Motor Evoked Potentials Research Articles

Low tourniquet pressure has less impact on lower extremity nerve innervation: comparison of different tourniquet pressures used with intraoperative neuromonitoring with a randomized controlled study

BackgroundWe aimed to investigate the compression and ischemic effects of two different tourniquet pressures on tissues during surgery show a clinical difference.MethodsPatients aged 18–65 years who underwent foot and ankle surgery and applied a tourniquet in a single center between September 2022 and November 2023 were included in this prospective randomized study. Accordingly, tourniquet pressures were applied as limb occlusion pressure (LOP) + 50 mmHg in group 1 (12 patients) and LOP + 100 mmHg in group 2 (12 patients). The time point at which the femoral nerve motor evoked potential (MEP) decreased by 50%, the time point at which the MEP decreased by 100% for all nerves (femoral, tibial, and deep peroneal), and the time point at which all responses returned after the tourniquet was deflated were identified as the time points for analysis.ResultsThere were no differences in demographic data (age, body mass index, and sex) between the two groups. The mean tourniquet pressure was 191 ± 16 mmHg in Group 1 and 247 ± 21 mmHg in Group 2 (p < 0.001). A 50% decrease in the femoral nerve MEP value was observed at an average of 47 min in Group 1 and 34 min in Group 2 (p < 0.001). A complete loss of MEP responses for all nerves was observed at an average of 69 min in Group 1 and 56 min in Group 2. After the tourniquet was deflated, all MEP responses returned to baseline values at an average of 8.5 min in Group 1 and 12.6 min in Group 2 (p = 0.007). The results showed that lower limb nerve innervation was affected later and returned to normal earlier after deflation of the tourniquet in Group 1 (low tourniquet pressure group).ConclusionsThe innervations of the lower extremity nerves were affected later in the group in which low tourniquet pressure was applied (average 191 mmHg). Again, in this group (LOP + 50 mmHg), nerve conduction recovered an average of 10 min after deflation and four minutes earlier than in the high tourniquet pressure group.Level of evidenceLevel I, diagnostic study.Trial registrationNCT05926154.

Intraoperative changes in electrophysiological monitoring can be used to predict clinical outcomes in patients with spinal cavernous malformation.

The study aimed to evaluate the sensitivity and specificity of these monitoring parameters in predicting postoperative neurological dysfunction. In this study, a total of 85 patients with spinal cavernous malformations (SCMs) treated at Xuanwu Hospital, Capital Medical University, from November 2012 to August 2017 were included. During the surgical procedures, all patients underwent monitoring of motor evoked potentials (MEP) and somatosensory evoked potentials (SEP). The criteria for warning included a reduction of ≥80% in MEP amplitude and ≥50% in SEP amplitude. Among 85 patients, 40 (47.1%) had SCMs located in the thoracic segment, 35 (41.2%) in the cervical segment, 6 (7.1%) in the cervical thoracic segment, and 4 (4.7%) in the lumbar segment. MEP recordings were obtained from 81 patients, and the preoperative McCormick score was 1.53 ± 0.69. The sensitivity of multimodal monitoring combined with the criteria of 80% reduction in MEP amplitude and SEP was 83.9%, with a specificity of 69%, a positive predictive value of 69%, and a negative predictive value of 90.4%. This study emphasizes the crucial role of electrophysiological monitoring, particularly MEP and SEP, during the surgical resection of SCMs. The findings demonstrate that this approach is effective in predicting and preventing postoperative neurological dysfunction, thereby improving patient outcomes.

Imagining Speeds up the Effect of Motor Imagery on Central Motor Conduction Time.

