Test Transcranial Magnetic Stimulation Research Articles

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.

Feasibility and Potential Value of TMS for Upper Extremity Motor Assessment at the Bedside During Acute Stroke Hospitalization

<h3>Research Objectives</h3> To assess the feasibility of collecting transcranial magnetic stimulation (TMS) measures at the bedside during acute stroke hospitalization and to associate TMS neurophysiology with upper extremity (UE) behavioral measures. <h3>Design</h3> The Stroke Motor reHabilitation and Recovery sTudy (SMaHRT; https://www.clinicaltrials.gov/ct2/show/NCT03485040?term=NCT03485040&draw=2&rank=1) is a prospective, observational cohort study <h3>Setting</h3> Inpatient neurology service, Massachusetts General Hospital, a large academic medical center. <h3>Participants</h3> Twenty-seven individuals (65.44 ± 12.52 years) with first-ever stroke resulting in UE weakness, who were 18 years or older, could follow simple commands in English and had no contraindications to receiving ipsilesional TMS were eligible for and included in this study. TMS was performed within 5.2 ± 2.2 days of stroke. <h3>Interventions</h3> N/A. <h3>Main Outcome Measures</h3> Feasibility of collecting TMS measures including motor evoked potentials (MEPs), resting motor threshold (RMT), cortical silent period (cSP) and ipsilateral silent period (iSP) at the hospital bedside was assessed. The main behavioral measures collected included upper extremity Fugl-Meyer Assessment (FMA-UE), grip strength, shoulder abduction finger extension (SAFE) score and 9-hole peg test. <h3>Results</h3> MEPs, RMT, cSP and iSP were collected in at least one hemisphere for 26/42 participants, of whom 15 participants did not receive testing due to medical and discharge factors. A mobile TMS cart facilitated efficient equipment transport. Additionally, coordination with nursing and use of hospital-bed or bedside chair positioning features maximized successful testing. Patients' whose lesioned hemisphere was MEP+ compared to MEP- at acute hospitalization had better affected FMA-UE, SAFE, 9HPT and grip strength scores (p<0.01). Lower RMT values were also associated with better affected FMA-UE (rho=-0.6, p<0.05), SAFE (rho=-0.5, p=0.07), and Grip Strength (rho=-0.4, p=0.23) scores. There were no clear linear trends between cSP or iSP and any behavioral outcome. <h3>Conclusions</h3> Several TMS measures are feasible to perform during acute stroke hospitalization. Interdisciplinary coordination, a mobile TMS cart, and participant positioning are essential to successful TMS testing at the hospital bedside. In addition to MEP, RMT has added value for relating to UE motor behavior during acute stroke hospitalization. <h3>Author(s) Disclosures</h3> See "Faculty Disclosures" task tab

Establishing the Minimum Intensity of Transcranial Magnetic Stimulation Superconditioning Pulses to Effect Inhibition and Facilitation of Motor Evoked Potentials.

Previously, we showed that a three-pulse train of weak transcranial magnetic stimulation (TMS) pulses-a superconditioning (SC) train-when followed by a stronger TMS pulse could enhance the inhibition or facilitation of the resultant motor evoked potential (MEP) compared with that seen with traditional dual-pulse inputs. The purpose of the present study was to establish the relative minimum intensity of SC pulses needed to influence MEP output and whether this differed for upper- versus lower-limb muscles. We examined 33 older adult subjects, targeting abductor pollicis brevis and tibialis anterior muscles. Older subjects were included in the anticipation of using findings from this study to guide further studies in persons with amyotrophic lateral sclerosis. Three-pulse trains of SC inputs of different intensities were delivered either 1 millisecond before (for inhibition) or 10 millisecond before (for facilitation) a stronger TMS test pulse. Motor evoked potential magnitudes for SC +test sets were normalized to test input responses and were compared within and between subjects. For inhibition, the minimum intensity of SC pulses needed to influence the follow-on MEP was found to be 60% of the target muscle's resting three-pulse MEP threshold for most abductor pollicis brevis and tibialis anterior muscles (2-millisecond interpulse intervals). For facilitation, somewhat higher intensities (70%) were typically needed to cause facilitation. Both values of SC pulses for inhibition/facilitation are considerably lower than the intensity of the conditioning pulse-often reported as 80% of the single-pulse threshold-typically used in dual-pulse TMS paradigms. This approach may allow testing of upper motor neuron function using weaker stimulus pulse intensities than are typically employed, improving testing compliance in persons whose thresholds are elevated because of injury or disease.

