Patterned sensory stimulation induces plasticity in reciprocal ia inhibition in humans

The effects of patterned electrical stimulation combined with voluntary contraction on spinal reciprocal inhibition in healthy individuals

The aim of this study was to examine the effects of voluntary contraction (VC) on the modulation of reciprocal inhibition induced by patterned electrical stimulation (PES) in healthy individuals. Twelve healthy volunteers participated in this study. PES was applied to the common peroneal nerve with a train of 10 pulses at 100 Hz every 2 s for 20 min. VC comprised repetitive ankle dorsiflexion at a frequency of 0.5 Hz for 20 min. All participants performed the following three tasks: (i) VC alone, (ii) PES alone, and (iii) PES combined with VC (PES+VC). Reciprocal inhibition was assessed using a soleus H-reflex conditioning-test paradigm at the time points of before, immediately after, 10 min after, 20 min after, and 30 min after the tasks. PES+VC increased the amount of reciprocal inhibition, with after-effects lasting up to 20 min. PES alone increased reciprocal inhibition and maintained the after-effects on reciprocal inhibition for 10 min, whereas VC alone increased only immediately after the task. VC could modulate the plastic changes in spinal reciprocal inhibition induced by PES in healthy individuals. PES combined with VC has a potential to modulate impaired reciprocal inhibition and it may facilitate functional recovery and improve locomotion after central nervous system lesions.

Effects of patterned peripheral nerve stimulation on soleus spinal motor neuron excitability

Spinal plasticity is thought to contribute to sensorimotor recovery of limb function in several neurological disorders and can be experimentally induced in animals and humans using different stimulation protocols. In healthy individuals, electrical continuous Theta Burst Stimulation (TBS) of the median nerve has been shown to change spinal motoneuron excitability in the cervical spinal cord as indexed by a change in mean H-reflex amplitude in the flexor carpi radialis muscle. It is unknown whether continuous TBS of a peripheral nerve can also shift motoneuron excitability in the lower limb. In 26 healthy subjects, we examined the effects of electrical TBS given to the tibial nerve in the popliteal fossa on the excitability of lumbar spinal motoneurons as measured by H-reflex amplitude of the soleus muscle evoked by tibial nerve stimulation. Continuous TBS was given at 110% of H-reflex threshold intensity and compared to non-patterned regular electrical stimulation at 15 Hz. To disclose any pain-induced effects, we also tested the effects of TBS at individual sensory threshold. Moreover, in a subgroup of subjects we evaluated paired-pulse inhibition of H-reflex. Continuous TBS at 110% of H-reflex threshold intensity induced a short-term reduction of H-reflex amplitude. The other stimulation conditions produced no after effects. Paired-pulse H-reflex inhibition was not modulated by continuous TBS or non-patterned repetitive stimulation at 15 Hz. An effect of pain on the results obtained was discarded, since non-patterned 15 Hz stimulation at 110% HT led to pain scores similar to those induced by EcTBS at 110% HT, but was not able to induce any modulation of the H reflex amplitude. Together, the results provide first time evidence that peripheral continuous TBS induces a short-lasting change in the excitability of spinal motoneurons in lower limb circuitries. Future studies need to investigate how the TBS protocol can be optimized to produce a larger and longer effect on spinal cord physiology and whether this might be a useful intervention in patients with excessive excitability of the spinal motorneurons.

Short-term effects of electrical nerve stimulation on spinal reciprocal inhibition depend on gait phase during passive stepping

A combination of electrical nerve stimulation (ENS) and passive or active cyclic movements (i.e., pedaling and stepping) has been suggested to induce stronger short-term effects in spinal circuits as compared to either intervention alone. The purpose of the present study is to determine whether the effects of ENS during passive stepping are dependent on the timing of the stimulation during the stepping cycle. A total of 10 able-bodied participants were recruited for the study. Two interventions were assessed during passive ground stepping: (1) ENS of the common peroneal nerve (CPN) during the swing phase (ENS_swing) and (2) stance phase (ENS_stance). ENS was applied at the motor threshold intensity on the tibialis anterior muscle for a total of 30 min. Spinal reciprocal inhibition (RI) was assessed by conditioning the H-reflex in the soleus muscle with electrical stimulation to the CPN before (baseline), as well as 5, 15, and 30 min after each intervention. Compared to the baseline, the amount of RI was increased 5 and 15 min after the ENS_swing intervention, whereas it was decreased after the ENS_stance intervention. This suggests that ENS has a phase-dependent effect on RI during passive stepping. Overall, the results imply that phase-dependent timing of ENS is essential for guiding plasticity in the spinal circuits.

Is quadriceps H-reflex excitability a risk factor for patellofemoral pain?

Patellofemoral pain (PFP) is one of the most common conditions in orthopedic practice while recent evidence has suggested that it may be a predisposing factor to patellofemoral osteoarthritis. In addition to biomechanical alterations associated with the pathomechanisms underlying PFP, the investigation of neurophysiological alterations has provided novel information in the understanding of the pathophysiology of PFP. For instance, women with PFP present lower amplitude of the vastus medialis (VM) H-reflexes compared to pain-free controls, which suggests that the excitability of spinal reflexes might be a promising tool for discriminating woman with PFP in clinical practice. However, the cross-sectional design of the current research does not inform whether the reduced excitability predisposes to or is the consequence of PFP. Therefore, two hypotheses can be raised: (1) the reduction in excitability of the α-motoneurons is a risk factor for PFP; Or, (2) the reduction in H-reflex excitability is a consequence of PFP due to pain. If the former hypothesis is proven correct, it may help in the early identification of individuals with PFP. If the latter, it may help understand the reduced excitability as a consequence of the long-term pain, which may be interfering in the recovery of individuals with PFP in a long-term basis. In addition, exploring such hypotheses may have direct rehabilitative and prevention implications for PFP and its putative progression to knee osteoarthritis.

