Changes In Corticospinal Excitability Research Articles

Determination of anodal tDCS intensity threshold for reversal of corticospinal excitability: an investigation for induction of counter-regulatory mechanisms

Transcranial direct current stimulation is applied to modulate activity, and excitability of the brain. Basically, LTP-like plasticity is induced when anodal tDCS (a-tDCS) is applied over the primary motor cortex. However, it has been shown that specific parameters of a-tDCS can induce a plasticity reversal. We aimed to systematically assess the intensity threshold for reversal of the direction of plasticity induced by a-tDCS, monitored by corticospinal excitability (CSE), and explored mechanisms regulating this reversal. Fifteen healthy participants received a-tDCS in pseudo-random order for 26 min with four intensities of 0.3, 0.7, 1, and 1.5 mA. To measure CSE changes, single-pulse TMS was applied over the left M1, and motor evoked potentials of a contralateral hand muscle were recorded prior to a-tDCS, immediately and 30-min post-intervention. Paired-pulse TMS was used to evaluate intracortical excitation and inhibition. CSE increased significantly following a-tDCS with an intensity of 0.7 mA; however, the expected effect decreased and even reversed at intensities of 1 and 1.5 mA. ICF was significantly increased while SICI and LICI decreased at 0.7 mA. On the other hand, a significant decrease of ICF, but SICI and LICI enhancement was observed at intensities of 1, and 1.5 mA. The present findings show an intensity threshold of ≥ 1 mA for 26 min a-tDCS to reverse LTP- into LTD-like plasticity. It is suggested that increasing stimulation intensity, with constant stimulation duration, activates counter-regulatory mechanisms to prevent excessive brain excitation. Therefore, stimulation intensity and plasticity induced by a-tDCS might non-linearly correlate in scenarios with prolonged stimulation duration.

The effect of breaking up prolonged sitting on paired associative stimulation-induced plasticity

Paired associative stimulation (PAS) can induce plasticity in the motor cortex, as measured by changes in corticospinal excitability (CSE). This effect is attenuated in older and less active individuals. Although a single bout of exercise enhances PAS-induced plasticity in young, physically inactive adults, it is not yet known if physical activity interventions affect PAS-induced neuroplasticity in middle-aged inactive individuals. Sixteen inactive middle-aged office workers participated in a randomized cross-over design investigating how CSE and short-interval intracortical inhibition (SICI) were affected by PAS preceded by 3 h of sitting (SIT), 3 h of sitting interrupted every 30 min by 3 min of frequent short bouts of physical activity (FPA) and 2.5 h of sitting followed by 25 min of moderate-intensity exercise (EXE). Transcranial magnetic stimulation was applied over the primary motor cortex (M1) of the dominant abductor pollicis brevis to induce recruitment curves before and 5 min and 30 min post-PAS. Linear mixed models were used to compare changes in CSE using time and condition as fixed effects and subjects as random effects. There was a main effect of time on CSE and planned within-condition comparisons showed that CSE was significantly increased from baseline to 5 min and 30 min post-PAS, in the FPA condition, with no significant changes in the SIT or EXE conditions. SICI decreased from baseline to 5 min post-PAS, but this was not related to changes in CSE. Our findings suggest that in middle-aged inactive adults, FPAs may promote corticospinal neuroplasticity. Possible mechanisms are discussed.

Sustained Isometric Wrist Flexion and Extension Maximal Voluntary Contractions on Corticospinal Excitability to Forearm Muscles during Low-Intensity Hand-Gripping.

The wrist extensors demonstrate an earlier fatigue onset than the wrist flexors. However, it is currently unclear whether fatigue induces unique changes in muscle activity or corticospinal excitability between these muscle groups. The purpose of this study was to examine how sustained isometric wrist extension/flexion maximal voluntary contractions (MVCs) influence muscle activity and corticospinal excitability of the forearm. Corticospinal excitability to three wrist flexors and three wrist extensors were measured using motor evoked potentials (MEPs) elicited via transcranial magnetic stimulation. Responses were elicited while participants exerted 10% of their maximal handgrip force, before and after a sustained wrist flexion or extension MVC (performed on separate sessions). Post-fatigue measures were collected up to 10-min post-fatigue. Immediately post-fatigue, extensor muscle activity was significantly greater following the wrist flexion fatigue session, although corticospinal excitability (normalized to muscle activity) was greater on the wrist extension day. Responses were largely unchanged in the wrist flexors. However, for the flexor carpi ulnaris, normalized MEP amplitudes were significantly larger following wrist extension fatigue. These findings demonstrate that sustained isometric flexion/extension MVCs result in a complex reorganization of forearm muscle recruitment strategies during hand-gripping. Based on these findings, previously observed corticospinal behaviour following fatigue may not apply when the fatiguing task and measurement task are different.