The Effect of Epilepsy and Antiepileptic Drugs on Cortical Motor Excitability in Patients With Temporal Lobe Epilepsy.

Transcranial magnetic stimulation (TMS) has been used to assess cortical disinhibition/excitation with epilepsy and determine the degree of patients' response to antiepileptic drugs (AEDs). However, the results of studies are variable and conflicting. We assessed cortical motor excitability in adults with temporal lobe epilepsy (TLE). The TMS parameters used for assessment were: resting (RMT) and active (AMT) motor thresholds, cortical silent period (CSP), and central motor conduction time (CMCT). This study included 40 adults (males, 22; females, 18) with TLE with impaired awareness or to bilateral tonic clonic seizures (mean age, 32.50 ± 3.38 years; duration of illness, 6.15 ± 2.02 years) and on treatment with AEDs (valproate, 15; carbamazepine, 15; levetiracetam, 10]. The majority (62.5%) were seizure-free for ≥1 year on AEDs before TMS testing. All had normal brain magnetic resonance imaging except two, who had mesial temporal sclerosis. Comparing the entire patients with controls, patients had significantly bihemispheric higher RMT and AMT particularly over the epileptic hemisphere and shorter CSP and CMCT in the epileptic hemisphere. Shorter CSP and CMCT were observed in patients on valproate or carbamazepine and those who were uncontrolled on medications but not with levetiracetam. Significant correlations were identified between RMT and AMT (P = 0.01) and between CSP and CMCT (P = 0.001). We conclude that chronic TLE had increased cortical disinhibition in the epileptic hemisphere which can spread outside the epileptogenic zone despite the apparent control on AEDs. The TMS studies using CSP and CMCT may help future prediction of pharmacoresistance and, therefore, the need of combined AEDs with multiple mechanisms of action.

TMS coil orientation and muscle activation influence lower limb intracortical excitability

IntroductionPrevious research with transcranial magnetic stimulation (TMS) indicates that coil orientation (TMS current direction) and muscle activation state (rest or active) modify corticospinal and intracortical excitability of upper limb muscles. However, the extent to which these factors influence corticospinal and intracortical excitability of lower limb muscles is unknown. This study aimed to examine how variations in coil orientation and muscle activation affect corticospinal and intracortical excitability of tibialis anterior (TA), a lower leg muscle. MethodsIn 21 young (21.6 ± 3.3 years, 11 female) adults, TMS was administered to the motor cortical representation of TA in posterior-anterior (PA) and mediolateral (ML) orientations at rest and during muscle activation. Single-pulse TMS measures of motor evoked potential amplitude, in addition to resting and active motor thresholds, were used to index corticospinal excitability, whereas paired-pulse TMS measures of short-interval intracortical inhibition (SICI) and facilitation (SICF), and long-interval intracortical inhibition (LICI), were used to assess excitability of intracortical circuits. ResultsFor single-pulse TMS, motor thresholds and test TMS intensity were lower for ML stimulation (all P < 0.05). In a resting muscle, ML TMS produced greater SICI (P < 0.001) and less SICF (both P < 0.05) when compared with PA TMS. In contrast, ML TMS in an active muscle resulted in reduced SICI but increased SICF (both P ≤ 0.001) when compared with PA TMS. ConclusionTMS coil orientation and muscle activation influence measurements of intracortical excitability recorded in the tibialis anterior, and are therefore important considerations in TMS studies of lower limb muscles.

