Changes In Corticomotor Excitability Research Articles

Fatiguing unilateral handgrip influences force during force-matching task with lower limb

This study aimed to test the hypotheses that fatiguing unilateral handgrip contraction exhibits different changes in corticomotor excitability, which is evaluated by motor-evoked potentials (MEPs), in the lower limbs ipsilateral and contralateral to the fatigued hand, and that the changes in corticomotor excitability estimated by MEPs in the non-fatigued lower limbs affect the force exerted based on the sense of effort. Ten healthy males completed fatiguing unilateral handgrip contraction and force-matching tasks by static dorsiflexion before, immediately after, and 10 min after handgrip contraction. MEPs in the tibialis anterior (TA) were also measured before, immediately after, and 10 min after handgrip contraction. Fatiguing handgrip contractions resulted in asymmetrical MEPs in the TA muscles. Specifically, MEPs in the contralateral TA muscle were significantly increased (158 ± 60 %) and MEPs in the contralateral TA muscle were greater after the handgrip contraction than the ipsilateral MEPs (111 ± 30 %). Moreover, the torque exerted during the force-matching task significantly increased only in the contralateral ankle after the fatiguing handgrip contraction. Fatiguing unilateral handgrip contraction results in asymmetric changes in corticomotor excitability in the TA muscle, and the force exerted during the force-matching task based on the sense of effort becomes higher in the TA muscle with greater corticomotor excitability than that before fatiguing unilateral handgrip contraction.

The effect of skilled motor training on corticomotor control of back muscles in different presentations of low back pain.

Transcranial magnetic stimulation (TMS) has revealed differences in the motor cortex (M1) between people with and without low back pain (LBP). There is potential to reverse these changes using motor skill training, but it remains unclear whether changes can be induced in people with LBP or whether this differs between LBP presentations. This study (1) compared TMS measures of M1 (single and paired-pulse) and performance of a motor task (lumbopelvic tilting) between individuals with LBP of predominant nociceptive (n=9) or nociplastic presentation (n=9) and pain-free individuals (n=16); (2) compared these measures pre- and post-training; and (3) explored correlations between TMS measures, motor performance, and clinical features. TMS measures did not differ between groups at baseline. The nociplastic group undershot the target in the motor task. Despite improved motor performance for all groups, only MEP amplitudes increased across the recruitment curve and only for the pain-free and nociplastic groups. TMS measures did not correlate with motor performance or clinical features. Some elements of motor task performance and changes in corticomotor excitability differed between LBP groups. Absence of changes in intra-cortical TMS measures suggests regions other than M1 are likely to be involved in skill learning of back muscles.

A cognitive task, deep breathing, and static stretching reduce variability of motor evoked potentials during subsequent transcranial magnetic stimulation

BackgroundMotor evoked potentials (MEPs) induced via transcranial magnetic stimulation (TMS) demonstrate trial-to-trial variability limiting detection and interpretation of changes in corticomotor excitability. This study examined whether performing a cognitive task, voluntary breathing, or static stretching before TMS could reduce MEP variability. Methods20 healthy young adults performed no-task, a cognitive task (Stroop test), deep breathing, and static stretching before TMS in a randomized order. MEPs were collected in the non-dominant tibialis anterior muscle at 130% active motor threshold. Variability of MEP amplitude was quantified as coefficient of variation (CV). ResultsMEP CV was greater after no-task (25.4 ± 7.0) than after cognitive task (23.3 ± 7.2; p < 0.05), deep breathing (20.1 ± 6.3; p < 0.001), and static stretching (20.9 ± 6.0; p = 0.004). MEP CV was greater after cognitive task than after deep breathing (p = 0.007) and static stretching (p = 0.01). There was no effect of condition on MEP amplitude. ConclusionsPerforming brief cognitive, voluntary breathing, and stretching tasks before TMS can reduce MEP variability with no effect on MEP amplitude in the tibialis anterior of healthy, young adults. Similar tasks could be incorporated into research and clinical settings to improve detection of changes, normative data, and clinical predictions.

