scholarly journals The Excitability of Ipsilateral Motor Evoked Potentials Is Not Task-specific and Spatially Distinct From the Contralateral Motor Hotspot

Author(s):  
Nelly Seusing ◽  
Sebastian Strauss ◽  
Robert Fleischmann ◽  
Christina Nafz ◽  
Sergiu Groppa ◽  
...  

Abstract ObjectiveThe role of ipsilateral descending motor pathways in voluntary movement of humans is still a matter of debate. Few studies have examined the task dependent modulation of ipsilateral motor evoked potentials (iMEPs). Here, we determined the location of upper limb biceps brachii (BB) representation within the ipsilateral primary motor cortex. MethodsMR-navigated transcranial magnetic stimulation mapping of the dominant hemisphere was undertaken with twenty healthy participants who made tonic unilateral, bilateral homologous or bilateral antagonistic elbow flexion-extension voluntary contractions. Map center of gravity (CoG) and area for each BB were obtained. ResultsThe map CoG of the ipsilateral BB was located more anterior-laterally than those of the contralateral BB within the primary motor cortex. However different tasks had no effect on either the iMEP CoG location or the size. ConclusionOur data suggests that ipsilateral and contralateral MEP might originate in distinct adjacent neural populations in the primary motor cortex, independent of task dependence.

2004 ◽  
Vol 100 (1) ◽  
pp. 155-160 ◽  
Author(s):  
Katsushige Watanabe ◽  
Takashi Watanabe ◽  
Akio Takahashi ◽  
Nobuhito Saito ◽  
Masafumi Hirato ◽  
...  

✓ The feasibility of high-frequency transcranial electrical stimulation (TES) through screw electrodes placed in the skull was investigated for use in intraoperative monitoring of the motor pathways in patients who are in a state of general anesthesia during cerebral and spinal operations. Motor evoked potentials (MEPs) were elicited by TES with a train of five square-wave pulses (duration 400 µsec, intensity ≤ 200 mA, frequency 500 Hz) delivered through metal screw electrodes placed in the outer table of the skull over the primary motor cortex in 42 patients. Myogenic MEPs to anodal stimulation were recorded from the abductor pollicis brevis (APB) and tibialis anterior (TA) muscles. The mean threshold stimulation intensity was 48 ± 17 mA for the APB muscles, and 112 ± 35 mA for the TA muscles. The electrodes were firmly fixed at the site and were not dislodged by surgical manipulation throughout the operation. No adverse reactions attributable to the TES were observed. Passing current through the screw electrodes stimulates the motor cortex more effectively than conventional methods of TES. The method is safe and inexpensive, and it is convenient for intraoperative monitoring of motor pathways.


2014 ◽  
Vol 111 (2) ◽  
pp. 405-414 ◽  
Author(s):  
Monica A. Perez ◽  
Jane E. Butler ◽  
Janet L. Taylor

Transcallosal inhibitory interactions between proximal representations in the primary motor cortex remain poorly understood. In this study, we used transcranial magnetic stimulation to examine the ipsilateral silent period (iSP; a measure of transcallosal inhibition) in the biceps and triceps brachii during unilateral and bilateral isometric voluntary contractions. Healthy volunteers performed 10% of maximal isometric voluntary elbow flexion or extension with one arm while the contralateral arm remained at rest or performed 30% of maximal isometric voluntary elbow flexion or extension. The iSP was measured in the arm performing 10% contractions, and electromyographic (EMG) recordings were comparable across conditions. The iSP onset and duration in the biceps and triceps brachii were comparable. In both muscles, the iSP depth and area were increased during bilateral contractions of homologous agonist muscles (extension-extension and flexion-flexion) compared with a unilateral contraction, whereas during bilateral contractions of nonhomologous antagonist muscles (extension-flexion and flexion-extension), the iSP depth and area were decreased compared with a unilateral contraction, and sometimes facilitation of EMG was seen. This effect was never observed during bilateral activation of homologous muscles. The size of responses evoked by cervicomedullary electrical stimulation in the arm that made 10% contractions remained unchanged across conditions. Thus transcallosal inhibition targeting triceps and biceps brachii is upregulated by voluntary contraction of the contralateral agonist muscle and downregulated by voluntary contraction of the contralateral antagonist muscle. We speculate that these reciprocal task-dependent interactions between bilateral flexor and extensor arm regions of the motor cortex may contribute to coupling between the arms during motor behavior.


