AAEM Minimonograph #13: H reflexes and F waves: physiology and clinical indications

F wave analysis based on the compound muscle action potential scan

INTRODUCTION/AIMS

Conventional F wave analysis involves a relatively uniform physiological environment induced by supramaximal stimulations. The F wave characteristics in a dynamic physiological condition, however, are rarely investigated. This study aimed to improve understanding of F wave properties in the more dynamic process by introducing a novel method to analyze F waves based on the compound muscle action potential (CMAP) scan technique.

METHODS

Twenty four healthy subjects participated in the study. The CMAP scan was applied to record muscle responses in the abductor pollicis brevis (APB) and abductor digiti minimi (ADM) muscles, respectively. F wave characteristics including mean F wave amplitude and latency (F-M latency), persistence and activating threshold were quantified.

RESULTS

An average of 200 F waves per muscle were obtained from the CMAP scan recording. Weak to moderate correlations between F wave amplitude and stimulating intensity were observed in most of the APB (19 muscles; r = 0.33 ± 0.14, all p < .05) and ADM (23 muscles, r = 0.46 ± 0.16, all p < .05) muscles. Significantly longer mean F latency and lower activating F-threshold were found in the ADM muscles (F-M latency: APB: 25.43 ± 2.39 ms, ADM: 26.15 ± 2.32 ms, p < .05; F-threshold: APB: 7.68 ± 8.96% CMAP, ADM: 2.35 ± 2.42% CMAP, p < .05).

DISCUSSION

This study introduces new features of F waves using the CMAP scan technique and identifies differences of F wave characteristics between the hand muscles. The CMAP scan based F waves analysis can be combined with the motor unit number estimation to assess functional alterations in motor neurons in neurological disorders.

On the origin of F-wave: involvement of central synaptic mechanisms

Neurophysiological methods are used widely to gain information about motor neuron excitability and axon conduction in neurodegenerative diseases. The F-wave is a common biomarker used to test motor neuron properties in the diagnosis of neurological diseases. Although the origin of the F-wave is a subject of debate, the most widely accepted mechanism posits that the F-wave is generated by the backfiring of motor neurons stimulated antidromically from the periphery. In this study, we developed an ex vivo mouse sciatic nerve-attached spinal cord preparation with sensory axons severed. In this preparation, stimulation of the whole sciatic nerve or its tibial branch evoked responses with the electrophysiological signatures of F-waves. Manipulations of synaptic transmission by either removal of extracellular calcium or block of post-synaptic glutamate receptors abolished these responses. These results suggest that F-waves are mediated by spinal microcircuits activated by recurrent motor axon collaterals via glutamatergic synapses.

Serotonergic and noradrenergic contributions to motor cortical and spinal motoneuronal excitability in humans

Animal models indicate that motor behaviour is shaped by monoamine neuromodulators released diffusely throughout the brain and spinal cord. As an alternative to conducting a single study to explore the effects of neuromodulators on the human motor system, we have identified and collated human experiments investigating motor effects of well-characterised drugs that act on serotonergic and noradrenergic networks. In doing so, we present strong neuropharmacology evidence that human motor pathways are affected by neuromodulators across both healthy and clinical populations, insight that cannot be determined from a single reductionist experiment. We have focused our review on the effects that monoaminergic drugs have on muscle responses to non-invasive stimulation of the motor cortex and peripheral nerves, and other closely related tests of motoneuron excitability, and discuss how these measurement techniques elucidate the effects of neuromodulators at motor cortical and spinal motoneuronal levels. Although there is some heterogeneity in study methods, we find drugs acting to enhance extracellular concentrations of serotonin tend to reduce the excitability of the human motor cortex, and enhanced extracellular concentrations of noradrenaline increases motor cortical excitability by enhancing intracortical facilitation and reducing inhibition. Both monoamines tend to enhance the excitability of spinal motoneurons. Overall, this review details the importance of neuromodulators for the output of human motor pathways and suggests that commonly prescribed monoaminergic drugs target the motor system in addition to their typical psychiatric/neurological indications.

Nordic hamstring exercises in functional knee rehabilitation after anterior cruciate ligament reconstruction: a prospective, randomised, controlled study

To study the effect of using Nordic hamstring exercise method on muscle strength and knee joint stability of patients after ACL reconstruction. 60 patients admitted to our hospital for ACL reconstruction were randomly divided into a test group (n = 30, applying Nordic hamstring exercise) and a control group (n = 30, applying conventional rehabilitation training methods), and the difference in the circumference of the thighs of the patients in the two groups was analysed after training, and the peak torque (PT), total torque (PT), and flexion and extension strength were measured by using the Biodex system3 Multi-joint Isokinetic Testing System at knee joints with an angular velocity of 60°/s and 120°/s. The peak torque (PT), total work (TW), and average peak torque (AVG PT) were measured by extension and flexion strength at angular velocity, and the Lysholm Knee Score was used to assess the knee function of 60 patients. There was no difference in the difference in thigh circumference between the two groups before surgery (P > 0.05); the difference in thigh circumference between the patients in the test group at 12 and 24 weeks after surgery was (- 0.35 ± 0.22) cm and (0.12 ± 0.03) cm, respectively, which were higher than those in the control group, (- 0.51 ± 0.15) cm and (- 0.41 ± 0.34) cm (P < 0.05). At the 12th and 24th postoperative weeks, the popliteal muscle strength of both groups was improved compared with that before surgery; among them, by comparing the popliteal peak moments with different angular velocities, the ratio of popliteal peak moment on the affected side/peak moment on the healthy side of the popliteal muscle of the experimental group was significantly higher than that of the control group, and the difference was significant (P < 0.05), but there was still a gap compared with that of the healthy side. The Lachmen test and the anterior drawer test were negative in the test and control groups at the 24th postoperative week of review, and the anterior tibial shift was < 5 mm in the KT-1000 test, and the difference in the anterior shift was < 3 mm compared with the healthy side, and there was no significant difference between the two groups. By Nordic hamstring exercise can make patients after knee ACL reconstruction reduce patient pain, accelerate the recovery of knee function, improve the swelling of the lower limb, reach the level of flexor strength of the healthy side within 24 weeks, and can increase the stability of the knee joint.

Fully automated F-wave corridor extraction and analysis algorithm for F-wave analyses and MUNE studies

F-waves are used in motor unit number estimation (MUNE) studies, which require rapid dedicated software to perform calculations. The aim of this study is to define a mathematical method for a fully automated F-wave extraction algorithm to perform F-wave and MUNE studies while performing baseline corrections without distorting traces. Ten recordings from each class, such as healthy controls, polio patients and ALS patients, were included. Submaximal stimuli were applied to the median and ulnar nerves to record 300 traces from the abductor pollicis brevis and abductor digiti minimi muscles. The autocorrelation function and the signal of sum of all traces were used to find the location for the maximum amplitude of the F-waves. F-waves were revealed by using a cutting window. Linear line estimation was preferred for baseline corrections because it did not cause any distortion in the traces. The algorithm automatically revealed F-waves from all 30 recordings in accordance with the locations marked by a neurophysiologist. The execution of the algorithm was less than 2 (usually < 1) minutes when 300 traces were analyzed. Mean sMUP amplitudes and MUNE values are important for differentiating healthy controls from patients. Moreover, F-wave parameters belonging to polio patients on whom there was a relatively low number of studies conducted were also evaluated.