Effect of standardized training in combination with masseter sensitization on corticomotor excitability in bruxer and control individuals: a proof of concept study

Recently, it has been proposed that bruxism could represent an overlearned behavior due to the absence of corticomotor plasticity following a relevant tooth-clenching task (TCT). This study assessed the modulatory effects of a nerve growth factor (NGF) injection on masseter muscle corticomotor excitability, jaw motor performance, pain, and limitation in bruxer and control participants following a TCT. Participants characterized as definitive bruxers or controls were randomly assigned to have injected into the right masseter muscle either NGF or isotonic saline (IS), resulting in a study with 4 arms: IS_Control (n = 7), IS_Bruxer (n = 7); NGF_Control (n = 6), and NGF_Bruxer (n = 8). The primary outcome was the masseter motor evoked potential (MEP) amplitude measured at baseline and after a TCT. After the interventions, significantly higher and lower MEP amplitude and corticomotor map area were observed, respectively, in the IS_Control and NGF_Control groups (P < 0.05). Precision and accuracy depended on the series and target force level with significant between-group differences (P < 0.01). NGF‐induced masseter muscle sensitization, in combination with a training-induced effect, can significantly impact the corticomotor excitability of the masseter muscle in control participants indicating substantial changes in corticomotor excitability, which are not observed in bruxers. These preliminary findings may have therapeuthic implications for the potential to “detrain” and manage bruxism, but further studies with larger sample sizes will be needed to test this new concept.

Effect of neuroanatomy on corticomotor excitability during and after transcranial magnetic stimulation and intermittent theta burst stimulation.

Individual neuroanatomy can influence motor responses to transcranial magnetic stimulation (TMS) and corticomotor excitability after intermittent theta burst stimulation (iTBS). The purpose of this study was to examine the relationship between individual neuroanatomy and both TMS response measured using resting motor threshold (RMT) and iTBS measured using motor evoked potentials (MEPs) targeting the biceps brachii and first dorsal interosseus (FDI). Ten nonimpaired individuals completed sham‐controlled iTBS sessions and underwent MRI, from which anatomically accurate head models were generated. Neuroanatomical parameters established through fiber tractography were fiber tract surface area (FTSA), tract fiber count (TFC), and brain scalp distance (BSD) at the point of stimulation. Cortical magnetic field induced electric field strength (EFS) was obtained using finite element simulations. A linear mixed effects model was used to assess effects of these parameters on RMT and iTBS (post‐iTBS MEPs). FDI RMT was dependent on interactions between EFS and both FTSA and TFC. Biceps RMT was dependent on interactions between EFS and and both FTSA and BSD. There was no groupwide effect of iTBS on the FDI but individual changes in corticomotor excitability scaled with RMT, EFS, BSD, and FTSA. iTBS targeting the biceps was facilitatory, and dependent on FTSA and TFC. MRI‐based measures of neuroanatomy highlight how individual anatomy affects motor system responses to different TMS paradigms and may be useful for selecting appropriate motor targets when designing TMS based therapies.

Effect of Neuroanatomy on Intermittent Theta Burst Stimulation Motor Evoked Potentials