Although motor imagery (MI) has been reported to increase motor cortical excitability, its effect on central motor conduction time (CMCT), a widely used neurophysiological diagnostic method, has not been investigated. In this study, we sought to determine the effect of MI on CMCT. In this cross-sectional study, 21 healthy volunteers (11 females, 10 males) aged 24 to 67 years (mean age: 38.8 years) were recruited between April 2022 and June 2023.CMCT was calculated during MI from the abductor digiti minimi (ADM) and tibialis anterior (TA) muscles. Measurements were also performed with conventional measurement methods, such as resting and voluntary contraction, to compare the effect of MI on CMCT. The ANOVAtest revealed that the CMCT session (rest, MI, and voluntary contraction) was a significant factor (p < 0.05). In both muscles, CMCT was shorter in the imagery state than in the resting state but longer than in the voluntary contraction state (p < 0.05). Similarly, motor-evoked potential (MEP) latencies obtained during imagery were shorter for both muscles than the resting state but longer for the voluntary contraction state. The study's findings suggest that MI is a mental activity that modulates CMCT measurement.MI shows a voluntary contraction-like effect on CMCT and MEP latency, although the effect is more uncertain.

The corticospinal tract in multiple sclerosis: correlation between cortical excitability and magnetic resonance imaging measures.

Multiple sclerosis (MS) is a central nervous system disease involving gray and white matters. Transcranial magnetic stimulation (TMS) and magnetic resonance imaging (MRI) could help identify potential markers of disease evolution, disability, and treatment response. This work evaluates the relationship between intracortical inhibition and facilitation, motor cortex lesions, and corticospinal tract (CST) integrity. Consecutive adult patients with progressive MS were included. Sociodemographic and clinical data were collected. MRI was acquired to assess primary motor cortex lesions (double inversion and phase-sensitive inversion recovery) and CST integrity (diffusion tensor imaging). TMS outcomes were obtained: motor evoked potentials (MEP) latency, resting motor threshold, short-interval intracortical facilitation (ICF) and inhibition. Correlation analysis was performed. Twenty-five patients completed the study (13 females, age: 55.60 ± 11.49 years, Expanded Disability Status Score: 6.00 ± 1.25). Inverse correlations were found between ICF mean and each of CST radial diffusivity (RD) (ρ =-0.56; p < 0.01), CST apparent diffusion coefficient (ADC) (ρ=-0.44; p = 0.03), and disease duration (ρ=-0.46; p = 0.02). MEP latencies were directly correlated with disability scores (ρ = 0.55; p < 0.01). High ADC/RD and low ICF have been previously reported in patients with MS. While the former could reflect structural damage of the CST, the latter could hint towards an aberrant synaptic transmission as well as a depletion of facilitatory compensatory mechanisms that helps overcoming functional decline. The findings suggest concomitant structural and functional abnormalities at later disease stages that would be accompanied with a heightened disability. The results should be interpreted with caution mainly because of the small sample size that precludes further comparisons (e.g., treated vs. untreated patients, primary vs. secondary progressive MS). The role of these outcomes as potential MS biomarkers merit to be further explored.

P11.09.B STRUCTURAL REORGANIZATION IN MOTOR-ELOQUENT GLIOMA PATIENTS EXHIBITING MOTOR DEFICITS

Abstract BACKGROUND Recent advancements in navigated transcranial magnetic stimulation (nTMS) have significantly improved the localization of motor functions in human subjects. Although previous studies have demonstrated the occurrence of tumor-induced motor plasticity, the detailed mechanisms of motor function plasticity and reorganization in patients with tumors affecting motor-eloquent regions are not fully elucidated. Our study aims to investigate the functional plasticity of motor functions in patients with gliomas located within motor-eloquent regions, providing deeper insights into the mechanisms of functional plasticity. MATERIAL AND METHODS In this research, we studied 60 glioma patients with tumors located in the motor-eloquent region. These patients were categorized into two groups depending on whether they experienced motor impairments in the upper extremities. We utilized nTMS, including Motor Evoked Potentials (MEP), to outline the control regions of motor function in terms of area, localization, and Center of Gravity (CoG). These identified regions also acted as seeds for tracing the Corticospinal Tract (CST). RESULTS The study unveiled significant variations in cortical and subcortical motor function localizations between the groups. Patients with motor impairments exhibited a broader cortical distribution connected to motor functions and increased volumes of CST, reflecting compensatory adaptations with different fractional anisotropy (FA) values (FA 0.15, p=0.02; FA 0.10, p=0.04). The analysis of the CST also showed overlapping regions, particularly within the hand-knob areas, which is indicative of these areas acting as critical motor output pathways. Despite varying degrees of functional impairment, all patients maintained some degree of motor output capability. CONCLUSION These findings suggest that motor-eloquent gliomas induce significant cortical and subcortical reorganization of motor functions. A persistent network of CST fibers, crucial for preserving motor function, highlights a complex interplay between cortical adaptation and subcortical reorganization. This study underscores the resilience of motor pathways and their pivotal role in functional recovery and plasticity, emphasizing the clinical relevance of nTMS in the therapeutic planning and monitoring of patients with motor-eloquent gliomas.