Modulation of Corticospinal Excitability by Two Different Somatosensory Stimulation Patterns; A Pilot Study.

Following amputation, almost two-thirds of amputees experience unpleasant to painful sensations in the area of the missing limb. Whereas the mechanism of phantom limb pain (PLP) remains unknown, it has been shown that maladaptive cortical plasticity plays a major role in PLP. Transcutaneous electrical nerve stimulation (TENS) generating sensory input is believed to be beneficial for PLP relief. TENS effect may be caused by possible reversing reorganization at the cortical level that can be evaluated by changes in the excitability of the corticospinal (CS) pathway. Excitability changes are dependent on the chosen stimulation patterns and parameters. The aim of this study was to investigate the effect of two TENS patterns on the excitability of the CS tract among healthy subjects. We compared a non-modulated TENS as a conventional pattern with pulse width modulated TENS pattern. Motor evoked potentials (MEPs) from APB muscles of stimulated arm (TENS-APB) and contralateral arm (Control-APB) were recorded. We applied single TMS pulses on two subjects for each TENS pattern. The results showed that both patterns increase the CS excitability, while the effects of the conventional TENS is stronger. However, the amplitude of MEPs from control-APB after TENS delivery remained almost the same.Clinical Relevance- The primary results revealed changes in the activity of CS pathway for both patterns. A future study on a larger population is needed to provide strong evidence on the changes in CS excitability. The evaluation part with more factors such as changes in intracortical inhibition (ICI) may be beneficial to find an optimal modulated TENS pattern to enhance pain alleviation process in PLP.

The effects of transcranial direct current stimulation on corticospinal and cortico-cortical excitability and response variability: Conventional versus high-definition montages

Response variability following transcranial direct current stimulation (tDCS) highlights need for exploring different tDCS electrode montages. Corticospinal excitability (CSE), cortico-cortical excitability and intra-individual variability was compared following conventional and high-definition (HD) anodal (a-tDCS) and cathodal (c-tDCS) tDCS. Fifteen healthy males attended four sessions at-least one-week apart: conventional a-tDCS, conventional c-tDCS, HD-a-tDCS, HD-c-tDCS. TDCS was administered (1 mA, 10-minutes) over primary motor cortex (M1), via 6 × 4 cm active and 7 × 5 cm return electrodes (conventional tDCS) and 4 × 1 ring-electrodes 3.5 cm apart over M1 (HD-tDCS). For CSE, twenty-five single-pulse transcranial magnetic stimulation (TMS) peak-to-peak motor evoked potentials (MEP) were recorded at baseline, 0-minutes and 30-minutes post-tDCS. Twenty-five paired-pulse MEPs with 3-millisecond (ms) inter-pulse interval (IPI) and twenty-five at 10 ms assessed short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF). MEP standardised z-values standard deviations represented intra-individual variability. No significant changes in CSE from baseline were reported for all four interventions. No significant differences were reported in CSE between conventional and HD a-tDCS, but significant differences between conventional and HD c-tDCS 0-minutes post-tDCS. Conventional tDCS significantly reduced intra-individual variability compared to HD-tDCS for a-tDCS (0-minutes) and c-tDCS (30-minutes). No changes were reported for SICI/ICF. These novel findings of increased intra-individual variability following HD-tDCS, at the current stimulus parameters, highlight need for further nuanced research and refinement to optimise the HD-tDCS dosage-response relationship.

Changes in corticospinal excitability during bilateral and unilateral lower-limb force control tasks.