<h3>Research Objectives</h3> Previous work noted that there are significant variabilities in motor response to intermittent theta-burst stimulation (iTBS). It is possible this variability results from individual neuroanatomical differences. The current objective was to investigate the effect of individual neuroanatomy on first dorsal interosseous (FDI) and biceps brachii motor evoked potentials (MEPs) in response to iTBS. <h3>Design</h3> Cross-sectional study using a convenience sample. <h3>Setting</h3> Research laboratory. <h3>Participants</h3> Ten healthy individuals (7 females, 23.5 ± 5 years) participated in this study. Participants completed two iTBS sessions (one each targeting the FDI and biceps cortical hotspots) and an MRI on separate days. <h3>Interventions</h3> Not applicable. <h3>Main Outcome Measures</h3> MEPs were calculated using data acquired with a Magstim Super Rapid2 Plus1 stimulator via a 70 mm double air film coil to the primary motor cortex and electromyography signals were measured from dominant FDI and biceps. Head models were generated from T1 & T2 weighted MRI. Diffusion tensor imaging was used to determine fiber tract geometry for FDI and biceps corticospinal tracts. We then established neuroanatomical parameters including: fiber tract surface area (FTSA), tract fiber count (TFC), and brain scalp distance (BSD). Cortical electric field strength (EFS) was calculated using simulated stimulation of head models and finite element analysis. <h3>Results</h3> For the FDI, there was no effect of iTBS (p = 0.223) but individual changes in corticomotor excitability scaled with stimulation type and resting motor potential (p < 0.001), EFS (p = 0.001), BSD (p = 0.004), and FTSA (p = 0.011). iTBS had a faciliatory response on the biceps and was dependent on FTSA (p < 0.001) and TFC (p < 0.001). <h3>Conclusions</h3> Our results show that MRI-based measures of neuroanatomy, specifically cortical architecture and tract anatomy, impact how the motor system responds to iTBS, subject to target-specific cortical control organization. MRI-based modeling of individual neuroanatomy may be a useful approach in selection of motor targets when designing iTBS-based therapies. <h3>Author(s) Disclosures</h3> None.

Exergaming and Treadmill Training in Stroke Patients

Treadmill training is nowadays considered more efficient in improving balance and mobility rather than simply walking on an even surface. In patients with chronic stroke, changes in cortico-motor excitability are induced to improve balance and gait performance. There is simple treadmill training that can enhance and motivate patients to walk but treadmill training with body support is safer and more comfortable for patients. In one study the effect of treadmill therapy with the optic flow on balance control and gait training helps the patients of stroke in regaining functional independence in the community. Outcome measures were used that were Time Up and Go test, Functional Reach Test (FRT), 10-minute walk test, and 6- minute walk test. It proved a better result for patients with chronic stroke [1]. Apart from gait training, treadmill training may be able to help in balance dysfunction in most individuals who have to complain of stroke [2]. It enhances the balance and mobility skills of chronic stroke patients. Treadmill training motivates the subject to give better physical performance after stroke. Exercise video games are an innovative idea not commonly used in Pakistan for stroke rehabilitation. Both these techniques are used to enhance motivation and self-confidence in walking and maintaining balance. It keeps the subject engaged in physical therapy sessions for a long time after stroke. Thus, video games and treadmill training are used in various clinical settings for stroke rehabilitation. A combination of both these techniques would help decrease balance and mobility impairments through effective use of Exergaming and Treadmill training in patients suffering from a stroke in the chronic phase. This study would help the therapists across the locality to enlist a better management approach to treat subjects with chronic stroke.

Unpleasant Tastants Do Not Influence Neuromuscular Function Or Corticomotor Excitability Despite Sympathetic Nervous System Activation.

Previous research suggests that ingesting a bitter tastant enhances exercise performance. This may be due to activation of the sympathetic nervous system (SNS) in response to the unpleasant taste. However, the mechanisms facilitating changes in performance after ingestion of unpleasant tastants are not yet clear. PURPOSE: To explore the effect of unpleasant tastants on SNS activity, corticomotor excitability, and neuromuscular function. METHODS: Five females and seven males participated in a three-phase experiment. Each phase had two presentations of five conditions in a random order. No solution, water and artificial sweetener were controls for the unpleasant salty (1 M) and bitter (2 mM quinine) solutions. Measurements were taken immediately after each 25 ml solution was mouth rinsed (10 s) and ingested. In Phase 1, hedonic value, nausea, heart rate, and mean arterial pressure were measured to determine perceptual and SNS responses. In Phase 2, quadricep motor evoked potentials (MEPs) were recorded following transcranial magnetic stimulation to assess corticomotor excitability. In Phase 3, quadricep maximal voluntary contractions were performed with electrical femoral nerve stimulation to assess neuromuscular function. One-way repeated measures ANOVAs, with Bonferroni post-hoc comparisons explored differences between conditions. RESULTS: Hedonic value rating was significantly higher (p < 0.05) in the salt (mean ± SD; 75 ± 8) and bitter (76 ± 8) conditions compared to water (47 ± 10) and artificial sweetener (28 ± 18). The increase in heart rate was significantly higher (p < 0.05) in the salt (23 ± 6 bpm) and bitter (21 ± 3 bpm) conditions compared to no solution (13 ± 4 bpm), water (17 ± 4 bpm), and artificial sweetener (18 ± 5 bpm). Change in mean arterial pressure was also significantly higher (p < 0.05) in the bitter (24 ± 5 mmHg) condition compared to no solution (18 ± 3 mmHg), but other conditions were not significantly different. There was no significant difference (p > 0.05) between conditions in nausea, neuromuscular function (max voluntary force, voluntary activation, rate of force development) or corticomotor excitability (MEPs). CONCLUSIONS: Unpleasant tastants influenced markers of SNS activation. However, this did not translate into changes in corticomotor excitability or neuromuscular function.

