Measures Of Corticospinal Excitability Research Articles

Acute hypoalgesic and neurophysiological responses to lower-limb ischaemic preconditioning.

The aim of this study was to assess if ischaemic preconditioning (IPC) can reduce pain perception and enhance corticospinal excitability during voluntary contractions. In a randomised, within-subject design, healthy participants took part in three experimental visits after a familiarisation session. Measures of pressurepain threshold (PPT), maximum voluntary isometric force, voluntary activation, resting twitch force, corticospinal excitability and corticospinal inhibition were performed before and ≥10min after either, unilateral IPC on the right leg (3 × 5min); a sham protocol (3 × 1min); or a control (no occlusion). Pain perception was then assessed in response to a hypertonic saline injection into the vastus lateralis muscle. In the right (occluded) leg, PPT was 10% greater after IPC compared to sham (P = 0.004). PPTs were also 9.5% greater in the contralateral leg for IPC compared to sham (P = 0.031). Maximum voluntary force, voluntary activation and resting twitch force were not different between conditions (all P ≥ 0.133). Measures of corticospinal excitability and inhibition also revealed no significant differences between conditions (all P ≥ 0.240). Hypertonic saline evoked pain revealed no difference in reported intensity or duration between conditions (P ≥ 0.082). IPC can reduce pain sensitivity in local and remote areas but does not subsequently impact neurophysiological measures of excitability or inhibition.

Accurate determination of motor evoked potential amplitude in TMS: The impact of personal and experimental factors.

Corticospinal excitability can be quantified using motor-evoked potentials (MEP) following transcranial magnetic stimulation (TMS). However, the inherent variability of MEPs poses significant challenges. We establish a framework using personal and experimental factors to select the optimal number of trials (nopt) required for reliable MEP estimates. 47 healthy younger underwent single-pulse TMS over the left primary motor cortex (M1). Per participant, 550 MEPs were collected at intensities ranging from 110% to 150% of the resting motor threshold (rMT), in 10% increments. Per intensity, we calculated nopt. We analyzed which personal and experimental factors affected nopt. nopt decreased with increasing TMS intensity, lower rMT baseline values, and exclusion of single-trial outliers. Sex had no significant effect. Our study indicates that even when TMS is used as an outcome measure, custom-tailoring its protocol to study-related circumstances is key, as TMS intensity, outliers, baseline rMT, and the desired precision level affect the number of TMS trials needed to obtain a reliable MEP. Thus, we underscore the absence of a universal rule-of-thumb rule, although our predictive equations and online tool provide future TMS experimenters with the means to estimate the required number of TMS trials based on individual characteristics and specific experimental conditions. Our predictive equations offer a tailored approach for selecting nopt, enhancing the reliability of TMS-derived corticospinal excitability measurements.

Examining motor evidence for the pause-then-cancel model of action-stopping: insights from motor system physiology.

Stopping initiated actions is fundamental to adaptive behavior. Longstanding, single-process accounts of action-stopping have been challenged by recent, two-process, "pause-then-cancel" models. These models propose that action-stopping involves two inhibitory processes: 1) a fast Pause process, which broadly suppresses the motor system as the result of detecting any salient event, and 2) a slower Cancel process, which involves motor suppression specific to the cancelled action. A purported signature of the Pause process is global suppression, or the reduced corticospinal excitability (CSE) of task-unrelated effectors early on in action-stopping. However, unlike the Pause process, few (if any) motor system signatures of a Cancel process have been identified. Here, we used single- and paired-pulse transcranial magnetic stimulation (TMS) methods to comprehensively measure the local physiological excitation and inhibition of both responding and task-unrelated motor effector systems during action-stopping. Specifically, we measured CSE, short-interval intracortical inhibition (SICI), and the duration of the cortical silent period (CSP). Consistent with key predictions from the pause-then-cancel model, CSE measurements at the responding effector indicated that additional suppression was necessary to counteract Go-related increases in CSE during action-stopping, particularly at later timepoints. Increases in SICI on Stop-signal trials did not differ across task-related and task-unrelated effectors, or across timepoints. This suggests SICI as a potential source of global suppression. Increases in CSP duration on Stop-signal trials were more prominent at later timepoints and were related to individual differences in CSE. Our study provides further evidence from motor system physiology that multiple inhibitory processes influence action-stopping.NEW & NOTEWORTHY Current debate surrounds whether single- or dual-process models better account for human action-stopping ability. We show that motor suppression of a successfully stopped muscle follows a distinct time course compared with when that same muscle is unrelated to the stopping task. Our results further suggest that distinct local inhibitory neuron populations contribute to these unique sources of suppression. Our study provides evidence from motor system physiology that multiple inhibitory processes influence action-stopping.