Influence of Voluntary Contraction Level, Test Stimulus Intensity and Normalization Procedures on the Evaluation of Short-Interval Intracortical Inhibition.

Short-interval intracortical inhibition (SICI) represents an inhibitory phenomenon acting at the cortical level. However, SICI estimation is based on the amplitude of a motor-evoked potential (MEP), which depends on the discharge of spinal motoneurones and the generation of compound muscle action potential (M-wave). In this study, we underpin the importance of taking into account the proportion of spinal motoneurones that are activated or not when investigating the SICI of the right flexor carpi radialis (normalization with maximal M-wave (Mmax) and MEPtest, respectively), in 15 healthy subjects. We probed SICI changes according to various MEPtest amplitudes that were modulated actively (four levels of muscle contraction: rest, 10%, 20% and 30% of maximal voluntary contraction (MVC)) and passively (two intensities of test transcranial magnetic stimulation (TMS): 120 and 130% of motor thresholds). When normalized to MEPtest, SICI remained unchanged by stimulation intensity and only decreased at 30% of MVC when compared with rest. However, when normalized to Mmax, we provided the first evidence of a strong individual relationship between SICI and MEPtest, which was ultimately independent from experimental conditions (muscle states and TMS intensities). Under similar experimental conditions, it is thus possible to predict SICI individually from a specific level of corticospinal excitability in healthy subjects.

Safety and Feasibility of Transcranial Magnetic Stimulation as an Exploratory Assessment of Corticospinal Connectivity in Infants After Perinatal Brain Injury: An Observational Study.

Perinatal brain injuries often impact the corticospinal system, leading to motor impairment and cerebral palsy. Although transcranial magnetic stimulation (TMS) has been widely used to study corticospinal connectivity in adults and older children, similar studies of young infants are limited. The objective was to establish the safety and feasibility of advanced TMS assessments of the corticospinal connectivity of young infants with perinatal brain injury. This was a pilot, cross-sectional study of 3- to 12-month-old (corrected age) infants with perinatal stroke or intracranial hemorrhage. Six participants (2 term, 4 preterm) were assessed with stereotactic neuronavigation-guided TMS. Single-pulse TMS was applied to each hemisphere and responses were recorded simultaneously from both upper limbs. During data collection, vital signs and stress responses were measured to assess safety. Developmental motor outcomes were evaluated using the General Movements Assessment and Bayley Scales of Infant and Toddler Development (3rd edition). A clinical diagnosis of cerebral palsy was recorded, if available. No adverse events occurred during TMS testing. All sessions were well tolerated. Contralateral motor evoked responses were detected in 4 of 6 participants. Both contralateral and ipsilateral responses were observed in 2 of 6 participants. TMS responses were not obtained in all participants. This could be related to the location of brain injury or developmental stage of the corticospinal system controlling the wrist flexor muscle group from which responses were recorded. This study provides a summary of the framework for performing novel TMS assessments in infants with perinatal brain injury. Implementing this approach to measure corticospinal connectivity in hypothesis-driven studies in young infants appears to be justified. Such studies could inform the characterization of corticospinal development and the neural mechanisms driving recovery following early interventions.

Parallel modulation of interhemispheric inhibition and the size of a cortical hand muscle representation during active contraction.