Dorsolateral prefrontal cortex to ipsilateral primary motor cortex intercortical interactions during inhibitory control enhance response inhibition in open-skill athletes

Numerous studies have reported that long-term sports training can affect inhibitory control and induce brain functional alterations. However, the influence of environmental dynamics in sports training on inter-cortical connectivity has not been well studied. In the current study, we used twin-coil transcranial magnetic stimulation to investigate the functional connectivity between dorsolateral prefrontal cortex (DLPFC) and ipsilateral primary motor cortex (M1) during proactive and reactive inhibition in participants with sports skills in dynamic environment (open-skill experts), stable environment (closed-skill experts), and no sports skills (controls). Using a modified stop signal task, proactive inhibition was measured by the response delay effect (RDE), and reactive inhibition was measured by the stop-signal reaction time (SSRT). Intra-hemispheric DLPFC-M1 interactions and single pulse motor-evoked potentials (MEPs) were measured during the task. A stronger inhibitory effect of the DLPFC over M1 was observed during early reactive control stages compared to baseline levels. In addition, this inhibitory effect was pronounced when comparing open-skill experts to non-athlete controls, a relationship that was significantly correlated with superior reactive control performance. Furthermore, DLPFC to M1 influencing direction shifted from late proactive control to reactive control. Behavioral results also demonstrated enhanced proactive control abilities in open-skill experts relative to controls. Such enhancement may be due to the combination of environmental complexity and physical fitness in long-term skill training.

Synaptic dynamics linked to widespread elevation of H-reflex before peripheral denervation in amyotrophic lateral sclerosis.

Changes in Hoffmann reflex (H-reflex) exhibit heterogeneity among patients with amyotrophic lateral sclerosis (ALS), likely due to phenotype diversity. Current knowledge primarily focuses on soleus H-reflex, which may demonstrate an initial increase before subsequent decline throughout the disease course. The main objective was to investigate other muscles, to determine whether H-reflex changes could be associated with patient phenotype (onset site, functional disabilities). Additional experiments were performed to elucidate the neurophysiological mechanisms underlying H-reflex modifications. In age- and sex-matched groups of controls and patients, we compared H-reflex recruitment curves in soleus, quadriceps, and forearm flexors. Additionally, we examined H-reflex and motor evoked potential (MEP) recruitment curves in quadriceps. Last, to assess potential changes in monosynaptic excitatory post-synaptic potentials (EPSPs) of both peripheral and cortical origins, we analyzed peri-stimulus time histograms (PSTH) and peristimulus frequencygrams (PSF) of single motor units, along with H-reflex occurrence after paired pulse stimuli. The ratio between maximal amplitudes of H-reflex and direct motor response increased in all muscles, irrespective of disease onset, and was found positively correlated with exaggerated osteotendinous reflexes and spasticity, but depressed in patients on-riluzole. This finding was accompanied by a reduction in MEP size and no changes in PSTH, PSF, and paired-pulse H-reflex probability. It is speculated that spinal interneurons may compensate for potential depression of monosynaptic EPSPs in ALS. From a clinical perspective, while the added value of H-reflex to osteotendinous reflex evaluation may be limited, it can serve as a valuable quantitative biomarker of pyramidal dysfunction in clinical trials.

