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All procedures involving human participants have been performed in compliance with the institutional, national, and international guidelines for human welfare and have been reviewed by the local institutional review board.
1. Experimental procedures (Figure 1)
<ol>
	<li>Select the muscle for positioning the electrodes.
	<ol>
		<li>Ask the subject to put their hand over the table, in a prone position. Select the FDI muscle, localized between the first and second metacarpal osseous. To identify the FDI, ask the subject to abduct their index finger against resistance, keeping the rest of the hand still and laying on the table, while you are palpating the area.</li>
		<li>Expose the selected area. Use a disposable razor to shave the area to improve electrode contact with the skin, if necessary, and clean the area with alcohol pads to remove skin oils and other factors that could increase impedance. Certify that there is free skin to ensure contact with the electrode. 
		NOTE: If evaluating lower limb activity, use the tibialis anterior (TA) muscle for electrode placement. It is localized on the lateral side of the tibia and lies near the superficies of the skin. It can be identified by ankle dorsiflexion.</li>
	</ol>
	</li>
	<li>Place the surface electromyography (EMG) electrodes
	<ol>
		<li>With the area exposed and cleaned, apply the conductive gel to each electrode of the channel to ensure good impedance.</li>
		<li>Place the negative electrode on the belly of the FDI muscle (the center or the most prominent bulge of the muscle belly) and the positive on the distal interphalangeal joint, with an inter-electrode distance of at least 1.5 cm. Place the reference electrode (neutral) on the wrist, over the ulnar styloid process. 
		NOTE: The presence of motor endpoints, muscle tendons, or other active muscles can impact the stability of the recordings, so it is important to avoid these locations. For the TA muscle, the electrodes should be placed at one-third on the line that connects the tip of the fibula and the tip of the medial malleolus. Provide a 20 mm distance between each electrode&#39;s pole and place the reference electrode in the ankle.</li>
	</ol>
	</li>
	<li>Determine the required muscle contraction force
	<ol>
		<li>Use a digital pinch dynamometer and a quadrangular pyramid support to minimize mechanical distortions and elevate the sensitivity for minimal contractions.</li>
		<li>Place the dynamometer between the first and second fingers with the help of the pyramidal support. Ensure that the third, fourth, and fifth fingers lay still on the table, while the 1st and 2nd generate the forces of the pinching movement.</li>
		<li>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.</li>
		<li>Using that value as reference, determine the 20% of maximum force. The participant must practice maintaining the target at 20% of sustained contraction. Allow for variations from 15%-25% of maximum voluntary contraction (MVC). 
		NOTE: Alternatively, in case of unavailability of a dynamometer that can catch the isolated muscle activity being investigated, use EMG feedback to standardize force. The recording software will measure the maximum peak-to-peak amplitude that corresponds to the subject&#39;s maximum force, and using that value as reference, will determine the 20% MVC. Subjects can receive visual and/or auditory clues of when 20% is achieved.</li>
	</ol>
	</li>
	<li>Identification of the initial location for hotspot searching
	<ol>
		<li>Put a swim cap on the subject&#39;s head. All the reference points will be marked on it.</li>
		<li>Measure the sagittal circumference of the head from the nasion (the point between the forehead and the nose) to the inion (the most prominent point in the occipital region). Divide that value by two and mark that middle spot on the head.</li>
		<li>Mark the location of the patient&#39;s nasion, inion, the helix of both right and left external ears, and right and left supraorbital ridge. This is to certify that the cap has not slipped during the procedure, and/or that in future experiments it will be equally positioned on the patient&#39;s head.</li>
		<li>As described above, measure the tragus-to-tragus distance and add a mark halfway. Mark the intersection between them, a point identified as the vertex (Cz).</li>
		<li>From the vertex, move 5 cm laterally in parallel to the midsagittal line, on the contralateral side to the selected muscle. This mark approximately 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.</li>
		<li>The hotspot is the area of the motor cortex where the lowest motor threshold is detectable. Set up a low intensity (e.g., 30% of maximum stimulator output [MSO]) and initiate the search by delivering multiple pulses to the first spot.</li>
		<li>Pursue with small intensity increments until identifying the lowest stimulus that detects an EMG-indexed response (i.e., MEP). For the delivery of the stimuli, angle the figure-of-eight coil at 45&#176; in relation to the midsagittal line with the handle pointed toward the posterior of the patient.</li>
		<li>To ensure that the best spot was identified, move around the first spot and test the subsequent ~3 MEPs at 1 cm anterior, 1 cm lateral, 1 cm medial, and 1 cm posterior to it. Repeat this procedure as many times as needed for a consistent response; stick to the spot that elicits the largest MEP.</li>
		<li>Once the hotspot is found, mark that spot in the patient&#39;s head (swim cap). Use this location during this experiment and the potential follow-up visits. Be cautious so as not to cause discomfort to the subject due to extra pressure. Use both hands to support the coil on the subject&#39;s head.</li>
	</ol>
	</li>
	<li>Determine resting motor threshold (RMT)
	<ol>
		<li>Estimate the motor threshold as the minimum intensity required to promote an MEP of a minimal detectable amplitude (usually at least 50-100 &#181;V).</li>
		<li>To determine the motor threshold, apply ten consecutive stimuli at the hotspot and select the lowest intensity that produced an MEP with a peak-to-peak amplitude of at least 50 &#181;V on the target muscle, in 50% of the trials. 
		NOTE: This protocol can be done with the target muscle at rest (RMT) or during active contraction (active motor threshold [AMT]). Both can further be used as references for the suprathreshold TMS pulses. The acquisition of the AMT is more prone to variability because it relies on the standardization of MVC, which can be an issue for longitudinal studies with multiple assessments.</li>
	</ol>
	</li>
	<li>CSP protocol
	<ol>
		<li>Deliver suprathreshold stimuli to elicit MEPs during tonic voluntary contraction of the target muscle.</li>
		<li>Deliver 10 stimuli with the stimulation intensity (SI) of 120% of the RMT with 10 s period in between them. During the application of the stimuli, ask the patient to maintain 20% of the maximum motor contraction of the target muscle, as practiced with the dynamometer.</li>
		<li>To ensure capturing the whole SP, certify that the EMG time window is long enough to capture up to 400 ms of EMG activity. Not infrequently - depending on the disease being studied - subjects might require higher SIs for a successful cSP to be obtained.</li>
	</ol>
	</li>
</ol>