Interhemispheric inhibition (IHI) between motor cortexes is thought to suppress unwanted mirror movements during voluntary behaviors and can be assessed using paired-pulse transcranial magnetic stimulation (TMS). The magnitude of IHI may be related to the size of the cortical representation for a given muscle as a mechanism for facilitating unimanual control. To date, the relationship between IHI and cortical muscle representations remains unknown. Fifteen healthy, right-handed individuals participated in the present study. IHI was examined in the right first dorsal interosseous (FDI) muscle by delivering conditioning TMS to ipsilateral (right) primary motor cortex (M1) followed by a test TMS pulse to contralateral (left) M1. The size of the FDI representation in M1 was determined by delivering suprathreshold TMS over a 5 × 5-cm grid centered on the FDI motor hotspot of the left M1. Both IHI and cortical territory were obtained during three conditions: rest, contralateral (right) FDI contraction, and ipsilateral (left) FDI contraction. Results indicate a significant association between IHI and the size of the FDI representation only in the context of contraction and not when the FDI muscle was relaxed. Specifically, reduced IHI corresponded to larger cortical FDI representations during both contralateral and ipsilateral contraction. These data demonstrate that, for a muscle of the hand, the magnitude of IHI and the cortical territory are associated within the context of muscle contraction. NEW & NOTEWORTHY This study provides evidence from noninvasive brain stimulation that communication between the motor cortexes of the two hemispheres plays a role in shaping the motor cortical map that outputs to a hand muscle during active contraction of that muscle. This relationship exists only when the hand muscle is contracted. The findings presented further our understanding of motor control during unilateral movement and may inform future research targeting clinical populations that exhibit impaired unilateral control.

Influence of Combined Transcranial Direct Current Stimulation and Motor Training on Corticospinal Excitability in Children With Unilateral Cerebral Palsy.

Combined non-invasive brain stimulation (NIBS) and rehabilitation interventions have the potential to improve function in children with unilateral cerebral palsy (UCP), however their effects on developing brain function are not well understood. In a proof-of-principle study, we used single-pulse transcranial magnetic stimulation (TMS) to measure changes in corticospinal excitability and relationships to motor performance following a randomized controlled trial consisting of 10 days of combined constraint-induced movement therapy (CIMT) and cathodal transcranial direct current stimulation (tDCS) applied to the contralesional motor cortex. Twenty children and young adults (mean age = 12 years, 9 months, range = 7 years, 7 months, 21 years, 7 months) with UCP participated. TMS testing was performed before, after, and 6 months after the intervention to measure motor evoked potential (MEP) amplitude and cortical silent period (CSP) duration. The association between neurophysiologic and motor outcomes and differences in excitability between hemispheres were examined. Contralesional MEP amplitude decreased as hypothesized in five of five participants receiving active tDCS immediately after and 6 months after the intervention, however no statistically significant differences between intervention groups were noted for MEP amplitude [mean difference = −323.9 μV, 95% CI = (−989, 341), p = 0.34] or CSP duration [mean difference = 3.9 ms, 95% CI = (−7.7, 15.5), p = 0.51]. Changes in corticospinal excitability were not statistically associated with improvements in hand function after the intervention. Across all participants, MEP amplitudes measured in the more-affected hand from both contralesional (mean difference = −474.5 μV) and ipsilesional hemispheres (−624.5 μV) were smaller compared to the less-affected hand. Assessing neurophysiologic changes after tDCS in children with UCP provides an understanding of long-term effects on brain excitability to help determine its potential as a therapeutic intervention. Additional investigation into the neurophysiologic effects of tDCS in larger samples of children with UCP are needed to confirm these findings.

Fast Intracortical Sensory-Motor Integration: A Window Into the Pathophysiology of Parkinson's Disease.

