Transcutaneous spinal direct current stimulation modulates human corticospinal system excitability

Modulations in neural pathways excitability post transcutaneous spinal cord stimulation among individuals with spinal cord injury: a systematic review

Introduction

Transcutaneous spinal cord stimulation (TSCS), a non-invasive form of spinal cord stimulation, has been shown to improve motor function in individuals living with spinal cord injury (SCI). However, the effects of different types of TSCS currents including direct current (DC-TSCS), alternating current (AC-TSCS), and spinal paired stimulation on the excitability of neural pathways have not been systematically investigated. The objective of this systematic review was to determine the effects of TSCS on the excitability of neural pathways in adults with non-progressive SCI at any level.

Methods

The following databases were searched from their inception until June 2022: MEDLINE ALL, Embase, Web of Science, Cochrane Library, and clinical trials. A total of 4,431 abstracts were screened, and 23 articles were included.

Results

Nineteen studies used TSCS at the thoracolumbar enlargement for lower limb rehabilitation (gait & balance) and four studies used cervical TSCS for upper limb rehabilitation. Sixteen studies measured spinal excitability by reporting different outcomes including Hoffmann reflex (H-reflex), flexion reflex excitability, spinal motor evoked potentials (SMEPs), cervicomedullay evoked potentials (CMEPs), and cutaneous-input-evoked muscle response. Seven studies measured corticospinal excitability using motor evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS), and one study measured somatosensory evoked potentials (SSEPs) following TSCS. Our findings indicated a decrease in the amplitude of H-reflex and long latency flexion reflex following AC-TSCS, alongside an increase in the amplitudes of SMEPs and CMEPs. Moreover, the application of the TSCS-TMS paired associative technique resulted in spinal reflex inhibition, manifested by reduced amplitudes in both the H-reflex and flexion reflex arc. In terms of corticospinal excitability, findings from 5 studies demonstrated an increase in the amplitude of MEPs linked to lower limb muscles following DC-TSCS, in addition to paired associative stimulation involving repetitive TMS on the brain and DC-TSCS on the spine. There was an observed improvement in the latency of SSEPs in a single study. Notably, the overall quality of evidence, assessed by the modified Downs and Black Quality assessment, was deemed poor.

Discussion

This review unveils the systematic evidence supporting the potential of TSCS in reshaping both spinal and supraspinal neuronal circuitries post-SCI. Yet, it underscores the critical necessity for more rigorous, high-quality investigations.

From brain to spinal cord: neuromodulation by direct current stimulation and its promising effects as a treatment option for restless legs syndrome

Neuromodulation is a fast-growing field of mostly non-invasive therapies, which includes spinal cord stimulation (SCS), transcranial direct current stimulation (tDCS), vagal nerve stimulation (VNS), peripheral nerve stimulation, transcranial magnetic stimulation (TMS) and transcutaneous spinal direct current stimulation (tsDCS). This narrative review offers an overview of the therapy options, especially of tDCS and tsDCS for chronic pain and spinal cord injury. Finally, we discuss the potential of tsDCS in Restless Legs Syndrome as a promising non-invasive, alternative therapy to medication therapy.

Transspinal Direct Current Electrical Stimulation Selectively Affects the Excitability of the Corticospinal System, Depending on the Intensity but Not Motor Skills

Transspinal direct current stimulation (tsDCS) is a non-invasive technique used to modulate spinal cord activity. However, the effects and mechanisms of this stimulation are currently not comprehensively known. This study aimed to estimate the effect of different intensities of tsDCS applied at the level of cervical enlargement of the spinal cord (C7-Th1 segments) on the excitability of the corticospinal system (CSS) and the correction of motor skills in healthy subjects. The effect of tsDCS was estimated by the motor-evoked potentials (MEP) elicited by transcranial magnetic stimulation (TMS) in the primary motor cortex (M1). The study involved 54 healthy adults aged 22 ± 4 years. The application of 11 min anodal tsDCS at the level of the cervical spine C7-Th1 with a current intensity of 2.5 mA did not change the MEP amplitude of the upper limb muscles, in contrast to the data that we previously obtained with a current intensity of 1.5 mA. We also found no difference in the effect of 2.5 mA stimulation on motor skill correction in healthy subjects in the nine-hole peg test (9-HPT) and the serial reaction time task (SRT) as with 1.5 mA stimulation. Our data show that an increase in the intensity of stimulation does not lead to an increase in the effects but rather reduces the effects of stimulation. These results provide information about the optimally appropriate stimulation current intensities to induce CSS excitability and the ability of tsDCS to influence motor skills in healthy adults.

Cortico-spinal tDCS in amyotrophic lateral sclerosis: A randomized, double-blind, sham-controlled trial followed by an open-label phase

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a progressive disease for which no curative treatment is currently available.

OBJECTIVE

This study aimed to investigate whether cortico-spinal transcranial direct current stimulation (tDCS) could mitigate symptoms in ALS patients via a randomized, double-blind, sham-controlled trial, followed by an open-label phase.

METHODS

Thirty-one participants were randomized into two groups for the initial controlled phase. At baseline (T0), Group 1 received placebo stimulation (sham tDCS), while Group 2 received cortico-spinal stimulation (real tDCS) for five days/week for two weeks (T1), with an 8-week (T2) follow-up (randomized, double-blind, sham-controlled phase). At the 24-week follow-up (T3), all participants (Groups 1 and 2) received a second treatment of anodal bilateral motor cortex and cathodal spinal stimulation (real tDCS) for five days/week for two weeks (T4). Follow-up evaluations were performed at 32-weeks (T5) and 48-weeks (T6) (open-label phase). At each time point, clinical assessment, blood sampling, and intracortical connectivity measures using transcranial magnetic stimulation (TMS) were evaluated. Additionally, we evaluated survival rates.

RESULTS

Compared to sham stimulation, cortico-spinal tDCS significantly improved global strength, caregiver burden, and quality of life scores, which correlated with the restoration of intracortical connectivity measures. Serum neurofilament light levels decreased among patients who underwent real tDCS but not in those receiving sham tDCS. The number of completed 2-week tDCS treatments significantly influenced patient survival.

CONCLUSIONS

Cortico-spinal tDCS may represent a promising therapeutic and rehabilitative approach for patients with ALS. Further larger-scale studies are necessary to evaluate whether tDCS could potentially impact patient survival.

CLINICAL TRIAL REGISTRATION

NCT04293484.

Long-term analgesic effect of trans-spinal direct current stimulation compared to non-invasive motor cortex stimulation in complex regional pain syndrome

The aim of the present study was to compare the analgesic effect of motor cortex stimulation using high-frequency repetitive transcranial magnetic stimulation or transcranial direct current stimulation and transcutaneous spinal direct current stimulation in patients with complex regional pain syndrome. Thirty-three patients with complex regional pain syndrome were randomized to one of the three treatment groups (repetitive transcranial magnetic stimulation, n = 11; transcranial direct current stimulation, n = 10; transcutaneous spinal direct current stimulation, n = 12) and received a series of 12 sessions of stimulation for 3 weeks (induction phase) and 11 sessions for 4 months (maintenance therapy). The primary end-point was the mean pain intensity assessed weekly with a visual numerical scale during the month prior to treatment (baseline), the 5-month stimulation period and 1 month after the treatment. The weekly visual numerical scale pain score was significantly reduced at all time points compared to baseline in the transcutaneous spinal direct current stimulation group, at the last two time points in the repetitive transcranial magnetic stimulation group (end of the 5-month stimulation period and 1 month later), but at no time point in the transcranial direct current stimulation group. A significant pain relief was observed at the end of induction phase using transcutaneous spinal direct current stimulation compared to repetitive transcranial magnetic stimulation (P = 0.008) and to transcranial direct current stimulation (P = 0.003). In this trial, transcutaneous spinal direct current stimulation was more efficient to relieve pain in patients with complex regional pain syndrome compared to motor cortex stimulation techniques (repetitive transcranial magnetic stimulation, transcranial direct current stimulation). This efficacy was found during the induction phase and was maintained thereafter. This study warrants further investigation to confirm the potentiality of transcutaneous spinal direct current stimulation as a therapeutic option in complex regional pain syndrome.

What Else Can Be Done by the Spinal Cord? A Review on the Effectiveness of Transpinal Direct Current Stimulation (tsDCS) in Stroke Recovery

Since the spinal cord has traditionally been considered a bundle of long fibers connecting the brain to all parts of the body, the study of its role has long been limited to peripheral sensory and motor control. However, in recent years, new studies have challenged this view pointing to the spinal cord's involvement not only in the acquisition and maintenance of new motor skills but also in the modulation of motor and cognitive functions dependent on cortical motor regions. Indeed, several reports to date, which have combined neurophysiological techniques with transpinal direct current stimulation (tsDCS), have shown that tsDCS is effective in promoting local and cortical neuroplasticity changes in animals and humans through the activation of ascending corticospinal pathways that modulate the sensorimotor cortical networks. The aim of this paper is first to report the most prominent tsDCS studies on neuroplasticity and its influence at the cortical level. Then, a comprehensive review of tsDCS literature on motor improvement in animals and healthy subjects and on motor and cognitive recovery in post-stroke populations is presented. We believe that these findings might have an important impact in the future making tsDCS a potential suitable adjunctive approach for post-stroke recovery.

