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

INTRODUCTION: 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. METHODS: 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. RESULTS: The ANOVA test 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. CONCLUSION: 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.

Neuromuscular electrical stimulation at submaximal intensity combined with motor imagery increases corticospinal excitability.

PURPOSE: There is sparse evidence in the literature that the combination of neuromuscular electrical stimulation (NMES) and motor imagery (MI) can increase corticospinal excitability more that the application of one or the other modality alone. However, the NMES intensity usually employed was below or at motor threshold, not allowing a proper activation of the whole neuromuscular system. This questions the effect of combined MI + NMES with higher intensities, closer to those used in clinical settings. The purpose here was to assess corticospinal excitability during either MI, NMES or a combination of both at different evoked forces. METHODS: Seventeen healthy participants were enrolled in one session consisting of 6 conditions targeting flexor carpi radialis muscle (FCR): rest, MI, NMES at 5% and 20% of maximal voluntary contraction (MVC) and MI and NMES performed simultaneously (MI + NMES). During each condition, corticospinal excitability was assessed by evoking MEP of FCR by using transcranial magnetic stimulation. Maximal M-wave (Mmax) was measured by using the stimulation of the median nerve. RESULTS: MEPs during MI were greater as compared to rest (P = 0.005). MEPs during MI were significantly lower than during MI + NMES at 5% (P = 0.02) and 20% (P = 0.001). Then, MEPs during NMES 5% was significantly lower than during MI + NMES 20% (P < 0.005). CONCLUSION: The present study showed that MI + NMES increased corticospinal excitability more than MI alone. However, corticospinal excitability was not higher as the intensity increase during MI + NMES. Therefore, MI + NMES targeting FCR may not significantly increase the corticospinal excitability between different low-submaximal contractions intensities.

Epidural magnetic stimulation of the motor cortex using an implantable coil.

BACKGROUND: Magnetic stimulation, represented by transcranial magnetic stimulation (TMS), is used to treat neurological diseases. Various strategies have been explored to improve the spatial resolution of magnetic stimulation. While reducing the coil size is the most impactful approach for increasing the spatial resolution, it decreases the stimulation intensity and increases heat generation. OBJECTIVE: We aim to demonstrate the feasibility of magnetic stimulation using an epidurally implanted millimeter-sized coil and that it does not damage the cortical tissue via heating even when a repetitive stimulation protocol is used. METHODS: A coil with dimensions of 3.5 × 3.5 × 2.6 mm3 was epidurally implanted on the left motor cortex of rat, corresponding to the right hindlimb. Before and after epidural magnetic stimulation using a quadripulse stimulation (QPS) protocol, changes in the amplitude of motor evoked potentials (MEPs) elicited by a TMS coil were compared. RESULTS: The experimental group showed an average increase of 88 % in MEP amplitude in the right hindlimb after QPS, whereas the MEP amplitude in the left hindlimb increased by 18 % on average. The control group showed no significant change in MEP amplitude after QPS in either hindlimb. The temperature changes at the coil surface remained <2 °C during repetitive stimulation, meeting the thermal safety limit for implantable medical devices. CONCLUSION: These results demonstrate the feasibility of epidural magnetic stimulation using an implantable coil to induce neuromodulation effects. This novel method is expected to be a promising alternative for focal magnetic stimulation with an improved spatial resolution and lowered stimulus current than previous magnetic stimulation methods.

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.

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

OBJECTIVE: Scalp 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. METHODS: This 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. RESULTS: We did not observe changes in MEP amplitude from single-pulse TMS, SICI, and ICF with any intervention protocol. CONCLUSION: Anodal 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. SIGNIFICANCE: We provide strong evidence that tDCS (1-mA/20-min) does not alter corticomotor and intracortical excitability with or without priming scalp cooling.

Fluctuations in resting motor threshold during electroconvulsive and magnetic seizure therapy.

