Name: measuring contralateral silent period induced by single-pulse transcranial magnetic stimulation to investigate m1 corticospinal inhibition
Uploaded: 2022-08-23T13:30:00
Description: Watch this Scientific Journal Video about Measuring Contralateral Silent Period Induced by Single-Pulse Transcranial Magnetic Stimulation to Investigate M1 Corticospinal Inhibition at JoVE.com

No acknowledgments.

This protocol involves research on human subjects and is in alliance with institutional and ethical guidelines of local ethical committees and the Declaration of Helsinki. Informed consent was obtained from subjects for using their data in the study.
1. Pre-experimental procedures
<ol>
	<li>Screening of the subject. Screen the subject for intracranial implants, epilepsy, history of seizures, and pregnancy. Use questionnaire guidelines to ensure compliance with up-to-date saf...

The default SI to elicit MEP and SPs can vary according to the population. Intensities as low as 80% RMT have been shown to elicit cSP in healthy individuals39, still studies on both healthy and diseased populations have used intensities as high as 150% RMT49,50,51. Although this source of heterogeneity can be inherent to the nature of the target population, it should not be neglected as different SIs hav...

The silent period (SP) is a period of electromyographic (EMG) silence that follows a motor-evoked potential (MEP) induced by transcranial magnetic stimulation (TMS) applied during sustained muscle contraction. The suprathreshold TMS pulse can either be applied to the contralateral or ipsilateral primary motor cortex (M1) of the target muscle from which the EMG activity is being recorded yielding two phenomena: contralateral silent period (cSP) and ipsilateral silent period (iSP).
Even though iSP and cSP share similar features, they may reflect slightly different components. The first is thought to reflect transcallosal inhibition and thus be entirely of cortical origin1,2. Conversely, cSP is investigated as a possible surrogate of corticospinal inhibition, most likely mediated by gamma-aminobutyric acid (GABA) B receptors within M13,4,5.
Supporting the role of cSP in GABA-mediated pathways, previous works have found an increase in cSP duration after oral administration of GABA-enhancing components5,6,7,8. Still, spinal processes are also involved in altering its duration. The earlier phase (&#60;50 ms) of the cSP is associated with decreased H-reflex values3-a reflex that is a product of peripheral neurocircuitry and that quantifies the excitability of spinal neurons9. Spinal processing is thought to be mediated through the activation of Renshaw cells, motoneuron after-hyperpolarization, and postsynaptic inhibition by spinal interneurons10,11,12,13,14.
Despite spinal contribution, cSP results mainly from the activation of cortical inhibitory neurons, which are responsible for generating the later part of the cSP (50-200 ms)3,10,13,15,16. In that respect, the early part of cSP duration has been associated with spinal inhibition mechanisms, whereas long cSPs request larger cortical inhibitory mechanisms3,13,17,18.
Therefore, cSP is a promising biomarker candidate for corticospinal maladaptation due to neurological disorders, whereas more significant cSP durations potentially reflect an increase in corticospinal inhibition and vice versa5,11. Accordingly, previous works have found an association between cSP duration and pathologies such as dystonia, Parkinson&#39;s Disease, chronic pain, stroke, and other neurodegenerative and psychiatric conditions19,20,21,22. To illustrate, in a knee osteoarthritis cohort, a higher intracortical inhibition (as indexed by cSP) was associated with younger age, greater cartilage degeneration, and less cognitive performance in the Montreal cognitive assessment scale23. Moreover, cSP changes could also longitudinally index treatment response and motor recovery24,25,26,27,28,29,30.
As promising as the role of cSP in the neuropsychiatry field is, a challenging aspect of its assessment is that it can be too sensitive to protocol variations. For instance, the cSP duration (~100-300 ms)11&#160;is distinguishable between upper and lower limbs. Salerno et al. found an average cSP duration of 121.2 ms (&#177; 32.5) for the first dorsal interosseous muscle (FDI) and 75.5 ms (&#177; 21) for the tibialis anterior muscle (TA), in a sample of fibromyalgia patients31. Thus, the literature conveys a myriad of divergences in the parameters used to elicit cSPs, which in turn jeopardizes comparability across studies and delays the translation to clinical practice. Within a similar population, protocols have been heterogeneous regarding the suprathreshold TMS pulse setting used to stimulate M1 and the target muscle, for example. On top of that, researchers have failed to properly report the parameters used in their protocols.
Therefore, the goal is to provide a visual guideline on how to apply a feasible, reliable, and easily reproducible cSP protocol for evaluating M1 corticospinal excitability of upper and lower limbs and to discuss the practical methodological challenges of that procedure. Also, to help illustrate the reasoning for the choice of parameters, we conducted a non-exhaustive literature review on Pubmed/MEDLINE to identify published papers on cSP in chronic pain and rehabilitation populations, using the search term: Rehabilitation (Mesh) or rehabilitation or chronic pain&#160;or stroke and terms such as transcranial magnetic stimulation and single pulse or cortical silent period. No inclusion criteria were defined for the extraction, and pooled results are displayed in Table 1 for illustrative purposes only.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Alcohol pads</td>
			<td>Medline</td>
			<td></td>
			<td>Preparation with 70% isopropyl alcohol</td>
		</tr>
		<tr>
			<td>Conductive gel</td>
			<td>Weaver and Company</td>
			<td></td>
			<td>Used on the electrode</td>
		</tr>
		<tr>
			<td>Echo Pinch</td>
			<td>JTECH medical</td>
			<td>0902A302</td>
			<td>Digital dynamometer.</td>
		</tr>
		<tr>
			<td>Mega-EMG</td>
			<td>Soterix Medical</td>
			<td>NS006201</td>
			<td>Digital multiple channel EMG with built in software.</td>
		</tr>
		<tr>
			<td>MEGA-TMS coil</td>
			<td>Soterix Medical</td>
			<td>NS063201</td>
			<td>8 shaped TMS coil</td>
		</tr>
		<tr>
			<td>Mega-TMS stimulator</td>
			<td>Soterix Medical</td>
			<td>6990061</td>
			<td>Single Pulse TMS</td>
		</tr>
		<tr>
			<td>Neuro-MEP.NET</td>
			<td>Soterix Medical</td>
			<td></td>
			<td>EMG software used to analyse the muscles eletrical activity.</td>
		</tr>
		<tr>
			<td>Swim cap</td>
			<td>Kiefer</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