F-waves induced by motor point stimulation are facilitated during handgrip and motor imagery tasks

The F-wave is a motor response elicited via the antidromic firings of motor nerves by the electrical stimulation of peripheral nerves, which reflects the motoneuron pool excitability. However, the F-wave generally has low robustness i.e., low persistence and small amplitude. We recently found that motor point stimulation (MPS), which provides the muscle belly with electrical stimulation, shows different neural responses compared to nerve stimulation, e.g., MPS elicits F-waves more robustly than nerve stimulation. Here, we investigated whether F-waves induced by MPS can identify changes in motoneuron pool excitability during handgrip and motor imagery. Twelve participants participated in the present study. We applied MPS on their soleus muscle and recorded F-waves during eyes-open (EO), eyes-closed (EC), handgrip (HG), and motor imagery (MI) conditions. In the EO and EC conditions, participants relaxed with their eyes open and closed, respectively. In the HG, participants matched the handgrip force level to 30% of the maximum voluntary force with visual feedback. In the MI, they performed kinesthetic MI of plantarflexion at the maximal strength with closed eyes. In the HG and MI, the amplitudes of the F-waves induced by MPS were increased compared with those in the EO and EC, respectively. These results indicate that the motoneuron pool excitability was facilitated during the HG and MI conditions, consistent with findings in previous studies. Our findings suggest that F-waves elicited by MPS can be a good tool in human neurophysiology to assess the motoneuron pool excitability during cognitive and motor tasks.

5-HT2 receptor antagonism reduces human motoneuron output to antidromic activation but not to stimulation of corticospinal axons

The intrinsic electrical properties of motoneurons strongly affect motoneuron excitability to fast-acting excitatory ionotropic inputs. Serotonin (5-HT) is a neurochemical that alters the intrinsic properties of motoneurons, whereby animal models and in vitro experiments indicate that 5-HT increases motoneuron excitability by activating 5-HT₂ receptors on the somato-dendritic compartment. In the current study, we examined how antagonism of the 5-HT₂ receptor affects motoneuron excitability in humans. We hypothesised that motoneuron excitability would be reduced. The 5-HT₂ antagonist cyproheptadine was administered to ten healthy participants in a double-blinded, placebo-controlled, crossover trial. Electrical cervicomedullary stimulation was used to deliver a synchronised excitatory volley to motoneurons to elicit cervicomedullary motor evoked potentials (CMEPs) in the surface electromyography (EMG) signal of the resting biceps brachii. Likewise, electrical peripheral nerve stimulation was used to generate antidromic spikes in motoneurons and cause recurrent discharges, which were recorded with surface EMG as F-waves in a resting hand muscle. Compared to placebo, we found that 5-HT₂ antagonism reduced the amplitude and persistence of F-waves but did not affect CMEP amplitude. 5-HT₂ antagonism also reduced maximal contraction strength. The reduced recurrent discharge of motoneurons with 5-HT₂ antagonism suggests that 5-HT₂ receptors modulate the electrical properties of the initial segment or soma to promote excitability. Conversely, as cyproheptadine did not affect motoneuron excitability to brief synaptic input, but affected maximal contractions requiring sustained input, it seems likely that the 5-HT₂ mediated amplification of synaptic input at motoneuron dendrites is functionally significant only when excitatory input activates persistent inward currents.

Motor point stimulation induces more robust F-waves than peripheral nerve stimulation

The F-wave is a motor response induced by electrical stimulation of peripheral nerves via the antidromic firing of motor nerves, which reflects the motoneuron excitability. To induce F-waves, transcutaneous peripheral nerve stimulation (PNS) is used, which activates nerve branches via transcutaneous electrodes over the nerve branches. An alternative method to activate peripheral nerves, i.e., motor point stimulation (MPS) which delivers electrical stimulation over the muscle belly, has not been used to induce F-waves. In our previous studies, we observed that MPS induced F-wave like responses, i.e., motor responses at the latency of F-waves at a supramaximal stimulation. Here we further investigated the F-wave like responses induced by MPS in comparison to PNS in the soleus muscle. Thirteen individuals participated in this study. We applied MPS and PNS on the participant's left soleus muscle. Using a monopolar double-pulse stimulation, the amplitude of the second H-reflex induced by PNS decreased, while the amplitude of the motor response at the F-wave latency induced by MPS did not decrease. These results suggest that the motor response at the F-wave latency induced by MPS was not an H-reflex but an F-wave. We also found that the F-wave induced by MPS had a greater amplitude, higher persistence, and caused less pain when compared to the F-waves induced using PNS. We conclude that MPS evokes antidromic firing inducing F-waves more consistently compared to PNS.

Chiropractic Spinal Adjustment Increases the Cortical Drive to the Lower Limb Muscle in Chronic Stroke Patients

This study aimed to investigate the effects of a single session of chiropractic spinal adjustment on the cortical drive to the lower limb in chronic stroke patients. In a single-blinded, randomized controlled parallel design study, 29 individuals with chronic stroke and motor weakness in a lower limb were randomly divided to receive either chiropractic spinal adjustment or a passive movement control intervention. Before and immediately after the intervention, transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs) were recorded from the tibialis anterior (TA) muscle of the lower limb with the greatest degree of motor weakness. Differences in the averaged peak-peak MEP amplitude following interventions were calculated using a linear regression model. Chiropractic spinal adjustment elicited significantly larger MEP amplitude (pre = 0.24 ± 0.17 mV, post = 0.39 ± 0.23 mV, absolute difference = +0.15 mV, relative difference = +92%, p &lt; 0.001) compared to the control intervention (pre = 0.15 ± 0.09 mV, post = 0.16 ± 0.09 mV). The results indicate that chiropractic spinal adjustment increases the corticomotor excitability of ankle dorsiflexor muscles in people with chronic stroke. Further research is required to investigate whether chiropractic spinal adjustment increases dorsiflexor muscle strength and walking function in people with stroke.

Automatic detection of F-waves and F-MUNE in Two Types of Motor Neuron Diseases

INTRODUCTION/AIMS

Motor unit number estimation by F-waves (F-MUNE) is an uncommonly used MUNE technique. The aim of this study was to analyze the sensitivity of F-MUNE values elicited with newly developed software in motor neuron diseases.

METHODS

F-waves were recorded by 300 submaximal stimuli from abductor digiti minimi (ADM) and abductor pollicis brevis (APB) muscles of 35 patients with amyotrophic lateral sclerosis, 18 with previous poliomyelitis, and 20 controls. The software extracted the surface motor unit action potentials (sMUAP) and calculated the F-MUNE values. CMAP Scans were also recorded to obtain step% and MScanFit.

RESULTS

sMUAP amplitudes were higher and F-MUNE values were lower in both muscles of the patients than in controls. F-MUNE values were able to distinguish the patients from controls. Significant correlations were found between F-MUNE and MScanFit in patient groups.

DISCUSSION

The new F-MUNE software gave promising results in revealing motor unit loss caused by motor neuron diseases.

Nerve Conduction Studies: Basic Concepts and Patterns of Abnormalities

Nerve conduction studies are a key component of the electrophysiologic evaluation of the peripheral nerve system, and provide important information about the integrity of the large, myelinated axons, neuromuscular junctions, and muscle. Nerve conduction studies involve eliciting nerve action potentials at sites along a peripheral nerve and recording the response from another site along the nerve or from a muscle innervated by that nerve. Attention to details of test performance, use of well-established normative values, and knowledge of the patterns of abnormality produced by disorders that affect neuronal, axonal, and myelin sheath function are fundamental for proper interpretation of results.

