensorimotor function have been shown. However, clinical studies are scarce, and the effect of RSS combined with robot-assisted training has not been evaluated yet. Therefore, our objective was to investigate the feasibility and sensorimotor effects of RSS (compared to a control group receiving sham stimulation) followed by robot-assisted arm therapy.

METHODS

Forty participants in the subacute phase (4.4-23.9 weeks) after stroke with a moderate to severe arm paresis were randomized to RSS or control group. Participants received 12 sessions of (sham-) stimulation within 3 weeks. Stimulation of the fingertips and the robot-assisted therapy were each applied in 45-min sessions. Motor and sensory outcome assessments (e.g. Fugl-Meyer-Assessment, grip strength) were measured at baseline, post intervention and at a 3-week follow-up.

RESULTS

Participants in both groups improved their sensorimotor function from baseline to post and follow-up measurements, as illustrated by most motor and sensory outcome assessments. However, no significant group effects were found for any measures at any time (P > 0.058). Stimulations were well accepted, no safety issues arose.

DISCUSSION AND CONCLUSIONS

Feasibility of robot-assisted therapy with preceding RSS in persons with moderate to severe paresis was demonstrated. However, RSS preceding robot-assisted training failed to show a preliminary effect compared to the control intervention. Participants might have been too severely affected to identify changes driven by the RSS, or these might have been diluted or more difficult to identify because of the additional robotic training and neurorehabilitation.

VIDEO ABSTRACT AVAILABLE

for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A478).

No effect of whole-hand water flow stimulation on skill acquisition and retention during sensorimotor adaptation

Introduction

Repetitive somatosensory stimulation (RSS) is a conventional approach to modulate the neural states of both the primary somatosensory cortex (S1) and the primary motor cortex (M1). However, the impact of RSS on skill acquisition and retention in sensorimotor adaptation remains debated. This study aimed to investigate whether whole-hand water flow (WF), a unique RSS-induced M1 disinhibition, influences sensorimotor adaptation by examining the hypothesis that whole-hand WF leads to M1 disinhibition; thereby, enhancing motor memory retention.

Methods

Sixty-eight young healthy participants were randomly allocated to three groups based on the preconditioning received before motor learning: control, whole-hand water immersion (WI), and whole-hand WF. The experimental protocol for all the participants spanned two consecutive days. On the initial day (day 1), baseline transcranial magnetic stimulation (TMS) assessments (T0) were executed before any preconditioning. Subsequently, each group underwent their respective 30 min preconditioning protocol. To ascertain the influence of each preconditioning on the excitability of the M1, subsequent TMS assessments were conducted (T1). Following this, all participants engaged in the motor learning (ML) of a visuomotor tracking task, wherein they were instructed to align a cursor with a target trajectory by modulating the pinch force. Upon completion of the ML session, final TMS assessments (T2) were conducted. All participants were required to perform the same motor learning 24 h later on day 2.

Results

The results revealed that whole-hand WF did not significantly influence skill acquisition during sensorimotor adaptation, although it did reduce intracortical inhibition. This phenomenon is consistent with the idea that S1, rather than M1, is involved in skill acquisition during the early stages of sensorimotor adaptation. Moreover, memory retention 24 h after skill acquisition did not differ significantly across the three groups, challenging our initial hypothesis that whole-hand WF enhances memory retention throughout sensorimotor adaptation. This could be due to the inability of whole-hand WF to alter sensorimotor connectivity and integration, as well as the nature of the plastic response elicited by the preconditioning.

Discussion

In conclusion, these findings suggest that although whole-hand WF attenuates intracortical inhibition, it does not modulate skill acquisition or motor memory retention during sensorimotor adaptation.

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.

Effects of mirror therapy on spasticity and sensory impairment after stroke: Systematic review and meta-analysis

OBJECTIVE

To review and synthesize existing evidence on the effectiveness of mirror therapy (MT) compared to active exercise-based interventions (ie, cross-training and conventional exercise) for reducing spasticity and sensory impairment in stroke survivors. TYPE: Systematic Review and Metanalysis.

LITERATURE SURVEY

Pubmed/MEDLINE, Cochrane, Embase, CINAHL, and Physiotherapy Evidence Database (PEDro), were searched.

METHODOLOGY

Randomized controlled trials (RCTs) that investigated MT effectiveness in improving spasticity and sensory impairment in stroke survivors compared to a control group.

SYNTHESIS

Fifteen RCTs (653 volunteers) were included. Spasticity improvements achieved with MT were similar to those obtained with cross-training (standard mean difference [SMD]: 0.12, 95% confidence interval [CI]: -0.43 to 0.68). In addition, when further combined with conventional exercise, spasticity improved similarly in both groups (SMD: 0.10, 95% CI: -0.16, 0.36). Lastly, when MT plus exercise was compared to exercise alone, spasticity decreased in both groups (SMD: 0.16, 95% CI: -0.16 to 0.48). Nevertheless, none of the Interventions seem effective on sensory impairment (SMD: 0.27, 95% CI: -0.28 to 0.81).

CONCLUSIONS

MT is equally effective as other exercise therapies, such as cross-training and conventional exercise, for improving spasticity in stroke survivors, whereas none of the explored interventions yielded beneficial effects on sensory impairment. Further well-designed RCTs are needed to confirm the results.

Attentional State-Dependent Peripheral Electrical Stimulation During Action Observation Enhances Cortical Activations in Stroke Patients

Brain-computer interface (BCI) is a promising technique that enables patients' interaction with computers or machines by analyzing specific brain signal patterns and provides patients with brain state-dependent feedback to assist in their rehabilitation. Action observation (AO) and peripheral electrical stimulation (PES) are conventional methods used to enhance rehabilitation outcomes by promoting neural plasticity. In this study, we assessed the effects of attentional state-dependent feedback in the combined application of BCI-AO with PES on sensorimotor cortical activation in patients after stroke. Our approach involved showing the participants a video with repetitive grasping actions under four different tasks. A mu band suppression (8-13 Hz) corresponding to each task was computed. A topographical representation showed that mu suppression of the dominant (healthy) and affected hemispheres (stroke) gradually became prominent during the tasks. There were significant differences in mu suppression in the affected motor and frontal cortices of the stroke patients. The involvement of both frontal and motor cortices became prominent in the BCI-AO+triggered PES task, in which feedback was given to the patients according to their attentive watching. Our findings suggest that synchronous stimulation according to patient attention is important for neurorehabilitation of stroke patients, which can be achieved with the combination of BCI-AO feedback with PES. BCI-AO feedback combined with PES could be effective in facilitating sensorimotor cortical activation in the affected hemispheres of stroke patients.