OBJECTIVES: Magnetic seizure therapy (MST) is more benign than electroconvulsive therapy (ECT) in terms of cognitive impairment. However, whether these two 'artificial seizures' facilitate the central motor neural pathway and the motor cortical effects have not been investigated. The study aimed to compare the effects of ECT and MST on motor-evoked potential (MEP) in patients with mental disorders. METHODS: Forty-nine patients with mental disorders (major depressive disorder, bipolar disorder type II and schizophrenia [SCZ]) received 6 treatment sessions of vertex MST versus 6 bifrontal ECT treatments in a nonrandomized comparative clinical design. Data on the duration of motor seizures were collected for each treatment. MEP latency and the resting motor threshold (rMT) were measured at baseline and after every two treatments. Comparisons were performed between or within the groups. RESULTS: Seizure durations were significantly longer in the ECT group compared to the MST group across multiple sessions. Both MST and ECT demonstrated a significant reduction in rMT in the left and right hemispheres after the fourth (T3) and sixth treatments (T4) compared to baseline (T1). However, there were no significant changes in MEP latency within or between the groups throughout the treatment sessions. The only difference was that the rMT in the left cerebral hemisphere was significantly lower after T4 than after the second treatment (T2). There was no difference in rMT between the ECT and MST groups. CONCLUSIONS: Both ECT and MST facilitate the central motor pathway, with a shared mechanism of increased motor cortex excitability.

Modulation of motor cortex inhibition during manual dexterity tasks: an adaptive threshold hunting study.

The ability to perform intricate movements is crucial for human motor function. The neural mechanisms underlying precision and power grips are incompletely understood. Corticospinal output from M1 is thought to be modulated by GABAA-ergic intracortical networks within M1. The objective of our study was to investigate the contribution of M1 intracortical inhibition to fine motor control using adaptive threshold hunting (ATH) with paired-pulse TMS during pinch and grasp. We hypothesized that short-interval intracortical inhibition (SICI) could be assessed during voluntary activation and that corticomotor excitability and SICI modulation would be greater during pinch than grasp, reflecting corticospinal control. Seventeen healthy participants performed gradual pinch and grasp tasks. Using ATH, paired-pulse TMS was applied in the anterior-posterior current direction to measure MEP latencies, corticomotor excitability, and SICI. MEP latencies indicated that the procedure preferentially targeted late I-waves. In terms of corticomotor excitability, there was no difference in the TMS intensity required to reach the MEP target during pinch and grasp. Greater inhibition was found during pinch than during grasp. ATH with paired-pulse TMS permits investigation of intracortical inhibitory networks and their modulation during the performance of dexterous motor tasks revealing a greater modulation of GABAA-ergic inhibition contributing to SICI during pinch compared with grasp. NEW & NOTEWORTHY Primary motor cortex intracortical inhibition was investigated during dexterous manual task performance using adaptive threshold hunting. Motor cortex intracortical inhibition was uniquely modulated during pinching versus grasping tasks.

Effects of auricular vagus nerve stimulation and electrical earlobe stimulation on motor-evoked potential changes induced by paired associative stimulation.

Paired associative stimulation (PAS) is a combination of transcranial magnetic stimulation (TMS) and peripheral nerve stimulation (PNS). PAS can induce long-term potentiation (LTP)-like plasticity in humans, manifested as motor-evoked potential (MEP) enhancement. We have developed a variant of PAS ("high-PAS"), which consists of high-frequency PNS and high-intensity TMS and targets spinal plasticity and promotes rehabilitation after spinal cord injury (SCI). Vagus nerve stimulation (VNS) promotes LTP-like plasticity and enhances recovery in SCI and stroke in humans and animals when combined with repetitive motor training. We combined high-PAS with simultaneous noninvasive transcutaneous auricular VNS (aVNS) to determine if aVNS enhances the extent of PAS-induced MEP amplitude increase. Sixteen healthy participants were stimulated for 20 min in four different sessions (PAS, PAS + aVNS, PAS + shamVNS, and aVNS) in a randomized single-blind setup. MEPs were measured before, immediately after, and at 30, 60, and 90 min post-stimulation. Stimulation protocols with PAS significantly potentiated MEPs (p = 0.005) when compared with aVNS (p = 0.642). Although not significant, MEP enhancement observed after PAS (43.5%) is further increased by aVNS (49.7%) and electrical earlobe stimulation (63.9%). Our aVNS setup failed to significantly enhance the effect of PAS, but sham VNS revealed a trend towards enhanced plasticity. Optimization of auricular VNS stimulation setup is required for possible tests of patients with SCI.

