Effects of cerebellar transcranial direct current stimulation on the excitability of spinal motor neurons and vestibulospinal tract in healthy individuals.

Cerebellar transcranial direct current stimulation (ctDCS) modulates cerebellar cortical excitability in a polarity-dependent manner and affects inhibitory pathways from the cerebellum. The cerebellum modulates spinal reflex excitability via the vestibulospinal tract and other pathways projecting to the spinal motor neurons; however, the effects of ctDCS on the excitability of spinal motor neurons and vestibulospinal tract remain unclear. The experiment involved 13 healthy individuals. ctDCS (sham-ctDCS, anodal-ctDCS, and cathodal-ctDCS) was applied to the cerebellar vermis at 2 mA with an interval of at least 3 days between each condition. We measured the maximal M-wave (Mmax) and maximal H-reflex (Hmax) in the right soleus muscle to assess the excitability of spinal motor neurons. We applied galvanic vestibular stimulation (GVS) for 200 ms at 100 ms before tibial nerve stimulation to measure Hmax conditioned by GVS (GVS-Hmax) and calculated the change rate of Hmax by GVS as the excitability of vestibulospinal tract. We measured the Mmax, Hmax, and GVS-Hmax before, during, and after ctDCS in the sitting posture. No main effects of tDCS condition, main effects of time, or interaction effects were observed in Hmax/Mmax or the change rate of Hmax by GVS. It has been suggested that ctDCS does not affect the excitability of spinal motor neurons and vestibulospinal tract, as measured by neurophysiological methods, such as the H-reflex, in healthy individuals in a sitting posture. Effect of ctDCS on other descending pathways to spinal motor neurons, the neurological mechanism of tDCS and the cerebellar activity during the experiment may have contributed to these results. Therefore, we need to investigate the involvement of the cerebellum in Hmax/Mmax and the change rate of Hmax by GVS under different neuromodulation techniques and postural conditions.

Effect of muscle length on the modulation of H reflex and inhibitory mechanisms of Ia afferent discharges during passive muscle lengthening.

The effectiveness of activated Ia afferents to discharge ᵯC-motoneurons is decreased during passive muscle lengthening compared with static and shortening muscle conditions. Evidence suggests that these regulations are explained by (1) greater post-activation depression induced by homosynaptic post-activation depression (HPAD) and (2) primary afferent depolarization (PAD). It remains uncertain whether muscle length impacts the muscle lengthening-related aspect of regulation of the effectiveness of activated Ia afferents to discharge ᵯC-motoneurons, HPAD, PAD and heteronymous Ia facilitation (HF). We conducted a study involving 15 healthy young individuals. We recorded conditioned or non-conditioned soleus Hoffmann (H) reflex with electromyography (EMG) to estimate the effectiveness of activated Ia afferents to discharge ᵯC-motoneurons, HPAD, PAD and HF during passive lengthening, shortening and static muscle conditions at short, intermediate and long lengths. Our results show that the decrease of effectiveness of activated Ia afferents to discharge ᵯC-motoneurons and increase of post-activation depression during passive muscle lengthening occur at all muscle lengths. For PAD and HF, we found that longer muscle length increases the magnitude of regulation related to muscle lengthening. To conclude, our findings support an inhibitory effect (resulting from increased post-activation depression) of muscle lengthening and longer muscle length on the effectiveness of activated Ia afferents to discharge α-motoneurons. The increase in post-activation depression associated with muscle lengthening can be attributed to the amplification of Ia afferents discharge.

Effects of Multimodal Physical Therapy on Pain, Disability, H-reflex, and Diffusion Tensor Imaging Parameters in Patients With Lumbosacral Radiculopathy Due to Lumbar Disc Herniation: A Preliminary Trial.

