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 ...

In this protocol, we'll demonstrate a feasible easily reproducible, and reliable method for upper and lower limb assessment of corticospinal inhibition. Contralateral silent period is a metric that provides information from complex corticospinal inhibitory circuitry. This method is that therefore a promising candidate of a diagnostic, surrogate, and predictive biomarker for different neurological diseases.Demonstrating the procedure will be Danielle Pimenta, Anne Pessotto, and Daniel Lima, research fellows from my laboratory. To select the muscle for positioning the electrodes, ask the subject to put their hand over the table in a prone position. Then to identify the first dorsal interosseous or FDI muscle, ask the subject to abduct the index finger against the resistance, keeping the rest of the hand still and laying on the table, while palpitating the area.Clean the area with alcohol pads to remove skin oils and other factors that can increase impedance. Place the negative electrode on the belly of the FDI muscle, and the positive on the distal interphalangeal joint with an interelectrode distance of at least 1.5 centimeters. Place the reference or neutral electrode on the wrist over the ulnar styloid process.Next, determine the required muscle contraction force. Use a digital pinch dynamometer and quadrangular pyramid support to minimize mechanical distortions and elevate the sensitivity for minimal contractions. Place the dynamometer between the first and second fingers with the help of the pyramidal support.Ensure that the first and second fingers generate the forces of the pinching movement and capture the electromyography or EMG. With the fixed position ask the participant to press the dynamometer with the first finger and the side of the pyramid with the index finger, squeezing the dynamometer pyramid system with their maximum force and creating a strong contraction of the FDI muscle. Using this value as reference, determine the 20%of maximum force.The participant must practice maintaining the target at 20%of sustained contraction. Next, to identify the initial location for hotspot searching put a swim cap on the subject's head. All the reference points will be marked on it.Measure the sagittal circumference of the head from the nasion to the inion. Divide the value by two and mark the middle spot on the head. Mark the location of the patient's nasion, inion, the helix of both right and left ears, and right and left supraorbital ridge.Measure the tragus to tragus distance and add a mark halfway. Mark the intersection between them, a point identified as the vertex. From the vertex, move five centimeters laterally in parallel to the mid sagittal line on the contralateral side to the selected muscle.This mark identifies the M1 on the same coronal level as the hand motor cortex. Use this as the first spot to initiate the search for the hotspot. The hotspot is the area of the motor cortex where the lowest motor threshold is detectable.Set up a low intensity, and initiate the search by delivering multiple pulses to the first spot. Pursue with small intensity increments until identifying the lowest stimulus that detects electromyography or EMG indexed response. To deliver the stimuli, angle the figure of eight coil at 45 degrees to the mid sagittal line with the handle pointed toward the posterior of the patient.To ensure that the best spot is identified, move around the first spot and test the subsequent three motor evoked potential or MEPs at one centimeter each anterior, lateral and posterior to it. Once the hotspot is identified, mark the spot in the patient's head. Use this location during the experiment and the potential follow-up visits.Use both hands to support the coil on the sub's head. Next to determine the resting motor threshold or RMT, apply 10 consecutive stimuli at the hotspot and select the lowest intensity that produced an MEP with a peak to peak amplitude of at least 50 microvolts on the target muscle in 50%of the trials. For the contralateral silent period or CSP, deliver the 10 suprathreshold stimuli with the stimulation intensity of 120%of the RMT with 10 seconds period in between them to elicit MEPs during tonic voluntary contraction of the target muscle.During stimulation ask the patient to maintain 20%of the maximum motor contraction of the target muscle. To capture the whole silent period or SP, confirm that the EMG time window is long enough to capture up to 400 milliseconds of activity. The delivery of suprathreshold transcranial magnetic stimulation or TMS pulse elicited an observable MEP in the EMG recording of the target muscle, and a subsequent period of background EMG activity suppression of approximately 150 to 300 milliseconds.The relative SP is measured from the MEP start to the reappearance of EMG activity. In contrast, absolute SP is measured from the end of the MEP to the onset of the reemergence of voluntary EMG activity. The stimulus intensity used to elicit MEP directly influence CSP metrics and can vary for difference in study populations.Check for previous successful experiments done in the population of interest to allow for standardization.

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