The relationship between corticospinal excitability and structural integrity in stroke patients.

BACKGROUND: Evaluation of the structural integrity and functional excitability of the corticospinal tract (CST) is likely to be important in predicting motor recovery after stroke. Previous reports are inconsistent regarding a possible link between CST structure and CST function in this setting. This study aims to investigate the structure‒function relationship of the CST at the acute phase of stroke (<7 days). METHODS: We enrolled 70 patients who had an acute ischaemic stroke with unilateral upper extremity (UE) weakness. They underwent a multimodal assessment including clinical severity (UE Fugl Meyer at day 7 and 3 months), MRI to evaluate the CST lesion load and transcranial magnetic stimulation to measure the maximum amplitude of motor evoked potential (MEP). RESULTS: A cross-sectional lesion load above 87% predicted the absence of MEPs with an accuracy of 80.4%. In MEP-positive patients, the CST structure/function relationship was bimodal with a switch from a linear relationship (rho=-0.600, 95% CI -0.873; -0.039, p<0.03) for small MEP amplitudes (<0.703 mV) to a non-linear relationship for higher MEP amplitudes (p=0.72). In MEP-positive patients, recovery correlated with initial severity. In patients with a positive MEP <0.703 mV but not in patients with an MEP ≥0.703 mV, MEP amplitude was an additional independent predictor of recovery. In MEP-negative patients, we failed to identify any factor predicting recovery. CONCLUSION: This large multimodal study on the structure/function of the CST and stroke recovery proposes a paradigm change for the MEP-positive patients phenotypes and refines the nature of the link between structural integrity and neurophysiological function, with implications for study design and prognostic information.

Sex-related differences in corticospinal excitability outcome measures of the biceps brachii during a submaximal elbow flexor contraction.

The purpose of this study was to investigate the effects of sex, muscle thickness, and subcutaneous fat thickness (SFT) on corticospinal excitability outcome measures of the biceps brachii. Eighteen participants (10 males and 8 females) completed this study. Ultrasound was used to assess biceps brachii muscle thickness and the overlying SFT. Transcranial magnetic stimulation (TMS) was used to determine corticospinal excitability by inducing motor-evoked potentials (MEPs) at eight different TMS intensities from 90% to 160% of active motor threshold (AMT) from the biceps brachii during an isometric contraction of the elbow flexors at 10% of maximum voluntary contraction (MVC). Biceps brachii maximal compound muscle action potential (Mmax) was also recorded prior to and after TMS. Males had higher (p < 0.001) biceps brachii muscle thickness and lower SFT, produced higher levels of MVC force and had, on average, higher (p < 0.001) MEP amplitudes at lower (p < 0.05) percentages of maximal stimulator output than females during the 10% elbow flexion MVC. Multiple linear regression modeling revealed that sex was not associated with any of the neurophysiological parameters examined, while SFT showed a positive association with the stimulation intensity required at AMT (p = 0.035) and a negative association with biceps brachii pre-stimulus electromyography (EMG) activity (p = 0.021). Additionally, there was a small positive association between muscle thickness and biceps brachii pre-stimulus EMG activity (p = 0.049). Overall, this study suggests that some measures of corticospinal excitability may be different between the sexes and influenced by SFT and muscle thickness.

Lowered ratio of corticospinal excitation to inhibition predicts greater disability, poorer motor and cognitive function in multiple sclerosis.