Modeling Electric Fields in Transcutaneous Spinal Direct Current Stimulation: A Clinical Perspective

Clinical findings suggest that transcutaneous spinal direct current stimulation (tsDCS) can modulate ascending sensitive, descending corticospinal, and segmental pathways in the spinal cord (SC). However, several aspects of the stimulation have not been completely understood, and realistic computational models based on MRI are the gold standard to predict the interaction between tsDCS-induced electric fields and anatomy. Here, we review the electric fields distribution in the SC during tsDCS as predicted by MRI-based realistic models, compare such knowledge with clinical findings, and define the role of computational knowledge in optimizing tsDCS protocols. tsDCS-induced electric fields are predicted to be safe and induce both transient and neuroplastic changes. This could support the possibility to explore new clinical applications, such as spinal cord injury. For the most applied protocol (2-3 mA for 20-30 min, active electrode over T10-T12 and the reference on the right shoulder), similar electric field intensities are generated in both ventral and dorsal horns of the SC at the same height. This was confirmed by human studies, in which both motor and sensitive effects were found. Lastly, electric fields are strongly dependent on anatomy and electrodes' placement. Regardless of the montage, inter-individual hotspots of higher values of electric fields were predicted, which could change when the subjects move from a position to another (e.g., from the supine to the lateral position). These characteristics underlines the need for individualized and patient-tailored MRI-based computational models to optimize the stimulation protocol. A detailed modeling approach of the electric field distribution might contribute to optimizing stimulation protocols, tailoring electrodes' configuration, intensities, and duration to the clinical outcome.

Combined neuromuscular electrical stimulation and transcutaneous spinal direct current stimulation increases motor cortical plasticity in healthy humans

Introduction

Neuromuscular electrical stimulation (NMES) induces neural plasticity of the central nervous system (CNS) and improves motor function in patients with CNS lesions. However, the extended stimulus duration of NMES reduces its clinical applicability. Transcutaneous spinal direct current stimulation (tsDCS), which increases afferent input, may enhance the effects and reduce the stimulus duration of NMES. This study investigated the excitability of the motor cortex, somatosensory cortex, and spinal motor neurons after the combined stimulation of NMES and tsDCS.

Methods

Among the 55 participants in this study, 24 were allocated to experiment 1, 15 to experiment 2, and 16 to experiment 3. They received intervention for 20 min on different days: (1) NMES combined with tsDCS (NMES + tsDCS), (2) NMES combined with sham tsDCS (NMES + sham tsDCS), and (3) sham NMES combined with tsDCS (sham NMES + tsDCS). NMES was delivered to the right common peroneal nerve at 25 Hz with the intensity at 120% of the motor threshold. For tsDCS, the cathodal electrode was positioned on the thoracic 10th–12th vertebral levels, and the anodal electrode was located on the right shoulder. The stimulus intensity was 2.5 mA. In experiment 1, motor evoked potentials (MEPs) and short-latency intracortical inhibition (SICI) were measured by transcranial magnetic stimulation up to 60 min after stimulation. The spinal motor neurons’ excitability was assessed by recording the posterior root muscle reflex (PRMR) induced via transcutaneous spinal cord stimulation in experiment 2, and the primary somatosensory cortex excitability was evaluated by recording the somatosensory evoked potentials (SEPs) in experiment 3 up to 15 min after stimulation.

Results

Compared to before the stimulation, NMES + tsDCS significantly increased MEP for 60 min or more, and significantly decreased SICI immediately after. Conversely contrast, the PRMR significantly decreased immediately after, and SEPs were unchanged.

Discussion

These results suggest that simultaneous afferent inputs from different stimulus positions critically induce primary motor cortex plasticity. The combined stimulation of NMES with tsDCS may facilitate the development of a new neurorehabilitation technique.

A dual-mode neurostimulation approach to enhance athletic performance outcome in experienced taekwondo practitioners

Transcranial Direct Current Stimulation (tDCS) is a growing empirical approach to improve athletic performance. Some recent studies have investigated the effects of transcutaneous spinal direct current stimulation (tsDCS) on the motor performance such as reaction time. TDCS and tsDCS can lead to alteration of the spontaneous neural activity, and the membrane potentials of motor neurons in cerebral cortex and spinal interneurons, respectively. Given the paucity of experimental studies on the non-invasive brain stimulation in the field of sports neuroscience, especially martial sports, the present study aimed at investigating the effects of neurostimulation in potentiating the motor and cognitive functions in experienced taekwondo practitioners. The study sample included 15 experienced male taekwondo players who received real or sham direct current stimulation on the primary motor cortex (M1) and the lumbar spinal segment (T12-L2) over two sessions, 72 h apart. Next, the performance of the participants was evaluated through a simulation of taekwondo exercise directly after the sham and real sessions. Moreover, a cognitive platform (CBS: Cambridge Brain Science) was used to investigate the participants' cognitive profile in each instance. Unlike sham stimulation, real tDCS was associated with improved selective attention and reaction time in both in the simulated task performance and cognitive examination. The concurrent cortical and trans-spinal tDCS was found to improve selective attention (31% performance improvement) (P < 0.0001) [EFFECT SIZE; 1.84]. and reduce reaction time (4.7% performance improvement) (P < 0.0001) [EFFECT SIZE; 0.02]. Meanwhile, the intervention failed to leave a significant change in cognitive functions evaluated through CBS (P > 0.05). As informed by our results, the present dual-mode neurostimulation could improve motor functions potentially through the effect of tsDCS over the spinal interneurons and tDCS over the primary motor cortex. Likewise, our findings suggested an improved performance in simulated taekwondo task after real- but not sham-stimulation. This study paves the way for designing neurostimulation protocols to improve the performance of professional athletes, namely martial art practitioners, including their accuracy and velocity of reactions. Such positive effects of neuostimulation in athletic performance as demonstrated in this research and similar reports are expected to enhance the athletes' success in professional competitions.

Shock waves modulate corticospinal excitability: A proof of concept for further rehabilitation purposes?

Background

Focal extracorporeal shock wave therapy (fESWT) is a physical therapy vastly studied and used for various musculoskeletal disorders. However, the effect of fESWT on central nervous system is still to be determined.

Objective

To elucidate spinal and supra-spinal mechanisms of fESWT in healthy subjects, in order to widen the spectrum of its clinical applications.

Methods

In this quasi-experimental, unblinded, proof-of-concept clinical study, 10 voluntary healthy subjects underwent fESWT and were assessed immediately before (T0), immediately after (T1) and seven days after (T2) the intervention. As neurophysiological outcomes, motor evoked potentials (resting motor threshold, maximal motor evoked potential and maximal compound muscle action potential ratio, cortical silent period, total conduction motor time, direct and indirect central motor conduction time), F-waves (minimal and mean latency, persistence and temporal dispersion) and H-reflex (threshold, amplitude, maximal H reflex and maximal compound muscle action potential ratio, latency) were considered.

Results

Resting motor threshold and F-waves temporal dispersion significantly decreased, respectively, from T1 and T2 and from T0 and T2 (for both, p <  0.05). H-reflex threshold increase between T0 and T1. Analysis disclosed a strong negative correlation between Δ3 cortical silent period (i.e., T2 -T1 recordings) and Δ1 Hr threshold (i.e., T1 -T0 recordings) (r = -0.66, p <  0.05), and a positive strong relationship between Δ3 cortical silent period and Δ3 Hr threshold (r = 0.63, p <  0.05).

Conclusions

fESWT modulates corticospinal tract excitability in healthy volunteers, possibly inducing an early inhibition followed by a later facilitation after one week.

Lumbar trans-spinal direct current stimulation: A modeling-experimental approach to dorsal root ganglia stimulation

Introduction

The excitability of spinal motor neurons (MN) can be altered through subthreshold currents, such as transcutaneous spinal direct-current stimulation (tsDCS). Current evidence shows that tsDCS can interfere with ascending somatosensory pathways and lower motor neurons' (LMN) excitability, which points to its therapeutic potential for repairing altered spinal responses. We aim to define the best tsDCS montage for maximizing the electric field (E-field) in the lumbar spinal cord (L-SC) by computer modeling; and to apply this montage to measure the effect on LMN excitability and somatosensory evoked potentials (SSEP).

Methods

A human volume conductor model was obtained from an available database. The E-field distribution was calculated considering three different electrode settings aiming at maximizing the field at L-SC and right dorsal root ganglia (DRG). The best electrode setting was then selected and applied in a blind crossover pseudo-randomized study including 14 subjects. tsDCS was delivered for 15 min (cathodal vs. sham) over L2 vertebra level (4 mA, 144 mC/cm²), and its effect on F-waves, H-reflex (including homosynaptic depression, HD) and SSEPs was investigated in the lower limbs.

Results

All simulated montages showed higher current density and E-field magnitudes between the electrodes (>0.15 V/m), with a major longitudinal component and with rostral-caudal direction. The induced E-field involved the sensory ganglia and was maximum in the right T8-left L2 montage, which was the one selected for the experimental protocol. We disclosed a statistically significant increase of the H-reflex amplitude at 0.1 Hz, after cathodal tsDCS (c-tsDCS) on both sides. No other significant change was observed.

