Single Motor Evoked Potential Research Articles

Acute Low-Intensity Aerobic Exercise Modulates Intracortical Inhibitory and Excitatory Circuits in an Exercised and a Non-exercised Muscle in the Primary Motor Cortex.

Recent studies have reported that acute aerobic exercise modulates intracortical excitability in the primary motor cortex (M1). However, whether acute low-intensity aerobic exercise can also modulate M1 intracortical excitability, particularly intracortical excitatory circuits, remains unclear. In addition, no previous studies have investigated the effect of acute aerobic exercise on short-latency afferent inhibition (SAI). The aim of this study was to investigate whether acute low-intensity aerobic exercise modulates intracortical circuits in the M1 hand and leg areas. Intracortical excitability of M1 (Experiments 1, 2) and spinal excitability (Experiment 3) were measured before and after acute low-intensity aerobic exercise. In Experiment 3, skin temperature was also measured throughout the experiment. Transcranial magnetic stimulation was applied over the M1 non-exercised hand and exercised leg areas in Experiments 1, 2, respectively. Participants performed 30 min of low-intensity pedaling exercise or rested while sitting on the ergometer. Short- and long-interval intracortical inhibition (SICI and LICI), and SAI were measured to assess M1 inhibitory circuits. Intracortical facilitation (ICF) and short-interval intracortical facilitation (SICF) were measured to assess M1 excitatory circuits. We found that acute low-intensity aerobic exercise decreased SICI and SAI in the M1 hand and leg areas. After exercise, ICF in the M1 hand area was lower than in the control experiment, but was not significantly different to baseline. The single motor-evoked potential, resting motor threshold, LICI, SICF, and spinal excitability did not change following exercise. In conclusion, acute low-intensity pedaling modulates M1 intracortical circuits of both exercised and non-exercised areas, without affecting corticospinal and spinal excitability.

Motor cortical excitability during voluntary inhibition of involuntary tic movements.

Tics can be voluntarily inhibited. However, the neurophysiology of voluntary tic inhibition remains underexplored. The objective of this study was to explore state-dependent effects of voluntary tic inhibition on M1 excitability. Neurophysiological assessments (single motor-evoked potentials, corticospinal recruitment curves, short-interval intracortical inhibition, H-reflex) were performed in 14 adults with Tourette syndrome during voluntary tic inhibition and free ticcing. Regressions between behavioral performance and neurophysiological measures were also performed. Voluntary tic inhibition reduced corticospinal excitability: the greater the ability to inhibit tics, the greater was the reduction in excitability. Voluntary tic inhibition was not associated with changes in the excitability of short-interval intracortical inhibition or the H-reflex. Voluntary inhibition of tics reduces the excitability of corticospinal output. The pattern of neurophysiological findings is consistent with a withdrawal of excitation, but not with modulation of the inhibitory interneuronal mechanisms involved in short-interval intracortical inhibition. © 2018 International Parkinson and Movement Disorder Society.

Chronic treatment with rivastigmine in patients with Alzheimer’s disease: A study on primary motor cortex excitability tested by 5 Hz-repetitive transcranial magnetic stimulation

ObjectiveTo investigate changes in cortical excitability and short-term synaptic plasticity we delivered 5Hz repetitive transcranial magnetic stimulation (rTMS) over the primary motor cortex in 11 patients with mild-to-moderate Alzheimer’s disease (AD) before and after chronic therapy with rivastigmine. MethodsResting motor threshold (RMT), motor evoked potential (MEP), cortical silent period (CSP) after single stimulus and MEP facilitation during rTMS trains were tested three times during treatment. All patients underwent neuropsychological tests before and after receiving rivastigmine. rTMS data in patients were compared with those from age-matched healthy controls. ResultsAt baseline, RMT was significantly lower in patients than in controls whereas CSP duration and single MEP amplitude were similar in both groups. In patients, rTMS failed to induce the normal MEP facilitation during the trains. Chronic rivastigmine intake significantly increased MEP amplitude after a single stimulus, whereas it left the other neurophysiological variables studied unchanged. No significant correlation was found between patients’ neuropsychological test scores and TMS measures. ConclusionsChronic treatment with rivastigmine has no influence on altered cortical excitability and short-term synaptic plasticity as tested by 5Hz-rTMS. SignificanceThe limited clinical benefits related to cholinesterase inhibitor therapy in patients with AD depend on factors other than improved plasticity within the cortical glutamatergic circuits.