2016 ◽  
Vol 115 (3) ◽  
pp. 1735-1739
Author(s):  
Alana B. McCambridge ◽  
James W. Stinear ◽  
Winston D. Byblow

Paired-pulse transcranial magnetic stimulation (TMS) can be used to examine intracortical inhibition in primary motor cortex (M1), termed short-interval intracortical inhibition (SICI). To our knowledge, SICI has only been demonstrated in contralateral motor evoked potentials (MEPs). Ipsilateral MEPs (iMEPs) are assumed to reflect excitability of an uncrossed oligosynaptic pathway, and can sometimes be evoked in proximal upper-limb muscles using high-intensity TMS. We examined whether iMEPs in the biceps brachii (BB) would be suppressed by subthreshold conditioning, therefore demonstrating SICI of iMEPs. TMS was delivered to the dominant M1 to evoke conditioned (C) and nonconditioned (NC) iMEPs in the nondominant BB of healthy participants during weak bilateral elbow flexion. The conditioning stimulus intensities tested were 85%, 100%, and 115% of active motor threshold (AMT), at 2 ms and 4 ms interstimulus intervals (ISI). The iMEP ratio (C/NC) was calculated for each condition to assess the amount of inhibition. Inhibition of iMEPs was present at 2 ms ISI with 100% and 115% AMT (both P < 0.03), mediated by a reduction in persistence and size (all P < 0.05). To our knowledge, this is the first demonstration of SICI of iMEPs. This technique may be useful as a tool to better understand the role of ipsilateral M1 during functional motor tasks.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Martje G. Pauly ◽  
Annika Steinmeier ◽  
Christina Bolte ◽  
Feline Hamami ◽  
Elinor Tzvi ◽  
...  

AbstractNon-invasive brain stimulation techniques including repetitive transcranial magnetic stimulation (rTMS), continuous theta-burst stimulation (cTBS), paired associative stimulation (PAS), and transcranial direct current stimulation (tDCS) have been applied over the cerebellum to induce plasticity and gain insights into the interaction of the cerebellum with neo-cortical structures including the motor cortex. We compared the effects of 1 Hz rTMS, cTBS, PAS and tDCS given over the cerebellum on motor cortical excitability and interactions between the cerebellum and dorsal premotor cortex / primary motor cortex in two within subject designs in healthy controls. In experiment 1, rTMS, cTBS, PAS, and tDCS were applied over the cerebellum in 20 healthy subjects. In experiment 2, rTMS and PAS were compared to sham conditions in another group of 20 healthy subjects. In experiment 1, PAS reduced cortical excitability determined by motor evoked potentials (MEP) amplitudes, whereas rTMS increased motor thresholds and facilitated dorsal premotor-motor and cerebellum-motor cortex interactions. TDCS and cTBS had no significant effects. In experiment 2, MEP amplitudes increased after rTMS and motor thresholds following PAS. Analysis of all participants who received rTMS and PAS showed that MEP amplitudes were reduced after PAS and increased following rTMS. rTMS also caused facilitation of dorsal premotor-motor cortex and cerebellum-motor cortex interactions. In summary, cerebellar 1 Hz rTMS and PAS can effectively induce plasticity in cerebello-(premotor)-motor pathways provided larger samples are studied.


2006 ◽  
Vol 95 (6) ◽  
pp. 3512-3518 ◽  
Author(s):  
P. G. Martin ◽  
S. C. Gandevia ◽  
J. L. Taylor

This study investigated transmission of corticospinal output through motoneurons over a wide range of voluntary contraction strengths in humans. During voluntary contraction of biceps brachii, motor evoked potentials (MEPs) to transcranial magnetic stimulation of the motor cortex grow up to about 50% maximal force and then decrease. To determine whether the decrease reflects events at a cortical or spinal level, responses to stimulation of the cortex and corticospinal tract (cervicomedullary motor evoked potentials, CMEPs) as well as maximal M-waves (Mmax) were recorded during strong contractions at 50 to 100% maximum. In biceps and brachioradialis, MEPs and CMEPs (normalized to Mmax) evoked by strong stimuli decreased during strong elbow flexions. Responses were largest during contractions at 75% maximum and both potentials decreased by about 25% Mmax during maximal efforts ( P < 0.001). Reductions were smaller with weaker stimuli, but again similar for MEPs and CMEPs. Thus the reduction in MEPs during strong voluntary contractions can be accounted for by reduced responsiveness of the motoneuron pool to stimulation. During strong contractions of the first dorsal interosseous, a muscle that increases voluntary force largely by frequency modulation, MEPs declined more than in either elbow flexor muscle (35% Mmax, P < 0.001). This suggests that motoneuron firing rates are important determinants of evoked output from the motoneuron pool. However, motor cortical output does not appear to be limited at high contraction strengths.