Discussion

Our results can suggest the c-tsDCS applied to the L-SC and DRG can modulate synaptic efficiency increasing lower motor neurons response to Ia fibers excitation. The possible implications of our findings for treating clinical conditions will be addressed in future studies.

Anodal transcutaneous DC stimulation enhances learning of dynamic balance control during walking in humans with spinal cord injury

Deficits in locomotor function, including impairments in walking speed and balance, are major problems for many individuals with incomplete spinal cord injury (iSCI). However, it remains unclear which type of training paradigms are more effective in improving balance, particularly dynamic balance, in individuals with iSCI. The purpose of this study was to determine whether anodal transcutaneous spinal direct current stimulation (tsDCS) can facilitate learning of balance control during walking in individuals with iSCI. Fifteen individuals with iSCI participated in this study and were tested in two sessions (i.e., tsDCS and sham conditions). Each session consisted of 1 min of treadmill walking without stimulation or perturbation (baseline), 10 min of walking with either anodal tsDCS or sham stimulation, paired with bilateral pelvis perturbation (adaptation), and finally 2 min of walking without stimulation and perturbation (post-adaptation). The outcome measures were the dynamic balance, assessed using the minimal margin of stability (MoS), and electromyography of leg muscles. Participants demonstrated a smaller MoS during the late adaptation period for the anodal tsDCS condition compared to sham (p = 0.041), and this MoS intended to retain during the early post-adaptation period (p = 0.05). In addition, muscle activity of hip abductors was greater for the anodal tsDCS condition compared to sham during the late adaptation period and post-adaptation period (p < 0.05). Results from this study suggest that anodal tsDCS may modulate motor adaptation to pelvis perturbation and facilitate learning of dynamic balance control in individuals with iSCI.

Trans-Spinal Direct Current Stimulation Targets Ca2+ Channels to Induce Persistent Motor Unit Responses

Trans-spinal direct current stimulation (tsDCS) is a neuromodulatory approach to augment spinal cord activity to improve function after neurological disease and injury. Little is known about the mechanisms underlying tsDCS actions on the motor system. The purpose of this study is to determine the role for a persistent inward current (PIC)-like response in motoneurons in mediating tsDCS actions. We recorded single motor units from the extensor and flexor carpi radialis muscles in healthy sedated rats and measured unit activity changes produced by cervical enlargement cathodal and anodal tsDCS (c-tsDCS; a-tsDCS). Both c-tsDCS and a-tsDCS immediately increased spontaneous motor unit firing during stimulation. After c-tsDCS was stopped, spontaneous firing persisted for a substantial period (165 ± 5s), yet after a-tsDCS activity shortly returned to baseline (27 ± 7s). Administration of the L-type calcium channel blocker Nimodipine reduced spontaneous motor unit firing during c-tsDCS and blocked the persistent response. By contrast, Nimodipine did not change unit firing during a-tsDCS but the short persistent response was blocked. Computer simulation using a two-compartment neuronal model replicated the main experimental observations: larger and more persistent responses during and after c-tsDCS than a-tsDCS. Using reduced Ca²⁺ conductance to model Nimodipine action, a reduced response during c-tsDCS and elimination of the persistent response was observed. Our experimental findings, supported by computer simulation, show that c-tsDCS can target Ca²⁺ conductances to augment motoneuron activity. As tsDCS is well-tolerated in humans, this knowledge informs therapeutic treatment strategies to achieve rehabilitation goals after injury; in particular, to increase muscle force.

Transcutaneous spinal direct current stimulation (tsDCS) does not affect postural sway of young and healthy subjects during quiet upright standing

Transcutaneous spinal direct current stimulation (tsDCS) is an effective non-invasive spinal cord electrical stimulation technique to induce neuromodulation of local and distal neural circuits of the central nervous system (CNS). Applied to the spinal cord lumbosacral region, tsDCS changes electrophysiological responses of the motor, proprioceptive and nociceptive pathways, alters the performance of some lower limb motor tasks and can even modulate the behavior of supramedullary neuronal networks. In this study an experimental protocol was conducted to verify if tsDCS (5 mA, 20 minutes) of two different polarizations, applied over the lumbosacral region (tenth thoracic vertebrae (T10)), can induce changes in postural sway oscillations of young healthy individuals during quiet standing. A novel initialization of the electrical stimulation was developed to improve subject blinding to the different stimulus conditions including the sham trials. Measures of postural sway, both global and structural, were computed before, during and following the DC stimulation period. The results indicated that, for the adopted conditions, tsDCS did not induce statistically significant changes in postural sway of young healthy individuals during quiet standing.

Trans-Spinal Electrical Stimulation Therapy for Functional Rehabilitation after Spinal Cord Injury: Review

Spinal cord injury (SCI) is one of the most debilitating injuries in the world. Complications after SCI, such as respiratory issues, bowel/bladder incontinency, pressure ulcers, autonomic dysreflexia, spasticity, pain, etc., lead to immense suffering, a remarkable reduction in life expectancy, and even premature death. Traditional rehabilitations for people with SCI are often insignificant or ineffective due to the severity and complexity of the injury. However, the recent development of noninvasive electrical neuromodulation treatments to the spinal cord have shed a ray of hope for these individuals to regain some of their lost functions, a reduction in secondary complications, and an improvement in their life quality. For this review, 250 articles were screened and about 150 were included to summarize the two most promising noninvasive spinal cord electrical stimulation methods of SCI rehabilitation treatment, namely, trans-spinal direct current stimulation (tsDCS) and trans-spinal pulsed current stimulation (tsPCS). Both treatments have demonstrated good success in not only improving the sensorimotor function, but also autonomic functions. Due to the noninvasive nature and lower costs of these treatments, in the coming years, we expect these treatments to be integrated into regular rehabilitation therapies worldwide.

Enhancing Locomotor Learning With Transcutaneous Spinal Electrical Stimulation and Somatosensory Augmentation: A Pilot Randomized Controlled Trial in Older Adults

This study investigated locomotor learning of a complex terrain walking task in older adults, when combined with two adjuvant interventions: transcutaneous spinal direct current stimulation (tsDCS) to increase lumbar spinal cord excitability, and textured shoe insoles to increase somatosensory feedback to the spinal cord. The spinal cord has a crucial contribution to control of walking, and is a novel therapeutic target for rehabilitation of older adults. The complex terrain task involved walking a 10-meter course consisting of nine obstacles and three sections of compliant (soft) walking surface. Twenty-three participants were randomly assigned to one of the following groups: sham tsDCS and smooth insoles (sham/smooth; control group), sham tsDCS and textured insoles (sham/textured), active tsDCS and smooth insoles (active/smooth), and active tsDCS and textured insoles (active/textured). The first objective was to assess the feasibility, tolerability, and safety of the interventions. The second objective was to assess preliminary efficacy for increasing locomotor learning, as defined by retention of gains in walking speed between a baseline visit of task practice, and a subsequent follow-up visit. Variability of the center of mass while walking over the course was also evaluated. The change in executive control of walking (prefrontal cortical activity) between the baseline and follow-up visits was measured with functional near infrared spectroscopy. The study results demonstrated feasibility based on enrollment and retention of participants, tolerability based on self-report, and safety based on absence of adverse events. Preliminary efficacy was supported based on trends showing larger gains in walking speed and more pronounced reductions in mediolateral center of mass variability at the follow-up visit in the groups randomized to active tsDCS or textured insoles. These data justify future larger studies to further assess dosing and efficacy of these intervention approaches. In conclusion, rehabilitation interventions that target spinal control of walking present a potential opportunity for enhancing walking function in older adults.

Backward Locomotor Treadmill Training Differentially Improves Walking Performance across Stroke Walking Impairment Levels

Background: Post-stroke walking impairment is a significant cause of chronic disability worldwide and often leads to loss of life roles for survivors and their caregivers. Walking impairment is traditionally classified into mild (>0.8 m/s), moderate (0.41–0.8 m/s), and severe (≤0.4 m/s), and those categorized as “severe” are more likely to be homebound and at greater risk of falls, fractures, and rehospitalization. In addition, there are minimal effective walking rehabilitation strategies currently available for this subgroup. Backward locomotor treadmill training (BLTT) is a novel and promising training approach that has been demonstrated to be safe and feasible across all levels of impairment; however, its benefits across baseline walking impairment levels (severe (≤0.4 m/s) vs. mild–moderate (>0.4 m/s)) have not been examined. Methods: Thirty-nine adults (>6 months post-stroke) underwent 6 days of BLTT (3×/week) over 2 weeks. Baseline and PRE to POST changes were measured during treadmill training and overground walking. Results: Individuals with baseline severe walking impairment were at a more significant functional disadvantage across all spatiotemporal walking measures at baseline and demonstrated fewer overall gains post-training. However, contrary to our working hypothesis, both groups experienced comparable increases in cadence, bilateral percent single support times, and step lengths. Conclusion: BLTT is well tolerated and beneficial across all walking impairment levels, and baseline walking speed (≤0.4 m/s) should serve as a covariate in the design of future walking rehabilitation trials.