Background Lumbosacral radiculopathy (LSR) due to lumbar disc herniation (LDH) is a condition caused by mechanical compression of nerve roots. Various physical therapy interventions have been proposed for the conservative management of LSR due to LDH. However, the study of physical therapy interventions in a multimodal form is lacking. Additionally, the effect of physical therapy on diffusion tensor imaging (DTI) parameters of the compressed nerve root has not been studied. This study aimed to investigate the effects of multimodal physical therapy (MPT) on pain, disability, soleus H-reflex, and DTI parameters of the compressed nerve root in patients with chronic unilateral LSR due to LDH. Methods A prospective preliminary pre-post clinical trial with a convenience sample was conducted. A total of 14 patients with chronic unilateral LSR due to paracentral L4-L5 or L5-S1 LDH were recruited for the study. Participants received a total of 18 sessions of a six-week MPT program that consisted of electrophysical agents, manual therapy interventions, and core stability exercises. Electrophysical agents involved interferential current and hot pack. Manual therapy interventions included myofascial release, side posture positional distraction, passive spinal rotation mobilization, and high-velocity low-amplitude manipulation. Visual analog scale (VAS), Roland-Morris Disability Questionnaire (RMDQ), soleus H-reflex amplitude, side-to-side amplitude (H/H) ratio, fractional anisotropy (FA), and apparent diffusion coefficient (ADC) of the compressed nerve root were measured at baseline and post-intervention. Results There were significant improvements in VAS, RMDQ, H/H ratio, FA, and ADC of the compressed nerve root. Furthermore, significant improvement was found in the affected side compared with the contralateral side in H-reflex amplitude. Conclusions The observations of this preliminary trial suggest that MPT is a successful intervention in patients with chronic unilateral LSR due to LDH. Regarding DTI parameters of the compressed nerve root, FA increased and ADC decreased. Future studies with a control group, large sample sizes, and longer follow-up periods are needed.

Surface recording of the H-reflex from a relaxed flexor carpi ulnaris: Reliability and normative values for healthy young adults.

Objective: H-reflex recordings of the relaxed flexor carpi ulnaris (FCU) muscle are not frequently performed in clinical or laboratory settings. There are no normative values or reliability standards. This is most likely because of technical difficulties associated with this technique. This study performed surface recordings of the H-reflex of relaxed FCU muscles to establish the normative values and the reliability of these recordings. Methods: The maximum amplitude and latency of the FCU H-reflex were recorded bilaterally in 53 healthy young adults. Normative values and interclass correlation coefficients (ICCs) were calculated. Results: The amplitude of the relaxed FCU H-reflex were recorded in nearly all participants (96 %). The FCU H-reflex average maximum amplitude was 1.35 mV. The average latency was 18.8 ms. H-reflex amplitude and latency were not statistically different among gender or limb sides. Amplitude and latency were recoded reliably both within and between sessions with ICCs ranging from 0.96 to 0.99. Conclusions: Recordings of the relaxed FCU H-reflex were readily available and could be assessed reliably within and between sessions. Significance: This method might be used more frequently in clinical and laboratory settings to examine C7 and C8 spinal segments and upper limb muscle normal function or neuromuscular pathology.

Inhibitory kinesiotaping has no effect on post-stroke spasticity: Prospective, randomised, controlled study.

OBJECTIVE: Motor neuron pool activity is high in spasticity. The effect of inhibitory kinesiotaping (KT) on spasticity is unclear. The aim of this study is to investigate the effect of inhibitory KT on spasticity after stroke. METHODS: Fifty stroke patients with ankle plantarflexor spasticity were randomised to intervention (27) and control (23) groups. Inhibitory KT was applied to the triceps surae muscle in the intervention group and sham KT to the Achilles tendon in the control group. Inhibitory and sham KT were applied for 72 h with a combined conventional rehabilitation programme. Spasticity was assessed at baseline and 72 h after KT using three instruments: Modified Ashworth Scale (MAS), Homosynaptic Post-Activation Depression (HPAD) reflecting the level of motor neuron pool activity, and joint torque as a measure of resistance to passive ankle dorsiflexion. RESULTS: The baseline MAS score, HPAD levels and dorsiflexion torque of the two groups were not significantly different. The change in MAS score was -3.7 ± 17.5 (p = 0.180) in the intervention group and 3.6 ± 33.3 (p = 0.655) in the control group. The change in dorsiflexion torque was -0.3 ± 16.1 kg m (p = 0.539) in the intervention group and 8.0 ± 24.1 kg m (p = 0.167) in the control group. The change in mean HPAD was 8.7 ± 34.7 (p = 0.911) in the intervention group and 10.1 ± 41.6 (p = 0.609) in the control group. CONCLUSIONS: The present study showed that inhibitory KT has no antispastic effect in stroke patients.

Soleus Muscle H-reflex: Reference Data of Adult Population From a Tertiary Care Center in India.