Difference between the Effects of Peripheral Sensory Nerve Electrical Stimulation on the Excitability of the Primary Motor Cortex: Examination of the Combinations of Stimulus Frequency and Duration

Peripheral sensory nerve electrical stimulation (PES) excites the primary motor cortex and is expected to improve motor dysfunction post-stroke. However, previous studies have reported a variety of stimulus frequencies and stimulus duration settings, and the effects of these different combinations on primary motor cortex excitability are not clear. We aimed to clarify the effects of different combinations of stimulus frequency and stimulus duration of PES on the excitation of primary motor cortex. Twenty-one healthy individuals (aged > 18 years, right-handed, and without a history of neurological or orthopedic disorders) were included. Each participant experienced three different stimulation frequencies (1, 10 and 50 Hz) and durations (20, 40 and 60 min). Motor-evoked potentials (MEPs) were recorded pre- and post-PES. The outcome measure was the change in primary motor cortex excitability using the MEP ratio. We used a D-optimal design of experiments and response surface analysis to define the optimal combination within nine different settings inducing more satisfying responses. The combination of stimulation frequency and stimulation time that maximized the desirability value was 10 Hz and 40 min, respectively. The results of this study may provide fundamental data for more minimally invasive and effective implementation of PES in patients with stroke.

Somatosensory targeted memory reactivation enhances motor performance via hippocampal-mediated plasticity

Increasing evidence suggests that reactivation of newly acquired memory traces during postlearning wakefulness plays an important role in memory consolidation. Here, we sought to boost the reactivation of a motor memory trace during postlearning wakefulness (quiet rest) immediately following learning using somatosensory targeted memory reactivation (TMR). Using functional magnetic resonance imaging, we examined the neural correlates of the reactivation process as well as the effect of the TMR intervention on brain responses elicited by task practice on 24 healthy young adults. Behavioral data of the post-TMR retest session showed a faster learning rate for the motor sequence that was reactivated as compared to the not-reactivated sequence. Brain imaging data revealed that motor, parietal, frontal, and cerebellar brain regions, which were recruited during initial motor learning, were specifically reactivated during the TMR episode and that hippocampo-frontal connectivity was modulated by the reactivation process. Importantly, the TMR-induced behavioral advantage was paralleled by dynamical changes in hippocampal activity and hippocampo-motor connectivity during task practice. Altogether, the present results suggest that somatosensory TMR during postlearning quiet rest can enhance motor performance via the modulation of hippocampo-cortical responses.

Electroacupuncture modulates cortical excitability in a manner dependent on the parameters used

INTRODUCTION

There is evidence that electroacupuncture (EA) acts through the modulation of brain activity, but little is known about its influence on corticospinal excitability of the primary motor cortex (M1).

OBJECTIVE

To investigate the influence of EA parameters on the excitability of M1 in healthy individuals.

METHODS

A parallel, double blind, randomized controlled trial in healthy subjects, evaluating the influence of an EA intervention on M1 excitability. Participants had a needle inserted at LI4 in the dominant hand and received electrical stimulation of different frequencies (10 or 100 Hz) and amplitude (sensory or motor threshold) for 20 min. In the control group, only a brief (30 s) electrical stimulation was applied. Single and paired pulse transcranial magnetic stimulation coupled with electromyography was applied before and immediately after the EA intervention. Resting motor threshold, motor evoked potential, short intracortical inhibition and intracortical facilitation were measured.

RESULTS

EA increased corticospinal excitability of M1 compared to the control group only when administered with a frequency of 100 Hz at the sensory threshold (p < 0.05). There were no significant changes in the other measures.

CONCLUSION

The results suggest that EA with an intensity level at the sensorial threshold and 100 Hz frequency increases the corticospinal excitability of M1. This effect may be associated with a decrease in the activity of inhibitory intracortical mechanisms.

TRIAL REGISTRATION NUMBER

U1111-1173-1946 (Registro Brasileiro de Ensaios Clínicos; http://www.ensaiosclinicos.gov.br/).

The effects of additional electrical stimulation combined with repetitive transcranial magnetic stimulation and motor imagery on upper extremity motor recovery in the subacute period after stroke: A preliminary study

BACKGROUND

To evaluate the therapeutic effects of additional electrical stimulation (ES) combined with low frequency (LF)-repetitive transcranial magnetic stimulation (rTMS) and motor imagery (MI) training on upper extremity (UE) motor function following stroke.

METHODS

The participants with subacute stroke in the experimental group (n = 8) received LF rTMS + MI + active ES interventions, and those in control group (n = 9) received LF rTMS + MI + sham ES interventions. Interventions were performed 5 days a week for 2 weeks, for a total of 10 sessions. All participants were given the same dosage of conventional rehabilitation during the study period. The primary outcome measure was the UE Fugl-Meyer Assessment (FMA). The secondary outcome measures were the shoulder abduction and finger extension scores, modified Barthel Index, Purdue Pegboard Test, and finger tapping test. All scores were measured before and just after the intervention.

RESULTS

After the 2-week intervention period, the FMA and modified Barthel Index scores were improved in both groups compared to baseline assessment (P < .001 in the experimental group and P = .008 in the control group). Of note, the change in FMA scores was significantly higher in the experimental group compared with that of the control group (P = .04).

CONCLUSION

These results suggest that the use of LF rTMS + MI combined with additional ES lead to greater improvement of UE motor function after stroke. As such, this intervention may be a promising adjuvant therapy in UE motor training.

Sensory electrical stimulation and postural balance: a comprehensive review

PURPOSE

Sensory electrical stimulation (SES)-i.e., low-intensity electrical currents below, at, or just above the sensory threshold but below the motor threshold-is mainly used to restore/improve postural balance in pathological and healthy subjects. However, the ins and outs of its application as well as the neurophysiological effects induced are not yet well known. Hence, the aim of this paper was to address the effects of SES on postural balance based on these considerations.

METHOD

The immediate/concurrent effects (SES applied during postural balance measurements), the acute effects (SES durably applied before measuring postural balance) and the chronic effects (SES included in training/rehabilitation programs, i.e., measurements performed before and after the programs) were analysed with a comprehensive review.

RESULT

SES can lead to the improvement of postural balance using any of the three applications (immediate/concurrent, acute and chronic), notably in pathological subjects. The beneficial effects of SES can take place at the peripheral (sensory receptors sensitivity), spinal (spinal motoneural excitablity) and supra-spinal (cortex reorganisation or adaptation) levels. In healthy subjects, SES appears interesting, but too few studies have been conducted with this population to report clear results. Moreover, the literature is relatively devoid of comparative studies about the characteristics of the stimulation current (e.g., location, current parameters, duration).

CONCLUSION

In practice, SES appears to be particularly useful to reinforce or restore the postural function in the immediate/concurrent, acute or chronic application in pathlogical populations while its effects should be confirmed in healthy sujects by future studies. Moreover, future research should focus on the different characteristics of stimulation.

Current Movement Follows Previous Nontarget Movement With Somatosensory Stimulation

This study examined whether the current movement follows the previous movement and whether this process is enhanced by somatosensory stimulation or is gated while retrieving and using the memory of the previously practiced target end point. Healthy humans abducted the index finger to a previously practiced target (target movement) or abducted it freely without aiming at the target (nontarget movement). The end point of the nontarget movement had a positive correlation with the previous nontarget movement only when somatosensory stimulation was given during the previous movement, indicating that the current nontarget movement follows the previous nontarget movement with somatosensory stimulation. No conclusive evidence of whether this process is gated by retrieving and using the memory of the previously practiced target was found.