Electrophysiological features of acute inflammatory demyelinating polyneuropathy associated with SARS-CoV-2 infection

Objective

To assess whether patients with acute inflammatory demyelinating polyneuropathy (AIDP) associated with SARS-CoV-2 show characteristic electrophysiological features.

Methods

Clinical and electrophysiological findings of 24 patients with SARS-CoV-2 infection and AIDP (S-AIDP) and of 48 control AIDP (C-AIDP) without SARS-CoV-2 infection were compared.

Results

S-AIDP patients more frequently developed respiratory failure (83.3% vs. 25%, P = 0.000) and required intensive care unit (ICU) hospitalization (58.3% vs. 31.3%, P = 0.000). In C-AIDP, distal motor latencies (DMLs) were more frequently prolonged (70.9% vs. 26.2%, P = 0.000) whereas in S-AIDP distal compound muscle action potential (dCMAP) durations were more frequently increased (49.5% vs. 32.4%, P = 0.002) and F waves were more often absent (45.6% vs. 31.8%, P = 0.011). Presence of nerves with increased dCMAP duration and normal or slightly prolonged DML was elevenfold higher in S-AIDP (31.1% vs. 2.8%, P = 0.000);11 S-AIDP patients showed this pattern in 2 nerves.

Conclusion

Increased dCMAP duration, thought to be a marker of acquired demyelination, can also be oserved in critical illness myopathy. In S-AIDP patients, an increased dCMAP duration dissociated from prolonged DML, suggests additional muscle fiber conduction slowing, possibly due to a COVID-19-related hyperinflammatory state. Absent F waves, at least in some S-AIDP patients, may reflect α-motor neuron hypoexcitability because of immobilization during the ICU stay. These features should be considered in the electrodiagnosis of SARS-CoV-2 patients with weakness, to avoid misdiagnosis.

The Effect of Spinal Manipulation on the Electrophysiological and Metabolic Properties of the Tibialis Anterior Muscle

There is growing evidence showing that spinal manipulation increases muscle strength in healthy individuals as well as in people with some musculoskeletal and neurological disorders. However, the underlying mechanism by which spinal manipulation changes muscle strength is less clear. This study aimed to assess the effects of a single spinal manipulation session on the electrophysiological and metabolic properties of the tibialis anterior (TA) muscle. Maximum voluntary contractions (MVC) of the ankle dorsiflexors, high-density electromyography (HDsEMG), intramuscular EMG, and near-infrared spectroscopy (NIRS) were recorded from the TA muscle in 25 participants with low level recurring spinal dysfunction using a randomized controlled crossover design. The following outcomes: motor unit discharge rate (MUDR), strength (force at MVC), muscle conduction velocity (CV), relative changes in oxy- and deoxyhemoglobin were assessed pre and post a spinal manipulation intervention and passive movement control. Repeated measures ANOVA was used to assess within and between-group differences. Following the spinal manipulation intervention, there was a significant increase in MVC (p = 0.02; avg 18.87 ± 28.35%) and a significant increase in CV in both the isometric steady-state (10% of MVC) contractions (p < 0.01; avg 22.11 ± 11.69%) and during the isometric ramp (10% of MVC) contractions (p < 0.01; avg 4.52 ± 4.58%) compared to the control intervention. There were no other significant findings. The observed TA strength and CV increase, without changes in MUDR, suggests that the strength changes observed following spinal manipulation are, in part, due to increased recruitment of larger, higher threshold motor units. Further research needs to investigate the longer term and potential functional effects of spinal manipulation in various patients who may benefit from improved muscle function and greater motor unit recruitment.

Clinical and Physiological Significance of F-Wave in Spinocerebellar Ataxia Type 3

Objective: To evaluate the characteristics of F-wave in spinocerebellar ataxia type 3 (SCA3) patients and preclinical carriers of SCA3 gene mutation (PreSCA3), and explore the relationship between disease severity and F-wave parameters and evaluate F-wave parameters as potential biomarkers for monitoring of disease progression in SCA3. Methods: We performed F-wave recordings in median, ulnar and tibial nerves of 39 SCA3 patients, 20 PreSCA3, and 27 healthy controls, and compared F-wave parameters between them. Results: In all nerves studied, the mean F-wave amplitude, maximum F-wave amplitude, and F/M amplitude ratio were significantly increased in the SCA3 patients in comparison with the normal controls. And the minimal F-wave latency of SCA3 patients was significantly prolonged and the F-wave persistence (%) was significantly decreased in the median nerve. For the PreSCA3, the maximum F-wave amplitude was significantly higher than normal controls for both median, ulnar, and tibial nerves. The mean F-wave amplitude and F/M amplitude ratio in all nerves were comparable between PreSCA3 and normal controls. The frequency of giant F-wave and frequency of patients with giant F-wave were similar between PreSCA3 and SCA3. The values of F/M amplitude ratio in both median, ulnar, and tibial nerves were correlated positively with disease severity and disease duration. Conclusion: Significant F-wave abnormalities occur in patients with SCA3, even in PreSCA3. F-wave may therefore reveal subclinical alterations and provide objective parameters for evaluating the progression of SCA3.

F-wave parameters for the tibial nerve in Miniature Dachshunds with and without naturally acquired thoracolumbar intervertebral disk herniation

OBJECTIVE

To determine values of F-wave parameters for the tibial nerve in clinically normal Miniature Dachshunds and those with thoracolumbar intervertebral disk herniation (IVDH).

ANIMALS

53 Miniature Dachshunds (10 clinically normal and 43 with various clinical grades of thoracolumbar IVDH).

PROCEDURES

F-waves were elicited in the interosseous muscles of 1 hind limb in each dog by stimulation of the tibial nerve. F-wave parameters were measured for 32 stimuli/dog, and mean values were calculated. Linear regression was performed to assess correlations between F-wave parameters and clinical severity of IVDH.

RESULTS

For clinically normal dogs, mean ± SD values of shortest F-wave latency, mean F-wave conduction velocity, mean F-wave duration, and ratio of the mean F-wave amplitude to M response amplitude were 8.6 ± 0.6 milliseconds, 83.7 ± 6.1 m/s, 6.6 ± 1.5 milliseconds, and 9.8 ± 8.5%, respectively. F-wave persistence was 100%. Mean F-wave duration was positively correlated with clinical grade of IVDH. Linear regression yielded the following regression equation: F-wave duration (milliseconds) = 6.0 + 2.7 × IVDH grade. One dog with grade 2 IVDH had a mean F-wave duration shorter than that of all 5 dogs with grade 1 IVDH; 1 dog with grade 3 IVDH had a longer duration than that of all 10 dogs with grade 4 IVDH.

CONCLUSIONS AND CLINICAL RELEVANCE

Mean F-wave duration was correlated with the severity of inhibitory motor tract dysfunction in the spinal cord of dogs. F-wave examination may be useful for objective functional evaluation of upper motor neurons in the spinal cord.

Emergence of F-waves after repetitive nerve stimulation

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Absence of F-waves in weak patients may be due to reduced F-wave excitability.

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Re-emergence of F-waves was elicited after a 1-second train of 20 Hz supramaximal RNS.

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“Re-awakening” of F-waves using RNS may help exclude AIDP as a cause of weakness.

Aim

Absence of the F-wave may represent the inability of spinal motor neurons to be excited after periods of inactivity. Repetitive stimulation in an otherwise immobile patient acts as a voluntary movement therefore allowing for the production of an F-wave in a patient with previously demonstrated absent F-waves. Through this case report, we attempt to highlight that the absence of the F-wave may result from inexcitability of spinal motor neurons after reduced mobilization.