Ankle dorsiflexion force control is essential for performing daily living activities. However, the involvement of the corticospinal pathway during different ankle dorsiflexion tasks is not well understood. The objective of this study was to compare the corticospinal excitability during: (1) unilateral and bilateral; and (2) ballistic and tonic ankle dorsiflexion force control. Fifteen healthy young adults (age: 25.2 ± 2.8years) participated in this study. Participants performed unilateral and bilateral isometric ankle dorsiflexion force-control tasks, which required matching a visual target (10% of maximal effort) as quickly and precisely as possible during ballistic and tonic contractions. Transcranial magnetic stimulation (TMS) was applied over the primary motor cortex to elicit motor-evoked potentials (MEPs) from the right tibialis anterior during: (i) pre-contraction phase; (ii) ascending contraction phase; (iii) plateau phase (tonic tasks only); and (iv) resting phase (control). Peak-to-peak MEP amplitude was computed to compare the corticospinal excitability during each experimental condition. MEP amplitudes significantly increased during unilateral contraction compared to bilateral contraction in the pre-contraction phase. There were no significant differences in the MEP amplitudes between the ballistic tasks and tonic tasks in any parts of the contraction phase. Although different strategies are required during ballistic and tonic contractions, the extent of corticospinal involvement appears to be similar. This could be because both tasks enhance the preparation for precise force control. Furthermore, our results suggest that unilateral muscle contractions may largely facilitate the central nervous system during movement preparation for unilateral force control compared to bilateral muscle contractions.

TDCS Anodal tDCS increases bilateral corticospinal excitability irrespective of hemispheric dominance

Background: Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that utilizes weak direct currents to induce polarity-dependent modulation of corticospinal excitability. Although tDCS exerts a modulatory effect over the stimulation region, several studies have also demonstrated that distal areas of the brain connected to the region of stimulation may also be affected, as well as the contralateral hemisphere. Objective: We examined the effect of a single session of anodal tDCS on corticospinal excitability and inhibition of both the stimulated and non-stimulated hemisphere and examined the influence of these responses by the brain-derived neurotrophic factor (BDNF) polymorphism. Methods: In a randomized cross-over design, changes in corticospinal excitability and inhibition of the stimulated and non-stimulated hemispheres were analysed in 13 participants in both the dominant and non-dominant primary motor cortex (M1). Participants were exposed to 20 min of anodal and sham tDCS and also undertook a blood sample for BDNF genotyping. Results: TMS revealed a bilateral increase in corticospinal excitability irrespective of which hemisphere (dominant vs non-dominant) was stimulated (all P < 0.05). Furthermore, the induction of corticospinal excitability was influenced by the BDNF polymorphism. Conclusion: This finding shows that anodal tDCS induces bilateral effects in corticospinal excitability irrespective of hemispheric dominance. This finding provides scientists and medical practitioners with a greater understanding as to how this technique may be used as a therapeutic tool for clinical populations.

Muscle length: A new feature to investigate neural control of lengthening contractions.

Muscle length: A new feature to investigate neural control of lengthening contractions.

Probing Context-Dependent Modulations of Ipsilateral Premotor-Motor Connectivity in Relapsing-Remitting Multiple Sclerosis.

Objective: We employed dual-site TMS to test whether ipsilateral functional premotor-motor connectivity is altered in relapsing-remitting Multiple Sclerosis (RR-MS) and is related to central fatigue.Methods: Twelve patients with RR-MS and 12 healthy controls performed a visually cued Pinch-NoPinch task with their right hand. During the reaction time (RT) period of Pinch and No-Pinch trials, single-site TMS was applied to the left primary motor cortex (M1) or dual-site TMS was applied to the ipsilateral dorsal premotor cortex (PMd) and to M1. We traced context-dependent changes of corticospinal excitability and premotor–motor connectivity by measuring Motor-Evoked Potentials (MEPs) in the right first dorsal interosseus muscle. Central fatigue was evaluated with the Fatigue Scale for Motor and Cognitive Functions (FSMS).Results: In both groups, single-pulse TMS revealed a consistent increase in mean MEP amplitude during the Reaction Time (RT) period relative to a resting condition. Task-related corticospinal facilitation increased toward the end of the RT period in Pinch trials, while it decreased in No-Pinch trials. Again, this modulation of MEP facilitation by trial type was comparable in patients and controls. Dual-site TMS showed no significant effect of a conditioning PMd pulse on ipsilateral corticospinal excitability during the RT period in either group. However, patients showed a trend toward a relative attenuation in functional PMd-M1 connectivity at the end of the RT period in No-Pinch trials, which correlated positively with the severity of motor fatigue (r = 0.69; p = 0.007).Conclusions: Dynamic regulation of corticospinal excitability and ipsilateral PMd-M1 connectivity is preserved in patients with RR-MS. MS-related fatigue scales positively with an attenuation of premotor-to-motor functional connectivity during cued motor inhibition.Significance: The temporal, context-dependent modulation of ipsilateral premotor-motor connectivity, as revealed by dual-site TMS of ipsilateral PMd and M1, constitutes a promising neurophysiological marker of fatigue in MS.