2013 ◽  
Vol 35 (5) ◽  
pp. 1969-1980 ◽  
Author(s):  
Florinda Ferreri ◽  
Fabrizio Vecchio ◽  
David Ponzo ◽  
Patrizio Pasqualetti ◽  
Paolo Maria Rossini

2020 ◽  
Vol 45 (1) ◽  
pp. 72-80
Author(s):  
Anna. P. Nippard ◽  
Evan. J. Lockyer ◽  
Duane. C. Button ◽  
Kevin. E. Power

The purpose of this study was to evaluate corticospinal excitability to the biceps and triceps brachii during forward (FWD) and backward (BWD) arm cycling. Corticospinal and spinal excitability were assessed using transcranial magnetic stimulation and transmastoid electrical stimulation to elicit motor evoked potentials (MEPs) and cervicomedullary evoked potentials (CMEPs), respectively. MEPs and CMEPs were recorded from the biceps and triceps brachii during FWD and BWD arm cycling at 2 positions, 6 and 12 o’clock. The 6 o’clock position corresponded to mid-elbow flexion and extension during FWD and BWD cycling, respectively, while 12 o’clock corresponded to mid-elbow extension and flexion during FWD and BWD cycling, respectively. During the flexion phase, MEP and CMEP amplitudes of the biceps brachii were higher during FWD cycling. However, during the extension phase, MEP and CMEP amplitudes were higher during BWD cycling. For the triceps brachii, MEP amplitudes were higher during FWD cycling regardless of phase. However, CMEP amplitudes were phase-dependent. During the flexion phase, CMEPs of the triceps brachii were higher during FWD cycling compared with BWD, but during the extension phase CMEPs were higher during BWD cycling compared with FWD. The data suggest that corticospinal and spinal excitability to the biceps brachii is phase- and direction-dependent. In the triceps brachii, spinal, but not corticospinal, excitability is phase-dependent when comparing FWD and BWD cycling. Novelty This is the first study to assess corticospinal excitability during FWD and BWD locomotor output. Corticospinal excitability during arm cycling depends on the direction, phase, and muscle being assessed.


1997 ◽  
Vol 82 (1) ◽  
pp. 144-151 ◽  
Author(s):  
J. R. Potvin

Potvin, J. R. Effects of muscle kinematics on surface EMG amplitude and frequency during fatiguing dynamic contractions. J. Appl. Physiol. 82(1): 144–151, 1997.—Fifteen male subjects performed a repetitive elbow flexion/extension task with a 7-kg mass until exhaustion. Average joint angle, angular velocity, and biceps brachii surface electromyographic (EMG) amplitude (aEMG) and mean power frequency (MPF) were calculated with each consecutive 250-ms segment of data during the entire trial. Data were separated into concentric or eccentric phases and into seven 20°-ranges from 0 to 140° of elbow flexion. A regression analysis was used to estimate the rested and fatigued aEMG and MPF values. aEMG values were expressed as a percentage of amplitudes from maximum voluntary contractions (MVC). Under rested dynamic conditions, the average concentric aEMG amplitude was 10% MVC higher than average eccentric values. Rested MPF values were similar for concentric and eccentric phases, although values increased ∼20 Hz from the most extended to flexed joint angles. Fatigue resulted in an average increase in concentric and eccentric aEMG of 35 and 10% MVC, respectively. The largest concentric aEMG increases (up to 58% MVC) were observed at higher joint velocities, whereas eccentric increases appeared to be related to decreases in velocity. Fatigue had a similar effect on MPF during both concentric and eccentric phases. Larger MPF decreases were observed at shorter muscle lengths such that values within each angle range were very similar by the end of the trial. It was hypothesized that this finding may reflect a biological minimum in conduction velocity before propagation failure occurs.


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