Noninvasive Neuromodulation Techniques in Difficult Tracheostomy Weaning of Patients With Spinal Cord Injury: Report of Two Cases

High spinal cord injured patients (SCI) are susceptible to respiratory muscle impairments. Transcranial direct current stimulation (tDCS) and peripheral electrical stimulation (PES) may influence the diaphragm's central control, but until now they are not described as a therapeutic resource for difficult weaning. We present two case reports of SCI patients (P1 and P2) with long-term tracheostomy (>40 days) and hospital stay (>50 days). In association with respiratory exercise, P1 received a combined application of anodal tDCS over the supplementary motor area plus sensory PES in the thoracic-abdominal muscles, and P2 received isolated excitatory PES in the abdominal muscles, applied daily except on weekends. Maximum inspiratory/expiratory pressure, peak cough flow, diaphragm excursion, and thickening fraction were measured in the first and last days of the protocol. Both patients had improvements, with clinical impact such as cough effectiveness, decannulated after 15 applications of stimulation. Augmentation of neural respiratory drive and corticospinal excitability is suggested.

Somatosensory Targeted Memory Reactivation Modulates Oscillatory Brain Activity but not Motor Memory Consolidation

Previous research has shown that targeted memory reactivation (TMR) protocols using acoustic or olfactory stimuli can boost motor memory consolidation. While somatosensory information is crucial for motor control and learning, the effects of somatosensory TMR on motor memory consolidation remain elusive. Here, healthy young adults (n = 28) were trained on a sequential serial reaction time task and received, during the offline consolidation period that followed, sequential electrical stimulation of the fingers involved in the task. This somatosensory TMR procedure was applied during either a 90-minute diurnal sleep (NAP) or wake (NONAP) interval that was monitored with electroencephalography. Consolidation was assessed with a retest following the NAP/NONAP episode. Behavioral results revealed no effect of TMR on motor performance in either of the groups. At the brain level, somatosensory stimulation elicited changes in oscillatory activity in both groups. Specifically, TMR induced an increase in power in the mu band in the NONAP group and in the beta band in both the NAP and NONAP groups. Additionally, TMR elicited an increase in sigma power and a decrease in delta oscillations in the NAP group. None of these TMR-induced modulations of oscillatory activity, however, were correlated with measures of motor memory consolidation. The present results collectively suggest that while somatosensory TMR modulates oscillatory brain activity during post-learning sleep and wakefulness, it does not influence motor performance in an immediate retest.

Intensity and Dose of Neuromuscular Electrical Stimulation Influence Sensorimotor Cortical Excitability

Neuromuscular electrical stimulation (NMES) of the nervous system has been extensively used in neurorehabilitation due to its capacity to engage the muscle fibers, improving muscle tone, and the neural pathways, sending afferent volleys toward the brain. Although different neuroimaging tools suggested the capability of NMES to regulate the excitability of sensorimotor cortex and corticospinal circuits, how the intensity and dose of NMES can neuromodulate the brain oscillatory activity measured with electroencephalography (EEG) is still unknown to date. We quantified the effect of NMES parameters on brain oscillatory activity of 12 healthy participants who underwent stimulation of wrist extensors during rest. Three different NMES intensities were included, two below and one above the individual motor threshold, fixing the stimulation frequency to 35 Hz and the pulse width to 300 μs. Firstly, we efficiently removed stimulation artifacts from the EEG recordings. Secondly, we analyzed the effect of amplitude and dose on the sensorimotor oscillatory activity. On the one hand, we observed a significant NMES intensity-dependent modulation of brain activity, demonstrating the direct effect of afferent receptor recruitment. On the other hand, we described a significant NMES intensity-dependent dose-effect on sensorimotor activity modulation over time, with below-motor-threshold intensities causing cortical inhibition and above-motor-threshold intensities causing cortical facilitation. Our results highlight the relevance of intensity and dose of NMES, and show that these parameters can influence the recruitment of the sensorimotor pathways from the muscle to the brain, which should be carefully considered for the design of novel neuromodulation interventions based on NMES.

Supplementary motor area contributes to carrying previous movement information over to current movement

The purpose of the present study was to determine the cortical areas contributing to the influence of the previous movement on the current movement. Right-handed healthy human participants abducted and then adducted the left index finger in response to a start cue. Twenty consecutive trials with 10 s intertrial intervals were performed in each trial block. An odd-numbered trial was considered to be the previous trial, and a trial immediately after the previous trial (even-numbered trial) was the current trial. In each trial block, transcranial magnetic stimulation (TMS) was given over one of the seven TMS sites with the start cue in the previous trial. The TMS site was over the supplementary motor area (SMA), right dorsolateral prefrontal cortex, right dorsal premotor cortex, right or left posterior parietal cortex or right primary sensory cortex. Sham TMS, producing magnetic stimulation with the coil tilting 90 degrees off the scalp, was delivered over the Cz. In the current trial, TMS was not delivered. The correlation coefficient of the reaction time between the previous and current trials was positive and significant in the sham TMS trial block. This indicates that the current movement is partially dependent on the previous movement. The correlation coefficient of the reaction time between the previous and current movements in the SMA trial block was significantly different from that in the sham TMS trial block, indicating that the SMA contributes to the influence of the previous movement on the current movement. The SMA contributes to carrying the responsiveness level in the previous movement over to the current movement.

Opposite modulations of corticospinal excitability by intermittent and continuous peripheral electrical stimulation in healthy subjects

Peripheral electrical stimulation (PES) modulates the excitability of the corticospinal tract (CST). This modulation of CST excitability depends on the PES intensity, defined by the amplitude and the width of each pulse, the total pulse number, the stimulation frequency, and the intervention duration. Another key PES parameter is the stimulation pattern; little is known about how PES pattern affects CST excitability, as previous studies did not control other PES parameters. Here, we investigated the effect of the net difference in PES pattern on CST excitability. We use three controlled PESs, intermittent PES (30 Hz) (stimulation trains at 30 Hz with pauses), continuous PES (12 Hz) (constant stimulation at 12 Hz without pauses), and continuous PES (30 Hz) with the same stimulation frequency as the intermittent PES (30 Hz), to compare the effect of the stimulation frequency. The motor evoked potentials (MEPs) and somatosensory evoked potentials (SEPs) of healthy subjects were recorded before and after these three types of PESs in separate sessions. We found that intermittent PES (30 Hz) increased MEP amplitudes, whereas continuous PES (12 and 30 Hz) decreased amplitudes. A significant change in subcortical SEP component occurred during continuous PES (12 and 30 Hz), but not intermittent PES (30 Hz), whereas cortical SEP components showed similar behavior in three types of PESs. We conclude that (1) opposing modulations of CST excitability were induced by the differences in the PES pattern, and (2) these modulations appear to be mediated through different processes in the sensorimotor system. Our findings suggest the possibility that it may be preferable to select the PES pattern in therapeutic interventions based on the putative desired effect and the neural structure being targeted.