Parkinson’s Disease (PD) is a prototypical basal ganglia disorder. Nigrostriatal dopaminergic denervation leads to progressive dysfunction of the cortico-basal ganglia-thalamo-cortical sensorimotor loops, causing the classical motor symptoms. Although the basal ganglia do not receive direct sensory input, they are important for sensorimotor integration. Therefore, the basal ganglia dysfunction in PD may profoundly affect sensory-motor interaction in the cortex. Cortical sensorimotor integration can be probed with transcranial magnetic stimulation (TMS) using a well-established conditioning-test paradigm, called short-latency afferent inhibition (SAI). SAI probes the fast-inhibitory effect of a conditioning peripheral electrical stimulus on the motor response evoked by a TMS test pulse given to the contralateral primary motor cortex (M1). Since SAI occurs at latencies that match the peaks of early cortical somatosensory potentials, the cortical circuitry generating SAI may play an important role in rapid online adjustments of cortical motor output to changes in somatosensory inputs. Here we review the existing studies that have used SAI to examine how PD affects fast cortical sensory-motor integration. Studies of SAI in PD have yielded variable results, showing reduced, normal or even enhanced levels of SAI. This variability may be attributed to the fact that the strength of SAI is influenced by several factors, such as differences in dopaminergic treatment or the clinical phenotype of PD. Inter-individual differences in the expression of SAI has been shown to scale with individual motor impairment as revealed by UPDRS motor score and thus, may reflect the magnitude of dopaminergic neurodegeneration. The magnitude of SAI has also been linked to cognitive dysfunction, and it has been suggested that SAI also reflects cholinergic denervation at the cortical level. Together, the results indicate that SAI is a useful marker of disease-related alterations in fast cortical sensory-motor integration driven by subcortical changes in the dopaminergic and cholinergic system. Since a multitude of neurobiological factors contribute to the magnitude of inhibition, any mechanistic interpretation of SAI changes in PD needs to consider the group characteristics in terms of phenotypical spectrum, disease stage, and medication.

Preliminary evidence of an association between increased cortical inhibition and reduced suicidal ideation in adolescents treated for major depression

BackgroundSuicide is a leading cause of death among youth. Prior research using transcranial magnetic stimulation (TMS) has implicated deficits in GABAergic cortical inhibition in adolescent suicidal behavior, yet no studies have assessed whether cortical inhibition varies over time in conjunction with changes in suicidal ideation (SI). This study examined dynamic changes in long-interval intracortical inhibition (LICI), a TMS measure of GABAB-mediated inhibition, and their relationship with changes in SI in a small sample of adolescents undergoing pharmacologic treatment for depression. MethodsTen depressed adolescents (aged 13–17) underwent clinical assessment and TMS testing at baseline and again at follow-up. All were treated with antidepressant medication in the interim. SI was measured with the Columbia Suicide Severity Rating Scale (C-SSRS) Intensity of Ideation subscale. LICI was measured at interstimulus intervals of 100 and 150 ms. ResultsThere was a significant partial correlation, controlling for change in depression severity, between ΔLICI-100 and change in SI as measured by ΔC-SSRS (ρ = .746, df = 7, p = .021), which remained after also controlling for time to follow-up assessment (ρ = .752, df = 6, p = .032). No significant correlation was observed between ΔLICI-150 and change in SI. LimitationsSample size; variable follow-up interval; inability to control for age, sex, and potential treatment effects. ConclusionsThese data offer preliminary signal of an association between increases in GABAB-mediated cortical inhibition and reduction in SI over time in adolescents treated for depression. Further studies are warranted to explore the role of cortical inhibition in adolescent suicidal ideation and behavior.

The effect of transcranial magnetic stimulation test intensity on the amplitude, variability and reliability of motor evoked potentials

High degrees of variability reported in Transcranial magnetic stimulation (TMS) assessment of corticospinal excitability (CSE) highlight the need to investigate its reliability as an assessment tool. This study investigated the effect of TMS test intensity on the amplitude, variability and test-retest reliability of motor evoked potentials (MEP). Twenty-five MEPs were recorded at 105%, 120%, 135%, 150% and 165% of resting motor threshold across three sessions in twelve participants. Repeated measures analysis of variance (RM-ANOVA), recruitment curve gradients and standardised z-value SDs were utilized to investigate the effect of TMS test intensity on MEP amplitude and variability. Test-retest reliability of MEP amplitude was assessed using RM-ANOVA and intraclass correlations (ICC). RM-ANOVA reported MEP amplitude significantly increased between 105–120% and 120–135% with non-significant increases thereafter. Recruitment curve gradients reduced as TMS test intensity increased. Standardised z-value SDs reported MEP amplitude variability reduced as TMS test intensity increased with the only significant reduction occurring between 120% and 135%. RM-ANOVA reported no significant effect of time on MEP amplitude, indicating agreement between sessions. ICCs indicated significant intra- and inter-session reliability for all TMS test intensities except for 105%. The only significant reduction in variability and final significant increase in MEP amplitude occurred between the same TMS test intensities. Reduced variability and increased reliability at higher TMS test intensities validate the use of higher TMS test intensities to assess changes in CSE in future research. To increase accuracy in capturing true changes in CSE we recommend assessing changes in CSE across a range of TMS test intensities.

