scholarly journals Stimulus Intensity Affects Variability of Motor Evoked Responses of the Non-Paretic, but Not Paretic Tibialis Anterior Muscle in Stroke

2020 ◽  
Vol 10 (5) ◽  
pp. 297
Author(s):  
Anjali Sivaramakrishnan ◽  
Sangeetha Madhavan
Keyword(s):  
Stimulus Intensity ◽  
Tibialis Anterior ◽  
Motor Evoked Potentials ◽  
Tibialis Anterior Muscle ◽  
Silent Period ◽  
Stimulus Response ◽  
Coefficients Of Variation ◽  
Magnetic Stimulus ◽  
Active Motor ◽  
Selection Of

Background: Transcranial magnetic stimulus induced motor evoked potentials (MEPs) are quantified either with a single suprathreshold stimulus or using a stimulus response curve. Here, we explored variability in MEPs influenced by different stimulus intensities for the tibialis anterior muscle in stroke. Methods: MEPs for the paretic and non-paretic tibialis anterior (TA) muscle representations were collected from 26 participants with stroke at seven intensities. Variability of MEP parameters was examined with coefficients of variation (CV). Results: CV for the non-paretic TA MEP amplitude and area was significantly lower at 130% and 140% active motor threshold (AMT). CV for the paretic TA MEP amplitude and area did not vary with intensity. CV of MEP latency decreased with higher intensities for both muscles. CV of the silent period decreased with higher intensity for the non-paretic TA, but was in reverse for the paretic TA. Conclusion: We recommend a stimulus intensity of greater than 130% AMT to reduce variability for the non-paretic TA. The stimulus intensity did not affect the MEP variability of the paretic TA. Variability of MEPs is affected by intensity and side tested (paretic and non-paretic), suggesting careful selection of experimental parameters for testing.

Task-dependent changes of motor cortical network excitability during precision grip compared to isolated finger contraction

2012 ◽  
Vol 107 (5) ◽  
pp. 1522-1529 ◽  
Author(s):  
Nezha Kouchtir-Devanne ◽  
Charles Capaday ◽  
François Cassim ◽  
Philippe Derambure ◽  
Hervé Devanne
Keyword(s):  
Stimulus Intensity ◽  
Motor Evoked Potentials ◽  
Precision Grip ◽  
Silent Period ◽  
Intracortical Inhibition ◽  
Emg Activity ◽  
Maximum Slope ◽  
Corticospinal Pathway ◽  
Long Latency ◽  
Motor Cortical

The purpose of this study was to determine whether task-dependent differences in corticospinal pathway excitability occur in going from isolated contractions of the index finger to its coordinated activity with the thumb. Focal transcranial magnetic stimulation (TMS) was used to measure input-output (I/O) curves—a measure of corticospinal pathway excitability—of the contralateral first dorsal interosseus (FDI) muscle in 21 healthy subjects performing two isometric motor tasks: index abduction and precision grip. The level of FDI electromyographic (EMG) activity was kept constant across tasks. The amplitude of the FDI motor evoked potentials (MEPs) and the duration of FDI silent period (SP) were plotted against TMS stimulus intensity and fitted, respectively, to a Boltzmann sigmoidal function. The plateau level of the FDI MEP amplitude I/O curve increased by an average of 40% during the precision grip compared with index abduction. Likewise, the steepness of the curve, as measured by the value of the maximum slope, increased by nearly 70%. By contrast, all I/O curve parameters [plateau, stimulus intensity required to obtain 50% of maximum response ( S50), and slope] of SP duration were similar between the two tasks. Short- and long-latency intracortical inhibitions (SICI and LICI, respectively) were also measured in each task. Both measures of inhibition decreased during precision grip compared with the isolated contraction. The results demonstrate that the motor cortical circuits controlling index and thumb muscles become functionally coupled when the muscles are used synergistically and this may be due, at least in part, to a decrease of intracortical inhibition and an increase of recurrent excitation.

Factors predicting the feasibility of monitoring lower-limb muscle motor evoked potentials in patients undergoing excision of spinal cord tumors

2011 ◽  
Vol 14 (6) ◽  
pp. 748-753 ◽  
Author(s):  
Vedantam Rajshekhar ◽  
Parthiban Velayutham ◽  
Mathew Joseph ◽  
K. Srinivasa Babu
Keyword(s):  
Spinal Cord ◽  
Evoked Potentials ◽  
Success Rate ◽  
Lower Limb ◽  
Tibialis Anterior ◽  
Muscle Power ◽  
Motor Evoked Potentials ◽  
Tibialis Anterior Muscle ◽  
Spinal Cord Tumors ◽  
Motor Outcome