Introduction The Hoffmann reflex (H reflex) is one of the most studied reflexes in human neurophysiological literature. Detection of the H reflex is useful in the diagnosis of early polyneuropathy, S1 radiculopathy, early GBS, tibial neuropathy and sciatica, and sacral plexopathy. The H reflex is also used as a tool to measure the excitability of the nervous components of the arc, regardless of the sensitivity of the sensory organs. The monosynaptic nature of reflex circuits makes H-reflex an attractive tool for clinical neurophysiology and research. Objective The objective is to create reference data of soleus H-reflex latency in an adult population from a tertiary care center in India. Materials and methods Seven hundred eighty-four healthy volunteers underwent a physical examination and brief electrophysiological examination before elicitation of the soleus H reflex of both lower extremities using standard techniques. Reference values ​​are expressed as mean ± standard deviation as well as the third and 97th percentiles for latency as the dependent variable. Results The study population included 346 (44.1%) women and 438 (55.9%) men. The men were aged 40.46 ± 14.76 years, and the women were aged 41.63 ± 13.49 years. The average weight of the men was 73.32 ± 10.28 kilograms, and the women were 62.91 ± 7.46 kilograms. The average height of the men was 172.06 ± 4.22 cm, and the women were 159.12 ± 2.42 cm. The third and 97th percentiles for H-reflex latency on the right side were 22.86 ms to 34.22 ms and on the left side were 22.86 ms to 35.39 ms. The average right tibial H latency and left tibial H latency were 28.18 ± 2.59 ms and 28.14 ± 2.70 ms, respectively. Conclusion A sizable subject population was used to provide reference data for this study. Because of the huge sample size and nearly appropriate coverage of different age groups, reference ranges have been established for various age, height, and BMI groups.

Impaired Vibratory and Reciprocal Inhibition in Soleus H-Reflex Testing in Children With Spastic Cerebral Palsy.

Introduction Cerebral palsy (CP) is a neurodevelopmental condition that results from an injury to a developing brain. Children with CP fail to execute precise, well-coordinated movements, and excessive muscular co-contraction or co-activation is a prominent attribute of CP. The normal reciprocal relationship between agonists and antagonists during voluntary movements is altered in patients with CP. H-reflex, which is often regarded as the electrical equivalent of the spinal stretch reflex, can be used to examine the overall reflex arc, including the Ia sensory afferent strength and the spinal motoneuron excitability state. Furthermore, neuromodulatory influence of vibration on H-reflex has been found, which has been increasingly investigated to ascertain its potential use as an intervention in patients with increased spinal reflex excitability. Our goal was to identify the brain mechanism underlying the motor deficits by studying Soleus H-reflex changes during voluntary movement (dorsiflexion) and also to determine the role of vibration in H-reflex modulation in children with spastic CP. Methods Soleus H-reflex was recorded in 12 children with spastic CP (10-16 years) and 15 age-matched controls. Recordings were obtained at rest, during dorsiflexion, and during vibratory stimulation for each subject. H-responses (Hmax amplitudes and Hmax-to-Mmax ratio) were compared among the controls and the cases (CP), for the experiments performed, by the Wilcoxon signed-rank test. The recruitment curves depicting the distribution of mean H-response amplitudes with stimulus intensity increment, for dorsiflexion and vibration were compared among controls and cases by the two-sample Kolmogorov-Smirnov (KS) test. p-value <0.05 was considered as statistically significant. Results Hmax amplitudes and the Hmax-to-Mmax ratio increased (15 % and 12.2 % increment, respectively) from the resting values in the children with CP (p<0.05), while controls exhibited a decrease (reduction of 62% and 57 %, respectively) during dorsiflexion (p<0.05). Vibratory stimulation produced a decreasing trend in H-response measures in both the groups. There was about 15 % and 16 % reduction respectively among children with CP while that of 24 % and 21 % respectively among the controls. The differences in the recruitment curves (distribution of average H-response amplitudes with stimulation intensity) recorded during dorsiflexion and vibration experiments among controls compared with those with CP were found to be statistically significant by the two-sample KS test (p<0.0001). Conclusion The failure of H-reflex suppression during voluntary antagonist muscle activation suggests the presence of impaired reciprocal inhibition in spastic CP. The relatively modest H-response reduction caused by vibratory stimulation in children with CP provides limited evidence of vibratory regulation of the H-reflex in CP. More research into the mechanisms driving motor abnormalities in children with CP is needed, which could aid in therapy planning.

Effect of Sympathetic Blockade on Spontaneous Discharge and the H-Reflex at Myofascial Trigger Points in Rats.