Task-Specific and Functional Effects of Speed-Focused Elliptical or Motor-Assisted Cycle Training in Children With Bilateral Cerebral Palsy: Randomized Clinical Trial

BACKGROUND

Locomotor training using treadmills or robotic devices is commonly utilized to improve gait in cerebral palsy (CP); however, effects are inconsistent and fail to exceed those of equally intense alternatives. Possible limitations of existing devices include fixed nonvariable rhythm and too much limb or body weight assistance.

OBJECTIVE

To quantify and compare effectiveness of a motor-assisted cycle and a novel alternative, an elliptical, in CP to improve interlimb reciprocal coordination through intensive speed-focused leg training.

METHODS

A total of 27 children with bilateral CP, 5 to 17 years old, were randomized to 12 weeks of 20 minutes, 5 days per week home-based training (elliptical = 14; cycle = 13) at a minimum of 40 revolutions per minute, with resistance added when speed target was achieved. Primary outcomes were self-selected and fastest voluntary cadence on the devices and gait speed. Secondary outcomes included knee muscle strength, and selective control and functional mobility measures.

RESULTS

Cadence on trained but not nontrained devices increased, demonstrating task specificity of training and increased exercise capability. Mean gait speed did not increase in either group, nor did parent-reported functional mobility. Knee extensor strength increased in both. An interaction between group and time was seen in selective control with scores slightly increasing for the elliptical and decreasing for the cycle, possibly related to tighter limb coupling with cycling.

CONCLUSIONS

Task-specific effects were similarly positive across groups, but no transfer was seen to gait or function. Training dose was low (≤20 hours) compared with intensive upper-limb training recommendations and may be insufficient to produce appreciable clinical change.

Supraspinal Control Predicts Locomotor Function and Forecasts Responsiveness to Training after Spinal Cord Injury

Restoration of walking ability is an area of great interest in the rehabilitation of persons with spinal cord injury. Because many cortical, subcortical, and spinal neural centers contribute to locomotor function, it is important that intervention strategies be designed to target neural elements at all levels of the neuraxis that are important for walking ability. While to date most strategies have focused on activation of spinal circuits, more recent studies are investigating the value of engaging supraspinal circuits. Despite the apparent potential of pharmacological, biological, and genetic approaches, as yet none has proved more effective than physical therapeutic rehabilitation strategies. By making optimal use of the potential of the nervous system to respond to training, strategies can be developed that meet the unique needs of each person. To complement the development of optimal training interventions, it is valuable to have the ability to predict future walking function based on early clinical presentation, and to forecast responsiveness to training. A number of clinical prediction rules and association models based on common clinical measures have been developed with the intent, respectively, to predict future walking function based on early clinical presentation, and to delineate characteristics associated with responsiveness to training. Further, a number of variables that are correlated with walking function have been identified. Not surprisingly, most of these prediction rules, association models, and correlated variables incorporate measures of volitional lower extremity strength, illustrating the important influence of supraspinal centers in the production of walking behavior in humans.

An affordable, adaptable, and hybrid assistive device for upper-limb neurorehabilitation

The paper presents a multisensory and multimodal device for neuromuscular rehabilitation of the upper limb, designed to enable enriched rehabilitation treatment in both clinical and home environments. Originating from an existing low-cost, variable-stiffness rehabilitation device, it expands its functionalities by integrating additional modules in order to augment application scenarios and applicable clinical techniques. The newly developed system focuses on the integration of a wearable neuromuscular electrical stimulation system, a virtual rehabilitation scenario, a low-cost unobtrusive sensory system and a patient model for adapting training task parameters. It also monitors the user behavior during each single session and its evolution throughout the entire training period. The result is a modular, integrated and affordable rehabilitation device, enabling a biomechanical, neurological, and physiological-based training of patients, including innovative features currently unavailable within off-the-shelf rehabilitation devices.

Resistance training with instability is more effective than resistance training in improving spinal inhibitory mechanisms in Parkinson's disease

This study assessed 1) the effects of 12 wk of resistance training (RT) and resistance training with instability (RTI) on presynaptic inhibition (PSI) and disynaptic reciprocal inhibition (DRI) of patients with Parkinson's disease (PD); 2) the effectiveness of RT and RTI in moving PSI and DRI values of patients toward values of age-matched healthy controls (HC; Z-score analysis); and 3) associations between PSI and DRI changes and clinical outcomes changes previously published. Thirteen patients in RT group, 13 in RTI group, and 11 in a nonexercising control group completed the trial. While RT and RTI groups performed resistance exercises twice a week for 12 wk, only the RTI group used unstable devices. The soleus H reflex was used to evaluate resting PSI and DRI before and after the experimental protocol. The HC (n = 31) was assessed at pretest only. There were significant group × time interactions for PSI (P < 0.0001) and DRI (P < 0.0001). RTI was more effective than RT in increasing the levels of PSI (P = 0.0154) and DRI (P < 0.0001) at posttraining and in moving PSI [confidence interval (CI) 0.1-0.5] and DRI (CI 0.6-1.1) levels to those observed in HC. There was association between DRI and quality of life changes (r = -0.69, P = 0.008) and a strong trend toward association between PSI and postural instability changes (r = 0.60, P = 0.051) after RTI. RTI increased PSI and DRI levels more than RT, reaching the average values of the HC. Thus RTI may cause plastic changes in PSI and DRI pathways that are associated with some PD clinical outcomes.

NEW & NOTEWORTHY

Patients with Parkinson's disease (PD) have motor dysfunction. Spinal inhibitory mechanisms are important for modulating both supraspinal motor commands and sensory feedback at the spinal level. Resistance training with instability was more effective than resistance training in increasing the levels of presynaptic inhibition and disynaptic reciprocal inhibition of lower limb at rest of the patients with PD, reaching the average values of the healthy controls.