Exercise-Induced Brain Excitability Changes in Progressive Multiple Sclerosis: A Pilot Study.

Even a single bout of aerobic exercise (AE) enhances corticospinal excitability (CSE), a biomarker of neuroplasticity. Because neurodegeneration limits capacity for neuroplasticity, it is not clear whether AE would induce CSE changes in people with progressive multiple sclerosis (MS). People with progressive MS (n = 10) requiring ambulatory assistive devices completed a graded maximal exercise test. Dual-energy x-ray absorptiometry was used to quantify body fat and lean mass. Before and following one 40-minute AE session using body weight-supported (<10% support) treadmill at moderate intensity, CSE was measured using transcranial magnetic stimulation. Variables included resting and active motor thresholds, motor evoked potential (MEP) amplitudes, recruitment curves, and length of the cortical silent period (CSP). Aerobic exercise reduced inhibition (shorter CSP) and increased excitation (increased MEP amplitude) only in the hemisphere corresponding to the stronger hand. Controlling for age, higher fitness and lower body fat significantly predicted exercise-induced reduction in resting motor threshold (ΔR = +0.458, P = 0.046) and CSP (ΔR = +0.568, P = 0.030), respectively. Despite high levels of disability, capacity for exercise-induced neuroplasticity was retained among people with progressive MS. The hemisphere contralateral to the weaker hand was resistant to exercise-induced CSE changes, suggesting less neuroplastic potential. Lower fitness and higher body fat were associated with diminished exercise-induced CSE benefits, suggesting that therapists should consider interventions aimed at improving fitness and combating sedentarism to ultimately enhance the benefits of exercise on the brain.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A302).

Mechanisms of neuromuscular fatigue and recovery in unilateral versus bilateral maximal voluntary contractions

The aim of this study was to investigate differences in neuromuscular function and corticospinal excitability in response to sustained unilateral (UNIL) and bilateral (BIL) isometric maximal voluntary contraction (IMVC) of the knee extensors. Eleven men performed a 1-min sustained IMVC of the knee extensors with one or both legs. Central and peripheral measures of neuromuscular function and corticospinal excitability were assessed via surface electromyography (EMG), peripheral nerve stimulation, and transcranial magnetic stimulation before, immediately after, and during recovery from IMVC. IMVC force and root-mean-squared EMG decreased during the fatiguing 1-min IMVC, with a larger decrease in EMG during BIL. All neuromuscular function indexes decreased significantly after the IMVC (P < 0.005), but the magnitude of these decreases did not differ between conditions. Changes in corticospinal excitability (motor evoked potential) and inhibition (silent period) did not differ between conditions. In contrast to previous studies utilizing submaximal exercise, no more peripheral fatigue was found after UNIL vs. BIL conditions, even though central drive was lower after BIL 1-min IMVC. Corticospinal excitability and inhibition were not found to be different between UNIL and BIL conditions, in line with maximal voluntary activation.NEW & NOTEWORTHY The present experiment used peripheral nerve stimulation and transcranial magnetic stimulations during a sustained isometric maximal voluntary contraction to investigate the influence of muscle mass on neuromuscular fatigue. Contrary to previous studies that used submaximal exercise, peripheral fatigue was not found to be greater in unilateral vs. bilateral knee extensions even though central drive was lower during bilateral contractions. Corticospinal excitability and inhibition were not found to be different between unilateral and bilateral conditions.

