ID 186 – Repetition suppression in resting motor evoked potentials evidenced by increase in intracortical inhibition

Fatiguing intermittent single-joint exercise causes an increase in corticospinal excitability and a decrease in intracortical inhibition when measured with peripherally recorded motor evoked potentials (MEPs) after transcranial magnetic stimulation (TMS). Combined TMS and electroencephalography (TMS-EEG) allows for more direct recording of cortical responses through the TMS-evoked potential (TEP). The aim of this study was to investigate the changes in the excitatory and inhibitory components of the TEP during fatiguing single-joint exercise. Twenty-three young (22 ± 2 yr) healthy subjects performed intermittent 30-s maximum voluntary contractions of the right first dorsal interosseous muscle, followed by a 30-s relaxation period repeated for a total of 15 min. Six single-pulse TMSs and one peripheral nerve stimulation (PNS) to evoke maximal M wave (Mmax) were applied during each relaxation period. A total of 90 TMS pulses and 5 PNSs were applied before and after fatiguing exercise to record MEP and TEP. The amplitude of the MEP (normalized to Mmax) increased during fatiguing exercise ( P < 0.001). There were no changes in local and global P30, N45, and P180 of TEPs during the development of intermittent single-joint exercise-induced fatigue. Global analysis, however, revealed a decrease in N100 peak of the TEP during fatiguing exercise compared with before fatiguing exercise ( P = 0.02). The decrease in N100 suggests a fatigue-related decrease in global intracortical GABAB-mediated inhibition. The increase in corticospinal excitability typically observed during single-joint fatiguing exercise may be mediated by a global decrease in intracortical inhibition. NEW & NOTEWORTHY Fatiguing intermittent single-joint exercise causes an increase in corticospinal excitability and a decrease in intracortical inhibition when measured with transcranial magnetic stimulation (TMS)-evoked potentials from the muscle. The present study provides new and direct cortical evidence, using TMS-EEG to demonstrate that during single-joint fatiguing exercise there is a global decrease in intracortical GABAB-mediated inhibition.

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Alterations in the cortical control of standing posture during varying levels of postural threat and task difficulty

Journal of Neurophysiology ◽

10.1152/jn.00709.2017 ◽

2018 ◽

Vol 120 (3) ◽

pp. 1010-1016 ◽

Cited By ~ 6

Author(s):

Craig D. Tokuno ◽

Martin Keller ◽

Mark G. Carpenter ◽

Gonzalo Márquez ◽

Wolfgang Taube

Keyword(s):

Evoked Potentials ◽

Task Difficulty ◽

Motor Evoked Potentials ◽

Intracortical Inhibition ◽

Perceived Threat ◽

Cortical Control ◽

Corticospinal Pathway ◽

Postural Threat ◽

Postural Tasks ◽

Postural Task

Cortical excitability increases during the performance of more difficult postural tasks. However, it is possible that changes in postural threat associated with more difficult tasks may in themselves lead to alterations in the neural strategies underlying postural control. Therefore, the purpose of this study was to examine whether changes in postural threat are responsible for the alterations in corticospinal excitability and short-interval intracortical inhibition (SICI) that occur with increasing postural task difficulty. Fourteen adults completed three postural tasks (supported standing, free standing, or standing on an unstable board) at two surface heights (ground level or 3 m above ground). Single- and paired-pulse magnetic stimuli were applied to the motor cortex to compare soleus (SOL) and tibialis anterior (TA) test motor-evoked potentials (MEPs) and SICI between conditions. SOL and TA test MEPs increased from 0.35 ± 0.29 to 0.82 ± 0.41 mV (SOL) and from 0.64 ± 0.51 to 1.96 ± 1.45 mV (TA), respectively, whereas SICI decreased from 52.4 ± 17.2% to 39.6 ± 15.4% (SOL) and from 71.3 ± 17.7% to 50.3 ± 19.9% (TA) with increasing task difficulty. In contrast to the effects of task difficulty, only SOL test MEPs were smaller when participants stood at high (0.49 ± 0.29 mV) compared with low height (0.61 ± 0.40 mV). Because the presence of postural threat did not lead to any additional changes in the excitability of the motor corticospinal pathway and intracortical inhibition with increasing task difficulty, it seems unlikely that alterations in perceived threat are primarily responsible for the neurophysiological changes that are observed with increasing postural task difficulty. NEW & NOTEWORTHY We examined how task difficulty and postural threat influence the cortical control of posture. Results indicated that the motor corticospinal pathway and intracortical inhibition were modulated more by task difficulty than postural threat. Furthermore, because the presence of postural threat during the performance of various postural tasks did not lead to summative changes in motor-evoked potentials, alterations in perceived threat are not responsible for the neurophysiological changes that occur with increasing postural task difficulty.

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Repetition suppression in transcranial magnetic stimulation induced motor evoked potentials is impaired in schizophrenic patients

Brain Stimulation ◽

10.1016/j.brs.2017.01.231 ◽

2017 ◽

Vol 10 (2) ◽

pp. 415 ◽

Cited By ~ 1

Author(s):

E. Kallioniemi ◽

S. Määttä ◽

M. Könönen ◽

P. Julkunen ◽

L. Säisänen ◽

...