Ejaculatory training lengthens the ejaculation latency and facilitates the functioning of the spinal generator for ejaculation of rats with rapid ejaculation

A spinal pattern generator controls the ejaculatory response. Central pattern generators (CPGs) may be entrained to improve the motor patterns under their control. In the present study we tested the hypothesis that training of the spinal generator for ejaculation (SGE) by daily copulation until ejaculation, could promote substantive changes in its functioning permitting a better SGE control of the genital motor pattern of ejaculation (GMPE) and, as a consequence, a normalization of the ejaculation latency of rats with rapid ejaculation. To that aim, we evaluated in sexually experienced male rats with rapid ejaculation (1) the effects of daily copulation to ejaculation, following different entrainment schedules, on their ejaculation latencies, (2) the impact of these different ejaculatory entrainment schedules upon the parameters of the GMPE and (3) the possible emergence of persistent changes in the functioning of the SGE associated to the daily ejaculation entrainment schedules. The data obtained show that intense ejaculatory training of rats with rapid ejaculation lengthens the ejaculation latency during copulation and augments the ejaculatory capacity of the SGE in this population when spinalized. Thus, present data reveal that like other CPGs, the SGE can be trained and put forward that training of the SGE by daily copulation to ejaculation might be a promising alternative that should be taken into consideration for the treatment of premature ejaculation.

Continuous positive airway pressure treatment does not normalize the prolonged reflex inhibition to inspiratory loading in obstructive sleep apnea

In obstructive sleep apnea (OSA), the short-latency inhibitory reflex (IR) of inspiratory muscles to airway occlusion is prolonged in proportion to the severity of the OSA. The mechanism underlying the prolongation may relate to chronic inspiratory muscle loading due to upper airway obstruction or sensory changes due to chronic OSA-mediated inflammation. Continuous positive airway pressure (CPAP) therapy prevents upper airway obstruction and reverses inflammation. We therefore tested whether CPAP therapy normalized the IR abnormality in OSA. The IR responses of scalene muscles to brief airway occlusion were measured in 37 adult participants with untreated, mostly severe, OSA, of whom 13 were restudied after the initiation of CPAP therapy (usage >4 h/night). Participants received CPAP treatment as standard clinical care, and the mean CPAP usage between initial and subsequent studies was 6.5 h/night (range 4.1-8.8 h/night) for a mean of 19 mo (range 4–41 mo). The duration of the IR in scalene muscles in response to brief (250 ms) inspiratory loading was confirmed to be prolonged in the participants with OSA. The IR was assessed before and after CPAP therapy. CPAP treatment did not normalize the prolonged duration of the IR to airway occlusion (60 ± 21 ms pretreatment vs. 59 ± 18 ms posttreatment, means ± SD) observed in participants with severe OSA. This suggests that the prolongation of IR reflects alterations in the reflex pathway that may be irreversible, or a specific disease trait.

Modulation of spinal inhibitory reflexes depends on the frequency of transcutaneous electrical nerve stimulation in spastic stroke survivors

Neurophysiological studies in healthy subjects suggest that increased spinal inhibitory reflexes from the tibialis anterior (TA) muscle to the soleus (SOL) muscle might contribute to decreased spasticity. While 50 Hz is an effective frequency for transcutaneous electrical nerve stimulation (TENS) in healthy subjects, in stroke survivors, the effects of TENS on spinal reflex circuits and its appropriate frequency are not well known. We examined the effects of different frequencies of TENS on spinal inhibitory reflexes from the TA to SOL muscle in stroke survivors. Twenty chronic stroke survivors with ankle plantar flexor spasticity received 50-, 100-, or 200-Hz TENS over the deep peroneal nerve (DPN) of the affected lower limb for 30 min. Before and immediately after TENS, reciprocal Ia inhibition (RI) and presynaptic inhibition of the SOL alpha motor neuron (D1 inhibition) were assessed by adjusting the unconditioned H-reflex amplitude. Furthermore, during TENS, the time courses of spinal excitability and spinal inhibitory reflexes were assessed via the H-reflex, RI, and D1 inhibition. None of the TENS protocols affected mean RI, whereas D1 inhibition improved significantly following 200-Hz TENS. In a time-series comparison during TENS, repeated stimulation did not produce significant changes in the H-reflex, RI, or D1 inhibition regardless of frequency. These results suggest that the frequency-dependent effect of TENS on spinal reflexes only becomes apparent when RI and D1 inhibition are measured by adjusting the amplitude of the unconditioned H-reflex. However, 200-Hz TENS led to plasticity of synaptic transmission from the antagonist to spastic muscles in stroke survivors.

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.

The effects of anodal transcranial direct current stimulation and patterned electrical stimulation on spinal inhibitory interneurons and motor function in patients with spinal cord injury

Supraspinal excitability and sensory input may play an important role for the modulation of spinal inhibitory interneurons and functional recovery among patients with incomplete spinal cord injury (SCI). Here, we investigated the effects of anodal transcranial direct current stimulation (tDCS) combined with patterned electrical stimulation (PES) on spinal inhibitory interneurons in patients with chronic incomplete SCI and in healthy individuals. Eleven patients with incomplete SCI and ten healthy adults participated in a single-masked, sham-controlled crossover study. PES involved stimulating the common peroneal nerve with a train of ten 100 Hz pulses every 2 s for 20 min. Anodal tDCS (1 mA) was simultaneously applied to the primary motor cortex that controls the tibialis anterior muscle. We measured reciprocal inhibition and presynaptic inhibition of a soleus H-reflex by stimulating the common peroneal nerve prior to tibial nerve stimulation, which elicits the H-reflex. The inhibition was assessed before, immediately after, 10 min after and 20 min after the stimulation. Compared with baseline, simultaneous application of anodal tDCS with PES significantly increased changes in disynaptic reciprocal inhibition and long-latency presynaptic inhibition in both healthy and SCI groups for at least 20 min after the stimulation (all, p < 0.001). In patients with incomplete SCI, anodal tDCS with PES significantly increased the number of ankle movements in 10 s at 20 min after the stimulation (p = 0.004). In conclusion, anodal tDCS combined with PES could induce spinal plasticity and improve ankle movement in patients with incomplete SCI.