Case

We present the case of a 48-year-old woman who had been hospitalized in an ICU setting for almost one month due to a subarachnoid hemorrhage, pancreatitis, and respiratory failure. An electromyogram and nerve conduction study (NCS) was performed for weakness in all four extremities. On routine NCS, her F-waves were absent, but after repetitive stimulation was performed, her F-waves appeared.

Discussion

This may be further evidence that the absence of the F-wave may result from inexcitability of spinal motor neurons after immobilization or reduced mobility rather than true pathology of the peripheral nerve. The ability to recover F-waves after an initial absence could assist in differentiating between inexcitability of the anterior horn cell and proximal nerve conduction block. This case presentation is an attempt to show that repetitive nerve stimulation may prove to be a useful technique to restore F-waves in patients who are unable to voluntarily contract their muscles, which may help exclude certain pathologic processes.

Intra- and intersession reliabilities of the flexor carpi radialis H-reflex while sitting with forearm pronation

Purpose: The flexor carpi radialis H-reflex recordings were more robust when the participants were in a sitting position with forearm pronation than with forearm supination. The reliability of flexor carpi radialis recordings obtained with the participant in sitting posture with forearm supination is well established. However, similar reliability utilizing a sitting posture with forearm pronation has not been established. The purpose of this study was to establish the intra and intersession reliabilities of flexor carpi radialis H-reflex recordings acquired with the participants in a sitting with forearm pronation.Materials and methods: The flexor carpi radialis maximum H-reflex amplitude and latency were recorded unilaterally in twenty participants. The forearm was positioned in either a supination or a pronation position on two separate days. Four traces were recorded, and the intraclass correlation coefficients were calculated.Results: The intrasession intraclass correlation coefficients of the four traces of the flexor carpi radialis H-reflex amplitude during pronation on days 1 (0.96) and 2 (0.94) were more consistent than those acquired during supination on days 1 (0.78) and 2 (0.93). The intersession intraclass correlation coefficients of the average traces of the flexor carpi radialis H-reflex amplitude during pronation between days 1 and 2 were more consistent (0.9) than those during supination (0.55).Conclusions: The flexor carpi radialis H-reflex recordings acquired with the participant in a sitting position are more reliable with forearm pronation than with supination within and between sessions. These results should encourage clinicians and researchers to use this position when examining the neuromuscular function of the upper extremities in healthy individuals and those with neuromuscular disorders.

Heteronymous H reflex in temporal muscle as sign of hyperexcitability in ALS patients

OBJECTIVE

The stimulation of the masseteric nerve elicits a homonymous and a heteronymous H reflex in the masseter muscle and in the temporalis one. The presence of the H reflex may be considered a sign of upper motor neuron (UMN) involvement in amyotrophic lateral sclerosis (ALS) patients. The aim of this study was to evaluate the presence of the heteronymous H reflex in patients with ALS and compare it with normal subjects.

METHODS

We enrolled 36 ALS patients and 52 healthy subjects. We stimulated the masseteric nerve in the infratemporal fossa and recorded the muscle responses ipsilaterally to the stimulation.

RESULTS

The heteronymous temporalis H reflex was elicitable in 88.9% of ALS patients and in none of the controls.

CONCLUSION

The heteronymous H reflex does not disappear when the stimulation intensity is increased. It can be used as sign of UMN involvement and may prove useful in patients with suspected MND/ALS with purely lower motor neurons (LMN) signs and no signs of UMN involvement.

SIGNIFICANCE

The heteronymous H reflex is present far more often in ALS patients than in healthy people. It is a simple test that may be used to detect UMN involvement in patients in whom the only evident signs are LMN impairment, improving diagnosis of ALS.

Somatosensory and transcranial direct current stimulation effects on manual dexterity and motor cortex function: A metaplasticity study

BACKGROUND

Non-invasive neuromodulation may provide treatment strategies for neurological deficits affecting movement, such as stroke. For example, weak electrical stimulation applied to the hand by wearing a "mesh glove" (MGS) can transiently increase primary motor cortex (M1) excitability. Conversely, transcranial direct current stimulation with the cathode over M1 (c-tDCS) can decrease corticomotor excitability.

OBJECTIVE/HYPOTHESIS

We applied M1 c-tDCS as a priming adjuvant to MGS and hypothesised metaplastic effects would be apparent in improved motor performance and modulation of M1 inhibitory and facilitatory circuits.

METHODS

Sixteen right-handed neurologically healthy individuals participated in a repeated measures cross-over study; nine minutes of sham- or c-tDCS followed by 30 min of suprasensory threshold MGS. Dexterity of the non-dominant (left) hand was assessed using the grooved pegboard task, and measures of corticomotor excitability, intracortical facilitation, short-latency afferent inhibition (SAI), short-interval intracortical inhibition (SICI), and SAI in the presence of SICI (SAIxSICI), were obtained at baseline, post-tDCS, and 0, 30 and 60 min post-MGS.

RESULTS

There was a greater improvement in grooved pegboard completion times with c-tDCS primed MGS than sham + MGS. There was also more pronounced disinhibition of SAI. However, disinhibition of SAI in the presence of SICI was less and rest motor threshold higher compared to sham + MGS.

CONCLUSIONS

The results indicate a metaplastic modulation of corticomotor excitability with c-tDCS primed MGS. Further studies are warranted to determine how various stimulation approaches can induce metaplastic effects on M1 neuronal circuits to boost functional gains obtained with motor practice.

Radial Nerve F-wave reference values with surface electrodes from the anconeus muscle

INTRODUCTION

We sought to obtain normative values for radial nerve F-wave variables, recording with surface electrodes from the anconeus muscle.

METHODS

We tested 30 healthy participants (17 women, 13 men) and measured the following variables: number of F waves/40 traces (F%); minimum, maximum, and mean F-wave latency (FMIN, FMAX, FMED, respectively); F-wave chronodispersion (FCHR); interside differences of F% and FMIN (DF% and DFMIN, respectively).

RESULTS

The mean F% was 41.3%; the normative values of FMIN, FMED, FMAX, and FCHR were < 21.2, <22.1, <23.3, and < 4.0 ms, respectively; and normative values of DF% and DFMIN were < 16.6% and < 1.1 ms, respectively. Height was the sole independent predictor in a regression model of FMIN, FMED, and FMAX; this explained 37%-44% of the variability.

DISCUSSION

We identified a feasible and useful technique to record radial nerve F waves from the anconeus muscle and obtained normative values of F-wave variables. Muscle Nerve 59:244-246, 2019.

Assessment of the F wave technique for motor unit number estimation in normal dogs

Motor unit number estimation (MUNE) is an electrophysiological technique to quantify the number of motor units in a muscle. A previous study examining MUNE in dogs used an incremental method. The purpose of this study was to examine the use of the F wave method in dogs and to provide information about this technique. Seven healthy laboratory dogs were examined using the F wave method by stimulating either a single site or multiple sites. In the multiple site stimulation F wave (MSS-F) method, the nerve was stimulated at several close sites along the deep peroneal nerve innervating the extensor digitorum brevis muscle. Test-retest was performed with a 1 week interval in all dogs using both techniques. In this preliminary study, median MUNE values were 88 (range 27-187) using the single site stimulation F wave (SSS-F) method and 68.5 (range 47-106) using the MSS-F method. The intra-class correlation coefficients between the two sets of data for each method were 0.20 and 0.09 for left and right SSS-F, respectively, and 0.77 and 0.69 for left and right MSS-F, respectively. MSS-F had less intra-individual variability of MUNE values and was more reproducible. These results indicate that MSS-F can be performed in dogs. MUNE using MSS-F might help with quantitative evaluation of motor neurone dysfunction and progression of diseases affecting motor neurones.