Purpose: Myofascial trigger points (MTrPs) are the main cause of myofascial pain syndrome (MPS), and patients with MPS also have symptoms of sympathetic abnormalities. Consequently, this study aimed to investigate the potential relationship between MTrPs and sympathetic nerves. Materials and Methods: Twenty-four seven-week-old male rats were randomly divided into four groups (six rats every group). Groups I and II were kept in normal condition (n=12), and groups III and IV underwent MTrPs modelling (n=12). After successful MTrPs modelling, differences in sympathetic outcomes between the MTrPs groups (III and IV) and non-MTrPs groups (I and II) were observed. Sympathetic blockade was then applied to groups III and I (n=12). Data were collected on peak inversion spontaneous potentials (PISPs) and the H-reflex-evoked electromyography during spontaneous discharge at the MTrPs before and after sympathetic blockade. Results: Systolic blood pressure, diastolic blood pressure, mean arterial pressure, and heart rate were significantly higher in the MTrPs group than in the non-MTrPs group (P<0.05). Compared with group I, group III had the PISPs potential lower wave amplitude, shorter duration and amplitude-to-duration ratio, and lower H latency and latency difference H-M (P<0.05). Compared with group IV, group III had the PISPs potential lower wave amplitude, duration, amplitude-to-duration ratio, M-wave latency, H maximum wave amplitude, and maximal wave amplitude ratio H/M (P<0.05). The changes before and after sympathetic blockade in the MTrPs group were significant, and the amplitude, duration, and amplitude-to-duration ratio of the PISPs potentials were lower after the blockade (P<0.05). Conclusion: MTrPs and sympathetic nerves interact with each other forming a specific relationship. MTrPs sensitize sympathetic nerves, and sympathetic nerve abnormalities affect local muscle myoelectric hyperactivity, leading to MTrPs. This finding is instructive for the clinical management of sympathetic disorders.

Motor learning changes the axon initial segment of the spinal motoneuron.

We are studying the mechanisms of H-reflex operant conditioning, a simple form of learning. Modelling studies in the literature and our previous data suggested that changes in the axon initial segment (AIS) might contribute. To explore this, we used blinded quantitative histological and immunohistochemical methods to study in adult rats the impact of H-reflex conditioning on the AIS of the spinal motoneuron that produces the reflex. Successful, but not unsuccessful, H-reflex up-conditioning was associated with greater AIS length and distance from soma; greater length correlated with greater H-reflex increase. Modelling studies in the literature suggest that these increases may increase motoneuron excitability, supporting the hypothesis that they may contribute to H-reflex increase. Up-conditioning did not affect AIS ankyrin G (AnkG) immunoreactivity (IR), p-p38 protein kinase IR, or GABAergic terminals. Successful, but not unsuccessful, H-reflex down-conditioning was associated with more GABAergic terminals on the AIS, weaker AnkG-IR, and stronger p-p38-IR. More GABAergic terminals and weaker AnkG-IR correlated with greater H-reflex decrease. These changes might potentially contribute to the positive shift in motoneuron firing threshold underlying H-reflex decrease; they are consistent with modelling suggesting that sodium channel change may be responsible. H-reflex down-conditioning did not affect AIS dimensions. This evidence that AIS plasticity is associated with and might contribute to H-reflex conditioning adds to evidence that motor learning involves both spinal and brain plasticity, and both neuronal and synaptic plasticity. AIS properties of spinal motoneurons are likely to reflect the combined influence of all the motor skills that share these motoneurons. KEY POINTS: Neuronal action potentials normally begin in the axon initial segment (AIS). AIS plasticity affects neuronal excitability in development and disease. Whether it does so in learning is unknown. Operant conditioning of a spinal reflex, a simple learning model, changes the rat spinal motoneuron AIS. Successful, but not unsuccessful, H-reflex up-conditioning is associated with greater AIS length and distance from soma. Successful, but not unsuccessful, down-conditioning is associated with more AIS GABAergic terminals, less ankyrin G, and more p-p38 protein kinase. The associations between AIS plasticity and successful H-reflex conditioning are consistent with those between AIS plasticity and functional changes in development and disease, and with those predicted by modelling studies in the literature. Motor learning changes neurons and synapses in spinal cord and brain. Because spinal motoneurons are the final common pathway for behaviour, their AIS properties probably reflect the combined impact of all the behaviours that use these motoneurons.

The Diagnostic Role of Adding the Hoffman Reflex for L5 Radiculopathy in the Electrodiagnostic Laboratory: A Cross-sectional Study.