Lower Amplitude of the Hoffmann Reflex in Women With Patellofemoral Pain: Thinking Beyond Proximal, Local, and Distal Factors

OBJECTIVES

To investigate whether vastus medialis (VM) Hoffmann reflexes (H-reflexes) differ on the basis of the presence or absence of patellofemoral pain (PFP) and to assess the capability of VM H-reflex measurements in accurately discriminating between women with and without PFP.

DESIGN

Cross-sectional study.

SETTING

Laboratory of biomechanics and motor control.

PARTICIPANTS

Women (N=30) aged 18 to 35 years were recruited, consisting of 2 groups: women with PFP (n=15) and asymptomatic controls (n=15).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Maximum evoked responses were obtained by electrical stimulation applied to the femoral nerve, and peak-to-peak amplitudes of maximal Hoffmann reflex (Hmax) and maximal motor wave (Mmax) ratios were calculated. Independent samples t tests were performed to identify differences between groups, and a receiver operating characteristic curve was constructed to assess the discriminatory capability of VM H-reflex measurements.

RESULTS

VM Hmax/Mmax ratios were significantly lower in participants with PFP than in pain-free participants (P=.007). In addition, the VM Hmax/Mmax ratios presented large and balanced discriminatory capability values (sensitivity, 73%; specificity, 67%).

CONCLUSIONS

This study is the first to show that VM H-reflexes are lower in women with PFP than in asymptomatic controls. Therefore, increasing the excitation of the spinal cord in PFP participants may be essential to maintaining the gains acquired during the rehabilitation programs.

The efficacy of neuromuscular electrical stimulation with alternating currents in the kilohertz frequency to stimulate gait rhythm in rats following spinal cord injury

Background

Rehabilitation facilitates the reorganization of residual/regenerated neural pathways and is key in improving motor function following spinal cord injury. Neuromuscular electrical stimulation (NMES) has been reported as being clinically effective. Although it can be used after the acute phase post-injury, the optimal stimulation conditions to improve motor function remain unclear. In this paper, we examined the effectiveness of NMES with alternating currents in the kilohertz (kHz) frequency in gait rhythm stimulation therapy.

Methods

Tests were performed using 20 mature female Fischer rats. Incomplete spinal cord injuries (T9 level) were made with an IH impactor using a force of 150 kdyn, and NMES was administered for 3 days from the 7th day post-injury. The needle electrodes were inserted percutaneously near the motor point of each muscle in conscious rats, and each muscle on the left and right leg was stimulated for 15 min at two frequencies, 75 Hz and 8 kHz, to induce a gait rhythm. Motor function was evaluated using Basso, Beattie, Bresnahan (BBB) scores and three-dimensional (3D) gait analysis. Rats were divided into four groups (5 rats/group), including the NMES treatment 75-Hz group (iSCI-NMES 75 Hz), 8-kHz group (iSCI-NMES 8 kHz), injury control group (iSCI-NT), and normal group (Normal-CT), and were compared.

Results

There was no significant difference in BBB scores among the three groups. In 3D gait analysis, compared with the injury control group, the 8-kHz group showed a significant improvement in synergistic movement of both hindlimbs.

Conclusion

We suggest that kHz stimulation is effective in gait rhythm stimulation using NMES.

Reciprocal inhibition becomes facilitation after spinal cord injury: clinical application of a system identification approach

Alteration in spinal inputs from descending pathways following spinal cord injury (SCI) affects different mechanisms including reciprocal Ia inhibition. However, whether there is a consistent pattern of change in reciprocal inhibition following SCI is uncertain. Typical attempts to evaluate reciprocal inhibition have been restricted to electrophysiological measurements, which may have limited translation to function. Our objective was to address the uncertainty regarding changes in reciprocal inhibition after SCI by quantitatively evaluating reciprocal inhibition of ankle extensors from ankle flexors using our novel, more functionally relevant system identification approach. To evaluate reciprocal inhibition using the system identification technique, a series of small-amplitude PseudoRandom Binary Sequence (PRBS) perturbations were applied to the ankle when subjects contracted their dorsiflexors. Depression of reflex stiffness with tibialis anterior (TA) activation was evaluated as reciprocal inhibition. Our results showed that reflex stiffness decreased continuously as dorsiflexor torque increased in the healthy control subjects whereas it remained almost unchanged in the SCI subjects, indicating the absence of reciprocal inhibition in patients. This pattern was consistent with the results obtained from electrophysiological measures in a exploratory control experiment revealing depression of the control H-reflex but no change to the SCI H-reflex. These findings suggest that our system identification mechanical technique is a reliable and valid approach for evaluating reciprocal inhibition. Furthermore, our results demonstrate that reciprocal inhibition can diminish or change to reciprocal facilitation after SCI, which in turn can result in reflex hyperexcitability and unwanted activity of ankle extensors triggered by TA activity. This suggests that reciprocal facilitation may play a major role in pathophysiology of spasticity and impaired function.

Short-term effect of electrical nerve stimulation on spinal reciprocal inhibition during robot-assisted passive stepping in humans

The purpose of this study was to investigate the effect of electrical stimulation to the common peroneal nerve (CPN) on the spinal reflex and reciprocal inhibition (RI) during robot-assisted passive ground stepping (PGS) in healthy subjects. Five interventions were applied for 30 min in healthy subjects: PGS alone; strong CPN stimulation [50% of the maximal tibialis anterior (TA) M-wave, functional electrical stimulation (FES)] alone; weak CPN stimulation [just above the MT for the TA muscle, therapeutic electrical stimulation (TES)] alone; PGS with FES; and PGS with TES. FES and TES were applied intermittently to the CPN at 25 Hz. The soleus (Sol) H-reflex and RI, which was assessed by conditioning the Sol H-reflex with CPN stimulation, were investigated before (baseline), and 5, 15 and 30 min after each intervention. The amplitudes of the Sol H-reflex were not significantly different after each intervention as compared with the baseline values. The amounts of RI were significantly decreased 5 min after PGS with FES as compared with the baseline values, whereas they were significantly increased 5 and 15 min after PGS with TES. The other interventions did not affect the amount of RI. These results suggest that interventions that combined PGS with CPN stimulation changed the spinal RI in an intensity-dependent manner.