<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 the contralateral silent period induced by transcranial magnetic stimulation

Source: Rebello-Sanchez, I., et al. <a href="https://app.jove.com/v/64231">Measuring Contralateral Silent Period Induced by Single-Pulse Transcranial Magnetic Stimulation to Investigate M1 Corticospinal Inhibition.</a> J. Vis. Exp. (2022).
This video demonstrates a technique for measuring the contralateral silent period (cSP) using transcranial magnetic stimulation. Position the patient&#39;s hand prone and place an electrode on the first dorsal interosseous (FDI) muscle. Then, place a force-measuring device between the thumb and index finger. Identify the primary motor cortex (M1) region of the brain. Maintain a standardized pressure on the force-measuring device and stimulate the M1 region to record the muscle activity, termed the motor-evoked potential (MEP), followed by the subsequent period of reduced muscle activity, termed cSP.

<img alt="Figure 1" src="/files/ftp_upload/22880/22880_Figure1.jpg" /> 
Figure 1: Experimental steps. 1. Electrode placement on the belly of the FDI muscle 2. Positioning of the dynamometer between fingers. 3. Voluntary contraction of the target muscle to test the standardization of 20% MVC 4. Head measurements and TMS pulses for identification of the hotspot and the RMT (lowest stimuli that elicits an MEP of at least 50 mV in five out of ten trials) 5. CSP protocol,...

Measuring the Contralateral Silent Period Induced by Transcranial Magnetic Stimulation

All procedures involving human participants have been performed in compliance with the institutional, national, and international guidelines for human ...

Take a human patient&#39;s hand. Place a negative electrode on the first dorsal interosseous, or FDI, muscle to record its activity. Place a positive electrode on the distal joint and a reference electrode on the wrist to establish baseline signal.
Position a force-measuring device between the thumb and the index finger.
Maintain a standardized force on the device and record the muscle activity.
Locate the primary motor cortex, or M1, on the contralateral side of the brain that regulates FDI activity.
Position a magnetic coil on M1 and identify the lowest-intensity threshold stimulus to generate action potentials in cortical neurons that lead to FDI contraction, known as motor-evoked potential or MEP.
Deliver a suprathreshold pulse to elicit a high-amplitude MEP.
The cortical interneurons release inhibitory neurotransmitters that block cortical neurons, preventing excessive muscle activity.
Record the contralateral silent period, or cSP, a period of reduced muscle activity before voluntary activity returns.

measuring-contralateral-silent-period-induced-transcranial-magnetic

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Neuroscience

Neurophysiology

Stimulation and Modulation Techniques

45 Views. Source: Rebello-Sanchez, I., et al. Measuring Contralateral Silent Period Induced by Single-Pulse Transcranial Magnetic Stimulation to Investigate M1 Corticospinal Inhibition. J. Vis. Exp. (2022). This video demonstrates a technique for measuring the contralateral silent period (cSP) using transcranial magnetic stimulation. Position the patient's hand prone and place an electrode on the first dorsal interosseous (FDI) muscle. Then, place a force-measuring device between the thumb and index ...