Double-Sine-Wave Quadri-Pulse Theta Burst Stimulation of Precentral Motor Hand Representation Induces Bidirectional Changes in Corticomotor Excitability.

Neuronal plasticity is considered to be the neurophysiological correlate of learning and memory and changes in corticospinal excitability play a key role in the normal development of the central nervous system as well as in developmental disorders. In a previous study, it was shown that quadri-pulse theta burst stimulation (qTBS) can induce bidirectional changes in corticospinal excitability (1). There, a quadruple burst consisted of four single-sine-wave (SSW) pulses with a duration of 160 μs and inter-pulse intervals of 1.5 ms to match I-wave periodicity (666 Hz). In the present study, the pulse shape was modified applying double-sine-waves (DSW) rather than SSW pulses, while keeping the pulse duration at 160 μs. In two separate sessions, we reversed the current direction of the DSW pulse, so that its second component elicited either a mainly posterior-to-anterior (DSW PA-qTBS) or anterior-to-posterior (DSW AP-qTBS) directed current in the precentral gyrus. The after-effects of DSW qTBS on corticospinal excitability were examined in healthy individuals (n = 10) with single SSW TMS pulses. For single-pulse SSW TMS, the second component produced the same preferential current direction as DSW qTBS but had a suprathreshold intensity, thus eliciting motor evoked potentials (PA-MEP or AP-MEP). Single-pulse SSW TMS revealed bidirectional changes in corticospinal excitability after DSW qTBS, which depended on the preferentially induced current direction. DSW PA-qTBS at 666 Hz caused a stable increase in PA-MEP, whereas AP-qTBS at 666 Hz induced a transient decrease in AP-MEP. The sign of excitability following DSW qTBS at I-wave periodicity was opposite to the bidirectional changes after SSW qTBS. The results show that the pulse configuration and induced current direction determine the plasticity-effects of ultra-high frequency SSW and DSW qTBS at I-wave periodicity. These findings may offer new opportunities for short non-invasive brain stimulation protocols that are especially suited for stimulation in children and patients with neurological or neurodevelopmental disorders.

A Single Mechanism for Global and Selective Response Inhibition under the Influence of Motor Preparation.