Intensity sensitive modulation effect of theta burst form of median nerve stimulation on the monosynaptic spinal reflex

The effects of electrical stimulation of median nerve with a continuous theta burst pattern (EcTBS) on the spinal H-reflex were studied. Different intensities and durations of EcTBS were given to the median nerve to 11 healthy individuals. The amplitude ratio of the H-reflex to maximum M wave (H/M ratio), corticospinal excitability and inhibition measured using motor evoked potentials (MEPs), short-interval intracortical inhibition and facilitation (SICI/ICF), spinal reciprocal inhibition (RI), and postactivation depression (PAD) were measured before and after EcTBS. In result, the H/M ratio was reduced followed by EcTBS at 90% H-reflex threshold, and the effect lasted longer after 1200 pulses than after 600 pulses of EcTBS. In contrast, EcTBS at 110% threshold facilitated the H/M ratio, while at 80% threshold it had no effect. Maximum M wave, MEPs, SICI/ICF, RI, and PAD all remained unchanged after EcTBS. In conclusion, EcTBS produced lasting effects purely on the H-reflex, probably, through effects on postsynaptic plasticity. The effect of EcTBS depends on the intensity and duration of stimulation. EcTBS is beneficial to research on mechanisms of human plasticity. Moreover, its ability to modulate spinal excitability is expected to have therapeutic benefits on neurological disorders involving spinal cord dysfunction.

Locomotor training improves reciprocal and nonreciprocal inhibitory control of soleus motoneurons in human spinal cord injury

Pathologic reorganization of spinal networks and activity-dependent plasticity are common neuronal adaptations after spinal cord injury (SCI) in humans. In this work, we examined changes of reciprocal Ia and nonreciprocal Ib inhibition after locomotor training in 16 people with chronic SCI. The soleus H-reflex depression following common peroneal nerve (CPN) and medial gastrocnemius (MG) nerve stimulation at short conditioning-test (C-T) intervals was assessed before and after training in the seated position and during stepping. The conditioned H reflexes were normalized to the unconditioned H reflex recorded during seated. During stepping, both H reflexes were normalized to the maximal M wave evoked at each bin of the step cycle. In the seated position, locomotor training replaced reciprocal facilitation with reciprocal inhibition in all subjects, and Ib facilitation was replaced by Ib inhibition in 13 out of 14 subjects. During stepping, reciprocal inhibition was decreased at early stance and increased at midswing in American Spinal Injury Association Impairment Scale C (AIS C) and was decreased at midstance and midswing phases in AIS D after training. Ib inhibition was decreased at early swing and increased at late swing in AIS C and was decreased at early stance phase in AIS D after training. The results of this study support that locomotor training alters postsynaptic actions of Ia and Ib inhibitory interneurons on soleus motoneurons at rest and during stepping and that such changes occur in cases with limited or absent supraspinal inputs.

Post-stroke balance rehabilitation under multi-level electrotherapy: a conceptual review

Stroke is caused when an artery carrying blood from heart to an area in the brain bursts or a clot obstructs the blood flow thereby preventing delivery of oxygen and nutrients. About half of the stroke survivors are left with some degree of disability. Innovative methodologies for restorative neurorehabilitation are urgently required to reduce long-term disability. The ability of the nervous system to respond to intrinsic or extrinsic stimuli by reorganizing its structure, function, and connections is called neuroplasticity. Neuroplasticity is involved in post-stroke functional disturbances, but also in rehabilitation. It has been shown that active cortical participation in a closed-loop brain machine interface (BMI) can induce neuroplasticity in cortical networks where the brain acts as a controller, e.g., during a visuomotor task. Here, the motor task can be assisted with neuromuscular electrical stimulation (NMES) where the BMI will act as a real-time decoder. However, the cortical control and induction of neuroplasticity in a closed-loop BMI is also dependent on the state of brain, e.g., visuospatial attention during visuomotor task performance. In fact, spatial neglect is a hidden disability that is a common complication of stroke and is associated with prolonged hospital stays, accidents, falls, safety problems, and chronic functional disability. This hypothesis and theory article presents a multi-level electrotherapy paradigm toward motor rehabilitation in virtual reality that postulates that while the brain acts as a controller in a closed-loop BMI to drive NMES, the state of brain can be can be altered toward improvement of visuomotor task performance with non-invasive brain stimulation (NIBS). This leads to a multi-level electrotherapy paradigm where a virtual reality-based adaptive response technology is proposed for post-stroke balance rehabilitation. In this article, we present a conceptual review of the related experimental findings.

Effect of remote sensory noise on hand function post stroke

Hand motor impairment persists after stroke. Sensory inputs may facilitate recovery of motor function. This pilot study tested the effectiveness of tactile sensory noise in improving hand motor function in chronic stroke survivors with tactile sensory deficits, using a repeated measures design. Sensory noise in the form of subthreshold, white noise, mechanical vibration was applied to the wrist skin during motor tasks. Hand dexterity assessed by the Nine Hole Peg Test and the Box and Block Test and pinch strength significantly improved when the sensory noise was turned on compared with when it was turned off in chronic stroke survivors. The subthreshold sensory noise to the wrist appears to induce improvements in hand motor function possibly via neuronal connections in the sensoriomotor cortex. The approach of applying concomitant, unperceivable mechanical vibration to the wrist during hand motor tasks is easily adoptable for clinic use as well as unsupervised home use. This pilot study suggests a potential for a wristband-type assistive device to complement hand rehabilitation for stroke survivors with sensorimotor deficit.