Balance of power: The choice between trial and participant numbers to optimize the detection of phase-dependent effects

Abstract The fields of neuroscience and psychology are currently in the midst of a so-called “reproducibility crisis”, with growing concerns regarding a history of weak effect sizes and low statistical power in much of the research published in these fields over the last few decades. Whilst the traditional approach for addressing this criticism has been to increase participant sample sizes, there are many research contexts in which the number of trials per participant may be of equal importance. The present study aimed to compare the relative importance of participants and trials in the detection of phase-dependent phenomena, which are measured across a range of neuroscientific contexts (e.g., neural oscillations, non-invasive brain stimulation). This was achievable within a simulated environment where one can manipulate the strength of this phase-dependency in two types of outcome variables: one with normally distributed residuals (idealistic) and one comparable to motor-evoked potentials (an MEP-like variable). We compared the statistical power across thousands of experiments with the same number of sessions per experiment but with different proportions of participants and number of sessions per participant (30 participants ⨉ 1 session, 15 participants ⨉ 2 sessions, and 10 participants ⨉ 3 sessions), with the trials being pooled across sessions for each participant. These simulations were performed for both outcome variables (idealistic and MEP-like) and four different effect sizes (0.075— ‘weak’, 0.1— ‘moderate’, 0.125— ‘strong’, 0.15— ‘very strong’), as well as separate control scenarios with no true effect. Across all scenarios with (true) discoverable effects, and for both outcome types, there was a statistical benefit for experiments maximising the number of trials rather than the number of participants (i.e., it was always beneficial to recruit fewer participants but have them complete more trials). These findings emphasise the importance of obtaining sufficient individual-level data rather than simply increasing participant numbers.

The Use of Diagnostic Transcranial Magnetic Stimulation as a Predictor of the Functional Outcome in Ischemic Stroke

ABSTRACT. Determination of rehabilitation potential (RP) is necessary for optimal rehabilitation strategy and the best rehabilitation measures. Navigational transcranial magnetic stimulation (nTMS) has been proposed as a method for PR determination in after-stroke patients.THE AIM. was to study the importance of navigational diagnostic transcranial magnetic stimulation as a neurofunctional predictor of motor function recovery after ischemic stroke.MATERIAL AND METHODS. The study included 28 after-stroke patients, 19 men and 9 women, the mean age was 60.07±5.67 years, who underwent a course of inpatient medical rehabilitation at the Moscow Research and Practice Center for Medical Rehabilitation, Restorative and Sports Medicine named after S.I. Spasokukotsky in 2022–2023. Clinical examination and assessment were conducted before and after the rehabilitation course using validated scales and questionnaires — the Medical Research Committee (MRCs) scale, the Box and Block Test (BBT), the modified Rankin scale (mRS); the rehabilitation routing scale (RRS). The patients were also examined using nTMS at the N.V. Sklifosovsky Research Institute for Emergency Medicine with the determination of motor evoked potential (MEP) parameters from the muscles of the upper and lower extremities.RESULTS. In patients with preserved MEP, there was a significant increase in the strength of the paretic limb on the MRCs scale from 4.00 (2.94–4.06) to 4.22 (3.83–4.89) points (p &lt;0.001) for the upper limb and from 4.00 (3.67–4.00) to 4.44 (3.83–4.61) (p&lt;0.001) for the lower limb. Improvements were revealed according to the mRS scale — the number of patients with an mRS score of 2 points in the group of patients with defined MEP increased by 26.1%, reached values of 1 point — 13.0% of patients, and the number of patients with an assessment of disability and self-care ability of 4 points decreased by 8.7%.CONCLUSION. Navigational transcranial magnetic stimulation is one of the methods for assessing the rehabilitation potential in patients with ischemic stroke. But TMS should not be used as the only method of evaluating rehabilitation potential. The assessment of RP should be comprehensive and based on the complex data obtained.

Detection of Severe Neurological Complications Caused by the Removal of Central Venous Catheter Accidentally Inserted in the Epidural Space via Motor-Evoked Potential: A Case Report

Detection of Severe Neurological Complications Caused by the Removal of Central Venous Catheter Accidentally Inserted in the Epidural Space via Motor-Evoked Potential: A Case Report

Application of a Dual Upper Limb Task-Oriented Robotic System for the Functional Recovery of the Upper Limb in Stroke Patients.