Keyword(s):

Transcranial Magnetic Stimulation ◽

Evoked Potentials ◽

Magnetic Stimulation ◽

Motor Evoked Potentials ◽

Repetition Suppression ◽

Schizophrenic Patients

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Intracortical inhibition of lower limb motor-evoked potentials after paired transcranial magnetic stimulation

Experimental Brain Research ◽

10.1007/s002210050238 ◽

1997 ◽

Vol 117 (3) ◽

pp. 437-443 ◽

Cited By ~ 40

Author(s):

D. S. Stokic´ ◽

W. Barry McKay ◽

Lillian Scott ◽

Arthur M. Sherwood ◽

Milan R. Dimitrijevic´

Keyword(s):

Transcranial Magnetic Stimulation ◽

Evoked Potentials ◽

Lower Limb ◽

Magnetic Stimulation ◽

Motor Evoked Potentials ◽

Intracortical Inhibition

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Modeling motor-evoked potentials from neural field simulations of transcranial magnetic stimulation

10.1101/847830 ◽

2019 ◽

Author(s):

Marcus T Wilson ◽

Bahar Moezzi ◽

Nigel C Rogasch

Keyword(s):

Transcranial Magnetic Stimulation ◽

Evoked Potentials ◽

Outcome Measures ◽

Magnetic Stimulation ◽

Motor Evoked Potentials ◽

Intracortical Inhibition ◽

Population Based ◽

Neural Field ◽

List Type ◽

Single Motor Unit

AbstractObjectiveTo develop a population-based biophysical model of motor-evoked potentials (MEPs) following transcranial magnetic stimulation (TMS).MethodsWe combined an existing MEP model with population-based cortical modeling. Layer 2/3 excitatory and inhibitory neural populations, modeled with neural-field theory, are stimulated with TMS and feed layer 5 corticospinal neurons, which also couple directly but weakly to the TMS pulse. The layer 5 output controls mean motoneuron responses, which generate a series of single motor-unit action potentials that are summed to estimate a MEP.ResultsA MEP waveform was generated comparable to those observed experimentally. The model captured TMS phenomena including a sigmoidal input-output curve, common paired pulse effects (short interval intracortical inhibition, intracortical facilitation, long interval intracortical inhibition) including responses to pharmacological interventions, and a cortical silent period. Changes in MEP amplitude following theta burst paradigms were observed including variability in outcome direction.ConclusionsThe model reproduces effects seen in common TMS paradigms.SignificanceThe model allows population-based modeling of changes in cortical dynamics due to TMS protocols to be assessed in terms of changes in MEPs, thus allowing a clear comparison between population-based modeling predictions and typical experimental outcome measures.HighlightsA model of motor-evoked potential formation gives a realistic electromyogram in response to TMS.The model reproduces effects of SICI, ICF and LICI.A link between existing neural field modeling and realistic outcome measures of TMS is provided.

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Are ipsilateral motor evoked potentials subject to intracortical inhibition?

Journal of Neurophysiology ◽

10.1152/jn.01139.2015 ◽

2016 ◽

Vol 115 (3) ◽

pp. 1735-1739

Author(s):

Alana B. McCambridge ◽

James W. Stinear ◽

Winston D. Byblow

Keyword(s):

Evoked Potentials ◽

Primary Motor Cortex ◽

Biceps Brachii ◽

Motor Evoked Potentials ◽

Short Interval ◽

Conditioning Stimulus ◽

Elbow Flexion ◽

Intracortical Inhibition ◽

Motor Tasks ◽

Active Motor

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.

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Proactive modulation of long-interval intracortical inhibition during response inhibition

Journal of Neurophysiology ◽

10.1152/jn.00144.2016 ◽

2016 ◽

Vol 116 (2) ◽

pp. 859-867 ◽

Cited By ~ 15

Author(s):

Matthew J. Cowie ◽

Hayley J. MacDonald ◽

John Cirillo ◽

Winston D. Byblow

Keyword(s):

Evoked Potentials ◽

Response Inhibition ◽

Primary Motor Cortex ◽

Motor Evoked Potentials ◽

Motor Evoked Potential ◽

Intracortical Inhibition ◽

Task Context ◽

Stop Trial ◽

First Dorsal Interosseous Muscle ◽

Dorsal Interosseous Muscle

Daily activities often require sudden cancellation of preplanned movement, termed response inhibition. When only a subcomponent of a whole response must be suppressed (required here on Partial trials), the ensuing component is markedly delayed. The neural mechanisms underlying partial response inhibition remain unclear. We hypothesized that Partial trials would be associated with nonselective corticomotor suppression and that GABAB receptor-mediated inhibition within primary motor cortex might be responsible for the nonselective corticomotor suppression contributing to Partial trial response delays. Sixteen right-handed participants performed a bimanual anticipatory response inhibition task while single- and paired-pulse transcranial magnetic stimulation was delivered to elicit motor evoked potentials in the left first dorsal interosseous muscle. Lift times, amplitude of motor evoked potentials, and long-interval intracortical inhibition were examined across the different trial types (Go, Stop-Left, Stop-Right, Stop-Both). Go trials produced a tight distribution of lift times around the target, whereas those during Partial trials (Stop-Left and Stop-Right) were substantially delayed. The modulation of motor evoked potential amplitude during Stop-Right trials reflected anticipation, suppression, and subsequent reinitiation of movement. Importantly, suppression was present across all Stop trial types, indicative of a “default” nonselective inhibitory process. Compared with blocks containing only Go trials, inhibition increased when Stop trials were introduced but did not differ between trial types. The amount of inhibition was positively correlated with lift times during Stop-Right trials. Tonic levels of inhibition appear to be proactively modulated by task context and influence the speed at which unimanual responses occur after a nonselective “brake” is applied.

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