measuring contralateral silent period induced by single-pulse transcranial magnetic stimulation to investigate m1 corticospinal inhibition

Contralateral silent period (cSP) is a period of suppression in the background electrical muscle activity captured by electromyography (EMG) after a motor evoked potential (MEP). To obtain this, an MEP is elicited by a suprathreshold transcranial magnetic stimulation (TMS) pulse delivered to the primary motor cortex (M1) of the target muscle selected, while the participant provides a standardized voluntary target muscle contraction. The cSP is a result of inhibitory mechanisms that occur after the MEP; it provides a broad temporal assessment of spinal inhibition in its initial ~50 ms, and cortical inhibition after. Researchers have tried to better understand the neurobiological mechanism behind the cSP to validate it as a potential diagnostic, surrogate, and predictive biomarker for different neuropsychiatric diseases. Therefore, this article describes a method to measure M1 cSP of lower and upper limbs, including a selection of target muscle, electrode placement, coil positioning, method of measuring voluntary contraction stimulation, intensity setup, and data analysis to obtain a representative result. It has the educational objective of giving a visual guideline in performing a feasible, reliable, and reproducible cSP protocol for lower and upper limbs and discussing practical challenges of this technique.

After following the step-by-step procedure, the delivery of a suprathreshold TMS pulse (120% of the RMT) will elicit an observable MEP in the EMG recording of the target muscle, and a subsequent period of background EMG activity suppression of approximately 150 ms to 300 ms (Figure 2). From that EMG pattern, it&#39;s possible to calculate the cSP metrics. The most reported outcomes are the duration (in the range of ms) of the relative and absolute SP. The relative SP is measured from the MEP...

Watch this Scientific Journal Video about Measuring Contralateral Silent Period Induced by Single-Pulse Transcranial Magnetic Stimulation to Investigate M1 Corticospinal Inhibition at JoVE.com

Measuring Contralateral Silent Period Induced by Single-Pulse Transcranial Magnetic Stimulation to Investigate M1 Corticospinal Inhibition

Contralateral silent period (cSP) assessment is a promising biomarker to index cortical excitability and treatment response. We demonstrate a protocol to assess cSP intended for studying M1 corticospinal inhibition of upper and lower limbs.

Contralateral silent period (cSP) is a period of suppression in the background electrical muscle activity captured by electromyography (EMG) after a motor ...

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