Task-dependent modulation of corticospinal excitability and inhibition following strength training

This study determined whether there are task-dependent differences in cortical excitability following different types of strength training. Transcranial magnetic stimulation (TMS) measured corticospinal excitability (CSE) and intracortical inhibition (ICI) of the biceps brachii muscle in 42 healthy subjects that were randomised to either paced-strength-training (PST, n = 11), self-paced strength-training (SPST, n = 11), isometric strength-training (IST, n = 10) or to a control group (n = 10). Single-pulse and paired-pulse TMS were applied prior to and following 4-weeks of strength-training. PST increased CSE compared to SPST, IST and the control group (all P < 0.05). ICI was only reduced (60%) following PST. Dynamic strength increased by 18 and 25% following PST and SPST, whilst isometric strength increased by 20% following IST. There were no associations between the behavioural outcome measures and the change in CSE and ICI. The corticospinal responses to strength-training are task-dependent, which is a new finding. Strength-training that is performed slowly could promote use-dependent plasticity in populations with reduced volitional drive, such as during periods of limb immobilization, musculoskeletal injury or stroke.

A Checklist to Reduce Response Variability in Studies Using Transcranial Magnetic Stimulation for Assessment of Corticospinal Excitability: A Systematic Review of the Literature

Response variability between individuals (interindividual variability) and within individuals (intraindividual variability) is an important issue in the transcranial magnetic stimulation (TMS) literature. This has raised questions of the validity of TMS to assess changes in corticospinal excitability (CSE) in a predictable and reliable manner. Several participant-specific factors contribute to this observed response variability with a current lack of consensus on the degree each factor contributes. This highlights a need for consistency and structure in reporting study designs and methodologies. Currently, there is no summarized review of the participant-specific factors that can be controlled and may contribute to response variability. This systematic review aimed to develop a checklist of methodological measures taken by previously published research to increase the homogeneity of participant selection criteria, preparation of participants before experimental testing, participant scheduling, and the instructions given to participants throughout experimental testing to minimize their effect on response variability. Seven databases were searched in full. Studies were included if CSE was measured via TMS and included methodological measures to increase the homogeneity of the participants. Eighty-four studies were included. Twenty-three included measures to increase participant selection homogeneity, 21 included measures to increase participant preparation homogeneity, while 61 included measures to increase participant scheduling and instructions during experimental testing homogeneity. These methodological measures were summarized into a user-friendly checklist with considerations, suggestions, and rationale/justification for their inclusion. This may provide the framework for further insights into ways to reduce response variability in TMS research.

Determination of anodal tDCS duration threshold for reversal of corticospinal excitability: An investigation for induction of counter-regulatory mechanisms

BackgroundTranscranial direct current stimulation (tDCS) is used to induce neuroplasticity in the human brain. Within certain limits of stimulation duration, anodal tDCS (a-tDCS) over the primary motor cortex induces long term potentiation- (LTP) like plasticity. A reversal of the direction of plasticity has however been described with prolonged a-tDCS protocols. ObjectiveWe aimed to systematically investigate the intervention duration threshold for reversal of a-tDCS-induced effects on corticospinal excitability (CSE) and to determine the probable mechanisms involved in these changes. MethodsFifteen healthy participants received a-tDCS of 1 mA for five different durations in pseudo-random session order. Transcranial magnetic stimulation (TMS) was delivered over the left M1, and motor evoked potentials (MEPs) of a contralateral hand muscle were recorded before, immediately and 30 min following intervention to measure CSE changes. Short-interval intracortical inhibition (SICI), intracortical facilitation (ICF), and long interval facilitation (LIF) were assessed via paired-pulse TMS protocols. ResultsA-tDCS significantly increased CSE as expected at stimulation durations of 22 and 24 min. However, this effect of a-tDCS on CSE decreased and even reversed when stimulation duration increased to 26, 28, and 30 min. Respective alterations of ICF, LIF, and SICI indicate the involvement of glutamatergic, and GABAergic systems in these effects. ConclusionsThese results confirm a duration threshold for reversal of the excitability-enhancing effect of a-tDCS with stimulation durations ≥ 26 min. Counter-regulatory mechanisms are discussed as a mechanistic foundation for these effects, which might prevent excessive brain activation.

