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

2018 ◽  
Vol 120 (3) ◽  
pp. 1010-1016 ◽  
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.

scholarly journals Modulation of intracortical inhibition during physically performed and mentally simulated balance tasks

2021 ◽  
Vol 121 (5) ◽  
pp. 1379-1388
Author(s):  
A. Mouthon ◽  
J. Ruffieux ◽  
W. Taube
Keyword(s):  
Motor Evoked Potentials ◽  
Action Observation ◽  
Short Interval ◽  
Intracortical Inhibition ◽  
Mental Simulation ◽  
Task Execution ◽  
Postural Tasks ◽  
Execution Condition ◽  
The One ◽  
Postural Task

Abstract Purpose Action observation (AO) during motor imagery (MI), so-called AO + MI, has been proposed as a new form of non-physical training, but the neural mechanisms involved remains largely unknown. Therefore, this study aimed to explore whether there were similarities in the modulation of short-interval intracortical inhibition (SICI) during execution and mental simulation of postural tasks, and if there was a difference in modulation of SICI between AO + MI and AO alone. Method 21 young adults (mean ± SD = 24 ± 6.3 years) were asked to either passively observe (AO) or imagine while observing (AO + MI) or physically perform a stable and an unstable standing task, while motor evoked potentials and SICI were assessed in the soleus muscle. Result SICI results showed a modulation by condition (F2,40 = 6.42, p = 0.009) with less SICI in the execution condition compared to the AO + MI (p = 0.009) and AO (p = 0.002) condition. Moreover, switching from the stable to the unstable stance condition reduced significantly SICI (F1,20 = 8.34, p = 0.009) during both, physically performed (− 38.5%; p = 0.03) and mentally simulated balance (− 10%, p < 0.001, AO + MI and AO taken together). Conclusion The data demonstrate that SICI is reduced when switching from a stable to a more unstable standing task during both real task execution and mental simulation. Therefore, our results strengthen and further support the existence of similarities between executed and mentally simulated actions by showing that not only corticospinal excitability is similarly modulated but also SICI. This proposes that the activity of the inhibitory cortical network during mental simulation of balance tasks resembles the one during physical postural task execution.

High-intensity, low-frequency repetitive transcranial magnetic stimulation enhances excitability of the human corticospinal pathway

2020 ◽  
Vol 123 (5) ◽  
pp. 1969-1978
Author(s):  
Jessica M. D’Amico ◽  
Siobhan C. Dongés ◽  
Janet L. Taylor
Keyword(s):  
Transcranial Magnetic Stimulation ◽  
High Intensity ◽  
Magnetic Stimulation ◽  
Corticospinal Tract ◽  
Motor Evoked Potentials ◽  
Repetitive Transcranial Magnetic Stimulation ◽  
Low Frequency ◽  
Intracortical Inhibition ◽  
Corticospinal Pathway ◽  
Plastic Changes

In this study, we present a novel, intensity-dependent repetitive transcranial magnetic stimulation (rTMS) protocol that induces lasting, plastic changes within the corticospinal tract. High-intensity rTMS at a frequency of 0.1 Hz induces facilitation of motor evoked potentials (MEPs) lasting at least 35 min. Additionally, these changes are not limited only to small MEPs but occur throughout the recruitment curve. Finally, facilitation of MEPs following high-intensity rTMS does not appear to be due to changes in intracortical inhibition or facilitation.

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.

scholarly journals Intermittent single-joint fatiguing exercise reduces TMS-EEG measures of cortical inhibition

2019 ◽  
Vol 121 (2) ◽  
pp. 471-479 ◽  
Author(s):  
Lavender A. Otieno ◽  
George M. Opie ◽  
John G. Semmler ◽  
Michael C. Ridding ◽  
Simranjit K. Sidhu
Keyword(s):  
Transcranial Magnetic Stimulation ◽  
Evoked Potentials ◽  
Magnetic Stimulation ◽  
Motor Evoked Potentials ◽  
Global Analysis ◽  
Intracortical Inhibition ◽  
Corticospinal Excitability ◽  
Cortical Inhibition ◽  
Relaxation Period ◽  
Fatiguing Exercise

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.

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

1997 ◽  
Vol 117 (3) ◽  
pp. 437-443 ◽  
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

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

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.

Variability of motor evoked potentials in stroke explained by corticospinal pathway integrity

2018 ◽  
Vol 11 (4) ◽  
pp. 929-931 ◽  
Author(s):  
Kelsey A. Potter-Baker ◽  
Yin-Liang Lin ◽  
Andre G. Machado ◽  
Adriana B. Conforto ◽  
David A. Cunningham ◽  
...  
Keyword(s):  
Evoked Potentials ◽  
Motor Evoked Potentials ◽  
Corticospinal Pathway

Reduction of Intracortical Inhibition in Soleus Muscle During Postural Activity

2006 ◽  
Vol 96 (4) ◽  
pp. 1711-1717 ◽  
Author(s):  
Oscar Soto ◽  
Josep Valls-Solé ◽  
Paul Shanahan ◽  
John Rothwell
Keyword(s):  
Muscle Contraction ◽  
Motor Evoked Potentials ◽  
Short Interval ◽  
Intracortical Inhibition ◽  
Voluntary Contraction ◽  
Similar Type ◽  
Similar Extent ◽  
Intracortical Facilitation ◽  
Postural Tasks ◽  
Cortical Involvement

Short-interval intracortical inhibition (SICI) decreases during voluntary contraction of the target muscle. It is unknown whether this effect also occurs with postural contractions. We have compared the effects of voluntary and postural contractions on SICI in the soleus (SOL) muscle. We applied transcranial magnetic stimuli (TMS) in subjects under three tasks: sitting at rest (Rest), sitting while activating the SOL muscle (Voluntary), or standing quietly (Postural). In control trials, we applied suprathreshold TMS to obtain unconditioned motor-evoked potentials (MEPs). In test trials, the same TMS was preceded by a subthreshold TMS at different interstimulus intervals (ISIs), to obtain a conditioned MEP. SICI and intracortical facilitation (ICF) were expressed as the decrease or increase in MEP size relative to unconditioned MEPs. There was significant effect of task in mean SICI or mean ICF in SOL. Mean SICI in SOL was 52% in Rest and decreased to 21% in Voluntary and 15% in Postural. Mean ICF in SOL was 132% and decreased to 113% in Voluntary and to 108% in Postural. Mean SICI in SOL was not different in Voluntary and Postural tasks. There was no effect of task in mean SICI or mean ICF in TA. Our results indicate that decrease of SICI with muscle contraction occurs to a similar extent with tonic voluntary and postural activation, suggesting that those contractions require a similar type of cortical involvement. However, it cannot be excluded that some part of the SICI reduction with muscle contraction depends on changes in segmental excitability.

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