OBJECTIVES: To investigate changes in the H-reflex in patients with monoradiculopathies involving L5 or S1 levels by stimulating the sciatic nerve and recording simultaneously from the tibialis anterior (TA), peroneus longus (PL), and soleus (S) muscles. METHODS: Patients with unilateral radicular back pain with L5 or S1 root compression on MRI, participated in this cross-sectional study. The H-reflex over the TA, PL, and S muscles was simultaneously recorded by sciatic nerve stimulation. The H-reflex latency was compared with that of the contralateral extremity. RESULTS: Fifty-eight patients (29 patients L5; 29 patients S1 radiculopathy) were included in the study. There were significant delays in the latency of the H-reflex over TA (30.95±2.31-29.21±1.4) and PL (31.05±2.85-29.02±1.99) muscles on the affected side in patients with L5 radiculopathy. However, the latency of the S H-reflex was similar on both sides. In contrast, in patients with S1 radiculopathy, there was a significant delay in the latency of soleus H reflex (32.76±3.45-29.9±3.19), while the significant delay was not detected in the TA and PL muscles. However, the cutoff values for the H-reflex latency of all muscles were not found to have clinical significance. CONCLUSIONS: The study presents that the H-reflex study, recorded from the TA, PL, and S muscles by sciatic nerve stimulation, is of interest but has minimal contribution to radiculopathy diagnosis in conventional electrodiagnostic tests.

Adaptive gait responses to varying weight-bearing conditions: Inferences from gait dynamics and H-reflex magnitude.

This study investigates the effects of varying loading conditions on excitability in neural pathways and gait dynamics. We focussed on evaluating the magnitude of the Hoffman reflex (H-reflex), a neurophysiological measure representing the capability to activate motor neurons and the timing and placement of the foot during walking. We hypothesized that weight manipulation would alter H-reflex magnitude, footfall and lower body kinematics. Twenty healthy participants were recruited and subjected to various weight-loading conditions. The H-reflex, evoked by stimulating the tibial nerve, was assessed from the dominant leg during walking. Gait was evaluated under five conditions: body weight, 20% and 40% additional body weight, and 20% and 40% reduced body weight (via a harness). Participants walked barefoot on a treadmill under each condition, and the timing of electrical stimulation was set during the stance phase shortly after the heel strike. Results show that different weight-loading conditions significantly impact the timing and placement of the foot and gait stability. Weight reduction led to a 25% decrease in double limb support time and an 11% narrowing of step width, while weight addition resulted in an increase of 9% in step width compared to body weight condition. Furthermore, swing time variability was higher for both the extreme weight conditions, while the H-reflex reduced to about 45% between the extreme conditions. Finally, the H-reflex showed significant main effects on variability of both stance and swing phases, indicating that muscle-motor excitability might serve as feedback for enhanced regulation of gait dynamics under challenging conditions.

Prediction of early bladder outcomes after spinal cord injury: The HALT score.

AIMS: Neurogenic bladder (NB) is a prevalent and debilitating consequence of spinal cord injury (SCI). Indeed, the accurate prognostication of early bladder outcomes is crucial for patient counseling, rehabilitation goal setting, and personalized intervention planning. METHODS: A retrospective exploratory analysis was conducted on a cohort of consecutive SCI patients admitted to a rehabilitation facility in China from May 2016 to December 2022. Demographic, clinical, and electrophysiological data were collected within 40 days post-SCI, with bladder outcomes assessed at 3 months following SCI onset. RESULTS: The present study enrolled 202 SCI patients with a mean age of 40.3 ± 12.3 years. At 3 months post-SCI, 79 participants exhibited complete bladder emptying. Least absolute shrinkage and selection operator (LASSO) and multivariate logistic regression analyses identified the H-reflex of the soleus muscle, the American Spinal Injury Association Lower Extremity Motor Score (ASIA-LEMS), and the time from lesion to rehabilitation facility (TLRF) as significant independent predictors for bladder emptying. A scoring system named HALT was developed, yielding a strong discriminatory performance with an area under the receiver operating characteristics curve (aROC) of 0.878 (95% CI: 0.823-0.933). A simplified model utilizing only the H-reflex exhibited excellent discriminatory ability with an aROC of 0.824 (95% CI: 0.766-0.881). Both models demonstrated good calibration via the Hosmer-Lemeshow test and favorable clinical net benefits through decision curve analysis (DCA). In comparison to ASIA-LEMS, both the HALT score and H-reflex showed superior predictive accuracy for bladder outcome. Notably, in individuals with incomplete injuries, the HALT score (aROC = 0.973, 95% CI: 0.940-1.000) and the H-reflex (aROC = 0.888, 95% CI: 0.807-0.970) displayed enhanced performance. CONCLUSION: Two reliable models, the HALT score and the H-reflex, were developed to predict bladder outcomes as early as 3 months after SCI onset. Importantly, this study provides hitherto undocumented evidence regarding the predictive significance of the soleus H-reflex in relation to bladder outcomes in SCI patients.