Therapeutic effects of functional electrical stimulation on gait in individuals post-stroke

Functional electrical stimulation (FES) to lower extremity (LE) muscles is used by individuals post-stroke as an alternative to mechanical orthotic devices during gait or as a training modality during rehabilitation. Technological developments which improve the feasibility, accessibility and effectiveness of FES systems as orthotic and training devices, highlight the potential of FES for rehabilitating LE function in individuals post-stroke. This study presents a systematic review of the carryover effects of LE FES to motor performance when stimulation is not applied (therapeutic effects) in subjects post-stroke. A description of advances in FES technologies, with an emphasis on systems designed to promote LE function is included, and mechanisms that may be associated with the observed therapeutic effects are discussed. Eligible studies were reviewed for methodological quality, population, intervention and outcome characteristics. Therapeutic effects of FES were consistently demonstrated at the body function and activity levels when it was used as a training modality. Compared to matched treatments that did not incorporate FES, no definite conclusions can be drawn regarding the superiority of FES. When FES was used as an alternative to an orthotic device, it had no superior therapeutic effects at the activity level, yet patients still seemed to prefer it.

Effect of neuromuscular electrical stimulation intensity over the tibial nerve trunk on triceps surae muscle fatigue

PURPOSE

This study was designed to investigate whether the intensity modulation of a neuromuscular electrical stimulation (NMES) protocol delivered over the nerve trunk of the plantar flexors would lead to differential peripheral and central contributions of muscle fatigue.

METHODS

Three fatiguing isometric protocols of the plantar flexors matched for the same amount of isometric torque-time integral (TTI) were randomly performed including a volitional protocol at 20 % of the maximal voluntary contraction (MVC) and two NMES protocols (one at constant intensity, CST; the other at intensity level progressively adjusted to maintain 20 % of MVC, PROG).

RESULTS

No time x protocol interaction was found for any of the variables. The MVC decreased similarly (≈12 %, p < 0.001) after all protocols, so did the potentiated twitch responses (p = 0.001). Although voluntary activation of the plantar flexors did not change, maximal H-reflex to M-wave ratio of the soleus (SOL) and the gastrocnemius medialis (GM) muscles showed an overall increase (SOL: p = 0.037, GM: p = 0.041), while it remained stable for the gastrocnemius lateralis muscle (p = 0.221). A main time effect was observed only for the SOL maximal V-wave to the superimposed M-wave ratio (p = 0.024) and to the superimposed H-reflex (p = 0.008). While similar central and peripheral adaptations were observed after the three fatiguing protocols, the individual contribution of the three different triceps surae muscles was different.

CONCLUSION

Whether the current intensity was increased or not, the adaptations after a NMES protocol yield to similar muscle fatigue adaptations as voluntary contractions likely through similar pathways matching a similar TTI.

Technological advances in interventions to enhance poststroke gait

Neurologic rehabilitation interventions may be either therapeutic or compensatory. Included in this article are lower extremity functional electrical stimulation, body weight-supported treadmill training, and lower extremity robotic-assisted gait training. These poststroke gait training therapies are predicated on activity-dependent neuroplasticity. All three interventions have been trialed extensively in research and clinical settings to show a positive effect on various gait parameters and measures of walking performance. This article provides an overview of evidence-based research that supports the efficacy of these three interventions to improve gait, as well as providing perspective on future developments to enhance poststroke gait in neurologic rehabilitation.

Accelerating locomotor recovery after incomplete spinal injury

A traumatic spinal injury can destroy cells, irreparably damage axons, and trigger a cascade of biochemical responses that increase the extent of injury. Although damaged central nervous system axons do not regrow well naturally, the distributed nature of the nervous system and its capacity to adapt provide opportunities for recovery of function. It is apparent that activity-dependent plasticity plays a role in this recovery and that the endogenous response to injury heightens the capacity for recovery for at least several weeks postinjury. To restore locomotor function, researchers have investigated the use of treadmill-based training, robots, and electrical stimulation to tap into adaptive activity-dependent processes. The current challenge is to maximize the degree of functional recovery. This manuscript reviews the endogenous neural system response to injury, and reviews data and presents novel analyses of these from a rat model of contusion injury that demonstrates how a targeted intervention can accelerate recovery, presumably by engaging processes that underlie activity-dependent plasticity.

Plasticity of corticospinal neural control after locomotor training in human spinal cord injury

Spinal lesions substantially impair ambulation, occur generally in young and otherwise healthy individuals, and result in devastating effects on quality of life. Restoration of locomotion after damage to the spinal cord is challenging because axons of the damaged neurons do not regenerate spontaneously. Body-weight-supported treadmill training (BWSTT) is a therapeutic approach in which a person with a spinal cord injury (SCI) steps on a motorized treadmill while some body weight is removed through an upper body harness. BWSTT improves temporal gait parameters, muscle activation patterns, and clinical outcome measures in persons with SCI. These changes are likely the result of reorganization that occurs simultaneously in supraspinal and spinal cord neural circuits. This paper will focus on the cortical control of human locomotion and motor output, spinal reflex circuits, and spinal interneuronal circuits and how corticospinal control is reorganized after locomotor training in people with SCI. Based on neurophysiological studies, it is apparent that corticospinal plasticity is involved in restoration of locomotion after training. However, the neural mechanisms underlying restoration of lost voluntary motor function are not well understood and translational neuroscience research is needed so patient-orientated rehabilitation protocols to be developed.