Highly repetitive and task-oriented training has been shown to promote the recovery of limb function in stroke patients. Additionally, bilateral arm training can help stroke survivors regain their upper limb function and improve their daily activities. The dual upper limb task-oriented robotic system is designed to assist the healthy side of the stroke patient in driving the affected side to perform bilateral arm training through the use of a robotic device. It can also guide the patient in carrying out dual upper limb coordinated movements and engage them in a task-oriented virtual game using force feedback and human-computer interaction technology. This study aimed to assess the efficacy of the system in enhancing upper limb function and activities of daily living in stroke patients. The assessment methods used included motor evoked potential (MEP), functional test for the hemiplegic upper extremity-Hong Kong (FTHUE-HK), Fugl-Meyer Assessment Upper Extremity Scale (FMA-UE), and modified Barthel index (MBI). The results of the study indicate that the dual upper limb task-oriented robotic system can significantly improve the corticospinal pathway, upper limb function, and activities of daily living in stroke patients after 6 weeks of treatment. This system can serve as an effective adjunct to upper limb functional rehabilitation in stroke survivors, reducing the dependence on rehabilitation therapists. In conclusion, the dual upper limb task-oriented robotic system provides a new strategy for post-stroke limb functional rehabilitation and holds great potential for application, as it offers certain social and financial benefits.

Investigating premotor corticospinal excitability in fast and slow voluntary contractions of the elbow flexors.

Corticospinal excitability (CSE) increases prior to a voluntary contraction; however, the relative contributions of premotor cortical and spinal mechanisms are poorly understood. It is unknown whether the intended voluntary contractile rate affects CSE. Eighteen young, healthy participants (nine females) completed isometric elbow flexion contractions targeting 50% maximal voluntary contraction (MVC) torque, at either fast (fast as possible) or slow (25% MVC/s) contractile rates. Participants were cued to contract with warning (red) and "GO" (green) visual signals. Magnetic and electric stimulations were applied to elicit motor evoked potentials (MEPs), cervicomedullary evoked potentials (CMEPs), and M-waves, in the surface electromyogram (EMG) recorded over the biceps brachii. MEPs and CMEPs were collected at 0, 25, 50 and 75% premotor reaction time (RT - defined as the time between the "GO" cue and onset of biceps brachii EMG) and compared to a resting baseline. MEP amplitude was greater than baseline at 75% RT (p=0.009), and CMEP amplitude was significantly increased at all RT points relative to baseline (p≤0.001). However, there were no differences in MEP and CMEP amplitudes when compared between fast and slow conditions (p≥0.097). Normalized to the CMEP, there was no difference in MEP amplitude from baseline in either contractile condition (p≥0.264). These results indicate that increased premotor CSE is a spinally-mediated response. Furthermore, premotor CSE is not influenced by the intended voluntary contractile rate. CMEP amplitudes were larger for females than males within the premotor RT period (p=0.038), demonstrating that premotor spinal excitability responses may be influenced by sex.

Neuromuscular characteristics of eccentric, concentric and isometric contractions of the knee extensors.