Haptic Adaptive Feedback to Promote Motor Learning With a Robotic Ankle Exoskeleton Integrated With a Video Game.

Background: Robotic devices have been used to rehabilitate walking function after stroke. Although results suggest that post-stroke patients benefit from this non-conventional therapy, there is no agreement on the optimal robot-assisted approaches to promote neurorecovery. Here we present a new robotic therapy protocol using a grounded exoskeleton perturbing the ankle joint based on tacit learning control.Method: Ten healthy individuals and a post-stroke patient participated in the study and were enrolled in a pilot intervention protocol that involved performance of ankle movements following different trajectories via video game visual feedback. The system autonomously modulated task difficulty according to the performance to increase the challenge. We hypothesized that motor learning throughout training sessions would lead to increased corticospinal excitability of dorsi-plantarflexor muscles. Transcranial Magnetic Stimulation was used to assess the effects on corticospinal excitability.Results: Improvements have been observed on task performance and motor outcomes in both healthy individuals and post-stroke patient case study. Tibialis Anterior corticospinal excitability increased significantly after the training; however no significant changes were observed on Soleus corticospinal excitability. Clinical scales showed functional improvements in the stroke patient.Discussion and Significance: Our findings both in neurophysiological and performance assessment suggest improved motor learning. Some limitations of the study include treatment duration and intensity, as well as the non-significant changes in corticospinal excitability obtained for Soleus. Nonetheless, results suggest that this robotic training framework is a potentially interesting approach that can be explored for gait rehabilitation in post-stroke patients.

Corticospinal responses during passive shortening and lengthening of tibialis anterior and soleus in older compared to younger adults.

What is the central question of this study? Are there age-related differences in corticospinal responses whilst passively changing muscle length? What is the main finding and its importance? In contrast to young, older adults exhibited no modulation of corticospinal excitability in tibialis anterior during passive ankle movement. These data show impaired sensorimotor response in older adults during length changes of tibialis anterior, thus contributing to our understanding of age-related changes in sensorimotor control. Corticospinal responses have been shown to increase and decrease with passive muscle shortening and lengthening, respectively, as a result of changes in muscle spindle afferent feedback. The ageing sensory system is accompanied by a number of alterations that might influence the processing and integration of sensory information. Consequently, corticospinal excitability might be modulated differently whilst changing muscle length. In 10 older adults (66±4years), corticospinal responses (MEP/Mmax ) were evoked in a static position, and during passive shortening and lengthening of soleus (SOL) and tibialis anterior (TA), and these data were compared to the re-analysed data pool of 18 younger adults (25±4years) published previously. Resting motor threshold was greater in SOL compared to TA (P<0.001), but did not differ between young and older (P=0.405). No differences were observed in MEP/Mmax between the static position, passive shortening or lengthening in SOL (young: all 0.02±0.01; older: 0.05±0.04, 0.03±0.02 and 0.04±0.01, respectively; P=0.298), and responses were not dependent on age (P=0.090). Conversely, corticospinal responses in TA were modulated differently between the age groups (P=0.002), with greater MEP/Mmax during passive shortening (0.22±0.12) compared to passive lengthening (0.13±0.10) and static position (0.10±0.05) in young (P<0.001), but unchanged in older adults (0.19±0.11, 0.22±0.11 and 0.18±0.07, respectively; P≥0.867). The present experiment shows that length-dependent changes in corticospinal excitability in TA of the young are not evident in older adults. This suggests impaired sensorimotor response during muscle length changes in older age that might only be present in ankle flexors, but not extensors.