Emergence of neurophysiological biomarkers of Alzheimer disease

Motta and coworkers ( in their JNNP paper1) used a non-invasive repetitive transcranial magnetic stimulation (TMS) protocol to evaluate brain plasticity in patients with Alzheimer disease (AD). More than 15...

The Impact of Repetitive Transcranial Magnetic Stimulation on Affected and Unaffected Sides of a Child with Hemiplegic Cerebral Palsy.

The purpose of this study was to investigate the therapeutic effects of neuro-navigated repetitive transcranial magnetic stimulation (rTMS) combined with occupational therapy (OT) on gait impairment of a child (male, age: 13.2) with spastic hemiplegic cerebral palsy (CP). The treatment included 4 days a week of rTMS sessions for 3 weeks and 4 days of rTMS and OT sessions per week for 3 weeks. Transcranial magnetic stimulation (TMS) was used to evaluate corticospinal tract (CST) activities and H-reflex test was used to assess reflex hyper-excitability. Common clinical tests demonstrate the clinical status of the patient. Evaluations were performed in 4 time steps: baseline, 3 weeks after the beginning of the treatment, at the end of the treatment, and 1 month after the end of the treatment. The patient did not receive any specific treatment after the end of the treatment up to the follow up evaluations. The tests' results were compared between the affected and unaffected legs of the patient. Four parameters of the TMS test were calculated (motor evoked potential (MEP) latency, MEP peak-to-peak amplitude, cortical silent period (cSP), and stimulation intensity). These parameters were all improved for the affected side and cSP improved for the unaffected side, but MEP p-p amplitude and intensity got worse slightly for the unaffected side. Recruitment curves of H response and M-wave of the H-reflex test for both sides were obtained. Improvements could be seen after the treatment for both sides. Max H response on max M-wave (H/M) and H response latency got better after the treatment for both sides. Walking speed for self and fast velocity, timed up and go, and walking endurance improved during and after the treatment. All the improvements persisted after one month of the end of the treatment in the follow up evaluations. These findings indicate that rTMS combined with OT can have effective and long-lasting impact on neuromuscular impairments in spastic CP children.

Four-pulse transcranial magnetic stimulation using multiple conditioning inputs. Normative MEP responses.

A four-pulse pattern of transcranial magnetic stimulation (TMS) was compared to traditional dual-pulse TMS for its ability to modulate motor cortical excitability. This novel pattern consisted of a three-pulse train of subthreshold conditioning pulses followed by a suprathreshold test pulse (i.e., SC-T). The intervals between these superconditioning (SC) pulses (1, 3, or 6ms) and the follow-on test pulse (1, 3, 10, or 25ms) were varied, and the resultant MEPs were compared to those elicited by: (1) single-pulse TMS; and (2) dual-pulse conditioning-test (C-T) TMS with either short (3ms) or long (10ms) intervals to elicit short-interval intracortical inhibition (SICI) or intracortical facilitation (ICF), respectively. Testing included abductor pollicis brevis (APB) and tibialis anterior (TA) in 15 neurologically normal adults. For superconditioning inputs, 10ms test intervals caused especially strong facilitation of the test MEP, while 1ms test intervals were particularly effective at causing inhibition of the test response. For both muscles and across all subjects, the most effective of the 12 SC-T inputs tested for causing either facilitation or inhibition was-with rare exception-superior to the dual-pulse TMS input for causing facilitation (i.e., ICF) or inhibition (i.e., SICI), while the overall magnitude of effect was more pronounced in APB compared to TA. Nevertheless, after normalization, the impact of a superconditioning input train on the test MEP was similar in APB and TA muscles, suggesting similar mechanisms of action. Limited findings from a single subject with amyotrophic lateral sclerosis (ALS) are included to further illustrate the potential advantages of using a train of conditioning pulses preceding a TMS test pulse to selectively investigate abnormal motor cortical excitatory and inhibitory circuitry.