Objective: Investigate excitatory-inhibitory (E/I) (im)balance using transcranial magnetic stimulation (TMS) in individuals with Multiple Sclerosis (MS) and determine its validity as a neurophysiological biomarker of disability. Methods: Participants with MS (n = 83) underwent TMS, cognitive, and motor function assessments. TMS-induced motor evoked potential amplitudes (excitability) and cortical silent periods (inhibition) were assessed bilaterally through recruitment curves. The E/I ratio was calculated as the ratio of excitation to inhibition. Results: Participants with greater disability (Expanded Disability Status Scale, EDSS≥3) exhibited lower excitability and increased inhibition compared to those with lower disability (EDSS<3). This resulted in lower E/I ratios in the higher disability group. Individuals with higher disability presented with asymmetrical E/I ratios between brain hemispheres, a pattern not present in the group with lower disability. In regression analyses controlling for demographics, lowered TMS-probed E/I ratio predicted variance in disability (R2 = 0.37, p < 0.001), upper extremity function (R2 = 0.35, p < 0.001), walking speed (R2 = 0.22, p = 0.005), and cognitive performance (R2 = 0.25, p = 0.007). Receiver Operating Characteristic curve analysis confirmed 'excellent' discriminative ability of the E/I ratio in distinguishing high and low disability. Finally, excitation superiorly correlated with the E/I ratio than overall inhibition in both hemispheres (p ≤ 0.01). Conclusion: The E/I ratio is a potential neurophysiological biomarker of disability level in MS, especially when assessed in the hemisphere corresponding to the weaker body side. Interventions aimed at increasing cortical excitation or reducing inhibition may restore E/I balance potentially stalling progression or improving function in MS.

Transcranial motor-evoked potentials disappear with pons transection.

Motor-evoked potential (MEP) monitoring by transcranial electrical stimulation (TES) is important for intraoperative motor function assessment in neurosurgery; however, false-negative results sometimes occur, and these findings should be interpreted with caution. Herein, we report an interesting MEP change resulting from a pons transection. The patient was a boy aged 5 years and 2 months. He underwent multiple craniotomies for cerebellar anaplastic ependymoma and was already paralyzed in the right upper and lower limbs. Therefore, we decided to remove the recurrent lesion from the left anterior pons. MEPs were recorded on both the right and left sides after the start of surgery but disappeared 1 h 30 min after the start of surgery in the TES on the operative side, even when the stimulation intensity was increased. The contralateral TES consistently recorded stable MEPs throughout the surgery. The tumor was completely resected on imaging. Immediately postoperatively, the patient experienced flaccid paralysis on the right side of the body, which recovered to preoperative levels over time. A transcranial MEP cannot be derived if the corticospinal tract is transected at the pons. Transcranial MEP findings may accurately reflect the corticospinal tract function if the injury is caudal to the pons.

Pilot study of using transcranial temporal interfering theta-burst stimulation for modulating motor excitability in rat.

Transcranial temporal interference stimulation (tTIS) is a promising brain stimulation method that can target deep brain regions by delivering an interfering current from surface electrodes. Most instances of tTIS stimulate the brain with a single-frequency sinusoidal waveform generated by wave interference. Theta burst stimulation is an effective stimulation scheme that can modulate neuroplasticity by generating long-term potentiation- or depression-like effects. To broaden tTIS application, we developed a theta burst protocol using tTIS technique to modulate neuroplasticity in rats. Two cannula electrodes were unilaterally implanted into the intact skull over the primary motor cortex. Electrical field of temporal interference envelopes generated by tTIS through cannula electrodes were recorded from primary motor cortex. Theta burst schemes were characterized, and motor activation induced by the stimulation was also evaluated simultaneously by observing electromyographic signals from the corresponding brachioradialis muscle. After validating the stimulation scheme, we further tested the modulatory effects of theta burst stimulation delivered by tTIS and by conventional transcranial electrical stimulation on primary motor cortex excitability. Changes in the amplitude of motor evoked potentials, elicited when the primary motor cortex was activated by electrical pulses, were measured before and after theta burst stimulation by both techniques. Significant potentiation and suppression were found at 15 to 30 min after the intermittent and continuous theta burst stimulation delivered using tTIS, respectively. However, comparing to theta burst stimulations delivered using conventional form of transcranial electrical stimulation, using tTIS expressed no significant difference in modulating motor evoked potential amplitudes. Sham treatment from both methods had no effect on changing the motor evoked potential amplitude. The present study demonstrated the feasibility of using tTIS to achieve a theta burst stimulation scheme for motor cortical neuromodulation. These findings also indicated the future potential of using tTIS to carry out theta burst stimulation protocols in deep-brain networks for modulating neuroplasticity.