Time-course of pain threshold after continuous theta burst stimulation of primary somatosensory cortex in pain-free subjects

Primary somatosensory cortex (S1) is involved in pain processing and thus its suppression using neuromodulatory techniques such as continuous theta burst stimulation (cTBS) might be a potential pain management strategy in patients with neuropathic pain. cTBS over S1 is known to elevate pain threshold in young adults. However, the time course of this after-effect is unknown. Furthermore, the effect of cTBS over S1 on pain threshold might be confounded by changes in the excitability of primary motor cortex (M1), an area known to be involved in pain processing, due to spread of current. Therefore, whether S1 plays a role in pain processing independent of M1 also remains unknown. The corticospinal excitability (CSE) can provide a measure of M1 excitability because cTBS over M1 is known to reduce CSE. Here, we studied the time-course of the effects of MRI-guided cTBS over S1 on electrical pain threshold (EPT) and CSE. Ten healthy young adults received cTBS over S1 and sham stimulation in counterbalanced sessions at least 5 days apart. EPT and CSE were recorded before and following cTBS over S1. We assessed each measure once before stimulation and then every 10 min starting immediately after stimulation until 40 min. cTBS over S1 elevated EPT compared to sham stimulation with the after-effect lasting for 40 min. We observed no change in CSE following cTBS and sham stimulation. Our findings suggest that cTBS over S1 can elevate EPT for 40 min without altering M1 excitability.

Acute high-intensity and moderate-intensity interval exercise do not change corticospinal excitability in low fit, young adults.

Previous research has demonstrated a lack of neuroplasticity induced by acute exercise in low fit individuals, but the influence of exercise intensity is unclear. In the present study, we assessed the effect of acute high-intensity (HI) or moderate-intensity (MOD) interval exercise on neuroplasticity in individuals with low fitness, as determined by a peak oxygen uptake (VO2peak) test (n = 19). Transcranial magnetic stimulation (TMS) was used to assess corticospinal excitability via area under the motor evoked potential (MEP) recruitment curve before and following training. Corticospinal excitability was unchanged after HI and MOD, suggesting no effect of acute exercise on neuroplasticity as measured via TMS in sedentary, young individuals. Repeated bouts of exercise, i.e., physical training, may be required to induce short-term changes in corticospinal excitability in previously sedentary individuals.

Neuromuscular Mechanisms Underlying Changes in Force Production during an Attentional Focus Task.

We examined the effects of attentional focus cues on maximal voluntary force output of the elbow flexors and the underlying physiological mechanisms. Eleven males participated in two randomized experimental sessions. In each session, four randomized blocks of three maximal voluntary contractions (MVC) were performed. The blocks consisted of two externally and two internally attentional focus cued blocks. In one of the sessions, corticospinal excitability (CSE) was measured. During the stimulation session transcranial magnetic, transmastoid and Erb’s point stimulations were used to induce motor evoked potentials (MEPs), cervicomedullary MEP (CMEPs) and maximal muscle action potential (Mmax), respectively in the biceps brachii. Across both sessions forces were lower (p = 0.024) under the internal (282.4 ± 60.3 N) compared to the external condition (310.7 ± 11.3 N). Muscle co-activation was greater (p = 0.016) under the internal (26.3 ± 11.5%) compared with the external condition (21.5 ± 9.4%). There was no change in CSE. Across both sessions, force measurements were lower (p = 0.033) during the stimulation (279.0 ± 47.1 N) compared with the no-stimulation session (314.1 ± 57.5 N). In conclusion, external focus increased force, likely due to reduced co-activation. Stimulating the corticospinal pathway may confound attentional focus. The stimulations may distract participants from the cues and/or disrupt areas of the cortex responsible for attention and focus.

Spinal direct current stimulation with locomotor training in chronic spinal cord injury.

Transcutaneous spinal direct current stimulation (tsDCS) is a non-invasive method of stimulating spinal circuits that can modulate and induce changes in corticospinal excitability (CE) in incomplete spinal cord injury (SCI). A double-blinded sham controlled study of 2 male patients (A and B) with SCI was carried out. Patient A received sham and cathodal tsDCS, while Patient B received sham and anodal tsDCS. Four baselines were recorded prior to each arm of stimulation. Outcomes were then measured post each arm of stimulation; 10-meter walk test, modified ashworth scale, berg balance scale, manual muscle testing, and spinal cord independence measure-III. Transcranial magnetic stimulation, assessed motor evoked potentials. Cathodal tsDCS increased the scores in few of the outcome measures and decreased others. Anodal stimulation increased scores in all measures. Motor evoked potentials increased in post-cathode and deteriorated in post-anode. In conclusion, tsDCS modulated gait parameters, spasticity, and CE in incomplete SCI.