Spatial and Temporal Characteristics of Set-Related Inhibitory and Excitatory Inputs from the Dorsal Premotor Cortex to the Ipsilateral Motor Cortex Assessed by Dual-Coil Transcranial Magnetic Stimulation.

The capacity to produce movements only at appropriate times is fundamental in successful behavior and requires a fine interplay between motor inhibition and facilitation. Evidence in humans indicates that the dorsal premotor cortex (PMCd) is involved in such preparatory and inhibitory processes, but how PMCd modulates motor output in humans is still unclear. We investigated this issue in healthy human volunteers, using a variant of the dual-coil transcranial magnetic stimulation (TMS) technique that allows testing the short-latency effects of conditioning TMS to the left PMCd on test TMS applied to the ipsilateral orofacial primary motor cortex (M1). Participants performed a delayed cued simple reaction time task. They were asked to produce a lip movement cued by an imperative GO-signal presented after a predictable SET-period, during which TMS was applied at different intervals. Results showed that the area of motor evoked potentials (MEPs) to test TMS was modulated by conditioning TMS. A transient inhibition cortico-bulbar excitability by PMCd stimulation was observed around the middle of the SET-period. Conversely, a ramping excitatory effect of PMCd stimulation appeared towards the end of the SET-period, as the time of the predicted GO-signal approached. The time-course of PMCd-M1 activity scaled to the varying SET-period duration. Our data indicate that inhibition and excitation of motor output during a delayed reaction time task are two distinct neural phenomena. They both originate in PMCd and are conveyed via cortico-cortical connections to the ipsilateral M1, where they are integrated to produce harmonic fluctuations of motor output.

The positive effect of venlafaxine on central motor conduction

ObjectivesUsing the triple stimulation technique (TST) and conventional transcranial magnetic stimulation (TMS), this study was designed to investigate the effect of venlafaxine on central motor conduction in healthy adults. Patients and MethodsIn this crossover, self-controlled trial, eight healthy adult volunteers were randomly divided into groups A and B. In group A, the volunteers were administered 1 venlafaxine capsule once daily for 7 consecutive days, followed by a 3-day break. Next, volunteers in this group received 1 placebo capsule once daily for 7 consecutive days. Group B received the treatments in the opposite order. The index finger tapping test, grip strength test, TST and conventional TMS examination for each hand were recorded before and one week after the administration of venlafaxine or placebo. ResultsCompared to the placebo stage, in the venlafaxine stage, the number of index finger taps was significantly increased for both hands, and the TST amplitude and area ratios were significantly increased. The improvement in the TST amplitude ratio was significantly and positively correlated with the improvements in performance on the index finger tapping test. ConclusionVenlafaxine positively regulates central motor conduction in healthy adults.

Neural Correlates to the Increase in Maximal Force after Dexamethasone Administration.