Reorganization of Higher-Order Somatosensory Cortex After Sensory Loss from Hand in Squirrel Monkeys

Unilateral dorsal column lesions (DCL) at the cervical spinal cord deprive the hand regions of somatosensory cortex of tactile activation. However, considerable cortical reactivation occurs over weeks to months of recovery. While most studies focused on the reactivation of primary somatosensory area 3b, here, for the first time, we address how the higher-order somatosensory cortex reactivates in the same monkeys after DCL that vary across cases in completeness, post-lesion recovery times, and types of treatments. We recorded neural responses to tactile stimulation in areas 3a, 3b, 1, secondary somatosensory cortex (S2), parietal ventral (PV), and occasionally areas 2/5. Our analysis emphasized comparisons of the responsiveness, somatotopy, and receptive field size between areas 3b, 1, and S2/PV across DCL conditions and recovery times. The results indicate that the extents of the reactivation in higher-order somatosensory areas 1 and S2/PV closely reflect the reactivation in primary somatosensory cortex. Responses in higher-order areas S2 and PV can be stronger than those in area 3b, thus suggesting converging or alternative sources of inputs. The results also provide evidence that both primary and higher-order fields are effectively activated after long recovery times as well as after behavioral and electrocutaneous stimulation interventions.

Effects of enhanced cutaneous sensory input on interlimb strength transfer of the wrist extensors

The relative contribution of cutaneous sensory feedback to interlimb strength transfer remains unexplored. Therefore, this study aimed to determine the relative contribution of cutaneous afferent pathways as a substrate for cross-education by directly assessing how "enhanced" cutaneous stimulation alters ipsilateral and contralateral strength gains in the forearm. Twenty-seven right-handed participants were randomly assigned to 1-of-3 training groups and completed 6 sets of 8 repetitions 3x/week for 5 weeks. Voluntary training (TRAIN) included unilateral maximal voluntary contractions (MVCs) of the wrist extensors. Cutaneous stimulation (STIM), a sham training condition, included cutaneous stimulation (2x radiating threshold; 3sec; 50Hz) of the superficial radial (SR) nerve at the wrist. TRAIN + STIM training included MVCs of the wrist extensors with simultaneous SR stimulation. Two pre- and one posttraining session assessed the relative increase in force output during MVCs of isometric wrist extension, wrist flexion, and handgrip. Maximal voluntary muscle activation was simultaneously recorded from the flexor and extensor carpi radialis. Cutaneous reflex pathways were evaluated through stimulation of the SR nerve during graded ipsilateral contractions. Results indicate TRAIN increased force output compared with STIM in both trained (85.0 ± 6.2 Nm vs. 59.8 ± 6.1 Nm) and untrained wrist extensors (73.9 ± 3.5 Nm vs. 58.8 Nm). Providing 'enhanced' sensory input during training (TRAIN + STIM) also led to increases in strength in the trained limb compared with STIM (79.3 ± 6.3 Nm vs. 59.8 ± 6.1 Nm). However, in the untrained limb no difference occurred between TRAIN + STIM and STIM (63.0 ± 3.7 Nm vs. 58.8 Nm). This suggests when 'enhanced' input was provided independent of timing with active muscle contraction, interlimb strength transfer to the untrained wrist extensors was blocked. This indicates that the sensory volley may have interfered with the integration of appropriate sensorimotor cues required to facilitate an interlimb transfer, highlighting the importance of appropriately timed cutaneous feedback.

Layer-specific sensory processing impairment in the primary somatosensory cortex after motor cortex infarction

Primary motor cortex (M1) infarctions sometimes cause sensory impairment. Because sensory signals play a vital role in motor control, sensory impairment compromises the recovery and rehabilitation of motor disability. However, the neural mechanism of the sensory impairment is poorly understood. We show that sensory processing in mouse primary somatosensory cortex (S1) was impaired in the acute phase of M1 infarctions and recovered in a layer-specific manner in the subacute phase. This layer-dependent recovery process and the anatomical connection pattern from M1 to S1 suggested that functional connectivity from M1 to S1 plays a key role in the sensory processing impairment. A simulation study demonstrated that the loss of inhibition from M1 to S1 in the acute phase of M1 infarctions could impair sensory processing in S1, and compensation for the inhibition could recover the temporal coding. Consistently, the optogenetic activation of M1 suppressed the sustained response in S1. Taken together, we revealed how focal stroke in M1 alters the cortical network activity of sensory processing, in which inhibitory input from M1 to S1 may be involved.

Modulation of Cortical Activity by Selective Steady-State Somatosensory Stimulation

Phantom limb pain (PLP) represents a major debilitating condition for amputees. No effective therapy has been reported. Non-painful surface electrical stimulation may induce temporary significant alleviation of PLP. Preliminary results of a study attempting to design a methodology for delivery and evaluation of possible quantifiable effects at the cortical level of steady-state surface stimulation are presented for two healthy subjects. Somatosensory evoked potentials (SEP) were evaluated before and after delivery of a steady-state stimulus applied at wrist along the median nerve. Characterization of evoked sensation induced in hand by the steady-state stimuli was performed. The sensory input artificially generated by the steady-state stimuli influenced cortical activation reflected in changes in N1 and P2 components of SEP. N1 suppression and changes in P2 amplitude after steady state stimulation between 1 to 7 minutes were observed. Analysis of changes in SEP components in a larger population may contribute to defining markers of temporary cortical plastic changes driven by steady-state stimuli possibly assessing the efficacy of these stimuli when attempting to reverse cortical plastic changes following amputation and relief of PLP upon specific delivery through surface electrical stimulation in the periphery.

Beyond the target area: an integrative view of tDCS-induced motor cortex modulation in patients and athletes

Transcranial Direct Current Stimulation (tDCS) is a non-invasive technique used to modulate neural tissue. Neuromodulation apparently improves cognitive functions in several neurologic diseases treatment and sports performance. In this study, we present a comprehensive, integrative review of tDCS for motor rehabilitation and motor learning in healthy individuals, athletes and multiple neurologic and neuropsychiatric conditions. We also report on neuromodulation mechanisms, main applications, current knowledge including areas such as language, embodied cognition, functional and social aspects, and future directions. We present the use and perspectives of new developments in tDCS technology, namely high-definition tDCS (HD-tDCS) which promises to overcome one of the main tDCS limitation (i.e., low focality) and its application for neurological disease, pain relief, and motor learning/rehabilitation. Finally, we provided information regarding the Transcutaneous Spinal Direct Current Stimulation (tsDCS) in clinical applications, Cerebellar tDCS (ctDCS) and its influence on motor learning, and TMS combined with electroencephalography (EEG) as a tool to evaluate tDCS effects on brain function.