Object This prospective study on intraoperative muscle motor evoked potentials (MMEPs) from lower-limb muscles in patients undergoing surgery for spinal cord tumors was performed to: 1) determine preoperative clinical features that could predict successful recording of lower-limb MMEPs; 2) determine the muscle in the lower limb from which MMEPs could be most consistently obtained; 3) assess the need to monitor more than 1 muscle per limb; and 4) determine the effect of a successful baseline MMEP recording on early postoperative motor outcome. Methods Of 115 consecutive patients undergoing surgery for spinal cord tumors, 110 were included in this study (44 intramedullary and 66 intradural extramedullary tumors). Muscle MEPs were generated using transcranial electrical stimulation under controlled anesthesia and were recorded from the tibialis anterior, quadriceps, soleus, and external anal sphincter muscles bilaterally. The effect of age (≤ 20 or > 20 years old), location of the tumor (intramedullary or extramedullary), segmental location of the tumor (cervical, thoracic, or lumbar), duration of symptoms (≤ 12 or > 12 months), preoperative functional grade (Nurick Grades 0–3 or 4–5), and muscle power (Medical Research Council Grades 0/5–3/5 or 4/5–5/5) on the success rate of obtaining MMEPs was studied using multiple regression analysis. The effect of the ability to monitor MMEPs on motor outcome at discharge from the hospital was also analyzed. Results The overall success rate for obtaining baseline lower-limb MMEPs was 68.2% (75 of 110 patients). Eighty-nine percent of patients with Nurick Grades 0–3 had successful MMEP recordings. Muscle MEPs could not be obtained in any patient in whom muscle power was 2/5 or less, but were obtained from 91.4% of patients with muscle power of 4/5 or more. Analysis showed that only preoperative Nurick grade (p ≤ 0.0001) and muscle power (p < 0.0001) were significant predictors of the likelihood of obtaining MMEPs. Responses were most consistently obtained from the tibialis anterior muscle (68%), but in the other 32% MMEPs could not be recorded from the tibialis anterior but could be recorded from another muscle. The ability to monitor MMEPs was associated with better motor outcome at discharge from the hospital (p = 0.052). Conclusions The likelihood of obtaining lower-limb MMEPs is significantly greater in patients with better functional grades and higher motor power. Muscle MEPs are most consistently obtained from the tibialis anterior muscle but other muscles should also be monitored to optimize the chances of obtaining MMEP responses from the lower limbs.

Changes in Excitability of the Cortical Projections to the Human Tibialis Anterior After Paired Associative Stimulation

2007 ◽  
Vol 97 (3) ◽  
pp. 1951-1958 ◽  
Author(s):  
N. Mrachacz-Kersting ◽  
M. Fong ◽  
B. A. Murphy ◽  
T. Sinkjær
Keyword(s):  
Tibialis Anterior ◽  
Evoked Potential ◽  
Motor Evoked Potentials ◽  
Paired Associative Stimulation ◽  
Central Processing ◽  
Cortical Projections ◽  
Magnetic Stimulus ◽  
Before And After ◽  
The Subject ◽  
Plastic Changes

Paired associative stimulation (PAS) based on Hebb's law of association can induce plastic changes in the intact human. The optimal interstimulus interval (ISI) between the peripheral nerve and transcranial magnetic stimulus is not known for muscles of the lower leg. The aims of this study were to investigate the effect of PAS for a variety of ISIs and to explore the efficacy of PAS when applied during dynamic activation of the target muscle. PAS was applied at 0.2 Hz for 30 min with the tibialis anterior (TA) at rest. The ISI was varied randomly in seven sessions ( n = 5). Subsequently, PAS was applied ( n = 14, ISI = 55 ms) with the TA relaxed or dorsi-flexing. Finally, an optimized ISI based on the subject somatosensory evoked potential (SEP) latency plus a central processing delay (6 ms) was used ( n = 13). Motor-evoked potentials (MEPs) were elicited in the TA before and after the intervention, and the size of the TA MEP was extracted. ISIs of 45, 50, and 55 ms increased and 40 ms decreased TA MEP significantly ( P = 0.01). PAS during dorsi-flexion increased TA MEP size by 92% ( P = 0.001). PAS delivered at rest resulted in a nonsignificant increase; however, when the ISI was optimized from SEP latency recordings, all subjects showed significant increases ( P = 0.002). No changes in MEP size occurred in the antagonist. Results confirm that the excitability of the corticospinal projections to the TA but not the antagonist can be increased after PAS. This is strongly dependent on the individualized ISI and on the activation state of the muscle.