Finding the Way to Improve Motor Recovery of Patients with Spinal Cord Lesions: A Case-Control Pilot Study on a Novel Neuromodulation Approach

Robot-assisted rehabilitation (RAR) and non-invasive brain stimulation (NIBS) are interventions that, both individually and combined, can significantly enhance motor performance after spinal cord injury (SCI). We sought to determine whether repetitive transcranial magnetic stimulation (rTMS) combined with active transvertebral direct current stimulation (tvDCS) (namely, NIBS) in association with RAR (RAR + NIBS) improves lower extremity motor function more than RAR alone in subjects with motor incomplete SCI (iSCI). Fifteen adults with iSCI received one daily session of RAR+NIBS in the early afternoon, six sessions weekly, for eight consecutive weeks. Outcome measures included the 6 min walk test (6MWT), the 10 m walk test (10MWT), the timed up and go (TUG) to test mobility and balance, the Walking Index for Spinal Cord Injury (WISCI II), the Functional Independence Measure-Locomotion (FIM-L), the manual muscle testing for lower extremity motor score (LEMS), the modified Ashworth scale for lower limbs (MAS), and the visual analog scale (VAS) for pain. The data of these subjects were compared with those of 20 individuals matched for clinical and demographic features who previously received the same amount or RAR without NIBS (RAR - NIBS). All patients completed the trial, and none reported any side effects either during or following the training. The 10MWT improved in both groups, but the increase was significantly greater following RAR + NIBS than RAR - NIBS. The same occurred for the FIM-L, LEMS, and WISCI II. No significant differences were appreciable concerning the 6MWT and TUG. Conversely, RAR - NIBS outperformed RAR + NIBS regarding the MAS and VAS. Pairing tvDCS with rTMS during RAR can improve lower extremity motor function more than RAR alone can do. Future research with a larger sample size is recommended to determine longer-term effects on motor function and activities of daily living.

The effect of cathodal transspinal direct current stimulation on tibialis anterior stretch reflex components in humans

Spinal DC stimulation (tsDCS) shows promise as a technique for the facilitation of functional recovery of motor function following central nervous system (CNS) lesion. However, the network mechanisms that are responsible for the effects of tsDCS are still uncertain. Here, in a series of experiments, we tested the hypothesis that tsDCS increases the excitability of the long-latency stretch reflex, leading to increased excitability of corticospinal neurons in the primary motor cortex. Experiments were performed in 33 adult human subjects (mean age 28 ± 7 years/14 females). Subjects were seated in a reclining armchair with the right leg attached to a footplate, which could be quickly plantarflexed (100 deg/s; 6 deg amplitude) to induce stretch reflexes in the tibialis anterior (TA) muscle at short (45 ms) and longer latencies (90-95 ms). This setup also enabled measuring motor evoked potentials (MEPs) and cervicomedullary evoked potentials (cMEPs) from TA evoked by transcranial magnetic stimulation (TMS) and electrical stimulation at the cervical junction, respectively. Cathodal tsDCS at 2.5 and 4 mA was found to increase the long-latency reflex without any significant effect on the short-latency reflex. Furthermore, TA MEPs, but not cMEPs, were increased following tsDCS. We conclude that cathodal tsDCS over lumbar segments may facilitate proprioceptive transcortical reflexes in the TA muscle, and we suggest that the most likely explanation of this facilitation is an effect on ascending fibers in the dorsal columns.

Effects of Transcutaneous Spinal Direct Current Stimulation (tsDCS) in Patients With Chronic Pain: A Clinical and Neurophysiological Study

Background and Aims: Chronic pain is a complex clinical condition, often devastating for patients and unmanageable with pharmacological treatments. Converging evidence suggests that transcutaneous spinal Direct Current Stimulation (tsDCS) might represent a complementary therapy in managing chronic pain. In this randomized, double-blind and sham-controlled crossover study, we assessed tsDCS effects in chronic pain patients.

Methods: Sixteen patients (aged 65.06 ± 16.16 years, eight women) with chronic pain of different etiology underwent sham and anodal tsDCS (anode over the tenth thoracic vertebra, cathode over the somatosensory cortical area: 2.5 mA, 20 min, 5 days for 1 week). As outcomes, we considered the Visual Analog Scale (VAS), the Neuropathic Pain Symptom Inventory (NPSI), and the components of the lower limb flexion reflex (LLFR), i.e., RIII threshold, RII latency and area, RIII latency and area, and flexion reflex (FR) total area. Assessments were conducted before (T0), immediately at the end of the treatment (T1), after 1 week (T2) and 1 month (T3).

Results: Compared to sham, anodal tsDCS reduced RIII area at T2 (p = 0.0043) and T3 (p = 0.0012); similarly, FR total area was reduced at T3 (p = 0.03). Clinically, anodal tsDCS dampened VAS at T3 (p = 0.015), and NPSI scores at T1 (p = 0.0012), and T3 (p = 0.0015), whereas sham condition left them unchanged. Changes in VAS and NPSI scores linearly correlated with the reduction in LLFR areas (p = 0.0004).

Conclusions: Our findings suggest that tsDCS could modulate nociceptive processing and pain perception in chronic pain syndromes.

Trans-Spinal Direct Current Stimulation for Managing Primary Orthostatic Tremor

BACKGROUND

Primary orthostatic tremor (POT) is a rare disorder, characterized by 13 to 18 Hz tremor in the legs when standing and is often refractory to medical treatment. Epidural spinal cord stimulation has been proposed as an alternative treatment. However, this approach is invasive, which limits its application.

OBJECTIVE

Trans-spinal direct current stimulation (tsDCS) is a non-invasive method to modulate spinal cord circuits. The aim of this proof-of-concept study was to investigate the potential beneficial effect of tsDCS in POT.

METHODS

We conducted a double-blind, sham-controlled study in 16 patients with POT. In two separate visits, patients received sham tsDCS first followed by active (either cathodal or anodal) tsDCS. The primary outcome was the change in time in standing position. Secondary outcomes comprised quantitative assessment of tremor, measurement of corticospinal excitability including short-latency afferent inhibition, and clinical global impression-improvement (CGI-I). Measurements were made at baseline, after sham tsDCS, 0-30 min, and 30-60 min after active conditions.

RESULTS

Cathodal-tsDCS reduced tremor amplitude and frequency and lowered corticospinal excitability whereas anodal-tsDCS reduced tremor frequency only. CGI-I scores positively correlated with the time in standing position after both active tsDCS conditions.

CONCLUSION

A single session of tsDCS can improve instability in POT. This opens a new vista for experimental treatment options using multiple sessions of spinal DC stimulation. © 2021 International Parkinson and Movement Disorder Society.

Characterization of Motor-Evoked Responses Obtained with Transcutaneous Electrical Spinal Stimulation from the Lower-Limb Muscles after Stroke

An increasing number of studies suggests that a novel neuromodulation technique targeting the spinal circuitry enhances gait rehabilitation, but research on its application to stroke survivors is limited. Therefore, we investigated the characteristics of spinal motor-evoked responses (sMERs) from lower-limb muscles obtained by transcutaneous spinal cord stimulation (tSCS) after stroke compared to age-matched and younger controls without stroke. Thirty participants (ten stroke survivors, ten age-matched controls, and ten younger controls) completed the study. By using tSCS applied between the L1 and L2 vertebral levels, we compared sMER characteristics (resting motor threshold (RMT), slope of the recruitment curve, and latency) of the tibialis anterior (TA) and medial gastrocnemius (MG) muscles among groups. A single pulse of stimulation was delivered in 5 mA increments, increasing from 5 mA to 250 mA or until the subjects reached their maximum tolerance. The stroke group had an increased RMT (27–51%) compared to both age-matched (TA: p = 0.032; MG: p = 0.005) and younger controls (TA: p < 0.001; MG: p < 0.001). For the TA muscle, the paretic side demonstrated a 13% increased latency compared to the non-paretic side in the stroke group (p = 0.010). Age-matched controls also exhibited an increased RMT compared to younger controls (TA: p = 0.002; MG: p = 0.007), suggesting that altered sMER characteristics present in stroke survivors may result from both stroke and normal aging. This observation may provide implications for altered spinal motor output after stroke and demonstrates the feasibility of using sMER characteristics as an assessment after stroke.

Effects of Transspinal Direct Current Stimulation on Cycling Perception of Effort and Time to Exhaustion

ABSTRACT

Ciccone, AB, Fry, AC, Emerson, DM, Gallagher, PM, Herda, TJ, and Weir, JP. Effects of transspinal direct current stimulation on cycling perception of effort and time to exhaustion. J Strength Cond Res 35(2): 347-352, 2021-In the past decade, researchers have investigated the efficacy of transspinal direct current stimulation (tsDCS) on the central nervous system and afferent neuron function in humans. Recently, data have suggested it may be possible for such tsDCS-induced changes in neuromuscular function to enhance performance. This study used noninvasive thoracic spine tsDCS to determine if cycling performance and perception of effort could be modulated by tsDCS. In 3 different stimulation conditions, anodal, cathodal, and sham, subjects cycled at 80% of their maximal aerobic capacity until exhaustion and reported their rating of perceived exertion (RPE) every minute. From this period, we compared the RPE responses over the first 3 minutes and time to exhaustion. There was no significant difference in time to exhaustion between anodal (408 ± 121 seconds), cathodal (413 ± 168 seconds), and sham (440 ± 189 seconds) conditions (p = 0.58). There was no significant difference in RPE from minutes 1-3 (collapsed across time) between anodal (12.9 ± 2.4 arbitrary units (AUs)), cathodal (13.3 ± 2.2 AUs), and sham (12.9 ± 2.1 AUs) conditions (p = 0.51). These data suggest tsDCS condition did not influence cycling performance or perception of effort during high-intensity cycling. Therefore, thoracic spine and lower abdominal montage delivering a current density of 0.071 mA·cm-2 for 20 minutes likely does not substantially improve high-intensity cycling work capacity. Therefore, more research is needed to investigate the efficacy of tsDCS and which stimulation methods may and may not enhance human performance.