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

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

Sensorimotor Integration in Chronic Low Back Pain

Objective: Chronic low back pain (CLBP) impacts on spine movement. Altered sensorimotor integration can be involved. Afferents from the lumbo-pelvic area might be processed differently in CLBP and impact on descending motor control. This study aimed to determine whether afferents influence the corticomotor control of paravertebral muscles in CLBP. Fourteen individuals with CLBP (11 females) and 13 pain-free controls (8 females) were tested with transcranial magnetic stimulation (TMS) to measure the motor-evoked potential [MEP] amplitude of paravertebral muscles. Noxious and non-noxious electrical stimulation, and magnetic stimulation in the lumbo-sacral area were used as afferent stimuli and triggered 20 to 200 ms prior to TMS. EMG modulation elicited by afferent stimulation alone was measured to control net motoneuron excitability. MEP/EMG ratio was used as a measure of corticospinal excitability with control of net motoneuron excitability. MEP/EMG ratio was larger at 60, 80 and 100-ms intervals in CLBP compared to controls, and afferent stimulations alone reduced EMG amplitude greater in CLBP than controls at 100 ms. Our results suggest alteration in sensorimotor integration in CLBP highlighted by a greater facilitation of the descending corticospinal input to paravertebral muscles. Our results can help to optimise interventions by better targeting mechanisms.

Motor function in multiple sclerosis assessed by navigated transcranial magnetic stimulation mapping.

Impaired motor function is a major cause of disability in multiple sclerosis (MS), involving various neuroplasticity processes typically assessed by neuroimaging. This study aimed to determine whether navigated transcranial magnetic stimulation (nTMS) could also provide biomarkers of motor cortex plasticity in patients with MS (pwMS). nTMS motor mapping was performed for hand and leg muscles bilaterally. nTMS variables included the amplitude and latency of motor evoked potentials (MEPs), corticospinal excitability measures, and the size of cortical motor maps (CMMs). Clinical assessment included disability (Expanded Disability Status Scale, EDSS), strength (MRC scale, pinch and grip), and dexterity (9-hole Pegboard Test). nTMS motor mapping was performed in 68 pwMS. PwMS with high disability (EDSS ≥ 3) had enlarged CMMs with less dense distribution of MEPs and various MEP parameter changes compared to pwMS with low disability (EDSS < 3). Patients with progressive MS had also various MEP parameter changes compared to pwMS with relapsing remitting form. MRC score correlated positively with MEP amplitude and negatively with MEP latency, pinch strength correlated negatively with CMM volume and dexterity with MEP latency. This is the first study to perform 4-limb cortical motor mapping in pwMS using a dedicated nTMS procedure. By quantifying the cortical surface representation of a given muscle and the variability of MEP within this representation, nTMS can provide new biomarkers of motor function impairment in pwMS. Our study opens perspectives for the use of nTMS as an objective method for assessing pwMS disability in clinical practice.

Virtual Reality Action Observation and Motor Imagery to Enhance Neuroplastic Capacity in the Human Motor Cortex: A Pilot Double-blind, Randomized Cross-over Trial