We compared voluntary drive and corticospinal responses during eccentric (ECC), isometric (ISOM) and concentric (CON) muscle contractions to shed light on neurophysiological mechanisms underpinning the lower voluntary drive in a greater force production in ECC than other contractions. Sixteen participants (20-33 years) performed ISOM and isokinetic (30°/s) CON and ECC knee extensor contractions (110°-40° knee flexion) in which electromyographic activity (EMG) was recorded from vastus lateralis. Voluntary activation (VA) was measured during ISOM, CON and ECC maximal voluntary contractions (MVCs). Transcranial magnetic stimulation elicited motor-evoked potentials (MEPs) and corticospinal silent periods (CSP) during MVCs and submaximal (30%) contractions, and short-interval intracortical inhibition (SICI) in submaximal contractions. MVC torque was greater (P < 0.01) during ECC (302.6 ± 90.0 Nm) than ISOM (269.8 ± 81.5 Nm) and CON (235.4 ± 78.6 Nm), but VA was lower (P < 0.01) for ECC (68.4 ± 14.9%) than ISOM (78.3 ± 13.1%) and CON (80.7 ± 15.4%). In addition, EMG/torque was lower (P < 0.02) for ECC (1.9 ± 1.1μV.Nm-1) than ISOM (2.2 ± 1.2μV.Nm-1) and CON (2.7 ± 1.6μV.Nm-1), CSP was shorter (p < 0.04) for ECC (0.097 ± 0.03s) than ISOM (0.109 ± 0.02s) and CON (0.109 ± 0.03s), and MEP amplitude was lower (P < 0.01) for ECC (3.46 ± 1.67mV) than ISOM (4.21 ± 2.33mV) and CON (4.01 ± 2.06mV). Similar results were found for EMG/torque and CSP during 30% contractions, but MEP and SICI showed no differences among contractions (p > 0.05). The lower voluntary drive indicated by reduced VA during ECC may be partly explained by lower corticospinal excitability, while the shorter CSP may reflect extra muscle spindle excitation of the motoneurons from vastus lateralis muscle lengthening.

Is Intraoperative Muscle Motor Evoked Potential Variability due to Fluctuating Lower Motor Neuron Background Excitability?

This pilot study tests the contribution of fluctuating lower motor neuron excitability to motor evoked potential (MEP) variability. In six pediatric patients with idiopathic scoliosis and normal neurologic examination, cascades of 30 intraoperative H-reflexes (HRs) and MEPs were evoked in the soleus muscle using constant-current stimulators and recorded through surface electrodes with a 20-second interstimulus interval. First, HRs were obtained with an intensity capable of evoking the maximum response. Subsequently, MEPs were obtained with double trains and an intensity of 700 to 900 mA. Coefficients of variation (CVs) of amplitude and area under the curve from HRs and MEPs were compared using a paired two-tailed Student t test. Coefficients of correlation between the mean CVs of HR and MEP parameters were also assessed. Pooling the results from the six patients, the mean CV of amplitude from the MEP (24.6 ± 3) was significantly higher than that from the HR (3.5 ± 4.4) (P = 0.000091). The mean CV of the MEP area under the curve (21.8 ± 4.8) was also statistically significantly higher than that from the HR area under the curve (3.4 ± 4.5) (P = 0.00091). The coefficients of correlation of the mean CV of the HR amplitude and area under the curve compared with the corresponding values of the MEP were low (r = 0.29) and very low (r = 0.03), respectively. Our results suggest that fluctuations in lower motor neuron excitability may be less important than previously thought to explain the magnitude of MEP variability. The efficacy of corticospinal volleys to recruit a larger and more stable lower motor neuron population would be critical to obtain reproducible MEPs.

Inducing ipsilateral motor-evoked potentials in the biceps brachii muscle in healthy humans.

To assess reticulospinal tract excitability, high-intensity transcranial magnetic stimulation (TMS) has been used to elicit ipsilateral motor-evoked potentials (iMEPs). However, there is no consensus on robust and valid methods for use in human studies. The present study proposes a standardized method for eliciting and analysing iMEPs in the biceps brachii. Twenty-four healthy young adults participated in this study. Electromyography (EMG) electrodes recorded contralateral MEPs (cMEPs) from the right and iMEPs from the left biceps brachii. A dynamic preacher curl task was used with ~15% of the subject's one-repetition maximum load. The protocol included maximal compound action potential (M-max) determination of the right biceps brachii muscle, TMS hotspot determination, and four sets of five repetitions where 100% stimulator output was delivered at an elbow angle of 110° of flexion. We normalized cMEP amplitude by M-max (% M-max) and iMEP by cMEP amplitude ratio (ICAR). Clear iMEPs above background EMG were observed in 21 subjects (88%, ICAR = .31 ± .19). Good-to-excellent agreement (intraclass correlation coefficient [ICC] = .795-1.000) and low bias (.01-.08 mV and .60-1.11 ms) were demonstrated when comparing two different analysis methods (i.e. fixed time-window vs. manual onset detection) to determine the cMEP and iMEP amplitude and latency, respectively. Most subjects demonstrated clear iMEPs above background EMG triggered at a pre-determined joint angle during a light-load dynamic preacher curl exercise. Similar results were obtained when comparing a single-trial manual identification of iMEP and a semi-automated time-window data analysis approach.