Cutaneous inputs from the back abolish locomotor-like activity and reduce spastic-like activity in the adult cat following complete spinal cord injury

Spasticity is a condition that can include increased muscle tone, clonus, spasms, and hyperreflexia. In this study, we report the effect of manually stimulating the dorsal lumbosacral skin on spontaneous locomotor-like activity and on a variety of reflex responses in 5 decerebrate chronic spinal cats treated with clonidine. Cats were spinalized 1 month before the terminal experiment. Stretch reflexes were evoked by stretching the left triceps surae muscles. Crossed reflexes were elicited by electrically stimulating the right tibial or superficial peroneal nerves. Wind-up of reflex responses was evoked by electrically stimulating the left tibial or superficial peroneal nerves. We found that pinching the skin of the back abolished spontaneous locomotor-like activity. We also found that back pinch abolished the rhythmic activity observed during reflex testing without eliminating the reflex responses. Some of the rhythmic episodes of activity observed during reflex testing were consistent with clonus with an oscillation frequency greater than 3 Hz. Pinching the skin of the back effectively abolished rhythmic activity occurring spontaneously or evoked during reflex testing, irrespective of oscillation frequency. The results are consistent with the hypothesis that locomotion and clonus are produced by common central pattern-generators. Stimulating the skin of the back could prove helpful in managing undesired rhythmic activity in spinal cord-injured humans.

Effect of airway inflammation on short-latency reflex inhibition to inspiratory loading in human scalene muscles

The short-latency reflex inhibition of human inspiratory muscles produced by loading is prolonged in asthma and obstructive sleep apnoea, both diseases involving airway and systemic inflammation. Both diseases also involve repetitive inspiratory loading. Although airway mucosal afferents are not critical components of the normal reflex arc, during airway inflammation, prolongation of the reflex may be caused by altered mucosal afferent sensitivity, or altered central processing of their inputs. We hypothesised that acute viral airway inflammation would replicate the reflex abnormality. The reflex was tested in 9 subjects with a "common cold" during both the acute infection and when well. Surface electrodes recorded electromyographic (EMG) activity bilaterally from scalene muscles. Latencies of the inhibitory response (IR) did not differ significantly (IR peak 67 vs 70 ms (p=0.12), and IR offset 87 vs 90 ms (p=0.23), between the inflamed and well conditions, respectively). There was no difference in any measure of the size of the reflex inhibition.

Spinal inhibition of descending command to soleus motoneurons is removed prior to dorsiflexion

It has recently been demonstrated that soleus motor-evoked potentials (MEPs) are facilitated prior to the onset of dorsiflexion. The purpose of this study was to examine if this could be explained by removal of spinal inhibition of the descending command to soleus motoneurons. To test this, we investigated how afferent inputs from the tibialis anterior muscle modulate the corticospinal activation of soleus spinal motoneurons at rest, during static contraction and prior to movement. MEPs activated by transcranial magnetic stimulation (TMS) and Hoffmann reflexes (H-reflexes), activated by electrical stimulation of the posterior tibial nerve (PTN), were conditioned by prior stimulation of the common peroneal nerve (CPN) at a variety of conditioning-test (CT) intervals. MEPs in the precontracted soleus muscle were inhibited when the TMS pulse was preceded by CPN stimulation with a CT interval of 35 ms, and they were facilitated for CT intervals of 50-55 ms. A similar inhibition of the soleus H-reflex was not observed. To investigate which descending pathways might be responsible for the afferent-evoked inhibition and facilitation, we examined the effect of CPN stimulation on short-latency facilitation (SLF) and long-latency facilitation (LLF) of the soleus H-reflex induced by a subthreshold TMS pulse at different CT intervals. SLF is known to reflect the excitability of the fastest conducting, corticomotoneuronal cells whereas LLF is believed to be caused by more indirect descending pathways. At CT intervals of 40-45 ms, the LLF was significantly more inhibited compared to the SLF when taking the effect on the H-reflex into account. Finally, we investigated how the CPN-induced inhibition and facilitation of the soleus MEP were modulated prior to dorsiflexion. Whereas the late facilitation (CT interval: 55 ms) was similar prior to dorsiflexion and at rest, no inhibition could be evoked at the earlier latency (CT interval: 35 ms) prior to onset of dorsiflexion. The observation that the CPN-induced inhibition of soleus MEPs disappears prior to onset of dorsiflexion may explain why soleus MEPs are facilitated prior to onset of dorsiflexion contraction. A possible mechanism involves the removal of inhibition of the descending command to the motoneurons at a spinal interneuronal level because the inhibition was seen in LLF and not in SLF, and the MEP inhibition was not observed in the H-reflex. The data illustrate that spinal interneuronal pathways modify descending commands to human spinal motoneurons and influence the size of MEPs elicited by TMS.

Does sensory transcutaneous electrical stimulation enhance motor recovery following a stroke? A systematic review

BACKGROUND

Somatosensory input may lead to long-lasting cortical plasticity enhanced by motor recovery in patients with neurological impairments. Sensory transcutaneous electrical stimulation (TENS) is a relatively risk-free and easy-to-implement modality for rehabilitation.

OBJECTIVE

The authors systematically examine the effects of sensory TENS on motor recovery after stroke.

METHODS

Eligible randomized or quasi-randomized trials were identified via searches of computerized databases. Two assessors reviewed independently the eligibility and methodological quality of the retrieved articles.

RESULTS

In all, 15 articles satisfied the inclusion criteria. Methodological quality was generally good, with a mean (standard deviation) PEDro score of 6.7/10 (1.2). Although the majority of studies reported significant effects on at least 1 outcome measure, effect sizes were generally small. Meta-analysis could not be performed for the majority of outcome measures because of variability between studies and insufficient data. A moderate effect was determined for force production of the ankle dorsiflexors and for the Timed Up and Go test.

CONCLUSIONS

Sensory stimulation via TENS may be beneficial to enhance aspects of motor recovery following a stroke, particularly when used in combination with active training. Because of the great variability between studies, particularly in terms of the timing of the intervention after the stroke, the outcome measures used, and the stimulation protocols, insufficient data are available to provide guidelines about strategies and efficacy.

Transcranial direct current stimulation modulates the spinal plasticity induced with patterned electrical stimulation

OBJECTIVE

Patterned sensory electrical stimulation (PES) has been shown to induce plasticity in spinal reciprocal Ia inhibition of the calf muscles. To study the cortical modulation of spinal plasticity, we examined the effects of giving transcranial direct current stimulation (tDCS) to the motor cortex before PES.