Neuromuscular electrical stimulation-promoted plasticity of the human brain

The application of neuromuscular electrical stimulation (NMES) to paretic limbs has demonstrated utility for motor rehabilitation following brain injury. When NMES is delivered to a mixed peripheral nerve, typically both efferent and afferent fibres are recruited. Muscle contractions brought about by the excitation of motor neurons are often used to compensate for disability by assisting actions such as the formation of hand aperture, or by preventing others including foot drop. In this context, exogenous stimulation provides a direct substitute for endogenous neural drive. The goal of the present narrative review is to describe the means through which NMES may also promote sustained adaptations within central motor pathways, leading ultimately to increases in (intrinsic) functional capacity. There is an obvious practical motivation, in that detailed knowledge concerning the mechanisms of adaptation has the potential to inform neurorehabilitation practice. In addition, responses to NMES provide a means of studying CNS plasticity at a systems level in humans. We summarize the fundamental aspects of NMES, focusing on the forms that are employed most commonly in clinical and experimental practice. Specific attention is devoted to adjuvant techniques that further promote adaptive responses to NMES thereby offering the prospect of increased therapeutic potential. The emergent theme is that an association with centrally initiated neural activity, whether this is generated in the context of NMES triggered by efferent drive or via indirect methods such as mental imagery, may in some circumstances promote the physiological changes that can be induced through peripheral electrical stimulation.

Sensory enhancement amplifies interlimb cutaneous reflexes in wrist extensor muscles

Interlimb neural connections support motor tasks such as locomotion and cross-education strength training. Somatosensory pathways that can be assessed with cutaneous reflex paradigms assist in subserving these connections. Many studies show that stimulation of cutaneous nerves elicits reflexes in muscles widespread across the body and induces neural plasticity after training. Sensory enhancement, such as long-duration trains of transcutaneous stimulation, facilitates performance during rehabilitation training or fatiguing motor tasks. Performance improvements due to sensory stimulation may be caused by altered spinal and corticospinal excitability. However, how enhanced sensory input regulates the excitability of interlimb cutaneous reflex pathways has not been studied. Our purpose was to investigate the effects of sensory enhancement on interlimb cutaneous reflexes in wrist extensor muscles. Stimulation to provide sensory enhancement (2-s trains at 150 Hz to median or superficial radial nerves) or evoke cutaneous reflexes (15-ms trains at 300 Hz to superficial radial nerve) was applied in different arms while participants (n = 13) performed graded isometric wrist extension. Wrist extensor electromyography and cutaneous reflexes were measured bilaterally. We found amplified inhibitory reflexes in the arm receiving superficial radial and median nerve sensory enhancement with net reflex amplitudes decreased by 709.5% and 695.3% repetitively. This suggests sensory input alters neuronal excitabilities in the interlimb cutaneous pathways. These findings have potential application in facilitating motor function recovery through alterations in spinal cord excitability enhancing sensory input during targeted rehabilitation and sports training.NEW & NOTEWORTHY We show that sensory enhancement increases excitability in interlimb cutaneous pathways and that these effects are not influenced by descending motor drive on the contralateral side. These findings confirm the role of sensory input and cutaneous pathways in regulating interlimb movements. In targeted motor function training or rehabilitation, sensory enhancement may be applied to facilitate outcomes.

PULSE-I - Is rePetitive Upper Limb SEnsory stimulation early after stroke feasible and acceptable? A stratified single-blinded randomised controlled feasibility study

BACKGROUND

Reduction in sensorimotor function of the upper limb is a common and persistent impairment after stroke, and less than half of stroke survivors recover even basic function of the upper limb after a year. Previous work in stroke has shown that repetitive sensory stimulation (RSS) of the upper limb may benefit motor function. As yet, there have been no investigations of RSS in the early-acute period despite this being the time window during which the neuroplastic processes underpinning sensorimotor recovery are likely to occur.

METHODS

A single-blinded, stratified, randomised controlled feasibility study was undertaken at two NHS acute trusts to determine the recruitment rate, intervention adherence, and safety and acceptability of an RSS intervention in the early period after stroke. Participants were recruited within 2 weeks of index stroke. Stratified on arm function, they were randomised to receive either 45 min of daily RSS and usual care or usual care alone (UC) for 2 weeks. Changes from baseline on the primary outcome of the Action Research Arm Test (ARAT) to measurements taken by a blinded assessor were examined after completion of the intervention (2 weeks) and at 3 months from randomisation.

RESULTS

Forty patients were recruited and randomised (RSS n = 23; UC n = 17) with a recruitment rate of 9.5% (40/417) of patients admitted with a stroke of which 52 (12.5%) were potentially eligible, with 10 declining to participate for various reasons. Participants found the RSS intervention acceptable and adherence was good. The intervention was safe and there were no serious adverse events.

CONCLUSIONS

This study indicates that recruitment to a trial of RSS in the acute period after stroke is feasible. The intervention was well tolerated and appeared to provide additional benefit to usual care. In addition to a definitive trial of efficacy, further work is warranted to examine the effects of varying doses of RSS upon arm function and the mechanism by which RSS induces sensorimotor recovery in the acute period after stroke.

TRIAL REGISTRATION

ISRCTN, registry no: ISRCTN17422343 ; IRAS Project ID: 215137. Registered on October 2016.

Somatosensory Electrical Stimulation Does Not Improve Motor Coordination in Patients with Unilateral Knee Osteoarthritis

Non-surgical treatment of knee osteoarthritis (KOA) is often focused on the motor component of KOA even though there is evidence that sensory dysfunctions play an important role in the impaired control of the affected joint. Excitation of sensory afferents can increase motor function by exploiting the nervous system's ability to adapt to changing environments (i.e., neuronal plasticity). Therefore, the aim of this study was to explore the acute effects of a single session (30 min) of sensory intervention targeting neuronal plasticity using low-frequency (10 Hz) somatosensory electrical stimulation (SES) of the femoral nerve. We evaluated the effects of SES on the position and force control of the affected knee and self-reported pain in KOA patients (n = 14) in a sham-controlled randomized trial. The results showed that SES did not improve measures of lower-limb motor coordination compared to sham stimulation in KOA patients, nor did it improve self-reported knee function and pain (all p > 0.05). In conclusion, despite sensory involvement in KOA, the sensory intervention used in the present explorative study did not relieve self-reported pain, which may underlie the absence of an effect on measures of motor coordination. In sum, the present explorative study showed that SES alone does not improve motor coordination in KOA patients.

Muscle plasticity of aged subjects in response to electrical stimulation training and inversion and/or limitation of the sarcopenic process

This review addresses the possible structural and functional adaptations of the muscle function to neuromuscular electrical stimulation (NMES) training in frail and/or aged (without advanced chronic disease) subjects. Evidence suggests that the sarcopenic process and its structural and functional effects would be limited and/or reversed through NMES training using excito-motor currents (or direct currents). From a structural viewpoint, NMES helps reduce muscle atrophy. From a functional viewpoint, NMES enables the improvement of motor output (i.e., muscle strength), gait, balance and activities of daily living which enhances the quality of life of aged subjects. Muscle plasticity of aged subjects in response to NMES training turns out to be undeniable, although many mechanisms are not yet explained and deserve to be explore further. Mechanistic explanations as well as conceptual models are proposed to explain how muscle plasticity operates in aged subjects through NMES training. NMES could be seen as a clinically applicable training technique, safe and efficient among aged subjects and could be used more often as part of prevention of sarcopenia. Therapists and physical conditioners/trainers could exploit this new knowledge in their professional practice to improve life conditions (including the risk of fall) of frail and/or aged subjects.