Soleus H-reflex amplitude modulation during walking remains physiological during transspinal stimulation in humans.

The soleus H-reflex modulation pattern was investigated during stepping following transspinal stimulation over the thoracolumbar region at 15, 30, and 50 Hz with 10 kHz carry-over frequency above and below the paresthesia threshold. The soleus H-reflex was elicited by posterior tibial nerve stimulation with a single 1 ms pulse at an intensity that the M-wave amplitudes ranged from 0 to 15% of the maximal M-wave evoked 80 ms after the test stimulus, and the soleus H-reflex was half the size of the maximal H-reflex evoked on the ascending portion of the recruitment curve. During treadmill walking, the soleus H-reflex was elicited every 2 or 3 steps, and stimuli were randomly dispersed across the step cycle which was divided in 16 equal bins. For each subject and condition, the soleus M-wave and H-reflex were normalized to the maximal M-wave. The soleus background electromyographic (EMG) activity was estimated as the linear envelope for 50 ms duration starting at 100 ms before posterior tibial nerve stimulation for each bin. The gain was determined as the slope of the relationship between the soleus H-reflex and the soleus background EMG activity. The soleus H-reflex phase-dependent amplitude modulation remained unaltered during transspinal stimulation, regardless frequency, or intensity. Similarly, the H-reflex slope and intercept remained the same for all transspinal stimulation conditions tested. Locomotor EMG activity was increased in knee extensor muscles during transspinal stimulation at 30 and 50 Hz throughout the step cycle while no effects were observed in flexor muscles. These findings suggest that transspinal stimulation above and below the paresthesia threshold at 15, 30, and 50 Hz does not block or impair spinal integration of proprioceptive inputs and increases activity of thigh muscles that affect both hip and knee joint movement. Transspinal stimulation may serve as a neurorecovery strategy to augment standing or walking ability in upper motoneuron lesions.

Neuromuscular Electrical Stimulation Does Not Influence Spinal Excitability in Multiple Sclerosis Patients.

(1) Background: Neuromuscular electrical stimulation (NMES) has beneficial effects on physical functions in Multiple sclerosis (MS) patients. However, the neurophysiological mechanisms underlying these functional improvements are still unclear. This study aims at comparing acute responses in spinal excitability, as measured by soleus Hoffmann reflex (H-reflex), between MS patients and healthy individuals, under three experimental conditions involving the ankle planta flexor muscles: (1) passive NMES (pNMES); (2) NMES superimposed onto isometric voluntary contraction (NMES+); and (3) isometric voluntary contraction (ISO). (2) Methods: In total, 20 MS patients (MS) and 20 healthy individuals as the control group (CG) took part in a single experimental session. Under each condition, participants performed 15 repetitions of 6 s at 20% of maximal voluntary isometric contraction, with 6 s of recovery between repetitions. Before and after each condition, H-reflex amplitudes were recorded. (3) Results: In MS, H-reflex amplitude did not change under any experimental condition (ISO: p = 0.506; pNMES: p = 0.068; NMES+: p = 0.126). In CG, H-reflex amplitude significantly increased under NMES+ (p = 0.01), decreased under pNMES (p < 0.000) and was unaltered under ISO (p = 0.829). (4) Conclusions: The different H-reflex responses between MS and CG might reflect a reduced ability of MS patients in modulating spinal excitability.

Mesencephalic Locomotor Region and Presynaptic Inhibition during Anticipatory Postural Adjustments in People with Parkinson's Disease.

Individuals with Parkinson's disease (PD) and freezing of gait (FOG) have a loss of presynaptic inhibition (PSI) during anticipatory postural adjustments (APAs) for step initiation. The mesencephalic locomotor region (MLR) has connections to the reticulospinal tract that mediates inhibitory interneurons responsible for modulating PSI and APAs. Here, we hypothesized that MLR activity during step initiation would explain the loss of PSI during APAs for step initiation in FOG (freezers). Freezers (n = 34) were assessed in the ON-medication state. We assessed the beta of blood oxygenation level-dependent signal change of areas known to initiate and pace gait (e.g., MLR) during a functional magnetic resonance imaging protocol of an APA task. In addition, we assessed the PSI of the soleus muscle during APA for step initiation, and clinical (e.g., disease duration) and behavioral (e.g., FOG severity and APA amplitude for step initiation) variables. A linear multiple regression model showed that MLR activity (R2 = 0.32, p = 0.0006) and APA amplitude (R2 = 0.13, p = 0.0097) explained together 45% of the loss of PSI during step initiation in freezers. Decreased MLR activity during a simulated APA task is related to a higher loss of PSI during APA for step initiation. Deficits in central and spinal inhibitions during APA may be related to FOG pathophysiology.