METHODS

Seven healthy volunteers participated in this study. PES involved stimulating the left common peroneal nerve at the fibular head with a train of 10 pulses at 100 Hz every 1.5s for 20 min using an intensity equal to the motor threshold of the tibialis anterior. tDCS was applied for 10 min before PES. For anodal stimulation, the electrode was placed over the motor cortex, and the cathodal electrode over the contralateral supraorbital area. For cathodal stimulation, the electrodes were reversed. Reciprocal inhibition was assessed using a soleus H reflex conditioning-test paradigm.

RESULTS

PES increased disynaptic reciprocal inhibition from the peroneal nerve to the soleus H reflex. When cathodal tDCS was applied before PES, PES no longer increased reciprocal inhibition.

CONCLUSIONS

Applying tDCS before PES modulated the effects of PES on spinal reciprocal inhibition in a polarity specific manner.

SIGNIFICANCE

We suggest that the motor cortex may play a role in spinal plasticity.

Immediate effect of transcutaneous electrical nerve stimulation on spasticity in patients with spinal cord injury

Objective: To investigate the immediate effect of transcutaneous electrical nerve stimulation (TENS) on spasticity in patients with spinal cord injury.

Design: Randomized controlled trial.

Setting: Extended rehabilitation centre.

Subjects and intervention: Eighteen subjects with spinal cord injury and symptoms of spasticity over lower limbs were randomly assigned to receive either 60 minutes of active TENS (0.25 ms, 100 Hz, 15 mA) or 60 minutes of placebo non-electrically stimulated TENS over the common peroneal nerve.

Outcome measures: Composite Spasticity Score was used to assess the spasticity level of ankle plantar flexors immediately before and after TENS application. Composite Spasticity Score consisted of Achilles tendon jerks, resistance to full-range passive ankle dorsiflexion and ankle clonus. Between-group statistical differences of reduction of Composite Spasticity Score, Achilles tendon jerks, resistance to full-range passive ankle dorsiflexion and ankle clonus were calculated using the Mann—Whitney test. Within-group statistical differences of Composite Spasticity Score, Achilles tendon jerks, resistance to full-range passive ankle dorsiflexion and ankle clonus were calculated using the Wilcoxon signed ranks test.

Results: Significant reductions were shown in Composite Spasticity Score by 29.5% (p = 0.017), resistance to full-range passive ankle dorsiflexion by 31.0% (p = 0.024) and ankle clonus by 29.6% (p = 0.023) in the TENS group but these reductions were not found in the placebo TENS group. The between-group differences of both Composite Spasticity Score and resistance to full-range passive ankle dorsiflexion were significant (p = 0.027 and p = 0.024, respectively).

Conclusion: This study showed that a single session of TENS could immediately reduce spasticity.

Increased Pinch Strength in Acute and Subacute Stroke Patients After Simultaneous Median and Ulnar Sensory Stimulation

Background. Peripheral nerve stimulation may induce cortical adaptations as it improves pinch strength in chronic stroke patients immediately after stimulation. Objective. Test the effects of peripheral sensory stimulation on pinch strength in patients with acute and subacute stroke. Methods. Stroke patients (N = 20) who had onset less than 6 months previously and could voluntarily pinch the thumb to the index finger participated in a randomized, single-blinded, controlled study. Ten patients received 2 hours of simultaneous electrical stimulation over the median and ulnar nerves at the wrist to the level of appreciating paresthesias (peripheral sensory stimulation group). Ten control patients received stimulation to the level of perception (sham-control group). Pinch strength of the thumb pad to tip and to lateral side of the index finger of the paretic hand and the Action Research Arm test were tested before and immediately after the stimulation. Results. Lateral and tip pinch strength were significantly increased in both groups ( P < .05). Mean ± SD of increased lateral pinch strength of peripheral sensory stimulation and sham-control groups were 1.24 ± 0.54 pounds and 0.20 ± 0.28 pounds, respectively. Mean ± SD of increased tip pinch strength of peripheral sensory stimulation and sham-control groups were 1.00 ± 0.72 pounds and 0.37 ± 0.36 pounds, respectively. Increase pinch strength of the peripheral sensory stimulation group was greater than the sham-control group, with significant difference ( P < .05). The Action Research Arm test was not significantly changed after stimulation in both groups ( P > .05). Conclusion. Peripheral sensory stimulation of the paretic hand may increase pinch strength of acute and subacute stroke patients immediately after stimulation.

Increased central facilitation of antagonist reciprocal inhibition at the onset of dorsiflexion following explosive strength training

At the onset of dorsiflexion disynaptic reciprocal inhibition (DRI) of soleus motoneurons is increased to prevent activation of the antagonistic plantar flexors. This is caused by descending facilitation of transmission in the DRI pathway. Because the risk of eliciting stretch reflexes in the ankle plantar flexors at the onset of dorsiflexion is larger the quicker the movement, it was hypothesized that DRI may be increased when subjects are trained to perform dorsiflexion movements as quickly as possible For this purpose, 14 healthy human subjects participated in explosive strength training of the ankle dorsiflexor muscles 3 times a week for 4 wk. Test sessions were conducted before, shortly after, and 2 wk after the training period. The rate of torque development measured at 30, 50, 100, and 200 ms after onset of voluntary explosive isometric dorsiflexion increased by 24–33% ( P < 0.05). DRI was measured as the depression of the soleus H reflex following conditioning stimulation of the peroneal nerve (1.1 × motor threshold) at an interval of 2–3 ms. At the onset of dorsiflexion the amount of DRI measured relative to DRI at rest increased significantly from 6% before the training to 22% after the training ( P < 0.05). We speculate that DRI at the onset of movement may be increased in healthy subjects following explosive strength training to ensure efficient suppression of the antagonist muscles as the dorsiflexion movement becomes faster.