Can somatosensory electrical stimulation relieve spasticity in post-stroke patients? A TMS pilot study

Evidence suggests that somatosensory electrical stimulation (SES) may decrease the degree of spasticity from neural drives, although there is no agreement between corticospinal modulation and the level of spasticity. Thus, stroke patients and healthy subjects were submitted to SES (3 Hz) for 30' on the impaired and dominant forearms, respectively. Motor evoked potentials induced by single-pulse transcranial magnetic stimulation were collected from two forearm muscles before and after SES. The passive resistance of the wrist joint was measured with an isokinetic system. We found no evidence of an acute carry-over effect of SES on the degree of spasticity.

Neurophysiological Mechanisms Underpinning Stretch-Induced Force Loss

It is well known that prolonged passive muscle stretch reduces maximal muscle force production. There is a growing body of evidence suggesting that adaptations occurring within the nervous system play a major role in this stretch-induced force reduction. This article reviews the existing literature, and some new evidence, regarding acute neurophysiological changes in response to passive muscle stretching. We discuss the possible contribution of supra-spinal and spinal structures to the force reduction after passive muscle stretch. In summary, based on the recent evidence reviewed we propose a new hypothesis that a disfacilitation occurring at the motoneuronal level after passive muscle stretch is a major factor affecting the neural efferent drive to the muscle and, subsequently, its ability to produce maximal force.

Median nerve stimulation induced motor learning in healthy adults: A study of timing of stimulation and type of learning

Median nerve stimulation (MNS) has been shown to change brain metaplasticity over the somatosensory networks, based on a bottom-up mechanism and may improve motor learning. This exploratory study aimed to test the effects of MNS on implicit and explicit motor learning as measured by the serial reaction time task (SRTT) using a double-blind, sham-controlled, randomized trial, in which participants were allocated to one of three groups: (a) online active MNS during acquisition, (b) offline active MNS during early consolidation and (c) sham MNS. SRTT was performed at baseline, during the training phase (acquisition period), and 30 min after training. We assessed the effects of MNS on explicit and implicit motor learning at the end of the training/acquisition period and at retest. The group receiving online MNS (during acquisition) showed a significantly higher learning index for the explicit sequences compared to the offline group (MNS during early consolidation) and the sham group. The offline group also showed a higher learning index as compared to sham. Additionally, participants receiving online MNS recalled the explicit sentence significantly more than the offline MNS and sham groups. MNS effects on motor learning have a specific effect on type of learning (explicit vs. implicit) and are dependent on timing of stimulation (during acquisition vs. early consolidation). More research is needed to understand and optimize the effects of peripheral electrical stimulation on motor learning. Taken together, our results show that MNS, especially when applied during the acquisition phase, is a promising tool to modulate motor leaning.

Somatosensory electrical stimulation improves skill acquisition, consolidation, and transfer by increasing sensorimotor activity and connectivity

The interaction between the somatosensory and motor systems is important for normal human motor function and learning. Enhancing somatosensory input using somatosensory electrical stimulation (SES) can increase motor performance, but the neuronal mechanisms underlying these effects are largely unknown. With EEG, we examined whether skill acquisition, consolidation, and interlimb transfer after SES was related to increased activity in sensorimotor regions, as assessed by the N30 somatosensory evoked potential or rather increased connectivity between these regions, as assessed by the phase slope index (PSI). Right- and left-hand motor performance and EEG measures were taken before, immediately after, and 24 h ( day 2) after either SES ( n = 12; 5 men) or Control ( n = 12; 5 men). The results showed skill acquisition and consolidation in the stimulated right hand immediately after SES (6%) and on day 2 (9%) and interlimb transfer to the nonstimulated left hand on day 2 relative to Control (8%, all P < 0.05). Increases in N30 amplitudes correlated with skill acquisition while PSI from electrodes that represent the posterior parietal and primary somatosensory cortex to the electrode representing the primary motor cortex correlated with skill consolidation. In contrast, interlimb transfer did not correlate with the EEG-derived neurophysiological estimates obtained in the present study, which may indicate the involvement of subcortical structures in interlimb transfer after SES. In conclusion, weak peripheral somatosensory inputs in the form of SES improve skill acquisition, consolidation, and interlimb transfer that coincide with different cortical adaptations, including enhanced N30 amplitudes and PSI. NEW & NOTEWORTHY The relationship between adaptations in synaptic plasticity and motor learning following somatosensory electrical stimulation (SES) is incompletely understood. Here, we used for the first time a multifactorial approach that examined skill acquisition, consolidation, and interlimb transfer following 20 min of SES. In addition, we quantified sensorimotor integration and the magnitude and direction of connectivity with EEG. Following artificial electrical stimulation, increases in sensorimotor integration and connectivity were found to correlate with skill acquisition and consolidation, respectively.

Weak but Critical Links between Primary Somatosensory Centers and Motor Cortex during Movement

Motor performance is improved by stimulation of the agonist muscle during movement. However, related brain mechanisms remain unknown. In this work, we perform a functional magnetic resonance imaging (fMRI) study in 21 healthy subjects under three different conditions: (1) movement of right ankle alone; (2) movement and simultaneous stimulation of the agonist muscle; or (3) movement and simultaneous stimulation of a control area. We constructed weighted brain networks for each condition by using functional connectivity. Network features were analyzed using graph theoretical approaches. We found that: (1) the second condition evokes the strongest and most widespread brain activations (5147 vs. 4419 and 2320 activated voxels); and (2) this condition also induces a unique network layout and changes hubs and the modular structure of the brain motor network by activating the most “silent” links between primary somatosensory centers and the motor cortex, particularly weak links from the thalamus to the left primary motor cortex (M1). Significant statistical differences were found when the strength values of the right cerebellum (P < 0.001) or the left thalamus (P = 0.006) were compared among the three conditions. Over the years, studies reported a small number of projections from the thalamus to the motor cortex. This is the first work to present functions of these pathways. These findings reveal mechanisms for enhancing motor function with somatosensory stimulation, and suggest that network function cannot be thoroughly understood when weak ties are disregarded.

Corticospinal and Spinal Excitabilities Are Modulated during Motor Imagery Associated with Somatosensory Electrical Nerve Stimulation

Motor imagery (MI), the mental simulation of an action, influences the cortical, corticospinal, and spinal levels, despite the lack of somatosensory afferent feedbacks. The aim of this study was to analyze the effect of MI associated with somatosensory stimulation (SS) on the corticospinal and spinal excitabilities. We used transcranial magnetic stimulation and peripheral nerve stimulation to induce motor-evoked potentials (MEP) and H-reflexes, respectively, in soleus and medialis gastrocnemius (MG) muscles of the right leg. Twelve participants performed three tasks: (1) MI of submaximal plantar flexion, (2) SS at 65 Hz on the posterior tibial nerve with an intensity below the motor threshold, and (3) MI + SS. MEP and H-reflex amplitudes were recorded before, during, and after the tasks. Our results confirmed that MI increased corticospinal excitability in a time-specific manner. We found that MI + SS tended to potentiate MEP amplitude of the MG muscle compared to MI alone. We confirmed that SS decreased spinal excitability, and this decrease was partially compensated when combined with MI, especially for the MG muscle. The increase of CSE could be explained by a modulation of the spinal inhibitions induced by SS, depending on the amount of afferent feedbacks.