Spinal Cord is the Primary Site of Action for Skeletal Muscle Relaxation by Sevoflurane

MINI: A modified selective anesthetics delivery rabbit model was used validated to a better preferential anesthesia than previous models. Furthermore, we found evidence that primarily the spinal cord mediated the skeletal muscle relaxation action of sevoflurane.

STUDY DESIGN

A randomized, in vivo study was performed to explore the skeletal muscle relaxation action site of sevoflurane.

OBJECTIVE

The aim of this study was to investigate the skeletal muscle relaxation action of sevoflurane by a modified selective anesthetics delivery rabbit model.

SUMMARY OF BACKGROUND DATA

The action site and mechanisms of skeletal muscle relaxation caused by sevoflurane were unclear, so a modified selective anesthetics delivery model was used.

METHODS

Sixteen male New Zealand White rabbits were randomly assigned to the sevoflurane or sham group. In situ measurement of train of four, maximum single twitch, and tetanic muscle force of left tibialis anterior muscle was repeatedly measured at three time points: at the beginning of lower torso bypass (baseline value), during preferential sevoflurane delivery to the brain (brain value), during preferential sevoflurane delivery to the spinal cord (spinal cord value).

RESULTS

When 1.5MAC sevoflurane was administrated via the lungs, the arterial concentration and partial pressure of sevoflurane in the upper torso were 205.27 ± 16.23 μg/mL and 29.16 ± 1.05 mmHg, whereas in the lower torso bypass circulation were 10.39 ± 4.50 μg/mL and 1.79 ± 0.97 mmHg. Conversely, the arterial concentration and partial pressure of sevoflurane in the upper torso were 14.04 ± 5.33 μg/mL and 2.25 ± 0.84 mmHg, whereas those values were 199.38 ± 11.61 μg/mLl and 29.20 ± 1.08 mmHg in the lower torso, when 1.5MAC sevoflurane was delivered via an oxygenator. In sevoflurane group, maximum single twitch and tetanic muscle force were significantly reduced compared with baseline (single: P = 0.046; tetanic: P = 0.001) or brain values (single: P = 0.005; tetanic: P = 0.001), when spinal cord was selectively anesthetized. In the sham group, there were no significant differences among the three conditions compared.

CONCLUSION

A modified selective anesthetics delivery rabbit model has been validated, which provided evidence that the spinal cord, not the brain, was the primary site mediating the skeletal muscle relaxation action of sevoflurane.

LEVEL OF EVIDENCE

5.

Changes in the soleus H-reflex test and correlations between its results and dynamic magnetic resonance imaging abnormalities in patients with Hirayama disease

OBJECTIVE

To investigate changes in soleus H-reflex tests in patients with Hirayama disease (HD) and to analyse correlations between these changes and forward-shifting of the cervical cord during neck flexion.

METHODS

The amplitude of the soleus H-reflex with and without vibration on the Achilles tendon was recorded bilaterally in 81 HD patients and 34 controls to measure both the vibratory inhibition index (VII) and the H_max/M_max ratio. The maximum forward-shifting degree of cervical cord during neck flexion was measured using dynamic magnetic resonance imaging in all HD patients.

RESULTS

Significantly higher VII was recorded in 6/81 (7.4%) HD patients, along with abnormal H_max/M_max ratios in 5 of 6 cases. Compared to illness duration (r = 0.29-0.36, p < 0.05), the maximum forward-shifting degree of the cervical cord was more strongly correlated with both VII and the H_max/M_max ratio (r = 0.51-0.81, p < 0.05).

CONCLUSIONS

HD patients may develop cervical spinal cord injury with disease progression, and these lesions may be more likely to occur in cases with relatively severe cervical-flexion structural abnormalities even during early stages.

SIGNIFICANCE

More caution should be taken when managing HD patients with severe cervical-flexion abnormalities because of the possible early occurrence of upper motor neuron lesions.

Neurophysiologic Studies in the Evaluation of Polyneuropathy

PURPOSE OF REVIEW

This article provides core information on the clinical neurophysiology techniques available for the investigation of disorders of the peripheral nervous system.

RECENT FINDINGS

The role of small fiber dysfunction in some types of polyneuropathy is being increasingly appreciated, and neurophysiologic techniques for evaluating the autonomic components of peripheral axons have enhanced our understanding of small fiber dysfunction.

SUMMARY

The principles of nerve conduction studies and needle EMG are presented in this article, along with the patterns of abnormality encountered in patients with polyneuropathy due to large and small fiber involvement.

The Relationship between Trans-Lesional Conduction, Motor Neuron Pool Excitability, and Motor Function in Dogs with Incomplete Recovery from Severe Spinal Cord Injury

Spontaneous, acute, complete thoracolumbar spinal cord injury (TL-SCI) in dogs frequently results in permanent deficits modeling chronic paralysis in people. Recovery of walking without recovery of sensation has been interpreted in dogs as reflexive spinal walking. To evaluate this assumption, this study characterized the electrophysiological status of motor and sensory long tracts and local reflex circuitry in dogs with absent recovery of sensation after acute TL-SCI and correlated findings to gait scores. Twenty dogs with permanent deficits after acute, clinically complete TL-SCI and 6 normal dogs were prospectively enrolled. Transcranial magnetic motor evoked potentials (MEPs), somatosensory evoked potentials (SSEPs), H-reflex, and F-waves were evaluated. Gait was quantified using an ordinal, open field scale (OFS) and treadmill-based stepping and coordination scores (SS, RI). MEP latency and H-reflex variables were compared between cases and controls. Associations between presence of MEPs, SSEPs, F-waves or H-reflex variables, and gait scores were determined. Pelvic limb MEPs were detected in 4 cases; no case had trans-lesional sensory conduction. Latency was longer and conduction velocity slower in cases than controls (p_a = 0.0064, 0.0023, respectively). Three of 4 cases with pelvic limb MEPs were ambulatory, and gait scores (OFS, SS, RI) were each associated with presence of trans-lesional conduction (p_a = 0.006, 0.006, 0.003, respectively). H threshold in cases (mean, 3.2mA ±2.5) was lower than controls (mean, 7.9mA ±3.1; p_a = 0.011) and was inversely associated with treadmill-based scores, SS, and RI (p_a = 0.042, 0.043, respectively). The association between pelvic limb MEPs and gait scores supports the importance of descending influence on regaining walking after severe TL-SCI in dogs rather than just activation of spinal walking. The inverse association between H-reflex threshold and gait scores implies that increases in motor neuron pool excitability might also contribute to motor recovery.

The relationship of corticospinal excitability with pain, motor performance and disability in subjects with chronic wrist/hand pain

There is a growing body of evidence of changes in corticospinal excitability associated with musculoskeletal disorders, however there is a lack of knowledge of how these changes relate to measures of pain, motor performance and disability. An exploratory study was performed utilizing Transcranial Magnetic Stimulation to investigate differences in corticospinal excitability in the Abductor Pollicis Brevis (APB) between 15 pain-free subjects and 15 subjects with chronic wrist/hand pain and to determine how corticospinal excitability was associated with measures of pain (visual analog scale, AUSCAN™), hand motor performance (isometric and key pinch strength, Purdue Pegboard Test), disability (AUSCAN™), and spinal motoneuronal excitability. Input-output curves demonstrated increased corticospinal excitability of the APB in the affected hand of subjects with chronic pain (p<0.01). Changes in corticospinal excitability were significantly correlated with pain intensity (r=0.77), disability (r=0.58), and negatively correlated with motoneuronal excitability (r=-0.57). Corticospinal excitability in subjects with heterogeneous injuries of the wrist/hand was associated with disability and pain.