Horizontal foot orientation affects the distribution of neural drive between gastrocnemii during plantarflexion, without changing neural excitability.

The distribution of activation among muscles from the same anatomical group can be affected by the mechanical constraints of the task, such as limb orientation. For example, the distribution of activation between the gastrocnemius medialis (GM) and lateralis (GL) muscles during submaximal plantarflexion depends on the orientation of the foot in the horizontal plane. The neural mechanisms behind these modulations are not known. The overall aim of this study was to determine whether the excitability of the two gastrocnemius muscles is differentially affected by changes in foot orientation. Nineteen males performed isometric plantarflexions with their foot internally (toes-in) or externally (toes-out) rotated. GM and GL motor unit discharge characteristics were estimated from high-density surface electromyography to estimate neural drive. GM and GL corticospinal excitability and intracortical activity were assessed using transcranial magnetic stimulation through motor-evoked potentials. The efficacy of synaptic transmission between Ia-afferent fibers and α-motoneurons of the GM and GL was evaluated through the Hoffmann reflex. We observed a differential change in neural drive between GM (toes-out > toes-in) and GL (toes-out < toes-in). However, there was no foot orientation-related modulation in corticospinal excitability of the GM or GL, either at the cortical level or through modulation of the efficacy of Ia-α-motoneuron transmission. These results demonstrate that change in the motor pathway excitability is not the mechanism controlling the different distribution of neural drive between GM and GL with foot orientation.NEW & NOTEWORTHY Horizontal foot orientation affects the distribution of neural drive between the gastrocnemii during plantarflexion. There is no foot orientation-related modulation in the corticospinal excitability of the gastrocnemii, either at the cortical level or through modulation of the efficacy of Ia-α-motoneuron transmission. Change in motor pathway excitability is not the mechanism controlling the different distribution of neural drive between gastrocnemius medialis and lateralis with foot orientation.

Segmental motor neuron dysfunction in amyotrophic lateral sclerosis: Insights from H reflex paradigms.

INTRODUCTION/AIMS: In amyotrophic lateral sclerosis (ALS), the role of spinal interneurons in ALS is underrecognized. We aimed to investigate pre- and post-synaptic modulation of spinal motor neuron excitability by studying the H reflex, to understand spinal interneuron function in ALS. METHODS: We evaluated the soleus H reflex, and three different modulation paradigms, to study segmental spinal inhibitory mechanisms. Homonymous recurrent inhibition (H'RI ) was assessed using the paired H reflex technique. Presynaptic inhibition of Ia afferents (H'Pre ) was evaluated using D1 inhibition after stimulation of the common peroneal nerve. We also studied inhibition of the H reflex after cutaneous stimulation of the sural nerve (H'Pos ). RESULTS: Fifteen ALS patients (median age 57.0 years), with minimal signs of lower motor neuron involvement and good functional status, and a control group of 10 healthy people (median age 57.0 years) were studied. ALS patients showed reduced inhibition, compared to controls, in all paradigms (H'RI 0.35 vs. 0.11, p = .036; H'Pre 1.0 vs. 5.0, p = .001; H'Pos 0.0 vs. 2.5, p = .031). The clinical UMN score was a significant predictor of the amount of recurrent and presynaptic inhibition. DISCUSSION: Spinal inhibitory mechanisms are impaired in ALS. We argue that hyperreflexia could be associated with dysfunction of spinal inhibitory interneurons. In this case, an interneuronopathy could be deemed a major feature of ALS.

Variability of corticospinal and spinal reflex excitability for the ankle dorsiflexor tibialis anterior across repeated measurements in people with and without incomplete spinal cord injury.