Is there hope that transpinal direct current stimulation corrects motoneuron excitability and provides neuroprotection in amyotrophic lateral sclerosis?

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease of largely unknown pathophysiology, characterized by the progressive loss of motoneurons (MNs). We review data showing that in presymptomatic ALS mice, MNs display reduced intrinsic excitability and impaired level of excitatory inputs. The loss of repetitive firing specifically affects the large MNs innervating fast contracting muscle fibers, which are the most vulnerable MNs in ALS. Interventions that aimed at restoring either the intrinsic excitability or the synaptic excitation result in a decrease of disease markers in MNs and delayed neuromuscular junction denervation. We then focus on trans‐spinal direct current stimulation (tsDCS), a noninvasive tool, since it modulates the activity of spinal neurons and networks. Effects of tsDCS depend on the polarity of applied current. Recent work shows that anodal tsDCS induces long‐lasting enhancement of MN excitability and synaptic excitation of spinal MNs. Moreover, we show preliminary results indicating that anodal tsDCS enhances the excitatory synaptic inputs to MNs in ALS mice. In conclusion, we suggest that chronic application of anodal tsDCS might be useful as a complementary method in the management of ALS patients.

Spinal direct current stimulation (tsDCS) in hereditary spastic paraplegias (HSP): A sham-controlled crossover study

Objective: Hereditary spastic paraplegia (HSP) represents a heterogeneous group of neurodegenerative diseases characterized by progressive spasticity and lower limb weakness. We assessed the effects of transcutaneous spinal direct current stimulation (tsDCS) in HSP.Design: A double-blind, randomized, crossover and sham-controlled study.Setting: Fondazione IRCCS Cà Granda, Ospedale Maggiore Policlinico, Milan.Participants: eleven patients with HSP (six men, mean age ± SD: 37.3 ± 8.1 years), eight affected by spastin/SPG4,1 by atlastin1/SPG3a, 1 by paraplegin/SPG7 and 1 by ZFYVE26/SPG15.Interventions: tsDCS (anodal or sham, 2.0 mA, 20', five days) delivered over the thoracic spinal cord (T10-T12).Outcome measures: Motor-evoked potentials (MEPs), the H-reflex (Hr), F-waves, the Ashworth scale for clinical spasticity, the Five Minutes Walking test and the Spastic Paraplegia Rating Scale (SPRS) were assessed. Patients were evaluated before tsDCS (T₀), at the end of the stimulation (T₁), after one week (T₂), one month (T₃) and two months (T₄).Results: The score of the Ashworth scale improved in the anodal compared with sham group, up to two months following the end of stimulation (T₁, P = .0137; T₄, P = .0244), whereas the Five Minutes Walking test and SPRS did not differ between the two groups. Among neurophysiological measures, both anodal and sham tsDCS left Hr, F-waves and MEPs unchanged over time.Conclusions: Anodal tsDCS significantly decreases spasticity and might be a complementary strategy for the treatment of spasticity in HSP.

Transcutaneous spinal direct current stimulation shows no effect on paired stimulation suppression of the somatosensory cortex

Transcutaneous spinal direct current stimulation (tsDCS) is a safe and convenient method of neuromodulation. It has been proven to alter sensory processing at cervicomedullary level by amplitude changes of the P30 response of tibial nerve somatosensory evoked potentials (TN SEPs). With knowledge that tsDCS affects cortical circuits, we hypothesized that tsDCS may also affect intracortical excitability of the somatosensory cortex assessed by paired stimulation suppression (PSS). Fourteen healthy men were included in this prospective, single-blinded, placebo-controlled crossover study. Single (SS) and paired stimulation (PS) TN SEPs were recorded over the scalp before, immediately as well as 30 and 60 min after applying 15 min of tsDCS over the twelfth thoracic vertebra. Each volunteer underwent three independent and randomized sessions of either cathodal, anodal or sham stimulation. tsDCS showed no effect on peak-to-peak amplitudes or latencies of cortical P40-N50 response after SS. Furthermore, tsDCS failed to induce significant changes on amplitude ratios of PSS, thus showing no impact on intracortical excitability of the somatosensory cortex in healthy subjects. Further research is required to reveal the different mechanisms and to strengthen clinical use of this promising technique.

Spinal or cortical direct current stimulation: Which is the best? Evidence from apraxia of speech in post-stroke aphasia

To date, new advances in technology have already shown the effectiveness of non-invasive brain stimulation and, in particular, of transcranial direct current stimulation (tDCS), in enhancing language recovery in post-stroke aphasia. More recently, it has been suggested that the stimulation over the spinal cord improves the production of words associated to sensorimotor schemata, such as action verbs. Here, for the first time, we present evidence that transpinal direct current stimulation (tsDCS) combined with a language training is efficacious for the recovery from speech apraxia, a motor speech disorder which might co-occur with aphasia. In a randomized-double blind experiment, ten aphasics underwent five days of tsDCS with concomitant treatment for their articulatory deficits in two different conditions: anodal and sham. In all patients, language measures were collected before (T0), at the end (T5) and one week after the end of treatment (F/U). Results showed that only after anodal tsDCS patients exhibited a better accuracy in repeating the treated items. Moreover, these effects persisted at F/U and generalized to other oral language tasks (i.e. picture description, noun and verb naming, word repetition and reading). A further analysis, which compared the tsDCS results with those collected in a matched group of patients who underwent the same language treatment but combined with tDCS, revealed no differences between the two groups. Given the persistency and severity of articulatory deficits in aphasia and the ease of use of tsDCS, we believe that spinal stimulation might result a new innovative approach for language rehabilitation.

Can Alzheimer's Disease Be Prevented? First Evidence from Spinal Stimulation Efficacy on Executive Functions

BACKGROUND

Recently, a growing body of evidence has shown that, from the early stage of impairment, Alzheimer's patients (AD) present difficulties on a variety of tasks mostly relying on executive functions. These strongly impact their daily life activities causing a severe loss of independency and autonomy.

OBJECTIVE

To evaluate the efficacy of transpinal direct current stimulation (tsDCS) combined with cognitive trainings for improving attentional and executive function abilities in a group of AD patients.

METHODS

In a randomized-double blind design, sixteen AD patients underwent different cognitive trainings combined with tsDCS. During the treatment, each subject received tsDCS (20 min, 2 mA) over the thoracic vertebrae (IX-X vertebrae) in two different conditions: 1) anodal, and 2) sham while performing three computerized tasks: alertness, selective attention, and executive functions. Each experimental condition was run in ten consecutive daily sessions over two weeks.

RESULTS

After anodal tsDCS, a greater improvement in executive functions compared to sham condition was found. More importantly, the follow-up testing revealed that these effects lasted over 1 month after the intervention and generalized to the different neuropsychological tests administered before, after the treatment and at one month after the end of the intervention. This generalization was present also in the attentional domain.

CONCLUSION

This evidence emphasizes, for the first time, that tsDCS combined with cognitive training results efficacious for AD patients. We hypothesize that enhancing activity into the spinal sensorimotor pathways through stimulation improved cognitive abilities which rely on premotor activity, such as attention and executive functions.

Transcutaneous spinal direct current stimulation increases corticospinal transmission and enhances voluntary motor output in humans

Optimization of motor performance is of importance in daily life, in relation to recovery following injury as well as for elite sports performance. The present study investigated whether transcutaneous spinal direct current stimulation (tsDCS) may enhance voluntary ballistic activation of ankle muscles and descending activation of spinal motor neurons in able-bodied adults. Forty-one adults (21 men; 24.0 ± 3.2 years) participated in the study. The effect of tsDCS on ballistic motor performance and plantar flexor muscle activation was assessed in a double-blinded sham-controlled cross-over experiment. In separate experiments, the underlying changes in excitability of corticospinal and spinal pathways were probed by evaluating soleus (SOL) motor evoked potentials (MEPs) following single-pulse transcranial magnetic stimulation (TMS) over the primary motor cortex, SOL H-reflexes elicited by tibial nerve stimulation and TMS-conditioning of SOL H-reflexes. Measures were obtained before and after cathodal tsDCS over the thoracic spine (T11-T12) for 10 min at 2.5 mA. We found that cathodal tsDCS transiently facilitated peak acceleration in the ballistic motor task compared to sham tsDCS. Following tsDCS, SOL MEPs were increased without changes in H-reflex amplitudes. The short-latency facilitation of the H-reflex by subthreshold TMS, which is assumed to be mediated by the fast conducting monosynaptic corticomotoneuronal pathway, was also enhanced by tsDCS. We argue that tsDCS briefly facilitates voluntary motor output by increasing descending drive from corticospinal neurones to spinal plantar flexor motor neurons. tsDCS can thus transiently promote within-session CNS function and voluntary motor output and holds potential as a technique in the rehabilitation of motor function following central nervous lesions.