Impact of Spinal Manipulation on Cortical Drive to Upper and Lower Limb Muscles

This study investigates whether spinal manipulation leads to changes in motor control by measuring the recruitment pattern of motor units in both an upper and lower limb muscle and to see whether such changes may at least in part occur at the cortical level by recording movement related cortical potential (MRCP) amplitudes. In experiment one, transcranial magnetic stimulation input-output (TMS I/O) curves for an upper limb muscle (abductor pollicus brevis; APB) were recorded, along with F waves before and after either spinal manipulation or a control intervention for the same subjects on two different days. During two separate days, lower limb TMS I/O curves and MRCPs were recorded from tibialis anterior muscle (TA) pre and post spinal manipulation. Dependent measures were compared with repeated measures analysis of variance, with p set at 0.05. Spinal manipulation resulted in a 54.5% ± 93.1% increase in maximum motor evoked potential (MEPmax) for APB and a 44.6% ± 69.6% increase in MEPmax for TA. For the MRCP data following spinal manipulation there were significant difference for amplitude of early bereitschafts-potential (EBP), late bereitschafts potential (LBP) and also for peak negativity (PN). The results of this study show that spinal manipulation leads to changes in cortical excitability, as measured by significantly larger MEPmax for TMS induced input-output curves for both an upper and lower limb muscle, and with larger amplitudes of MRCP component post manipulation. No changes in spinal measures (i.e., F wave amplitudes or persistence) were observed, and no changes were shown following the control condition. These results are consistent with previous findings that have suggested increases in strength following spinal manipulation were due to descending cortical drive and could not be explained by changes at the level of the spinal cord. Spinal manipulation may therefore be indicated for the patients who have lost tonus of their muscle and/or are recovering from muscle degrading dysfunctions such as stroke or orthopaedic operations and/or may also be of interest to sports performers. These findings should be followed up in the relevant populations.

Generation of Repeater F Waves in Healthy Subjects

PURPOSE

F waves identical in latency, size, and shape, known as repeater F waves, have been observed occasionally in normal motor conduction recordings. The purpose of this study was to examine the occurrence and characteristics of repeater F waves in healthy subjects under different testing conditions, aiming to selectively excite lower and higher threshold motor fibers.

METHODS

Sessions of 40 traces were recorded from the ulnar nerve in 12 volunteers, applying/using supramaximal, submaximal stimuli (intensity able to elicit 30% and 60% of the maximum compound muscle action potential amplitude), and a collision technique. Repeater F waves were identified and their numbers and relative frequency were estimated. For this purpose, a custom-designed software program was developed, to avoid misjudgments of simple visual inspection.

RESULTS

Repeater occurrence was significantly higher using 30% submaximal intensity compared with the standard supramaximal stimulation. There was an inverse significant association between repeater index and overall F wave quantity. Repeaters' latency, amplitude, and duration measurements were within the ranges of the nonrepeaters.

CONCLUSIONS

We herein showed that in healthy subjects the presence of repeater F waves might increase, when stimulation conditions other than standard single, supramaximal impulses were used. The frequency of repeaters was dependent on the overall F wave persistence, but there was no evidence to support a relationship with the type of motoneurons that was preferentially stimulated.

Clinical uses of H reflexes of upper and lower limb muscles

H reflexes can be recorded from virtually all muscles that have muscle spindles, but reflex reinforcement may be required for the reflex response to be demonstrable. This can allow conduction across proximal nerve segments and most nerve root segments commonly involved by pathology. Stimulus rate is critical in subjects who are at rest. However the reflex attenuation with higher rates is greatly reduced during a background contraction of the test muscle, with only minor changes in latency if any. In addition the contraction ensures that the reflex response occurs in the desired muscle. Reflex latencies should be corrected for height (or limb length) and age. Because the reflex discharge requires a synchronised volley in group Ia afferents, large increases in reflex latency occur rarely with purely sensory lesions. If the H reflex of soleus, quadriceps femoris or flexor carpi radialis is absent at rest but appears during a voluntary contraction at near-normal latency, there is either low central excitability or a predominantly sensory abnormality. With the former H reflexes will be difficult to elicit throughout the body. If H reflexes can be recorded at rest from muscles for which no reflex can normally be demonstrated, there is good evidence for hyperreflexia. In the context of possible ALS, this is an important finding when there is EMG evidence of chronic partial denervation in that muscle.

Differences in Dysfunction of Thenar and Hypothenar Motoneurons in Amyotrophic Lateral Sclerosis

This study aimed to determine differences in spinal motoneuron dysfunction between the abductor pollicis brevis (APB) and the abductor digiti minimi (ADM) in amyotrophic lateral sclerosis (ALS) patients based on studying F-waves. Forty ALS patients and 20 normal controls (NCs) underwent motor nerve conduction studies on both median and ulnar nerves, including F-waves elicited by 100 electrical stimuli. The F-wave persistence (P < 0.05), index repeating neuron (RN; P < 0.001), and index repeater F-waves (Freps; P < 0.001) significantly differed between the APB and the ADM in the NC participants. For the hands of the ALS patients that lacked detectable wasting or weakness and exhibited either no or mild impairment of discrete finger movements, significantly reduced F-wave persistence (P < 0.001), increased index RN (P < 0.001), and increased index Freps (P < 0.001) were observed in APB in comparison with the normal participants, with relatively normal ADM F-wave parameters. For the hands of ALS patients that exhibited wasting and weakness, the mean F-wave amplitude (P < 0.05), the F/M amplitude ratio (P < 0.05), F-wave persistence (P < 0.001), index RN (P < 0.05), and index Freps (P < 0.05) significantly differed between APB and ADM. The differences in the dysfunction of motoneurons innervating APB and ADM are unique manifestations in ALS patients. The F-wave persistence (P = 0.002), index RN (P < 0.001), and index Freps (P < 0.001) in the APB seemed to differentiate ALS from the NCs more robustly than the ADM/APB Compound muscle action potential (CMAP) amplitude ratio. Thus, F-waves may reveal subclinical alterations in anterior horn cells, and may potentially help to distinguish ALS from mimic disorders.

Importance of sample size for the estimation of repeater F waves in amyotrophic lateral sclerosis

BACKGROUND

In amyotrophic lateral sclerosis (ALS), repeater F waves are increased. Accurate assessment of repeater F waves requires an adequate sample size.

METHODS

We studied the F waves of left ulnar nerves in ALS patients. Based on the presence or absence of pyramidal signs in the left upper limb, the ALS patients were divided into two groups: One group with pyramidal signs designated as P group and the other without pyramidal signs designated as NP group. The Index repeating neurons (RN) and Index repeater F waves (Freps) were compared among the P, NP and control groups following 20 and 100 stimuli respectively. For each group, the Index RN and Index Freps obtained from 20 and 100 stimuli were compared.