In our everyday behavior, we frequently cancel one movement while continuing others. Two competing models have been suggested for the cancellation of such specific actions: (1) the abrupt engagement of a unitary global inhibitory mechanism followed by reinitiation of the continuing actions; or (2) a balance between distinct global and selective inhibitory mechanisms. To evaluate these models, we examined behavioral and physiological markers of proactive control, motor preparation, and response inhibition using a combination of behavioral task performance measures, electromyography, electroencephalography, and motor evoked potentials elicited with transcranial magnetic stimulation. Healthy human participants of either sex performed two versions of a stop signal task with cues incorporating proactive control: a unimanual task involving the initiation and inhibition of a single response, and a bimanual task involving the selective stopping of one of two prepared responses. Stopping latencies, motor evoked potentials, and frontal β power (13-20 Hz) did not differ between the unimanual and bimanual tasks. However, evidence for selective proactive control before stopping was manifest in the bimanual condition as changes in corticomotor excitability, μ (9-14 Hz), and β (15-25 Hz) oscillations over sensorimotor cortex. Together, our results favor the recruitment of a single inhibitory stopping mechanism with the net behavioral output depending on the levels of action-specific motor preparation.SIGNIFICANCE STATEMENT Response inhibition is a core function of cognitive flexibility and movement control. Previous research has suggested separate mechanisms for selective and global inhibition, yet the evidence is inconclusive. Another line of research has examined the influence of preparation for action stopping, or what is called proactive control, on stopping performance, yet the neural mechanisms underlying this interaction are unknown. We combined transcranial magnetic stimulation, electroencephalography, electromyography, and behavioral measures to compare selective and global inhibition models and to investigate markers of proactive control. The results favor a single inhibitory mechanism over separate selective and global mechanisms but indicate a vital role for preceding motor activity in determining whether and which actions will be stopped.

Neck rotation modulates motor-evoked potential duration of proximal muscle cortical representations in healthy adults

Transcranial magnetic stimulation (TMS) produces motor-evoked potentials (MEP) used to infer changes in corticomotor excitability. In humans, neck rotation can probe reticulospinal input on corticomotor output. This study investigated the effect of neck rotation on MEP duration in a proximal and distal upper limb muscle and compared responses between rest and preactivation. Single-pulse TMS to motor cortex was used to evoke MEPs at two stimulus intensities in 18 healthy adults (20-40years). Surface electromyography recorded MEPs from the non-dominant biceps brachii (BB) and first dorsal interosseous (FDI). Participants were seated with the target muscle at rest or 10% preactivated, and head rotated ipsilateral, contralateral, or in neutral position. The primary outcome was MEP tail, defined as the mean difference in MEP duration between active and rest trials. Secondary outcomes were MEP duration and amplitude. MEP tail was modulated by neck rotation in the proximal BB (P = 0.03) but not distal FDI (P > 0.19), with shorter duration during ipsilateral or contralateral rotation relative to neutral. In a neutral neck position, MEP duration was prolonged by muscle preactivation and higher TMS intensities in the FDI and BB (P < 0.03). Neck rotation attenuated the prolongation of MEP duration during preactivation in the BB, but not the FDI. Neck rotation had no effect on MEP amplitude for either muscle (P > 0.05). Modulation of the late portion of the MEP by rotation of the neck could indicate subcortical projections to alpha-motoneuron pools are stronger in proximal than distal upper limb muscles. These findings may have relevance for using MEP duration as a neural biomarker in neurological diseases.

The Effects of Nicotine on Cortical Excitability After Exercise: A Double-Blind Randomized, Placebo-controlled, Crossover Study.

The use of smokeless tobacco/nicotine products is common among athletes, but clear evidence for their positive or negative effect on sports performance is lacking. Nicotine is a psychoactive substance involved in numerous neuronal processes including cortical excitability. The aim of this study was to evaluate its effect on cortical excitability associated with aerobic exercise in nicotine-naive healthy volunteers. Ten nicotine-naive healthy volunteers were recruited for this double-blind, randomized, crossover study to compare the effect of snus (8 mg nicotine), an oral, smokeless tobacco product, to placebo on cortical excitability before and after aerobic exercise. Transcranial magnetic stimulation (TMS) was used to measure changes in corticomotor excitability (motor-evoked potentials, MEPs) and electromyography of leg muscles during maximal voluntary contractions (MVC) to assess changes in muscle contractions. Before and after aerobic exercise and with or without nicotine treatment, MEPs and MVCs were measured. Analysis of TMS data showed lower motor cortex activation (lower MEP amplitude) after snus administration compared with placebo, whereas electromyography data showed no difference in muscle contraction between snus and placebo treatment. These findings suggest a general reduction in cortical excitability, without no relevant effect on physical performance.

Corticomotor Excitability Changes Associated With Freezing of Gait in People With Parkinson Disease.