To adequately evaluate the corticospinal and spinal plasticity in health and disease, it is essential to understand whether and to what extent the corticospinal and spinal responses fluctuate systematically across multiple measurements. Thus, in this study, we examined the session-to-session variability of corticospinal excitability for the ankle dorsiflexor tibialis anterior (TA) in people with and without incomplete spinal cord injury (SCI). In neurologically normal participants, the following measures were obtained across 4 days at the same time of day (N = 13) or 4 sessions over a 12-h period (N = 9, at 8:00, 12:00, 16:00, and 20:00): maximum voluntary contraction (MVC), maximum M-wave and H-reflex (Mmax and Hmax), motor evoked potential (MEP) amplitude, and silent period (SP) after MEP. In participants with chronic incomplete SCI (N = 17), the same measures were obtained across 4 days. We found no clear diurnal variation in the spinal and corticospinal excitability of the TA in individuals with no known neurological conditions, and no systematic changes in any experimental measures of spinal and corticospinal excitability across four measurement days in individuals with or without SCI. Overall, mean deviations across four sessions remained in a range of 5-13% for all measures in participants with or without SCI. The study shows the limited extent of non-systematic session-to-session variability in the TA corticospinal excitability in individuals with and without chronic incomplete SCI, supporting the utility of corticospinal and spinal excitability measures in mechanistic investigation of neuromodulation interventions. The information provided through this study may serve as the reference in evaluating corticospinal plasticity across multiple experimental sessions.

Botulinum neurotoxin-A in a patient with post-stroke spasticity: a neurophysiological study.

INTRODUCTION: Post-stroke spasticity (PSS) is a disorder of the sensory-motor control, leading to upper motor neuron lesions manifesting either as intermittent or sustained involuntary activation of muscles. Botulinum neurotoxin-A (BoNT-A) is mostly utilized in a variety of therapeutic indications, and it is effective and safe in the management of focal PSS in the rehabilitation scenario. The study aimed to evaluate the effect of BoNT-A administration on H-reflex of upper and lower limbs following PSS. In addition, the investigation of the association among the degree of spasticity (assessed by the Modified Ashworth Scale [MAS]) and motor neuron pool excitability (assessed by analysing H-reflex excitability) was done. MATERIAL AND METHODS: Fifty patients with a stroke of either sex aged 30 to 60 years presented with either upper or lower limb focal spasticity were studied. BoNT-A was given on two occasions to the gastrocnemius, soleus, biceps brachii muscles and flexor carpi radialis (FCR). H-reflex was documented from the FCR and soleus muscles at baseline and 3-4 weeks post BoNT-A injection. Medical Research Council scale and MAS were used to assess the PSS and muscle strength. RESULTS: H-reflex latency and amplitude, H/M ratio recorded from FCR and soleus muscles were significantly different between pre- and post-management. The MRC scale was significantly increased whereas the MAS was significantly reduced post BoNT-A injection. CONCLUSIONS: BoNT-A causes obvious improvement in PSS clinically as assessed by MAS and MRC scale as well as neurophysiologically by H-reflex. A negative correlation between H-reflex latency but not the amplitude or H max /M max ratio and MAS was observed.

Effects of Extracorporeal Shock Wave Therapy in Different Output Pressures on Triceps Surae Spasticity after Stroke / 中国康复理论与实践

Objective:To evaluate the effects of different output pressures of extracorporeal shock wave therapy (ESWT) on triceps surae spasticity after stroke, and to explore the electrophysiologic mechanism involved. Methods:From January, 2015 to December, 2017, 90 hemiplegic stroke patients with triceps surae spasticity were randomly assigned into control group (n = 30), treatment group 1 (n = 30) and treatment group 2 (n = 30). All the patients accepted routine medicine and rehabilitation, while the treatment groups 1 and 2 received ESWT of 1.5 bar and 2.0 bar in addition, respectively, for four weeks. They were assessed with Composite Spasticity Scale (CSS), passive range of motion (PROM), 10-meter walk test (10MWT), and H reflex latency and the Hmax/Mmax ratio before and after treatment, and the two treatment groups were assessed with Visual Analogue Scale (VAS) immediately after ESWT. Results:All the groups improved in scores of CSS, PROM and 10MWT after treatment (t > 7.261, P < 0.001), and improved more in scores of CSS and 10MWT in the two treatment groups than in the control group (P < 0.05), and the 10MWT was less in the treatment group 2 than in the treatment group 1 (P < 0.05). H reflex latency lengthened (t > 15.025, P < 0.001) and Hmax/Mmax ratio decreased (t > 14.850, P < 0.001) after treatment in the two treatment groups, and the H reflex latency was longer in the two treatment groups than in the control group (P < 0.01). There was no significant difference in VAS between the two treatment groups (t = 0.735, P > 0.05). Conclusion:ESWT of both 2.0 bar and 1.5 bar can improve triceps surae spasticity after stroke, and ESWT of 2.0 bar may more benefit the ability of walking. Further study is needed to explore the involved electrophysiologic mechanism.