Video: Measuring the Contralateral Silent Period Induced by Transcranial Magnetic Stimulation - Concept

Bilateral Assessment of the Corticospinal Pathways of the Ankle Muscles Using Navigated Transcranial Magnetic Stimulation

Distal leg muscles receive neural input from motor cortical areas via the corticospinal tract, which is one of the main motor descending pathway in humans and can be assessed using transcranial magnetic stimulation (TMS). Given the role of distal leg muscles in upright postural and dynamic tasks, such as walking, a growing research interest in the assessment and modulation of the corticospinal tracts relative to the function of these muscles has emerged in the last decade. However, methodological parameters used in previous work have varied across studies making the interpretation of results from cross-sectional and longitudinal studies less robust. Therefore, use of a standardized TMS protocol specific to the assessment of leg muscles&#39; corticomotor response (CMR) will allow for direct comparison of results across studies and cohorts. The objective of this paper is to present a protocol that provides the flexibility to simultaneously assess the bilateral CMR of two main ankle antagonistic muscles, the tibialis anterior and soleus, using single pulse TMS with a neuronavigation system. The present protocol is applicable while the examined muscle is either fully relaxed or isometrically contracted at a defined percentage of maximum isometric voluntary contraction. Using each subject&#39;s structural MRI with the neuronavigation system ensures accurate and precise positioning of the coil over the leg cortical representations during assessment. Given the inconsistency in CMR derived measures, this protocol also describes a standardized calculation of these measures using automated algorithms. Though this protocol is not conducted during upright postural or dynamic tasks, it&#160;can be used to assess bilaterally any pair of leg muscles, either antagonistic or synergistic, in both neurologically intact and impaired subjects.

The present protocol describes the simultaneous, bilateral assessment of the corticomotor response of the tibialis anterior and soleus during rest and tonic voluntary activation using a single pulse transcranial magnetic stimulation and neuronavigation system.

Distal leg muscles receive neural input from motor cortical areas via the corticospinal tract, which is one of the main motor descending pathway in humans ...

JoVE Journal

Employing Transcranial Magnetic Stimulation in a Resource Limited Environment to Establish Brain-Behavior Relationships

Neuroimaging is typically perceived as a resource demanding discipline. While this is the case in certain circumstances, institutions with limited resources have historically contributed significantly to the field of neuroscience, including neuroimaging. In the study of self-deception, we have successfully employed single-pulse TMS to determine the brain correlates of abilities including overclaiming and self-enhancement. Even without the use of neuro-navigation, methods provided here lead to successful outcomes. For example, it was discovered that decreases in self-deceptive responding lead to a decrease in affect. These methods provide data that are reliable and valid, and such methods provide research opportunities otherwise unavailable.&#160;Through the use of these methods, the overall knowledge base in the field of neuroscience is expanded, providing research opportunities to students such as those at our institution&#160;(Montclair State University is a Hispanic-Serving Institute) who are often denied such research experiences.

Transcranial Magnetic Stimulation (TMS) and low-frequency TMS (lfTMS) have&#160;been demonstrated to be major contributors to brain literature. Here we highlight the methods for investigating the cortical correlates of self-deception using TMS.

Neuroimaging is typically perceived as a resource demanding discipline. While this is the case in certain circumstances, institutions with limited ...

Study Design for Navigated Repetitive Transcranial Magnetic Stimulation for Speech Cortical Mapping

The cortical areas involved in human speech should be characterized reliably prior to surgery for brain tumors or drug-resistant epilepsy. The functional mapping of language areas for surgical decision-making is usually done invasively by electrical direct cortical stimulation (DCS), which is used to identify the organization of the crucial cortical and subcortical structures within each patient. Accurate preoperative non-invasive mapping aids surgical planning, reduces time, costs, and risks in the operating room, and provides an alternative for patients not suitable for awake craniotomy. Non-invasive imaging methods like MRI, fMRI, MEG, and PET are currently applied in presurgical design and planning. Although anatomical and functional imaging can identify the brain regions involved in speech, they cannot determine whether these regions are critical for speech. Transcranial magnetic stimulation (TMS) non-invasively excites the cortical neuronal populations by means of electric field induction in the brain. When applied in its repetitive mode (rTMS) to stimulate a speech-related cortical site, it can produce speech-related errors analogous to those induced by intraoperative DCS. rTMS combined with neuronavigation (nrTMS) enables neurosurgeons to preoperatively assess where these errors occur and to plan the DCS and the operation to preserve the language function. A detailed protocol is provided here for non-invasive speech cortical mapping (SCM) using nrTMS. The proposed protocol can be modified to best fit the patient- and site-specific demands. It can also be applied to language cortical network studies in healthy subjects or in patients with diseases that are not amenable to surgery.

Navigated repetitive transcranial magnetic stimulation is a highly efficient non-invasive tool for mapping speech-related cortical areas. It helps in designing brain surgery and speeds up the direct cortical stimulation conducted during the surgery. This report describes how to perform speech cortical mapping reliably for preoperative evaluation and research.

The cortical areas involved in human speech should be characterized reliably prior to surgery for brain tumors or drug-resistant epilepsy. The functional ...

Measuring the Contralateral Silent Period Induced by Transcranial Magnetic Stimulation

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