Background and PurposeFreezing of gait (FOG) is a debilitating gait disorder in people with Parkinson’s disease (PD). While various neuroimaging techniques have been used to investigate the pathophysiology of FOG, changes in corticomotor excitability associated with FOG have yet to be determined. Research to date has not concluded if changes in corticomotor excitability are associated with gait disturbances in this patient population. This study aimed to use transcranial magnetic stimulation (TMS) to investigate corticomotor excitability changes associated with FOG. Furthermore, the relationship between corticomotor excitability and gait performances would be determined.MethodsEighteen participants with PD and FOG (PD + FOG), 15 without FOG (PD − FOG), and 15 non-disabled adults (Control) were recruited for this study. Single and paired-pulse TMS paradigms were used to assess corticospinal and intracortical excitability, respectively. Gait performance was measured by the 10-Meter-Walk test. Correlation analysis was performed to evaluate relationships between TMS outcomes and gait parameters.ResultsCompared with the Control group, the PD + FOG group showed a significantly lower resting motor threshold and reduced short intracortical inhibition (SICI). Correlation analysis revealed a relationship between resting motor evoked potential and step length, and between SICI and walking velocity in the Control group. While the silent period correlated with step length in the PD − FOG group, no significant relationship was observed in the PD + FOG group.Discussion and ConclusionCompared to the Control group, the PD + FOG group exhibited reduced corticomotor inhibition. Distinct correlations observed among the three groups suggest that the function of the corticomotor system plays an important role in mediating walking ability in non-disabled adults and people with PD − FOG, while people with PD + FOG may rely on neural networks other than the corticomotor system to control gait.

Peripheral Electrical Stimulation Paired With Movement-Related Cortical Potentials Improves Isometric Muscle Strength and Voluntary Activation Following Stroke.

BackgroundEndogenous paired associative stimulation (ePAS) is a neuromodulatory intervention that has potential to aid stroke recovery. ePAS involves pairing endogenous electroencephalography (EEG) signals known as movement-related cortical potentials (MRCPs), with peripheral electrical stimulation. Previous studies have used transcranial magnetic stimulation (TMS) to demonstrate changes in corticomotor excitability following ePAS. However, the use of TMS as a measure in stroke research is limited by safety precautions, intolerance, and difficulty generating a measurable response in more severely affected individuals. We were interested in evaluating the effect of ePAS using more feasible measures in people with stroke. This study asks whether ePAS produces immediate improvements in the primary outcomes of maximal voluntary isometric contraction (MVIC) and total neuromuscular fatigue of the dorsiflexor muscles, and in the secondary outcomes of muscle power, voluntary activation (VA), central fatigue, peripheral fatigue, and electromyography activity.MethodIn this repeated-measures cross-over study, 15 participants with chronic stroke completed two interventions, ePAS and sham, in a randomized order. During ePAS, 50 repetitions of visually cued dorsiflexion were completed, while single pulses of electrical stimulation were delivered to the deep branch of the common peroneal nerve. Each somatosensory volley was timed to arrive in the primary motor cortex at the peak negativity of the MRCP. Univariate and multivariate linear mixed models were used to analyze the primary and secondary data, respectively.ResultsThere was a statistically significant increase in dorsiflexor MVIC immediately following the ePAS intervention (mean increase 7 N), compared to the sham intervention (mean change 0 N) (univariate between-condition analysis p = 0.047). The multivariate analysis revealed a statistically significant effect of ePAS on VA of the tibialis anterior muscle, such that ePAS increased VA by 7 percentage units (95% confidence interval 1.3–12.7%). There was no statistically significant effect on total neuromuscular fatigue, muscle power, or other secondary measures.ConclusionA single session of ePAS can significantly increase isometric muscle strength and VA in people with chronic stroke. The findings confirm that ePAS has a central neuromodulatory mechanism and support further exploration of its potential as an adjunct to stroke rehabilitation. In addition, the findings offer alternative, feasible outcome measures for future research.Clinical trial registrationAustralia New Zealand Clinical Trials Registry ACTRN12617000838314 (www.anzctr.org.au), Universal Trial Number U111111953714.