Interfacing With Alpha Motor Neurons in Spinal Cord Injury Patients Receiving Trans-spinal Electrical Stimulation

Trans-spinal direct current stimulation (tsDCS) provides a non-invasive, clinically viable approach to potentially restore physiological neuromuscular function after neurological impairment, e.g., spinal cord injury (SCI). Use of tsDCS has been hampered by the inability of delivering stimulation patterns based on the activity of neural targets responsible to motor function, i.e., α-motor neurons (α-MNs). State of the art modeling and experimental techniques do not provide information about how individual α-MNs respond to electrical fields. This is a major element hindering the development of neuro-modulative technologies highly tailored to an individual patient. For the first time, we propose the use of a signal-based approach to infer tsDCS effects on large α-MNs pools in four incomplete SCI individuals. We employ leg muscles spatial sampling and deconvolution of high-density fiber electrical activity to decode accurate α-MNs discharges across multiple lumbosacral segments during isometric plantar flexion sub-maximal contractions. This is done before, immediately after and 30 min after sub-threshold cathodal stimulation. We deliver sham tsDCS as a control measure. First, we propose a new algorithm for removing compromised information from decomposed α-MNs spike trains, thereby enabling robust decomposition and frequency-domain analysis. Second, we propose the analysis of α-MNs spike trains coherence (i.e., frequency-domain) as an indicator of spinal response to tsDCS. Results showed that α-MNs spike trains coherence analysis sensibly varied across stimulation phases. Coherence analyses results suggested that the common synaptic input to α-MNs pools decreased immediately after cathodal tsDCS with a persistent effect after 30 min. Our proposed non-invasive decoding of individual α-MNs behavior may open up new avenues for the design of real-time closed-loop control applications including both transcutaneous and epidural spinal electrical stimulation where stimulation parameters are adjusted on-the-fly.

Backward locomotor treadmill training combined with transcutaneous spinal direct current stimulation in stroke: a randomized pilot feasibility and safety study

Walking impairment impacts nearly 66% of stroke survivors and is a rising cause of morbidity worldwide. Despite conventional post-stroke rehabilitative care, the majority of stroke survivors experience continued limitations in their walking speed, temporospatial dynamics and walking capacity. Hence, novel and comprehensive approaches are needed to improve the trajectory of walking recovery in stroke survivors. Herein, we test the safety, feasibility and preliminary efficacy of two approaches for post-stroke walking recovery: backward locomotor treadmill training and transcutaneous spinal direct current stimulation. In this double-blinded study, 30 chronic stroke survivors (>6 months post-stroke) with mild-severe residual walking impairment underwent six 30-min sessions (three sessions/week) of backward locomotor treadmill training, with concurrent anodal (N = 19) or sham transcutaneous spinal direct current stimulation (N = 11) over the thoracolumbar spine, in a 2:1 stratified randomized fashion. The primary outcomes were: per cent participant completion, safety and tolerability of these two approaches. In addition, we collected data on training-related changes in overground walking speed, cadence, stride length (baseline, daily, 24-h post-intervention, 2 weeks post-intervention) and walking capacity (baseline, 24-h post-intervention, 2 weeks post-intervention), as secondary exploratory aims testing the preliminary efficacy of these interventions. Eighty-seven per cent (N = 26) of randomized participants completed the study protocol. The majority of the study attrition involved participants with severe baseline walking impairment. There were no serious adverse events in either the backward locomotor treadmill training or transcutaneous spinal direct current stimulation approaches. Also, both groups experienced a clinically meaningful improvement in walking speed immediately post-intervention that persisted at the 2-week follow-up. However, in contrast to our working hypothesis, anodal-transcutaneous spinal direct current stimulation did not enhance the degree of improvement in walking speed and capacity, relative to backward locomotor treadmill training + sham, in our sample. Backward locomotor treadmill training and transcutaneous spinal direct current stimulation are safe and feasible approaches for walking recovery in chronic stroke survivors. Definitive efficacy studies are needed to validate our findings on backward locomotor treadmill training-related changes in walking performance. The results raise interesting questions about mechanisms of locomotor learning in stroke, and well-powered transcutaneous spinal direct current stimulation dosing studies are needed to understand better its potential role as a neuromodulatory adjunct for walking rehabilitation.

Spinal direct current stimulation with locomotor training in chronic spinal cord injury

Transcutaneous spinal direct current stimulation (tsDCS) is a non-invasive method of stimulating spinal circuits that can modulate and induce changes in corticospinal excitability (CE) in incomplete spinal cord injury (SCI). A double-blinded sham controlled study of 2 male patients (A and B) with SCI was carried out. Patient A received sham and cathodal tsDCS, while Patient B received sham and anodal tsDCS. Four baselines were recorded prior to each arm of stimulation. Outcomes were then measured post each arm of stimulation; 10-meter walk test, modified ashworth scale, berg balance scale, manual muscle testing, and spinal cord independence measure-III. Transcranial magnetic stimulation, assessed motor evoked potentials. Cathodal tsDCS increased the scores in few of the outcome measures and decreased others. Anodal stimulation increased scores in all measures. Motor evoked potentials increased in post-cathode and deteriorated in post-anode. In conclusion, tsDCS modulated gait parameters, spasticity, and CE in incomplete SCI.

Looking at ancillary systems for verb recovery: Evidence from non-invasive brain stimulation

Several behavioural and neuroimaging studies have suggested that the language function is not restricted into the left areas but it involves regions not predicted by the classical language model. Accordingly, the Embodied Cognition theory postulates a close interaction between the language and the motor system. Indeed, it has been shown that non-invasive brain stimulation (NIBS) is effective for language recovery also when applied over sensorimotor regions, such as the motor cortex, the cerebellum and the spinal cord. We will review a series of NIBS studies in post-stroke aphasic people aimed to assess the impact of NIBS on verb recovery. We first present results which, following the classical assumption of the Broca's area as the key region for verb processing, have shown that the modulation over this area is efficacious for verb improvement. Then, we will present experiments which, according to Embodied Cognition, have directly investigated through NIBS the role of different sensorimotor regions in enhancing verb production. Since verbs play a crucial role for sentence construction which are most often impaired in the aphasic population, we believe that these results have important clinical implications. Indeed, they address the possibility that different structures might support verb processing.

Jumping Height Does Not Increase in Well Trained Volleyball Players After Transcutaneous Spinal Direct Current Stimulation

Transcutaneous spinal direct current stimulation (tsDCS) increases corticospinal and spinal reflex excitability, and may be a new tool for increasing muscle explosive performance in sports training. The aim of the study was to evaluate whether tsDCS can enhance jumping ability in trained humans practicing volleyball. Twenty eight participants completed the study, including 21 men and 7 women. We investigated the effects of a single 15-minute session of sham, anodal, and cathodal tsDCS over spine and shoulder on repeated counter movement jump (CMJ) and squat jump (SJ) performance at 0, 30 and 60 min post-stimulation. The order of SJs and CMJs sets in each session was randomized. Each SJ and CMJ set consisted of 3 jumps. The break between each attempt was 1 min and the interval between the sets was 3 min. Two-way repeated measures ANOVA did not show effect of time, nor stimulation method, nor stimulation method × time interactions on SJ (time: F_(1.8,_142.1) = 1.054; p = 0.346, stimulation: F₍₂,₇₈₎ = 0.019; p = 0.981, stimulation × time: F_(3.6,_142.1) = 0.725; p = 0.564) or CMJ (time: F_(1.8,_140.9) = 2.092; p = 0.132, stimulation: F₍₂,₇₈₎ = 0.005; p = 0.995, stimulation × time: F_(3.6,_140.9) = 0.517; p = 0.705) performance. Single session of tsDCS over spine and shoulder does not increase jumping height in well-trained volleyball players. This is an important finding for coaches and strength conditioning professionals for understanding the practical utility of tsDCS for enhancing muscular explosiveness.

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.

Transcutaneous spinal direct current stimulation improves locomotor learning in healthy humans

BACKGROUND

Ambulation is an essential aspect of daily living and is often impaired after brain and spinal cord injuries. Despite the implementation of standard neurorehabilitative care, locomotor recovery is often incomplete.

OBJECTIVE

In this randomized, sham-controlled, double-blind, parallel design study, we aimed to determine if anodal transcutaneous spinal direct current stimulation (anodal tsDCS) could improve training effects on locomotion compared to sham (sham tsDCS) in healthy subjects.

METHODS

43 participants underwent a single backwards locomotion training (BLT) session on a reverse treadmill with concurrent anodal (n = 22) or sham (n = 21) tsDCS. The primary outcome measure was speed gain measured 24 h post-training. We hypothesized that anodal tsDCS + BLT would improve training effects on backward locomotor speed compared to sham tsDCS + BLT. A subset of participants (n = 31) returned for two additional training days of either anodal (n = 16) or sham (n = 15) tsDCS and underwent (n = 29) H-reflex testing immediately before, immediately after, and 30 min post-training over three consecutive days.

RESULTS

A single session of anodal tsDCS + BLT elicited greater speed gain at 24 h relative to sham tsDCS + BLT (p = 0.008, two-sample t-test, adjusted for one interim analysis after the initial 12 subjects). Anodal tsDCS + BLT resulted in higher retention of the acquired skill at day 30 relative to sham tsDCS + BLT (p = 0.002) in the absence of significant group differences in online or offline learning over the three training days (p = 0.467 and p = 0.131). BLT resulted in transient down-regulation of H-reflex amplitude (Hmax/Mmax) in both test groups (p < 0.0001). However, the concurrent application of anodal-tsDCS with BLT elicited a longer lasting effect than sham-tsDCS + BLT (p = 0.050).