This study investigated the effects of short-term glucocorticoid administration on voluntary activation and intracortical inhibitory and facilitatory circuits. Seventeen healthy men participated in a pseudorandomized double-blind study to receive either dexamethasone (8 mg·d, n = 9 subjects) or placebo (n = 8 subjects) for 7 d. The ankle dorsiflexion torque, corresponding EMG of the tibialis anterior, and voluntary activation assessed by the interpolated twitch method using transcranial magnetic stimulation (TMS) were measured during a maximal voluntary contraction (MVC). Short-latency intracortical inhibition (SICI) and intracortical facilitation (ICF) were assessed at rest and during submaximal contraction (50% MVC torque) by paired-pulse TMS with the conditioning stimulus set at 0.8× of motor threshold and delivered 2 ms (SICI) and 13 ms (ICF) before the test stimulus (1.2× motor threshold). The MVC torque (+14%), tibialis anterior EMG (+31%), and voluntary activation (+3%) increased after glucocorticoid treatment (P < 0.05). The increase in voluntary activation was associated with the gain in MVC torque (r = 0.56; P = 0.032). The level of SICI and the duration of the EMG silent period that followed the test TMS decreased (-18.6% and -13.5%, respectively) during the 50% MVC after treatment (P < 0.05), whereas no significant change was observed for ICF. Neither SICI nor ICF changed after treatment when assessed at rest. Short-term dexamethasone treatment induced specific decrease in the excitability of intracortical inhibitory circuits that likely contributed to the increase in the voluntary activation and associated MVC torque.

P219 Cortical excitability in Dystrophia Myotonica type 1

Objectives Dystrophia Myotonica type 1 (DM1) is characterized by distal muscle weakness, atrophy, myotonia and CNS involvement. Electrophysiological assessment of CNS involvement in DM1 patient refers to multimodal evoked potential studies. Herein we investigated the function of central motor pathways in DM1 patients by transcranial magnetic stimulation (TMS) and the possible relationships with disease duration, muscular impairment and MRI findings. Methods Eight right-handed DM1 patients and 10 healthy adult volunteers (control group) were included in the study. Fazekas scale was used to quantify the amount of white matter lesion (WMLs) in MRI performed to all DM1 patients. TMS test battery consisted of AMT, RMT, central conduction time (CCT), cortical silent period (SP), and paired-pulse TMS paradigm. Results Mean age and disease durations of patients’ were 37.2 and 7.02 years, respectively. WMLs were found in 62.5% of the patients. There were no significant differences between DM1 and control group in terms of AMT, RMT and SP (p ⩽ 0.05). DM1 cases showed statistically significant lower long interval intracortical inhibitions (LICI) as compared to the control group. Discussion The number of cortical excitability studies in neuromuscular and especially DM1 patients is limited. In this study, lower LICI in DM1 patients suggests that cortical excitability in these patients is less inhibited. Also, WML incidence in DM1 patients was found relatively high. The nature, significance and relationship of these findings can be investigated further by different cohorts and TMS protocols. Conclusion TMS might help demonstrate the nature of CNS involvements. Significance Cortical excitability changes in DM1.

Modulation of fronto‐parietal connections during the rubber hand illusion

Accumulating evidence suggests that parieto-frontal connections play a role in adjusting body ownership during the Rubber Hand Illusion (RHI). Using a motor version of the rubber hand illusion paradigm, we applied single-site and dual-site transcranial magnetic stimulation (TMS) to investigate cortico-spinal and parietal-frontal connectivity during perceived rubber hand ownership. Healthy volunteers received a conditioning TMS pulse over left anterior intraparietal sulcus (aIPS) and a test TMS pulse over left primary motor cortex (M1). Motor Evoked Potentials (MEPs) were recorded at rest and during three RHI conditions: (i) agency and ownership, (ii) agency but no ownership and (iii) neither agency nor ownership. Parietal-motor communication differed among experimental conditions. The induction of action ownership was associated with an inhibitory parietal-to-motor connectivity, which was comparable to the aIPS-to-M1 inhibition present at rest. This aIPS-to-M1 inhibition disappeared during movement conditions not inducing ownership. Cortico-spinal excitability was not significantly modulated during the motor RHI as indicated by the task-constant MEP amplitude elicited by the M1 test pulse alone. Our results indicate that the perceived ownership over the rubber hand is associated with normal parietal-motor communication. This communication is disturbed if the sensorimotor conflict between one's own hand and the rubber hand is not resolved.