Somatosensory Electrical Stimulation Does Not Augment Motor Skill Acquisition and Intermanual Transfer in Healthy Young Adults-A Pilot Study

Sensory input can modify motor function and magnify interlimb transfer. We examined the effects of low-intensity somatosensory electrical stimulation (SES) on motor practice-induced skill acquisition and intermanual transfer. Participants practiced a visuomotor skill for 25 min and received SES to the practice or the transfer arm. Responses to single- and double-pulse transcranial magnetic stimulation were measured in both extensor carpi radialis. SES did not further increase skill acquisition (motor practice with right hand [RMP]: 30.8% and motor practice with right hand + somatosensory electrical stimulation to the right arm [RMP + RSES]: 27.8%) and intermanual transfer (RMP: 13.6% and RMP + RSES: 9.8%) when delivered to the left arm (motor practice with right hand + somatosensory electrical stimulation to the left arm [RMP + LSES]: 44.8% and 18.6%, respectively). Furthermore, transcranial magnetic stimulation measures revealed no changes in either hand. Future studies should systematically manipulate SES parameters to better understand the mechanisms of how SES affords motor learning benefits documented but not studied in patients.

Specific brain activation patterns associated with two neuromuscular electrical stimulation protocols

The influence of neuromuscular electrical stimulation (NMES) parameters on brain activation has been scarcely investigated. We aimed at comparing two frequently used NMES protocols - designed to vary in the extent of sensory input. Whole-brain functional magnetic resonance imaging was performed in sixteen healthy subjects during wide-pulse high-frequency (WPHF, 100 Hz–1 ms) and conventional (CONV, 25 Hz–0.05 ms) NMES applied over the triceps surae. Each protocol included 20 isometric contractions performed at 10% of maximal force. Voluntary plantar flexions (VOL) were performed as control trial. Mean force was not different among the three protocols, however, total current charge was higher for WPHF than for CONV. All protocols elicited significant activations of the sensorimotor network, cerebellum and thalamus. WPHF resulted in lower deactivation in the secondary somatosensory cortex and precuneus. Bilateral thalami and caudate nuclei were hyperactivated for CONV. The modulation of the NMES parameters resulted in differently activated/deactivated regions related to total current charge of the stimulation but not to mean force. By targeting different cerebral brain regions, the two NMES protocols might allow for individually-designed rehabilitation training in patients who can no longer execute voluntary movements.

Tactile stimulation during sleep alters slow oscillation and spindle densities but not motor skill

Studies using targeted memory reactivation have shown that presentation of auditory or olfactory contextual cues during sleep can bias hippocampal reactivations towards the preferential replay of the cue-associated material, thereby resulting in enhanced consolidation of that information. If the same cortical ensembles are indeed used for encoding and storage of a given piece of information, forcing the sleeping brain to re-engage in task-intrinsic information processing should disturb the natural ongoing consolidation processes and therefore impair possible sleep benefits. Here we aimed at recreating an integral part of the sensory experience of a motor skill in a daytime nap, by means of a tactile stimulation. We hypothesized that tampering with the tactile component of a motor skill during sleep would result in hindered performance at retest, due to interference between the highly congruent incoming stimuli and the core skill trace. Contrary to our predictions, the tactile stimulation did not influence neither speed nor accuracy, when compared to natural sleep. However, an exploratory sleep EEG analysis revealed stimulation-induced alterations in the abundance and cortical topography of slow oscillations and spindles. These findings suggest that despite the lack of a significant effect on motor behavior, tactile stimulation induced changes in EEG features suggestive of a possible uncoupling between the sleep oscillations thought to underlie consolidation processes, i.e. slow oscillations and sleep spindles.

Priming Hand Motor Training with Repetitive Stimulation of the Fingertips; Performance Gain and Functional Imaging of Training Effects

BACKGROUND

Application of repetitive electrical stimulation (rES) of the fingers has been shown to improve tactile perception and sensorimotor performance in healthy individuals.

OBJECTIVE

To increase motor performance by priming the effects of active motor training (arm ability training; AAT) using rES.

METHODS

We compared the performance gain for the training increase of the averaged AAT tasks of both hands in two groups of strongly right-handed healthy volunteers. Functional Magnetic Resonance Imaging (fMRI) before and after AAT was assessed using three tasks for each hand separately: finger sequence tapping, visually guided grip force modulation, and writing. Performance during fMRI was controlled for preciseness and frequency. A total of 30 participants underwent a two-week unilateral left hand AAT, 15 participants with 20 minutes of rES priming of all fingertips of the trained hand, and 15 participants without rES priming.

RESULTS

rES-primed AAT improved the trained left-hand performance across all training tasks on average by 32.9%, non-primed AAT improved by 29.5%. This gain in AAT performance with rES priming was predominantly driven by an increased finger tapping velocity. Functional imaging showed comparable changes for both training groups over time. Across all participants, improved AAT performance was associated with a higher contralateral primary somatosensory cortex (S1) fMRI activation magnitude during the grip force modulation task.

CONCLUSIONS

This study highlights the importance of S1 for hand motor training gain. In addition, it suggests the usage of rES of the fingertips for priming active hand motor training.

Rehabilitation of Motor Function after Stroke: A Multiple Systematic Review Focused on Techniques to Stimulate Upper Extremity Recovery

Stroke is one of the leading causes for disability worldwide. Motor function deficits due to stroke affect the patients' mobility, their limitation in daily life activities, their participation in society and their odds of returning to professional activities. All of these factors contribute to a low overall quality of life. Rehabilitation training is the most effective way to reduce motor impairments in stroke patients. This multiple systematic review focuses both on standard treatment methods and on innovating rehabilitation techniques used to promote upper extremity motor function in stroke patients. A total number of 5712 publications on stroke rehabilitation was systematically reviewed for relevance and quality with regards to upper extremity motor outcome. This procedure yielded 270 publications corresponding to the inclusion criteria of the systematic review. Recent technology-based interventions in stroke rehabilitation including non-invasive brain stimulation, robot-assisted training, and virtual reality immersion are addressed. Finally, a decisional tree based on evidence from the literature and characteristics of stroke patients is proposed. At present, the stroke rehabilitation field faces the challenge to tailor evidence-based treatment strategies to the needs of the individual stroke patient. Interventions can be combined in order to achieve the maximal motor function recovery for each patient. Though the efficacy of some interventions may be under debate, motor skill learning, and some new technological approaches give promising outcome prognosis in stroke motor rehabilitation.

Transcutaneous electrical acupoint stimulation as an adjunct therapy for obsessive-compulsive disorder: A randomized controlled study

BACKGROUND

Transcutaneous electrical acupoint stimulation (TEAS) is thought to have potential to treat obsessive-compulsive disorder (OCD).