CONCLUSION

tsDCS improved locomotor skill acquisition and retention in healthy subjects and prolonged the physiological exercise-mediated downregulation of excitability of the alpha motoneuron pool. These results suggest that this strategy is worth exploring in neurorehabilitation of locomotor function.

Modeling Trans-Spinal Direct Current Stimulation in the Presence of Spinal Implants

Trans-spinal direct current stimulation (tsDCS) is a technique considered for the treatment of corticospinal damage or dysfunction. TsDCS aims to induce functional modulation in the corticospinal circuitry via a direct current (DC) generated an electric field (EF). To ensure subject safety, subjects with metallic implants are generally excluded from receiving neural dc stimulation. However, spinal injuries often require spinal implants for stabilization. Our goal was to investigate implant imposed changes to EF and current density (CD) magnitude during tsDCS. We simulated the EF and CD, generated by tsDCS in the presence of spinal rods for two electrode configurations and four implant locations along the spinal cord. For each scenario, a no-implant condition was computed for comparison. We assessed changes in EF and CD at the implant location and the EF inside the spinal cord. Our results show that implant presence was able to influence peak CD, compared to the no-implant condition. Nonetheless, the highest calculated CD levels were a factor six lower than those thought to lead to hazardous tissue-damaging effects. Additionally, implant presence did not considerably affect the average EF inside the spinal cord. Our findings do therefore not indicate potentially unsafe CD levels, or significant alterations to stimulation intensity inside the spinal cord, caused by a spinal implant during tsDCS. Our results are relevant to the safety of transcutaneous spinal stimulation applied in the presence of metallic spinal implants.

Dose-response relationship of transcutaneous spinal direct current stimulation in healthy humans: A proof of concept study

BACKGROUND

Non-invasive transcranial direct current stimulation has been shown to modulate cortical excitability in various studies. Similarly, recent preliminary studies suggest that transcutaneous spinal direct current stimulation (tsDCS) may engender a modulation effect on spinal and cortical neurons.

OBJECTIVE

The purpose of this study was to evaluate the dose-response effects of tsDCS in healthy subjects and thereby lay groundwork for expanding treatment options for patients with spinal cord injury (SCI).

METHODS

Nine healthy subjects received each of the following 2 tsDCS conditions: Anodal and cathodal, in random order with at least 1 week washout period between each session. In order to test safety and dose response, various current intensities were used (2, 2.5 and 3 mA) for 20 minutes. The active electrode was placed vertically over T10-T11, and the reference electrode was placed over the left shoulder. To evaluate corticospinal excitability, motor evoked potentials over soleus muscle elicited by transcranial magnetic stimulation were measured. To assess spinal cord excitability, H- and M- wave over soleus muscle to calculate Hmax/ Mmax ratio were measured.

RESULTS

Linear regression showed a dose response with cathodal tsDCS on motor evoked potentials measured from the left leg as well as with anodal tsDCS on Hmax/ Mmax ratio measured from the left leg.

CONCLUSIONS

These findings indicate tsDCS effects are dose-dependent. These effects should be investigated in a larger sample.

Neuromodulation in the restoration of function after spinal cord injury

Neuromodulation, the use of electrical interfaces to alter neuronal activity, has been successful as a treatment approach in several neurological disorders, including deep brain stimulation for Parkinson's disease and epidural spinal stimulation for chronic pain. Neuromodulation can also be beneficial for spinal cord injury, from assisting basic functions such as respiratory pacing and bladder control, through to restoring volitional movements and skilled hand function. Approaches range from electrical stimulation of peripheral muscles, either directly or via brain-controlled bypass devices, to stimulation of the spinal cord and brain. Limitations to widespread clinical application include durability of neuromodulation devices, affordability and accessibility of some approaches, and poor understanding of the underlying mechanisms. Efforts to overcome these challenges through advances in technology, together with pragmatic knowledge gained from clinical trials and basic research, could lead to personalised neuromodulatory interventions to meet the specific needs of individuals with spinal cord injury.

Cerebello-spinal tDCS in ataxia: A randomized, double-blind, sham-controlled, crossover trial

OBJECTIVE

To investigate whether a 2-week treatment with cerebellar anodal and spinal cathodal transcranial direct current stimulation (tDCS) could reduce symptoms in patients with neurodegenerative ataxia and could modulate cerebello-motor connectivity at the short and long terms.

METHODS

We performed a double-blind, randomized, sham-controlled, crossover trial with cerebello-spinal tDCS (5 d/wk for 2 weeks) in 20 patients with neurodegenerative ataxia. Each patient underwent a clinical evaluation before and after real tDCS or sham stimulation. A follow-up evaluation was performed at 1 and 3 months with a crossover washout period of 3 months. Cerebello-motor connectivity was evaluated with transcranial magnetic stimulation at baseline and at each follow-up.

RESULTS

Cerebello-spinal tDCS showed a significant improvement in all performance scores (Scale for the Assessment and Rating of Ataxia, International Cooperative Ataxia Rating Scale, 9-Hole Peg Test, 8-m walking time), in motor cortex excitability, and in cerebellar brain inhibition compared to sham stimulation.

CONCLUSIONS

A 2-week treatment with cerebello-spinal tDCS reduces symptoms in patients with ataxia and restores motor cortex inhibition exerted by cerebellar structures. Cerebello-spinal tDCS might represent a promising future therapeutic and rehabilitative approach in patients with neurodegenerative ataxia, still an orphan disorder of any pharmacologic intervention.

CLINICAL TRIAL REGISTRATION

NCT03120013.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that cerebello-spinal stimulation is effective and safe in cerebellar ataxia.

Neuromodulation of lower limb motor responses with transcutaneous lumbar spinal cord direct current stimulation

OBJECTIVE

Trans-spinal direct current stimulation (tsDCS) is a promising technique to modulate spinal circuits. Combining clinical with modelling studies can improve effectiveness of tsDCS protocols. The aim of this study is to measure the effects of lumbar tsDCS on motor spinal responses and observe if these are consistent with the electric field (E-field) predicted from a computational model.

METHODS

The exploratory study design was double-blind crossover and randomized. tsDCS was delivered for 15 min (anodal, cathodal, sham) at L2 vertebra level (2.5 mA, 90 C/cm²) in 14 healthy subjects. F-wave, H-reflex, cortical silent period, motor evoked potential and sympathetic skin response were analyzed. Statistical methods were applied with Bonferroni correction for multiple comparisons, a p < 0.05 was set as significant. A human volume conductor model was obtained from available databases. E-field distributions in the spinal grey matter (GM) and white matter (WM) were calculated.

RESULTS

No tsDCS effects were observed. E-field magnitude predicted in the lumbosacral spinal GM and WM was <0.15 V/m, insufficient to ensure neuromodulation, which is consistent with the absence of effects.

CONCLUSION

The tsDCS protocol applied did not change motor response to delivered stimulus, thus we observed no effect on motor spinal circuits.

SIGNIFICANCE

Future tsDCS protocols should be supported by computational models.

Changes in H-Reflex Recruitment After Trans-Spinal Direct Current Stimulation With Multiple Electrode Configurations

Trans-spinal direct current stimulation (tsDCS) is an electro-modulatory tool with possible application in the rehabilitation of spinal cord injury. TsDCS generates a small electric field, aiming to induce lasting, functional neuromodulation in the targeted neuronal networks. Earlier studies have shown significant modulatory effects after application of lumbar tsDCS. However, for clinical application, a better understanding of application specific factors is required. Our goal was to investigate the effect of different electrode configurations using lumbar spinal tsDCS on spinal excitability. We applied tsDCS (2.5 mA, 15 min) in 10 healthy subjects with three different electrode configurations: (1) Anode and cathode placed over vertebra T11, and the posterior left shoulder respectively (LSC-S) (one polarity), and (2) Both electrodes placed in equal distance (ED) (7 cm) above and below vertebra T11, investigated for two polarities (ED-Anodal/Cathodal). The soleus H-Reflex is measured before, during and after tsDCS in either electrode configuration or a sham condition. To account for genetic predispositions in response to direct current stimulation, subject BDNF genotype was assessed. Stimulation in configuration ED-Cathodal induced an amplitude reduction of the H-reflex, 30 min after tsDCS with respect to baseline, whereas none of the other configurations led to significant post intervention effects. BDNF genotype did not correlate with post intervention effects. Furthermore, we failed to replicate effects shown by a previous study, which highlights the need for a better understanding of methodological and subject specific influences on tsDCS outcome. The H-reflex depression after tsDCS (Config. ED-Cathodal) provides new insights and may foster our understanding of the working mechanism of tsDCS.

Static magnetic field stimulation applied over the cervical spinal cord can decrease corticospinal excitability in finger muscle

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Static magnetic field stimulation was delivered on cervical spinal cord.

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Trans-spinal static magnetic field stimulation (tsSMS) decreased MEP amplitudes.

•

The suppressive effect of tsSMS was not maintained after the intervention ceased.