Neuroplasticity is important for learning, development and recovery from injury. Therapies that can upregulate neuroplasticity are therefore of interest across a range of fields. We developed a novel virtual reality action observation and motor imagery (VR-AOMI) intervention and evaluated whether it could enhance the efficacy of mechanisms of neuroplasticity in the human motor cortex of healthy adults. A secondary question was to explore predictors of the change in neuroplasticity following VR-AOMI. A pre-registered, pilot randomized controlled cross-over trial was performed. Twenty right-handed adults (13 females; mean age: 23.0 ± 4.53 years) completed two experimental conditions in separate sessions; VR-AOMI and control. We used intermittent theta burst stimulation (iTBS) to induce long term potentiation-like plasticity in the motor cortex and recorded motor evoked potentials at multiple timepoints as a measure of corticospinal excitability. The VR-AOMI task did not significantly increase the change in MEP amplitude following iTBS when compared to the control task (Group × Timepoint interaction p = 0.17). However, regression analysis identified the change in iTBS response following VR-AOMI was significantly predicted by the baseline iTBS response in the control task. Specifically, participants that did not exhibit the expected increase in MEP amplitude following iTBS in the control condition appear to have greater excitability following iTBS in the VR-AOMI condition (r = −0.72, p < 0.001). Engaging in VR-AOMI might enhance capacity for neuroplasticity in some people who typically do not respond to iTBS. VR-AOMI may prime the brain for enhanced neuroplasticity in this sub-group.

Investigating the effects of dopamine on short- and long-latency afferent inhibition.

Short- and long-latency afferent inhibition (SAI and LAI respectively) are phenomenon whereby the motor evoked potential induced by transcranial magnetic stimulation (TMS) is inhibited by a sensory afferent volley consequent to nerve stimulation. It remains unclear whether dopamine participates in the genesis or modulation of SAI and LAI. The present study aimed to determine if SAI and LAI are modulated by levodopa (l-DOPA). In this placebo-controlled, double-anonymized study Apo-Levocarb (100mg l-DOPA in combination with 25mg carbidopa) and a placebo were administered to 32 adult males (mean age 24±3 years) in two separate sessions. SAI and LAI were evoked by stimulating the median nerve and delivering single-pulse TMS over the motor hotspot corresponding to the first dorsal interosseous muscle of the right hand. SAI and LAI were quantified before and 1h following ingestion of drug or placebo corresponding to the peak plasma concentration of Apo-Levocarb. The results indicate that Apo-Levocarb increases SAI and does not significantly alter LAI. These findings support literature demonstrating increased SAI following exogenous dopamine administration in neurodegenerative disorders. KEY POINTS: Short- and long-latency afferent inhibition (SAI and LAI respectively) are measures of corticospinal excitability evoked using transcranial magnetic stimulation. SAI and LAI are reduced in conditions such as Parkinson's disease which suggests dopamine may be involved in the mechanism of afferent inhibition. 125mg of Apo-Levocarb (100mg dopamine) increases SAI but not LAI. This study increases our understanding of the pharmacological mechanism of SAI and LAI.

Effects of Lactate on Corticospinal Excitability: A Scoping Review.

Aerobic exercise has been shown to impact corticospinal excitability (CSE), however the mechanism(s) by which this occurs is unclear. Some evidence suggests an increase in blood lactate concentration resulting from exercise may be what is driving these changes in corticospinal excitability. The extent of literature examining this effect and whether it is consistent across the literature is unknown. As such, the objective of this scoping review was to summarize the existing literature examining the effect of lactate on corticospinal excitability and to determine any trend(s) in the effect. Embase, CINAHL, Medline, SPORTDiscus, and PsycInfo were systematically searched to retrieve original research reporting on blood lactate concentration and measures of corticospinal excitability associated with aerobic or high intensity interval exercise. Two reviewers independently determined study eligibility, and one reviewer extracted data from all eligible studies. The database search yielded 717 papers of which 9 were determined eligible. Multiple studies in which participants completed high intensity and/or exhaustive exercise showed a correlation between large increases in blood lactate concentration and increased corticospinal excitability, however several other studies noted no difference in corticospinal excitability following an increase in blood lactate concentration. This review showed that the existing body of literature is small and highly variable in both methods and results, therefore we can draw limited conclusions about the role of lactate, however based on the evidence available lactate does not appear to be the key player in the modulation of CSE. In addition, evidence from other literature supports moderate intensity aerobic exercise as a modulator of neuroplasticity, suggesting that there may be other key factors contributing to the changes in the brain following exercise.