A Rare Case of Unruptured Small Aneurysm Arising from the Posterior Surface of Proximal A1 Segment, Projecting Posterior-Inferiorly and Entangled with Multiple Perforators from the A1 Segment.

Aneurysm arising from the A1 segment of the anterior cerebral artery is rare. Aneurysm of the A1 segment even being small tend to rupture early. They tend to develop along the with various vascular anomalies of the vessels arising from the A1 segment. Use of computational fluid dynamics and hemodynamic consideration is of importance in this aneurysm. In this report we describe a 57-year-old woman with a small, unruptured A1 segment aneurysm arising from the proximal segment of the posterior surface of A1, and pointing posterior-inferiorly with multiple perforators entangling around for which microsurgical clipping was done. Intraoperative clipping of the aneurysm and salvaging the multiple perforators were challenging. We report a rare case of an A1 segment aneurysm arising from the posterior surface facing with multiple perforators. It is of significance to understand that a small, unruptured A1 aneurysm can arise from the posterior surface of the A1 segment with projection posterior-inferiorly making it deeper in location with multiple perforators entangling it; hence, it is challenging to treat without causing neurological deficits.

Quantitative Analysis of the Effect of Neuromuscular Blockade on Motor-Evoked Potentials in Patients Undergoing Brain Tumor Removal Surgery: A Prospective, Single-Arm, Open-Label Observational Study.

Background: We aimed to elucidate the quantitative relationship between the neuromuscular blockade depth and intraoperative motor-evoked potential amplitudes. Methods: This prospective, single-arm, open-label, observational study was conducted at a single university hospital in Seoul, Korea, and included 100 adult patients aged ≥19 years undergoing brain tumor removal surgery under general anesthesia. We measured the neuromuscular blockade degree and motor-evoked potential amplitude in the deltoid, abductor pollicis brevis, tibialis anterior, and abductor hallucis muscles until dural opening. Results: The pharmacokinetic-pharmacodynamic model revealed the exposure-response relationship between the rocuronium effect-site concentration and motor-evoked potential amplitudes. The mean motor-evoked potential amplitudes decreased proportionally with increasing neuromuscular blockade depth. As the mean amplitude increased, the coefficient of variation decreased bi-exponentially. The critical ratio of the first evoked response to the train-of-four stimulation (T1)/control response (Tc) thresholds beyond which the coefficient of variation exhibited minimal change were found to be 0.63, 0.65, 0.68, and 0.63 for the deltoid, abductor pollicis brevis, tibialis anterior, and abductor hallucis muscles, respectively. Conclusions: Our results reveal that the motor-evoked potential amplitude exhibits deterioration proportional to the degree of neuromuscular blockade. In light of the observed bi-exponential decline of the coefficient of variation with the motor-evoked potential amplitude, we recommend maintaining a T1/Tc ratio higher than 0.6 for partial neuromuscular blockade.

The predictive value of intraoperative facial motor evoked potentials in cerebellopontine angle tumor surgery.