Paired Associative Stimulation Fails to Induce Plasticity in Freely Behaving Intact Rats.

Paired associative stimulation (PAS) has been explored in humans as a noninvasive tool to drive plasticity and promote recovery after neurologic insult. A more thorough understanding of PAS-induced plasticity is needed to fully harness it as a clinical tool. Here, we tested the efficacy of PAS with multiple interstimulus intervals in an awake rat model to study the principles of associative plasticity. Using chronically implanted electrodes in motor cortex and forelimb, we explored PAS parameters to effectively drive plasticity. We assessed changes in corticomotor excitability using a closed-loop, EMG-controlled cortical stimulation paradigm. We tested 11 PAS intervals, chosen to force the coincidence of neuronal activity in the motor cortex and spinal cord of rats with timings relevant to the principles of Hebbian spike timing-dependent plasticity. However, despite a relatively large number of stimulus pairings (300), none of the tested intervals reliably changed corticospinal excitability relative to control conditions. Our results question PAS effectiveness under these conditions.

Neuromodulatory Effects of Transcranial Direct Current Stimulation on Motor Excitability in Rats.

Transcranial direct current stimulation (tDCS) is a noninvasive technique for modulating neural plasticity and is considered to have therapeutic potential in neurological disorders. For the purpose of translational neuroscience research, a suitable animal model can be ideal for providing a stable condition for identifying mechanisms that can help to explore therapeutic strategies. Here, we developed a tDCS protocol for modulating motor excitability in anesthetized rats. To examine the responses of tDCS-elicited plasticity, the motor evoked potential (MEP) and MEP input-output (IO) curve elicited by epidural motor cortical electrical stimulus were evaluated at baseline and after 30 min of anodal tDCS or cathodal tDCS. Furthermore, a paired-pulse cortical electrical stimulus was applied to assess changes in the inhibitory network by measuring long-interval intracortical inhibition (LICI) before and after tDCS. In the results, analogous to those observed in humans, the present study demonstrates long-term potentiation- (LTP-) and long-term depression- (LTD-) like plasticity can be induced by tDCS protocol in anesthetized rats. We found that the MEPs were significantly enhanced immediately after anodal tDCS at 0.1 mA and 0.8 mA and remained enhanced for 30 min. Similarly, MEPs were suppressed immediately after cathodal tDCS at 0.8 mA and lasted for 30 min. No effect was noted on the MEP magnitude under sham tDCS stimulation. Furthermore, the IO curve slope was elevated following anodal tDCS and presented a trend toward diminished slope after cathodal tDCS. No significant differences in the LICI ratio of pre- to post-tDCS were observed. These results indicated that developed tDCS schemes can produce consistent, rapid, and controllable electrophysiological changes in corticomotor excitability in rats. This newly developed tDCS animal model could be useful to further explore mechanical insights and may serve as a translational platform bridging human and animal studies, establishing new therapeutic strategies for neurological disorders.

Changes in corticomotor excitability of the calf muscles during postural tasks

Changes in corticomotor excitability of the calf muscles during postural tasks

Influence of neurovascular mechanisms on response to tDCS: an exploratory study.

The beneficial effects of transcranial direct current stimulation (tDCS) for stroke rehabilitation are limited by the variability in changes in corticomotor excitability (CME) after tDCS. Neuronal activity is closely related to cerebral blood flow; however, the cerebral hemodynamics of neuromodulation in relation to neural effects have been less explored. In this study, we examined the effects of tDCS on cerebral blood velocity (CBv) in chronic stroke survivors using transcranial Doppler (TCD) ultrasound in relation to changes in CME and described the neurovascular characteristics of tDCS responders. Middle cerebral artery (MCA) CBv, cerebrovascular resistance (CVRi) and other cerebral hemodynamics-related variables were continuously measured before and after 15min of 1mA anodal tDCS to the lesioned lower limb M1. tDCS did not modulate CBv in thewhole group and upon TMS-based stratification of responders and non-responders. However, at baseline, responders demonstrated lower CME levels, lower CBv and higher CVRi as compared to non-responders. These results indicate a possible difference in baseline CME and CBv intDCS responders that may influence their response to neuromodulation. Future trials with a large sample size and repeated baseline measurements may help validate these findings and establish a relationship between neuromodulation and neurovascular mechanisms in stroke.