Influence of Preoperative Motor Score and Patient Comorbidities on Transcranial Motor-Evoked Potential Acquisition in Intracranial Surgery: A Retrospective Cohort Study.

Intraoperative neurophysiological monitoring plays a pivotal role in modern neurosurgery, aiding in real-time assessment of eloquent neural structures to mitigate iatrogenic neural injury. This study represents the largest retrospective series to date in monitoring corticospinal tract integrity during intracranial surgery with transcranial motor-evoked potentials (TCMEPs), focusing on the influence of demographic factors, comorbidities, and preoperative motor deficits on the reliability of intraoperative neurophysiological monitoring. While the impact of patient-specific factors affecting TCMEP monitoring in spine surgery is well-documented, similar insights for intracranial surgery are lacking. A total of 420 craniotomy patients were retrospectively analyzed from electronic medical records from December 2017 to February 2023, excluding patients without preoperative Medical Research Council scores or medical histories. Using intrinsic hand muscles as a robust data set, 840 hand TCMEPs acquired during intracranial surgery were assessed. Demographic and clinical factors, including preoperative motor scores, were analyzed to identify associations with TCMEP acquisition and amplitude. Nonparametric statistics and multivariate regression analysis were employed. TCMEPs were successfully acquired in 734 (87.7%) patient hands, even in the presence of preoperative motor deficits in 13.9% of total patient hands. Preoperative motor scores did not predict the ability to acquire baseline TCMEPs ( P = .6). Notably, older age ( P < .001) and hypertension ( P = .01) were independent predictors of lower TCMEP acquisition rates. Preoperative motor scores significantly influenced TCMEP amplitudes, with higher scores correlating with higher amplitudes (1771 [SD = 1550] eve vs 882 [SD = 856] μV, P < .0001). Older age ( P < .001) and chronic kidney disease ( P = .04) were also associated with reduced TCMEP amplitudes. Our investigation into TCMEPs during intracranial surgery demonstrated a notably high acquisition rate in hand muscles, irrespective of preoperative motor deficits. Preoperative motor scores reliably correlated with TCMEP amplitudes in a linear fashion while advanced age and renal disease emerged as independent predictors of lower TCMEP amplitudes.

Potentiation of cortico-spinal output via targeted electrical stimulation of the motor thalamus

Cerebral white matter lesions prevent cortico-spinal descending inputs from effectively activating spinal motoneurons, leading to loss of motor control. However, in most cases, the damage to cortico-spinal axons is incomplete offering a potential target for therapies aimed at improving volitional muscle activation. Here we hypothesize that, by engaging direct excitatory connections to cortico-spinal motoneurons, stimulation of the motor thalamus could facilitate activation of surviving cortico-spinal fibers thereby immediately potentiating motor output. To test this hypothesis, we identify optimal thalamic targets and stimulation parameters that enhance upper-limb motor-evoked potentials and grip forces in anesthetized monkeys. This potentiation persists after white matter lesions. We replicate these results in humans during intra-operative testing. We then design a stimulation protocol that immediately improves strength and force control in a patient with a chronic white matter lesion. Our results show that electrical stimulation targeting surviving neural pathways can improve motor control after white matter lesions.

TDCS and local scalp cooling do not change corticomotor and intracortical excitability in healthy humans