OBJECTIVE: Our aim is to explore the value of intraoperative facial motor evoked potentials (FMEP) for facial outcomes in cerebellopontine angle (CPA) tumor surgery to provide an evidence-based consensus standard for future clinical practice and prospective studies. METHODS: Electronic databases were searched from inception to June 2023. Study quality was assessed with the QUADAS-2 tool. Bivariate and random-effects models for meta-analysis and meta-regression generated summary receiver operating characteristic curves (ROC) and forest plots for estimates of sensitivity and specificity. RESULTS: We included 17 studies (1,206 participants). Sensitivity was lower in the immediate (IM) post-operative (0.76, 95% CI 0.65-0.84) compared to follow-up (FU) period (0.82, 95% CI 0.74-0.88) while specificity was similar in both groups (IM, 0.94, 95% CI 0.89-0.97; FU, 0.93, 95% CI 0.87-0.96). Data driven estimates improved FMEP performance but require confirmation from future studies. Amplitude cutoff criteria and studies that scored new deficits as worse than House-Brackmann (HB) grade 2 yielded best sensitivities. CONCLUSIONS: FMEP demonstrated statistically significant accuracy for facial function monitoring. Implementation of FMEPs varied widely across studies. SIGNIFICANCE: Our study is the first systematic review with meta-analysis to demonstrate that intraoperative FMEP is valuable in CPA tumor surgery for facial outcomes. Meta-regression identified the methods that were most useful in the application of FMEPs.

Motor Learning in a Complex Motor Task Is Unaffected by Three Consecutive Days of Transcranial Alternating Current Stimulation.

Transcranial alternating current stimulation (tACS) delivered to the primary motor cortex (M1) can increase cortical excitability, entrain neuronal firing patterns, and increase motor skill acquisition in simple motor tasks. The primary aim of this study was to assess the impact of tACS applied to M1 over three consecutive days of practice on the motor learning of a challenging overhand throwing task in young adults. The secondary aim was to examine the influence of tACS on M1 excitability. This study implemented a double-blind, randomized, SHAM-controlled, between-subjects experimental design. A total of 24 healthy young adults were divided into tACS and SHAM groups and performed three identical experimental sessions that comprised blocks of overhand throwing trials of the right dominant arm concurrent with application of tACS to the left M1. Performance in the overhand throwing task was quantified as the endpoint error. Motor evoked potentials (MEPs) were assessed in the right first dorsal interosseus (FDI) muscle with transcranial magnetic stimulation (TMS) to quantify changes in M1 excitability. Endpoint error was significantly decreased in the post-tests compared with the pre-tests when averaged over the three days of practice (p = 0.046), but this decrease was not statistically significant between the tACS and SHAM groups (p = 0.474). MEP amplitudes increased from the pre-tests to the post-tests (p = 0.003), but these increases were also not different between groups (p = 0.409). Overall, the main findings indicated that tACS applied to M1 over multiple days does not enhance motor learning in a complex task to a greater degree than practice alone (SHAM).

Diagnostic Accuracy of Somatosensory Evoked Potential and Transcranial Motor Evoked Potential in Detection of Neurological Injury in Intradural Extramedullary Spinal Cord Tumor Surgeries: A Short-Term Follow-Up Prospective Interventional Study Experience from Tertiary Care Center of India.