RESULTS

In the P group, the Index RN (P = 0.004) and Index Freps (P = 0.001) obtained from 100 stimuli were significantly higher than from 20 stimuli. For F waves obtained from 20 stimuli, no significant differences were identified between the P and NP groups for Index RN (P = 0.052) and Index Freps (P = 0.079); The Index RN (P < 0.001) and Index Freps (P < 0.001) of the P group were significantly higher than the control group; The Index RN (P = 0.002) of the NP group was significantly higher than the control group. For F waves obtained from 100 stimuli, the Index RN (P < 0.001) and Index Freps (P < 0.001) of the P group were significantly higher than the NP group; The Index RN (P < 0.001) and Index Freps (P < 0.001) of the P and NP groups were significantly higher than the control group.

CONCLUSIONS

Increased repeater F waves reflect increased excitability of motor neuron pool and indicate upper motor neuron dysfunction in ALS. For an accurate evaluation of repeater F waves in ALS patients especially those with moderate to severe muscle atrophy, 100 stimuli would be required.

Riluzole promotes motor and respiratory recovery associated with enhanced neuronal survival and function following high cervical spinal hemisection

Cervical spinal cord injury (SCI) can result in devastating functional deficits that involve the respiratory and hand function. The mammalian spinal cord has limited ability to regenerate and restore meaningful functional recovery following SCI. Riluzole, 2-amino-6-trifluoromethoxybenzothiazole, an anti-glutamatergic drug has been shown to reduce excitotoxicity and confer neuroprotection at the site of injury following experimental SCI. Based on promising preclinical studies, riluzole is currently under Phase III clinical trial for the treatment of SCI (ClinicalTrials.gov: NCT01597518). Riluzole's anti-glutamatergic role has the potential to regulate neuronal function and provide neuroprotection and influence glutamatergic connections distal to the initial injury leading to enhanced functional recovery following SCI. In order to investigate this novel role of riluzole we used a high cervical hemisection model of SCI, which interrupts all descending input to motoneurons innervating the ipsilateral forelimb and diaphragm muscles. Following C2 spinal cord hemisection, animals were placed into one of two groups: one group received riluzole (8 mg/kg) 1 h after injury and every 12 h thereafter for 7 days at 6 mg/kg, while the second group of injured rats received vehicle solution for the same duration of time. A third group of sham injured rats underwent a C2 laminectomy without hemisection and served as uninjured control rats. Interestingly, this study reports a significant loss of motoneurons within the cervical spinal cord caudal to C2 hemisection injury. Disruption of descending input led to a decrease in glutamatergic synapses and motoneurons caudal to the injury while riluzole treatment significantly limited this decline. Functionally, Hoffmann reflex recordings revealed an increase in the excitability of the remaining ipsilateral cervical motoneurons and significant improvements in skilled and unskilled forelimb function and respiratory motor function in the riluzole-treated animals. In conclusion, using a C2 hemisection injury model, this study provides novel evidence of motoneuron loss caudal to the injury and supports riluzole's capacity to promote neuronal preservation and function of neural network caudal to the SCI resulting in early and sustained functional improvements.

Investigation of the H reflexes, F waves and sympathetic skin response with electromyography (EMG) in patients with stroke and the determination of the relationship with functional capacity

The purpose of the study was to evaluate the relationship between sympathetic skin responses (SSR), electrodiagnostic reflex activities (F wave, H reflex), and functional capacity in post-stroke patients. The study comprised 40 hemiplegia patients (mean age 57.8 ± 10.9 years) and 40 healthy volunteers (mean age 557 ± 85 years). In electrophysiological studies, SSR, F wave and H reflex were evaluated and for the functional capacities of patients, FIM scores and Brunnstrom stages were calculated. There was no statistical significant difference between SSR latency and amplitude in the hemiplegic and non-hemiplegic extremities of patients (p > 0.05). SSR latency values of patients were higher than those of controls (p < 0.05). Amplitude values of paretic arms were significantly lower than the control group extremities (p < 0.05). There was a significant correlation between SSR amplitude values and FIM scores. A significant increase in H max/M max amplitude rate was detected in the affected side (p < 0.05) and F-wave mean latency values of the affected side were found to be significantly lower in the control group (p < 0.05).

Application of the F-Response for Estimating Motor Unit Number and Amplitude Distribution in Hand Muscles of Stroke Survivors

The F-response was used in this study to assess changes in the first dorsal interosseous (FDI) muscle after a hemispheric stroke. The number of motor units and their sizes were estimated bilaterally in 12 stroke survivors by recording both the compound muscle action potential (CMAP) and F wave responses. These F waves were induced by applying a large number of electrical stimuli to the ulnar nerve. The amplitude distribution of individual motor unit action potentials (MUAPs) was also compared between paretic and contralateral muscles. When averaged across all the subjects, a significantly lower motor unit number estimate was obtained for the paretic FDI muscle ( 88 ±13) compared with the contralateral side ( 139 ±11) ( ). Pooled surface MUAP amplitude analysis demonstrated a right-skewed distribution for both paretic (kurtosis 3.0) and contralateral (kurtosis 8.52) muscles. When normalized to each individual muscle's CMAP, the surface MUAP amplitude ranged from 0.22% to 4.94% (median 1.17%) of CMAP amplitude for the paretic muscle, and from 0.13% to 3.2% (median 0.62%) of CMAP amplitude for the contralateral muscle. A significant difference in MUAP outliers was also observed between the paretic and contralateral muscles. The findings of this study suggest significant motor unit loss and muscle structural reorganization after stroke.

Transcutaneous spinal direct current stimulation modulates human corticospinal system excitability

This study aimed to assess the effects of thoracic anodal and cathodal transcutaneous spinal direct current stimulation (tsDCS) on upper and lower limb corticospinal excitability. Although there have been studies assessing how thoracic tsDCS influences the spinal ascending tract and reflexes, none has assessed the effects of this technique over upper and lower limb corticomotor neuronal connections. In 14 healthy subjects we recorded motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) from abductor hallucis (AH) and hand abductor digiti minimi (ADM) muscles before (baseline) and at different time points (0 and 30 min) after anodal or cathodal tsDCS (2.5 mA, 20 min, T9-T11 level). In 8 of the 14 subjects we also tested the soleus H reflex and the F waves from AH and ADM before and after tsDCS. Both anodal and cathodal tsDCS left the upper limb MEPs and F wave unchanged. Conversely, while leaving lower limb H reflex unchanged, they oppositely affected lower limb MEPs: whereas anodal tsDCS increased resting motor threshold [(mean ± SE) 107.33 ± 3.3% increase immediately after tsDCS and 108.37 ± 3.2% increase 30 min after tsDCS compared with baseline] and had no effects on MEP area and latency, cathodal tsDCS increased MEP area (139.71 ± 12.9% increase immediately after tsDCS and 132.74 ± 22.0% increase 30 min after tsDCS compared with baseline) without affecting resting motor threshold and MEP latency. Our results show that tsDCS induces polarity-specific changes in corticospinal excitability that last for >30 min after tsDCS offset and selectively affect responses in lower limb muscles innervated by lumbar and sacral motor neurons.

Establishment of a method to measure length of the ulnar nerve and standardize F-wave values in clinically normal beagles

We designed a new method of measuring the length of the ulnar nerve and determining standard values for F-wave parameters of the ulnar nerve in clinically normal beagles. Nerve length must be precisely measured to determine F-wave latency and conduction velocity. The length of the forelimb has served as the length of the ulnar nerve for F-wave assessments, but report indicates that F-wave latency is proportional to the length of the pathway traveled by nerve impulses. Therefore, we measured the surface distance from a stimulus point to the spinous process of the first thoracic vertebra (nerve length 1) and the anterior horn of the scapula (nerve length 2) as landmarks through the olecranon and the shoulder blade acromion. The correlation coefficients between the shortest F-wave latency and the length of nerves 1, 2 or the forelimb were 0.61, 0.7 and 0.58. Nerve length 2 generated the highest value. Furthermore, the anterior horn of the scapula was easily palpated in any dog regardless of well-fed body. We concluded that nerve length 2 was optimal for measuring the length of the ulnar nerve.