Human corticospinal-motoneuronal output is reduced with 5-HT2 receptor antagonism

2021 ◽  
Author(s):  
Jacob R Thorstensen ◽  
Janet Louise Taylor ◽  
Justin J Kavanagh
Keyword(s):  
Repeated Measures ◽  
Biceps Brachii ◽  
Motor Evoked Potentials ◽  
Silent Period ◽  
Human Movement ◽  
Moderate Intensity ◽  
Response Curves ◽  
Stimulus Response ◽  
Repeated Measures Design ◽  
Double Blinded

Animal models indicate that serotonin (5-HT) release onto motoneurons facilitates motor output, particularly during strong motor activities. However, evidence for 5-HT effects during human movement are limited. This study examined how antagonism of the 5-HT2 receptor, which is a 5-HT receptor that promotes motoneuron excitability, affects human movement. Ten healthy participants (24.2 ± 1.9 yr) ingested 8 mg of cyproheptadine (competitive 5-HT2 antagonist) in a double-blinded, placebo-controlled, repeated-measures design. Transcranial magnetic stimulation (TMS) of the motor cortex was used to elicit motor evoked potentials (MEPs) from biceps brachii. First, stimulus-response curves (90-160% active motor threshold) were obtained during very weak elbow flexions (10% of maximal). Second, to determine if 5-HT effects are scaled to the intensity of muscle contraction, TMS at a fixed intensity was applied during elbow flexions of 20, 40, 60, 80 and 100% of maximal. Cyproheptadine reduced the size of MEPs across the stimulus-response curves (P = 0.045). Notably, MEP amplitude was 22.3% smaller for the cyproheptadine condition for the strongest TMS intensity. In addition, cyproheptadine reduced maximal torque (P = 0.045), lengthened the biceps silent period during maximal elbow flexions (P = 0.037), and reduced superimposed twitch amplitude during moderate-intensity elbow flexions (P = 0.035). This study presents novel evidence that 5-HT2 receptors influence corticospinal-motoneuronal output, which was particularly evident when a large number of descending inputs to motoneurons were active. While it is likely that antagonism of 5-HT2 receptors reduces motoneuron gain to ionotropic inputs, supraspinal mechanisms may have also contributed to the study findings.

Abstract 73: Neurophysiology Of Ipsilateral Corticomotor Projections After Perinatal Stroke

Stroke ◽  
2013 ◽  
Vol 44 (suppl_1) ◽  
Author(s):  
Omar Damji ◽  
Oleg Kotsovsky ◽  
Robert Chen ◽  
Adam Kirton
Keyword(s):  
Developmental Plasticity ◽  
Motor Evoked Potentials ◽  
Intracortical Inhibition ◽  
Response Curves ◽  
Perinatal Stroke ◽  
Motor Disability ◽  
Stimulus Response ◽  
Active Motor ◽  
Stroke Type ◽  
Cortical Physiology

Objectives: Perinatal stroke (PS) causes most hemiparetic cerebral palsy. Persistence of ipsilateral corticomotor connections from unlesioned hemisphere to affected hand are established. Their neurophysiology is not understood and developmental plasticity models suggest they are a therapeutic target. We hypothesized that ipsi projections have distinct neurophysiology that correlates with motor disability. Methods: Children 6-18 years with PS (arterial or PVI) and hemiparesis were recruited (Alberta Perinatal Stroke Project). Transcranial magnetic stimulation (TMS) protocols were applied to the non-lesioned M1. Outcomes included rest motor thresholds and bilateral stimulus response curves (SRC). Paired pulse TMS at 2 and 10 ms (90% active motor threshold conditioning) explored short-latency intracortical inhibition (SICI) and intracortical facilitation (ICF). Ipsi motor evoked potentials (MEPs) were quantified (≥0.05mV at 120% RMT in ≥5/20 trials). Motor outcomes were Assisting Hand (AHA) and Melbourne (MA) assessments. Ipsi physiology was compared to contra and motor outcome (t-test, (rm)ANOVA). Safety and tolerability was assessed. Results: Of 35 children (20 male; 55% arterial, 45% PVI), 14 (40%) met ipsi criteria. Presence of ipsi projections correlated with motor disability (AHA, p=0.03, MA p=0.10) but not stroke type. Ipsi intensity correlated with AHA (r=-0.58; p=0.004) and MA (r=-0.45; p=0.013). Ipsi SRC slope was lower than contra (p=0.01). SICI (contra -38.5%, ipsi -30.7%; p<0.05) and ICF (contra +15.4%, ipsi +23.1%; p<0.05) were present and differed between sides (p= 0.004). Procedures were well tolerated. Conclusions: Cortical physiology of ipsilateral projections can be measured in children with PS. Differences between ipsi and contralateral physiology may be relevant central therapeutic targets.

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