Determinants of Inter-Individual Variability in Corticomotor Excitability Induced by Paired Associative Stimulation.

Transcranial magnetic stimulation (TMS) is a well-established tool in probing cortical plasticity in vivo. Changes in corticomotor excitability can be induced using paired associative stimulation (PAS) protocol, in which TMS over the primary motor cortex is conditioned with an electrical peripheral nerve stimulation of the contralateral hand. PAS with an inter-stimulus interval of 25 ms induces long-term potentiation (LTP)-like effects in cortical excitability. However, the response to a PAS protocol tends to vary substantially across individuals. In this study, we used univariate and multivariate data-driven methods to investigate various previously proposed determinants of inter-individual variability in PAS efficacy, such as demographic, cognitive, clinical, neurophysiological, and neuroimaging measures. Forty-one right-handed participants, comprising 22 patients with amnestic mild cognitive impairment (MCI) and 19 healthy controls (HC), underwent the PAS protocol. Prior to stimulation, demographic, genetic, clinical, as well as structural and resting-state functional MRI data were acquired. The two groups did not differ in any of the variables, except by global cognitive status. Univariate analysis showed that only 61% of all participants were classified as PAS responders, irrespective of group membership. Higher PAS response was associated with lower TMS intensity and with higher resting-state connectivity within the sensorimotor network, but only in responders, as opposed to non-responders. We also found an overall positive correlation between PAS response and structural connectivity within the corticospinal tract, which did not differ between groups. A multivariate random forest (RF) model identified age, gender, education, IQ, global cognitive status, sleep quality, alertness, TMS intensity, genetic factors, and neuroimaging measures (functional and structural connectivity, gray matter (GM) volume, and cortical thickness as poor predictors of PAS response. The model resulted in low accuracy of the RF classifier (58%; 95% CI: 42 − 74%), with a higher relative importance of brain connectivity measures compared to the other variables. We conclude that PAS variability in our sample was not well explained by factors known to influence PAS efficacy, emphasizing the need for future replication studies.

Repetitive transcranial magnetic stimulation of the primary motor cortex expedites recovery in the transition from acute to sustained experimental pain: a randomised, controlled study.

Repetitive transcranial magnetic stimulation (rTMS) of the primary motor cortex (M1) is increasingly being investigated as a means of alleviating chronic pain. However, rTMS interventions are typically initiated once pain has already become chronic and maladaptive patterns of neural activity are likely to have been established. A critical question is whether M1 rTMS applied soon after pain onset can prevent the development of maladaptive neural activity and promote recovery. This study investigated the effect of 5 consecutive days of excitatory M1 rTMS on pain, functional limitation, mechanical hyperalgesia, descending inhibitory pain control, and M1 organisation in the transition from acute to sustained pain. Thirty healthy participants attended 8 sessions over a 16-day period. On days 0, 2, and 4, nerve growth factor was injected into the right forearm to induce progressively developing muscle soreness and mechanical hyperalgesia. Active or sham excitatory rTMS was delivered on days 4 to 8. Clinical and neurophysiological outcomes were recorded on days 0, 2, 4, 6, 8, 11, and 14. Active rTMS promoted recovery of muscle soreness, pain, and mechanical hyperalgesia when compared with sham rTMS (all between-group P < 0.05). Corticomotor excitability and descending inhibitory pain control did not differ between groups. These findings suggest that active excitatory M1 rTMS promotes recovery of muscle soreness, pain, and mechanical hyperalgesia in the transition from acute to sustained experimental pain. The analgesic effects of M1 rTMS do not seem to be modulated by descending inhibitory pain control or local changes in corticomotor excitability.