Reference value of f-wave latency in the facial nerve based on human subjects

PURPOSE

The aim of this study was to investigate an appropriate methodology to record F waves and establish the reference value of F-wave latency in the facial nerve, which provides an electrophysiological basis for facial nerve evaluation in clinical patients.

METHODS

One hundred fifty-eight healthy subjects were recruited and divided into seven groups based on their age. With percutaneous electrical nerve stimulation at the mastoid process, surface electrodes were placed onto the orbicularis oculi muscles bilaterally, and F-wave latency (Flat) and F-persistence in the facial nerve were measured.

RESULTS

The average latency was 30.65 ± 4.22 milliseconds among subjects under 10 years old; 28.17 ± 2.28 milliseconds among subjects 10 to 19 years of age; 27.97 ± 3.48 milliseconds among subjects 20 to 29 years old; 29.60 ± 1.78 milliseconds among subjects 30 to 39 years of age; 30.06 ± 1.94 milliseconds among subjects 40 to 49 years old; 30.52 ± 2.08 milliseconds among subjects 50 to 59 years of age, and 32.12 ± 3.0 milliseconds among subjects above 60 years old. According to this study, Flat in the facial nerve was associated with subjects' age. In addition, the average F-persistence of the facial nerve was 98.07%.

CONCLUSIONS

Flat showed a U-shaped distribution among subjects with increasing age. Among subjects younger than 10 years, Flat shortened with increasing age, but among subjects 10 to 29 years old, Flat did not change significantly and was the shortest among all groups. Among subjects older than 30 years, Flat became longer with increasing age, and the longest Flat was in subjects older than 60 years.

Potential advantages of the H-reflex of the biceps femoris-long head in documenting S1 radiculopathy

PURPOSE

A novel H-reflex method using the biceps femoris-long head (BF-LH) was investigated to collect the normative data for this reflex arc and assess its clinical utility for S1 radiculopathy evaluation. Comparability with conventional tibial and Sol H-reflex findings was also determined.

METHODS

BF-LH H-reflexes were recorded using surface electrodes to S1-root stimulation in 43 unilateral S1 radiculopathy patients (radiculopathy group) and 34 normal subjects (control group) from March 2009 to December 2011. H-M interval and peak-to-peak amplitudes were measured. The BF-LH H-reflex and the H-reflex from the soleus muscle (Sol H-reflex) to both tibial nerve stimulation (tibial H-reflex) and S1-root stimulation were used and compared for application in S1 radiculopathy evaluation.

RESULTS

BF-LH H-reflexes were reliably recorded for all control group subjects. Abnormal BF-LH H-reflexes were recorded for 40 (93.0%) radiculopathy group patients in the involved extremity, and abnormal involved side tibial H-reflexes and Sol H-reflexes were recorded in 31 (72.1%) and 41 (95.3%) radiculopathy group patients, respectively. The BF-LH H-reflex exhibited significantly higher sensitivity for evaluation of S1 radiculopathy, accurate in 40 (93.0%) radiculopathy group patients, than that provided by the conventional tibial H-reflex of only 31 (72.1%) (P < 0.05).

CONCLUSIONS

The BF-LH H-reflex is a highly sensitive and reliable clinical tool for evaluation of the S1 spinal reflex pathway in radiculopathy that is distinct from the Sol H-reflex and conventional tibial H-reflex arcs.

Sensorimotor modulation differs with load type during constant finger force or position

During submaximal isometric contraction, there are two different load types: production of a constant force against a rigid restraint (force task), and maintenance of position against a constant load (position task). Previous studies reported that the time to task failure during a fatigue task was twice as long in the force task compared with the position task. Sensory feedback processing may contribute to these differences. The purpose of the current study was to determine the influence of load types during static muscle contraction tasks on the gating effect, i.e., attenuation of somatosensory-evoked potentials (SEPs) and the cortical silent period (cSP). Ten healthy subjects contracted their right first dorsal interosseus muscle by abducting their index finger for 90 s, to produce a constant force against a rigid restraint that was 20% of the maximum voluntary contraction (force task), or to maintain a constant position with 10° abduction of the metacarpophalangeal joint against the same load (position task). Somatosensory evoked potentials (SEPs) were recorded from C3' by stimulating either the right ulnar or median nerve at the wrist while maintaining contraction. The cortical silent period (cSP) was also elicited by transcranial magnetic stimulation. Reduction of the amplitude of the P45 component of SEPs was significantly larger during the position task than during the force task and under control rest conditions when the ulnar nerve, but not the median nerve, was stimulated. The position task had a significantly shorter cSP duration than the force task. These results suggest the need for more proprioceptive information during the position task than the force task. The shorter duration of the cSP during the position task may be attributable to larger amplitude of heteronymous short latency reflexes. Sensorimotor modulations may differ with load type during constant finger force or position tasks.

Diagnostic advantage of S1 foramen-evoked H-reflex for S1 radiculopathy in patients with diabetes mellitus

Hoffmann reflex to tibial nerve stimulation at the popliteal fossa (tibial H-reflex) is routinely used to evaluate S1 radiculopathy. However, it lacks sensitivity because other lesions along this reflex circuit affect the H-reflex bilaterally. This study was undertaken to determine whether the H-reflex evoked by stimulating proximally at the S1 foramen (S1 foramen H-reflex) could improve S1 root lesion evaluation sensitivity in patients with diabetes mellitus. A randomized paired study was designed to evaluate tibial and S1 foramen H-reflexes; bilateral H-M interval (HMI) and H-reflex latency were compared in 22 diabetic patients with unilateral S1 radiculopathy. Other electrophysiological evaluations included standard tibial conduction studies, sural conduction studies and needle electromyography (EMG). The S1 foramen H-reflex had a significantly higher sensitivity (91.0%, 20 of 22) in evaluating S1 radiculopathy than the conventional tibial H-reflex (63.6%, 14 of 22, p < 0.05). Bilateral tibial compound muscle action potential amplitudes were reduced in 3 patients, and sural sensory nerve action potential amplitudes decreased in 7 patients. Needle EMG revealed denervation restricted to the paraspinal muscle and myotomes supplied by the S1 nerve root on the ipsilateral side in 18 patients, and multiple lumbosacral nerve roots were involved bilaterally in the other 4 patients. Our results demonstrate that the S1 foramen H-reflex is a more sensitive assessment of S1 compressive radiculopathy in patients with diabetes mellitus.

Testing the excitability of human motoneurons

The responsiveness of the human central nervous system can change profoundly with exercise, injury, disuse, or disease. Changes occur at both cortical and spinal levels but in most cases excitability of the motoneuron pool must be assessed to localize accurately the site of adaptation. Hence, it is critical to understand, and employ correctly, the methods to test motoneuron excitability in humans. Several techniques exist and each has its advantages and disadvantages. This review examines the most common techniques that use evoked compound muscle action potentials to test the excitability of the motoneuron pool and describes the merits and limitations of each. The techniques discussed are the H-reflex, F-wave, tendon jerk, V-wave, cervicomedullary motor evoked potential (CMEP), and motor evoked potential (MEP). A number of limitations with these techniques are presented.