OBJECTIVE

The purpose of this study was to determine whether adding TEAS to cognitive behavioral therapy (CBT) and clomipramine would improve the efficacy of these conventional treatments in OCD.

METHODS

In this randomized controlled trial, 360 OCD patients were assigned to receive TEAS combined with CBT plus clomipramine (Group A, n = 120), TEAS combined with CBT plus placebo (Group B, n = 120), and simulated (placebo) TEAS combined with CBT plus clomipramine (Group C, n = 120) for 12 weeks. The primary outcome was measured using the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS).

RESULTS

OCD symptoms in all patients reduced over time, however Groups A and B had a significantly greater reduction in Y-BOCS total score and the subscale for obsession and compulsion between week 2 and week 12 compared to Group C. Groups A and B had similar scores on these measures. Both groups had significantly higher rates of clinical response than Group C (88.3% and 81.7% vs. 67.5%, respectively, p < 0.001); and higher rates of remission (30.0% and 22.5% vs. 9.2%, respectively, p < 0.001). Group B experienced fewer adverse events than the other two groups.

CONCLUSIONS

TEAS enhances the efficacy of conventional OCD interventions and avoids the adverse effects associated with conventional pharmacological treatment. It can be considered as an effective adjunct intervention for OCD.

Temporary deafferentation evoked by cutaneous anesthesia: behavioral and electrophysiological findings in healthy subjects

Motor function and motor excitability can be modulated by changes of somatosensory input. Here, we performed a randomized single-blind trial to investigate behavioral and neurophysiological changes during temporary deafferentation of left upper arm and forearm in 31 right-handed healthy adults. Lidocaine cream was used to anesthetize the skin from wrist to shoulder, sparing the hand. As control condition, on a different day, a neutral cream was applied to the same skin area. The sequence (first Lidocaine, then placebo or vice versa) was randomized. Behavioral measures included the Grating Orientation Task, the Von Frey hair testing and the Nine-hole-peg-test. Transcranial magnetic stimulation was used to investigate short-interval intracortical inhibition, stimulus response curves, motor evoked potential amplitudes during pre-innervation and the cortical silent period (CSP). Recordings were obtained from left first dorsal interosseous muscle and from left flexor carpi radialis muscle. During deafferentation, the threshold of touch measured at the forearm was significantly worse. Other behavioral treatment-related changes were not found. The CSP showed a significant interaction between treatment and time in first dorsal interosseous muscle. CSP duration was longer during Lidocaine application and shorter during placebo exposure. We conclude that, in healthy subjects, temporary cutaneous deafferentation of upper and lower arm may have minor effects on motor inhibition, but not on sensory or motor function for the adjacent non-anesthetized hand.

Motor Skill Acquisition and Retention after Somatosensory Electrical Stimulation in Healthy Humans

Somatosensory electrical stimulation (SES) can increase motor performance, presumably through a modulation of neuronal excitability. Because the effects of SES can outlast the period of stimulation, we examined the possibility that SES can also enhance the retention of motor performance, motor memory consolidation, after 24 h (Day 2) and 7 days (Day 7), that such effects would be scaled by SES duration, and that such effects were mediated by changes in aspects of corticospinal excitability, short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF). Healthy young adults (n = 40) received either 20 (SES-20), 40 (SES-40), or 60 min (SES-60) of real SES, or sham SES (SES-0). The results showed SES-20 increased visuomotor performance on Day 2 (15%) and Day 7 (17%) and SES-60 increased visuomotor performance on Day 7 (11%; all p < 0.05) compared with SES-0. Specific responses to transcranial magnetic stimulation (TMS) increased immediately after SES (p < 0.05) but not on Days 2 and 7. In addition, changes in behavioral and neurophysiological parameters did not correlate, suggesting that paths and structures other than the ones TMS can assay must be (also) involved in the increases in visuomotor performance after SES. As examined in the present study, low-intensity peripheral electrical nerve stimulation did not have acute effects on healthy adults' visuomotor performance but SES had delayed effects in the form of enhanced motor memory consolidation that were not scaled by the duration of SES.

Is the Frequency in Somatosensory Electrical Stimulation the Key Parameter in Modulating the Corticospinal Excitability of Healthy Volunteers and Stroke Patients with Spasticity?

Somatosensory electrical stimulation (SES) has been proposed as an approach to treat patients with sensory-motor impairment such as spasticity. However, there is still no consensus regarding which would be the adequate SES parameters to treat those deficits. Therefore, the aim of this study was to evaluate the effects of applying SES over the forearm muscles at four different frequencies of stimulation (3, 30, 150, and 300 Hz) and in two intervals of time (5′ and 30′) by means of transcranial magnetic stimulation and Hoffmann's reflex (H-reflex) in healthy volunteers (Experiments  I and II). A group of stroke patients (Experiment  III) was also preliminary evaluated to ascertain SES effects at a low frequency (3 Hz) applied for 30′ over the forearm spastic flexors muscles by measuring the wrist joint passive torque. Motor evoked potentials and the H-reflex were collected from different forearm and hand muscles immediately before and after SES and up to 5′ (Experiment  I) and 10′ (Experiments  I and II) later. None of the investigated frequencies of SES was able to operate as a key in switching modulatory effects in the central nervous system of healthy volunteers and stroke patients with spasticity.

Investigating the Effects of Peripheral Electrical Stimulation on Corticomuscular Functional Connectivity Stroke Survivors

BACKGROUND

Electrical stimulation (ES) in the periphery can induce brain plasticity and has been used clinically to promote motor recovery in patients with central nervous system lesion. Electroencephalogram (EEG) and electromyogram (EMG) are readily applicable in clinical settings and can detect real-time functional connectivity between motor cortex and muscles with EEG-EMG (corticomuscular) coherence.

OBJECTIVE

The purpose of this study was to determine whether EEG-EMG coherence can detect changes in corticomuscular control induced by peripheral ES.

METHODS

Fifteen healthy young adults and 15 stroke survivors received 40-min electrical stimulation session on median nerve. The stimulation (1-ms rectangular pulse, 100 Hz) was delivered with a 20-s on-20-s off cycle, and the intensity was set at the subjects' highest tolerable level without muscle contraction or pain. Both before and after the stimulation session, subjects performed a 20-s steady-hold thumb flexion at 50% maximal voluntary contraction (MVC) while EEG and EMG were collected.

RESULTS

Our results demonstrated that after ES, EEG-EMG coherence in gamma band increased significantly for 22.1 and 48.6% in healthy adults and stroke survivors, respectively. In addition, after ES, force steadiness was also improved in both groups, as indicated by the decrease in force fluctuation during steady-hold contraction (-1.7% MVC and -3.9%MVC for healthy and stroke individuals, respectively).

CONCLUSIONS

Our results demonstrated that EEG-EMG coherence can detect ES-induced changes in the neuromuscular system. Also, because gamma coherence is linked to afferent inputs encoding, improvement in motor performance is likely related to ES-elicited strong sensory input and enhanced sensorimotor integration.