ObjectiveScalp cooling might increase the long-term potentiation (LTP)-like effect of transcranial direct current stimulation (tDCS) by reducing the threshold for after-effects according to metaplasticity and increasing electrical current density reaching the cortical neurons. We aimed to investigate whether priming scalp cooling potentiates the tDCS after-effect on motor cortex excitability. MethodsThis study had a randomized, parallel-arms, sham-controlled, double-blinded design with an adequately powered sample of 105 healthy subjects. Corticomotor and intracortical excitability were assessed with motor evoked potentials (MEP) from transcranial magnetic stimulation (TMS) in short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) paradigms. Subjects were randomly allocated into six intervention groups, including anodal and cathodal tDCS (1-mA/20-min), scalp cooling, and sham. MEPs were recorded before, immediately, and 15 min after the interventions. ResultsWe did not observe changes in MEP amplitude from single-pulse TMS, SICI, and ICF with any intervention protocol. ConclusionAnodal and cathodal tDCS did not have an LTP-like neuromodulatory effect on corticospinal and did not provide detectable GABAergic and glutamatergic neurotransmission changes, which were not influenced by priming scalp cooling. SignificanceWe provide strong evidence that tDCS (1-mA/20-min) does not alter corticomotor and intracortical excitability with or without priming scalp cooling.

Post-Movement Beta Synchrony Inhibits Cortical Excitability.

This study investigates the relationship between movement-related beta synchrony and primary motor cortex (M1) excitability, focusing on the time-dependent inhibition of movement. Voluntary movement induces beta frequency (13-30 Hz) event-related desynchronisation (B-ERD) in M1, followed by post-movement beta rebound (PMBR). Although PMBR is linked to cortical inhibition, its temporal relationship with motor cortical excitability is unclear. This study aims to determine whether PMBR acts as a marker for post-movement inhibition by assessing motor-evoked potentials (MEPs) during distinct phases of the beta synchrony profile. Twenty-five right-handed participants (mean age: 24 years) were recruited. EMG data were recorded from the first dorsal interosseous muscle, and TMS was applied to the M1 motor hotspot to evoke MEPs. A reaction time task was used to elicit beta oscillations, with TMS delivered at participant-specific time points based on EEG-derived beta power envelopes. MEP amplitudes were compared across four phases: B-ERD, early PMBR, peak PMBR, and late PMBR. Our findings demonstrate that MEP amplitude significantly increased during B-ERD compared to rest, indicating heightened cortical excitability. In contrast, MEPs recorded during peak PMBR were significantly reduced, suggesting cortical inhibition. While all three PMBR phases exhibited reduced cortical excitability, a trend toward amplitude-dependent inhibition was observed. This study confirms that PMBR is linked to reduced cortical excitability, validating its role as a marker of motor cortical inhibition. These results enhance the understanding of beta oscillations in motor control and suggest that further research on altered PMBR could be crucial for understanding neurological and psychiatric disorders.

Neurophysiological Assessment in Children with Vocal Fold Paralysis: A Tertiary Center Experience.

The aim of this study is to report on experience acquired during the laryngeal electrophysiological assessment with Co-MEP and L-EMG in pediatric patients with acquired, congenital, and syndromic vocal fold paralysis (VFP), and correlate our findings with patients' characteristics, their comorbidities, and VFP etiology. Pediatric patients with suspected or previously diagnosed unilateral or bilateral VFP underwent electrophysiological records under general anesthesia; corticobulbar motor-evoked potentials (Co-MEPs) and laryngeal electromyography (L-EMG) of thyroarytenoid (TA) and posterior cricoarytenoid (PCA) muscles were recorded. Statistical analysis revealed a statistically significant correlation between early gestational age at childbirth and TA muscle intensity (p = 0.002) and PCA muscle intensity (p = 0.002); tracheostomy presence and TA muscle intensity (p = 0.002) and PCA muscle intensity (p = 0.002); presence of genetic anomalies with intensity and latency for TA muscle and latency for PCA muscle (TA latency p = 0.015, TA intensity p = 0.021, PCA latency p = 0.035); congenital presentation of VFP and an increased intensity for TA muscle (p = 0.04); latency and intensity for TA muscle (p = 0.024); TA muscle intensity and PCA intensity (p = 0.005). Intraoperative Co-MEPs and L-EMG are two complementary tools for evaluating the functional integrity of the structures involved in conveying signals from the motor cortex to TA and PCA muscles in children with vocal fold paralysis. Further studies are needed to establish their ability to predict the recovery of VF mobility, which could potentially lead to decannulation. Level 4 Laryngoscope, 2024.