Objective Intraoperative neuromonitoring (IONM) is an acknowledged tool for real-time neuraxis assessment during surgery. Somatosensory evoked potential (SSEP) and transcranial motor evoked potential (MEP) are commonest deployed modalities of IONM. Role of SSEP and MEP in intradural extramedullary spinal cord tumor (IDEMSCT) surgery is not well established. The aim of this study was to evaluate sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of SSEP and transcranial MEP, in detection of intraoperative neurological injury in IDEMSCT patients as well as their postoperative limb-specific neurological improvement assessment at fixed intervals till 30 days. Materials and Methods Symptomatic patients with IDEMSCTs were selected according to the inclusion criteria of study protocol. On modified McCormick (mMC) scale, their sensory-motor deficit was assessed both preoperatively and postoperatively. Surgery was done under SSEP and MEP (transcranial) monitoring using appropriate anesthetic agents. Gross total/subtotal resection of tumor was achieved as per IONM warning alarms. Sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of SSEP and MEP were calculated considering postoperative neurological changes as "reference standard." Patients were followed up at postoperative day (POD) 0, 1, 7, and 30 for convalescence. Statistical Analysis With appropriate tests of significance, statistical analysis was carried out. Receiver-operating characteristic curve was used to find cutoff point of mMC for SSEP being recordable in patients with higher neurological deficit along with calculation of sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of SSEP and MEP for prediction of intraoperative neurological injury. Results Study included 32 patients. Baseline mean mMC value was 2.59. Under neuromonitoring, gross total resection of IDEMSCT was achieved in 87.5% patients. SSEP was recordable in subset of patients with mMC value less than or equal to 2 with diagnostic accuracy of 100%. MEP was recordable in all patients and it had 96.88% diagnostic accuracy. Statistically significant neurological improvement was noted at POD-7 and POD-30 follow-up. Conclusion SSEP and MEP individually carry high diagnostic accuracy in detection of intraoperative neurological injuries in patients undergoing IDEMSCT surgery. MEP continues to monitor the neuraxis, even in those subsets of patients where SSEP fails to record.

Non-Dominant Hemisphere Excitability Is Unaffected during and after Transcranial Direct Current Stimulation of the Dominant Hemisphere.

Transcranial direct current stimulation (tDCS) increases primary motor cortex (M1) excitability and improves motor performance when applied unilaterally to the dominant hemisphere. However, the influence of tDCS on contralateral M1 excitability both during and after application has not been quantified. The purpose was to determine the influence of tDCS applied to the dominant M1 on the excitability of the contralateral non-dominant M1. This study employed a double-blind, randomized, SHAM-controlled, within-subject crossover experimental design. Eighteen young adults performed two experimental sessions (tDCS, SHAM) in counterbalanced order separated by a one-week washout. Transcranial magnetic stimulation (TMS) was used to quantify the excitability of the contralateral M1 to which anodal tDCS was applied for 20 min with a current strength of 1 mA. Motor evoked potential (MEP) amplitudes were assessed in 5 TMS test blocks (Pre, D5, D10, D15, and Post). The Pre and Post TMS test blocks were performed immediately before and after tDCS application, whereas the TMS test blocks performed during tDCS were completed at the 5, 10, and 15 min stimulation timepoints. MEPs were analyzed with a 2 condition (tDCS, SHAM) × 5 test (Pre, D5, D10, D15, Post) within-subject ANOVA. The main effect for condition (p = 0.213), the main effect for test (p = 0.502), and the condition × test interaction (p = 0.860) were all not statistically significant. These results indicate that tDCS does not modulate contralateral M1 excitability during or immediately after application, at least under the current set of common tDCS parameters of stimulation.

Exploring the Influence of Inter-Trial Interval on the Assessment of Short-Interval Intracortical Inhibition.

Short-interval intracortical inhibition (SICI) is a common paired-pulse transcranial magnetic stimulation (TMS) measure used to assess primary motor cortex (M1) interneuron activity in healthy populations and in neurological disorders. Many of the parameters of TMS stimulation to most accurately measure SICI have been determined. However, one TMS parameter that has not been investigated is the time between SICI trials (termed inter-trial interval; ITI). This is despite a series of single-pulse TMS studies which have reported that motor evoked potential (MEP) amplitude were suppressed for short, but not long ITIs in approximately the initial ten trials of a TMS block of 20-30 trials. The primary purpose was to examine the effects of ITI on the quantification of SICI at rest. A total of 23 healthy adults completed an experimental session that included four SICI trial blocks. Each block utilized a different ITI (4, 6, 8, and 10 s) and was comprised of a total of 26 SICI trials divided into three epochs. ANOVA revealed that the main effects for ITI and epoch as well as their interaction were all non-statistically significant for SICI. We conclude that the shorter (4-6 s) ITIs used in studies investigating SICI should not alter the interpretation of M1 activity, while having the advantages of being more comfortable to participants and reducing the experimental time needed to evaluate perform single and paired-pulse TMS experiments.