Objective

Transcranial static magnetic field stimulation has recently been demonstrated to modulate cortical excitability. In the present study, we investigated the effect of transspinal static magnetic field stimulation (tsSMS) on excitability of the corticospinal tract.

Methods

A compact magnet for tsSMS (0.45 Tesla) or a stainless steel cylinder for sham stimulation was positioned over the neck (C8 level) of 24 able-bodied subjects for 15 min. Using 120% of the resting motor threshold transcranial magnetic stimulation intensity, motor evoked potentials (MEPs) were measured from the first digital interosseous muscle before, during, and after the tsSMS or sham intervention.

Results

Compared with baseline MEP amplitudes were decreased during tsSMS, but not during sham stimulation. Additionally, during the intervention, MEP amplitudes were lower with tsSMS than sham stimulation, although these effects did not last after the intervention ceased.

Conclusions

The results suggest that static magnetic field stimulation of the spinal cord by a compact magnet can reduce the excitability of the corticospinal tract.

Significance

Transspinal static magnetic field stimulation may be a new non-invasive neuromodulatory tool for spinal cord stimulation. Its suppressive effect may be applied to patients who have pathological hyperexcitability of the spinal neural network.

Transspinal Direct Current Stimulation Produces Persistent Plasticity in Human Motor Pathways

The spinal cord is an integration center for descending, ascending, and segmental neural signals. Noninvasive transspinal stimulation may thus constitute an effective method for concomitant modulation of local and distal neural circuits. In this study, we established changes in cortical excitability and input/output function of corticospinal and spinal neural circuits before, at 0–15 and at 30–45 minutes after cathodal, anodal, and sham transspinal direct current stimulation (tsDCS) to the thoracic region in healthy individuals. We found that intracortical inhibition was different among stimulation polarities, however remained unchanged over time. Intracortical facilitation increased after cathodal and anodal tsDCS delivered with subjects seated, and decreased after cathodal tsDCS delivered with subjects lying supine. Both cathodal and anodal tsDCS increased corticospinal excitability, yet facilitation was larger and persisted for 30 minutes post stimulation only when cathodal tsDCS was delivered with subjects lying supine. Spinal input/output reflex function was decreased by cathodal and not anodal tsDCS. These changes may be attributed to altered spontaneous neural activity and membrane potentials of corticomotoneuronal cells by tsDCS involving similar mechanisms to those mediating motor learning. Our findings indicate that thoracic tsDCS has the ability to concomitantly alter cortical, corticospinal, and spinal motor output in humans.

The effect of transcutaneous spinal direct current stimulation on corticospinal excitability in chronic incomplete spinal cord injury

OBJECTIVES

This study investigated the feasibility of modulating bilateral corticospinal excitability with different polarities of transcutaneous spinal direct current stimulation (tsDCS) in chronic, incomplete spinal cord injury (SCI).

METHODS

Six subjects with chronic incomplete SCI (>12 months post injury) participated in this crossover study. Intervention consisted of 3 sessions, separated by at least 1 week, in which each subject received the conditions cathodal, anodal, and sham tsDCS. Stimulation was delivered at 2.5 mA for 20 minutes with the active electrode positioned over the spinous processes of T10-T11 and the reference electrode over left deltoid. To measure the effects of tsDCS on corticospinal excitability, motor evoked potentials (MEPs) from transcranial magnetic stimulation were measured bilaterally from soleus before and after tsDCS.

RESULTS

Five subjects completed all 3 sessions. One subject withdrew after 2 sessions due to complications unrelated to the study. MEPs were measurable in 5 subjects. No significant differences in change of MEP amplitudes were found between the 3 conditions. However, there were trends that indicated laterality of response, particularly with cathodal tsDCS increasing corticospinal excitability contralateral to the reference electrode and decreasing corticospinal excitability ipsilateral to the reference electrode.

CONCLUSION

Corticospinal excitability may be modulated with laterality by tsDCS in individuals with chronic, incomplete SCI. Further research is needed to 1) determine whether different placement of the reference electrode can lead to uniform modulation bilaterally, and 2) reveal whether these alterations in corticospinal excitability can lead to improved movement function in individuals with chronic, incomplete SCI.

Low intensity transcranial electric stimulation: Safety, ethical, legal regulatory and application guidelines

Low intensity transcranial electrical stimulation (TES) in humans, encompassing transcranial direct current (tDCS), transcutaneous spinal Direct Current Stimulation (tsDCS), transcranial alternating current (tACS), and transcranial random noise (tRNS) stimulation or their combinations, appears to be safe. No serious adverse events (SAEs) have been reported so far in over 18,000 sessions administered to healthy subjects, neurological and psychiatric patients, as summarized here. Moderate adverse events (AEs), as defined by the necessity to intervene, are rare, and include skin burns with tDCS due to suboptimal electrode-skin contact. Very rarely mania or hypomania was induced in patients with depression (11 documented cases), yet a causal relationship is difficult to prove because of the low incidence rate and limited numbers of subjects in controlled trials. Mild AEs (MAEs) include headache and fatigue following stimulation as well as prickling and burning sensations occurring during tDCS at peak-to-baseline intensities of 1-2mA and during tACS at higher peak-to-peak intensities above 2mA. The prevalence of published AEs is different in studies specifically assessing AEs vs. those not assessing them, being higher in the former. AEs are frequently reported by individuals receiving placebo stimulation. The profile of AEs in terms of frequency, magnitude and type is comparable in healthy and clinical populations, and this is also the case for more vulnerable populations, such as children, elderly persons, or pregnant women. Combined interventions (e.g., co-application of drugs, electrophysiological measurements, neuroimaging) were not associated with further safety issues. Safety is established for low-intensity 'conventional' TES defined as <4mA, up to 60min duration per day. Animal studies and modeling evidence indicate that brain injury could occur at predicted current densities in the brain of 6.3-13A/m2 that are over an order of magnitude above those produced by tDCS in humans. Using AC stimulation fewer AEs were reported compared to DC. In specific paradigms with amplitudes of up to 10mA, frequencies in the kHz range appear to be safe. In this paper we provide structured interviews and recommend their use in future controlled studies, in particular when trying to extend the parameters applied. We also discuss recent regulatory issues, reporting practices and ethical issues. These recommendations achieved consensus in a meeting, which took place in Göttingen, Germany, on September 6-7, 2016 and were refined thereafter by email correspondence.

Moving Beyond the Brain: Transcutaneous Spinal Direct Current Stimulation in Post-Stroke Aphasia

Over the last 20 years, major advances in cognitive neuroscience have clearly shown that the language function is not restricted into the classical language areas but it involves brain regions, which had never previously considered. Indeed, recent lines of evidence have suggested that the processing of words associated to motor schemata, such as action verbs, modulates the activity of the sensorimotor cortex, which, in turn, facilitates its retrieval. To date, no studies have investigated whether the spinal cord, which is functionally connected to the sensorimotor system, might also work as an auxiliary support for language processing. We explored the combined effect of transcutaneous spinal direct current stimulation (tsDCS) and language treatment in a randomized double-blind design for the recovery of verbs and nouns in 14 chronic aphasics. During each treatment, each subject received tsDCS (20 min, 2 mA) over the thoracic vertebrae (10th vertebra) in three different conditions: (1) anodic, (2) cathodic and (3) sham, while performing a verb and noun naming tasks. Each experimental condition was run in five consecutive daily sessions over 3 weeks. Overall, a significant greater improvement in verb naming was found during the anodic condition with respect to the other two conditions, which persisted at 1 week after the end of the treatment. No significant differences were present for noun naming among the three conditions. The hypothesis is advanced that anodic tsDCS might have influenced activity along the ascending somatosensory pathways, ultimately eliciting neurophysiological changes into the sensorimotor areas which, in turn, supported the retrieval of verbs. These results further support the evidence that action words, due to their sensorimotor semantic properties, are partly represented into the sensorimotor cortex. Moreover, they also document, for the first time, that tsDCS enhances verb recovery in chronic aphasia and it may represent a promising new tool for language treatment.

Polarity-dependent improvement of maximal-effort sprint cycling performance by direct current stimulation of the central nervous system

Sprint motor performance, such as in short-distance running or cycling, gradually decreases after reaching a maximum speed or cadence. This may be attributed to the central nervous system. Brain stimulation studies have recently revealed the plastic nature of the human brain and spinal cord, but it is unclear how direct current stimulation (DCS) affects sprint motor performance. To address this issue, we investigated DCS's effect on healthy volunteers' sprint cycling performance. DCS was applied to the lumbar spinal cord (3mA) or the leg area of the motor cortex (2mA) for 15min with 3 different polarities: anodal, cathodal, and sham. After DCS, the subjects performed maximal-effort sprint cycling for 30s under a constant load. Pooled mean power during the 30s was significantly greater after cathodal transcutaneous spinal DCS to the lumbar spinal cord (tsDCS) than anodal or sham tsDCS. The improvement with cathodal stimulation was notable both 0-5 and 20-25s after the performance onset. There were no significant inter-conditional differences in peak power. Pooled mean power was significantly greater after anodal transcranial DCS to the motor cortex (tDCS) than after cathodal tDCS, although mean powers of anodal and sham tDCS were not significantly different. The increase in mean power after cathodal tsDCS could result from a reduction in central fatigue. This stimulus method might improve sprint performance.