False Negative and Positive Motor Evoked Potentials in One Patient: Is Single Motor Evoked Potential Monitoring Reliable Method?

A case report and literature review. To report a false negative and delayed positive motor-evoked potential (MEP) in 1 patient. An unreliable MEP can result in fatal outcomes because surgeons have recently begun to depend on the MEP for intraoperative decision-making. We report a case of a false MEP during scoliosis surgery that showed false negative and positive MEPs during a series of operations. A 23-year-old man with a history of spondyloepiphyseal dysplasia presented with severe kyphoscoliosis. The initial neurologic examination did not reveal any neurologic abnormalities. Surgical correction and fusion were performed with transcranial MEP monitoring. During the entire procedure, the MEP did not reveal any signs of cord injury. However, lower limb paralysis and paresthesia was observed when the patient awakened. After 2 additional surgical procedures to recover the neurologic deficit, the MEP did not show any signs of cord injury but the patient's neurologic status had recovered slightly. At postoperative day 8, the neurologic status recovered, and a third operation was performed to fix the long rods. However, there were abnormal amplitudes in both lower limbs but the patient's neurologic status was almost normal. From our experience of false negative and positive MEP in 1 patient, it is concluded that undesirable events can occur with use of MEP in scoliosis or other spinal surgery. Therefore, we warn the surgeons too heavily rely on the MEP monitoring, and propose a further prospective study as well as use of alternative method that can improve the reliability of single MEP.

Intra‐cortical excitability in healthy human subjects after tongue training

Training of specific muscles causes plastic changes in corticomotor pathways which may underlie the effect of various clinical rehabilitation procedures. The paired pulse transcranial magnetic stimulation (ppTMS) technique can be used to assess short interval intra-cortical inhibitory (SICI) and intra-cortical facilitatory (ICF) networks. This study examined changes in SICI and ICF in tongue motor cortex after tongue training in 11 healthy volunteers using ppTMS. Paired pulse TMS was applied to the 'hot-spot' for the tongue motor cortex and motor-evoked potentials (MEPs) were recorded from tongue muscles. In tongue motor cortex, bilateral SICI (P < 0.019) and ICF (P < 0.001) was detected before and after training. There were no significant effects of training on single MEPs or SICI/ICF (P > 0.063). The success rate improved during training (P < 0.001) and changes in success were correlated to changes in single MEP amplitude (P < 0.006) but not to SICI/ICF (P > 0.113). This first study of SICI/ICF after tongue training showed no training-related changes in intra-cortical inhibitory or facilitatory networks. However, there was an association between task performance and changes in corticomotor excitability. Further studies are required to determine the clinical utility of muscle specific training for oral rehabilitation purposes.

Variability of motor potentials evoked by transcranial magnetic stimulation depends on muscle activation

The purpose of this research was to determine whether motor cortex excitability assessed using transcranial magnetic stimulation (TMS) is less variable when subjects maintain a visually controlled low-level contraction of the muscle of interest. We also examined the dependence of single motor evoked potential (MEP) amplitude on stimulation intensity and pre-stimulus muscle activation level using linear and non-linear multiple regression analysis. Eight healthy adult subjects received single pulse TMS over the left motor cortex at a point where minimal stimulation intensity was required to produce MEPs in extensor digitorum communis (EDC). Voluntary activation of the muscle was controlled by visual display of a target force (indicated by a stable line on an oscilloscope) and the isometric force produced as the subject attempted to extend the fingers (indicated by a line on the oscilloscope representing the finger extension force) while subjects were instructed to: exert zero extension force (0%) and produce forces equal to 5 and 10% of maximum voluntary finger extension under separate conditions. Relative variability (coefficient of variation) of single MEPs at a constant stimulus intensity and of pre-stimulus muscle EMG was lower during maintained 5 and 10% contractions than at 0% contraction levels. Therefore, maintaining a stable low intensity contraction helps stabilize cortical and spinal excitability. Multiple regression analyses showed that a linear dependence of single MEPs on stimulation intensity and pre-stimulus muscle activation level produced similar fits to those for a non-linear dependence on stimulus intensity and a linear dependence on pre-stimulus EMG. Thus, a simple linear method can be used to assess dependence of single MEP amplitudes on both stimulus intensity (to characterize slope of the recruitment curve) and low intensity background muscle activation level.