GABAA Receptor Availability in Relation to Cortical Excitability in Depressed and Healthy: A Positron Emission Tomography and Transcranial Magnetic Stimulation Study

Introduction: Gamma-aminobutyric acid (GABA) deficiency is suggested in depressive disorders, along with alterations in cortical excitability. However, whether these excitability changes are related to GABA_A receptor availability is largely unknown. Our aim was to assess the correlation between these measures in depressed patients and healthy controls. Methods: Twenty-eight patients with a major depressive episode, measured before and after participating in a clinical trial with repetitive transcranial magnetic stimulation (TMS), and 15 controls underwent [¹¹C]flumazenil positron emission tomography to assess GABA_A receptor availability and paired pulse TMS (ppTMS) to evaluate cortical excitability. Both whole-brain voxel-wise GABA_A receptor availability and mean values from left hand motor cortex and left paracentral lobule were correlated to the ppTMS outcomes: short-interval intracortical inhibition reflecting GABA_A receptor activity, long-interval intracortical inhibition representing GABA_B receptor activity, intracortical facilitation reflecting glutamate N-methyl-D-aspartate-receptor activity, as well as the resting motor threshold (rMT), considered a global measure of corticospinal excitability. Results: No significant differences in baseline GABA_A receptor availability or cortical excitability were found between patients and controls. Additionally, no correlations were observed between baseline measurements of GABA_A receptor availability and TMS outcomes. Changes in GABA_A receptor availability in the hand motor cortex, between pre- and post-assessments, were inversely related to pre-post changes in hand rMT. Conclusion: We found that a change in GABA_A receptor availability was inversely related to a change in rMT, suggesting a link between GABA deficiency and increased rMT previously observed in depressive episodes. The results highlight the complex mechanisms governing cortical excitability measures and offer new insight into their properties during the depressive state.

Remote ischaemic conditioning combined with bimanual task training to enhance bimanual skill learning and corticospinal excitability in children with unilateral cerebral palsy: a study protocol of a single centre, phase II randomised controlled trial

IntroductionChildren with unilateral cerebral palsy (UCP) have difficulty in bimanual coordination that restricts the child’s independence in daily activities. Although several efficacious interventions to improve bimanual coordination exist, these interventions...

Measuring the nonselective effects of motor inhibition using isometric force recordings.

Inhibition is a key cognitive control mechanism humans use to enable goal-directed behavior. When rapidly exerted, inhibitory control has broad, nonselective motor effects, typically demonstrated using corticospinal excitability measurements (CSE) elicited by transcranial magnetic stimulation (TMS). For example, during rapid action-stopping, CSE is suppressed at both stopped and task-unrelated muscles. While such TMS-based CSE measurements have provided crucial insights into the fronto-basal ganglia circuitry underlying inhibitory control, they have several downsides. TMS is contraindicated in many populations (e.g., epilepsy or deep-brain stimulation patients), has limited temporal resolution, produces distracting auditory and haptic stimulation, is difficult to combine with other imaging methods, and necessitates expensive, immobile equipment. Here, we attempted to measure the nonselective motor effects of inhibitory control using a method unaffected by these shortcomings. Thirty male and female human participants exerted isometric force on a high-precision handheld force transducer while performing a foot-response stop-signal task. Indeed, when foot movements were successfully stopped, force output at the task-irrelevant hand was suppressed as well. Moreover, this nonselective reduction of isometric force was highly correlated with stop-signal performance and showed frequency dynamics similar to established inhibitory signatures typically found in neural and muscle recordings. Together, these findings demonstrate that isometric force recordings can reliably capture the nonselective effects of motor inhibition, opening the door to many applications that are hard or impossible to realize with TMS.

The severity of acute hypoxaemia determines distinct changes in intracortical and spinal neural circuits.

The purpose of this study was to examine how two common methods of continuous hypoxaemia impact the activity of intracortical circuits responsible for inhibition and facilitation of motor output, and spinal excitability. Ten participants were exposed to 2h of hypoxaemia at 0.13 fraction of inspired oxygen ( clamping protocol) and 80% of peripheral capillary oxygen saturation ( clamping protocol) using a simulating altitude device on two visits separated by a week. Using transcranial magnetic and peripheral nerve stimulation, unconditioned motor evoked potential (MEP) area, short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF), and F-wave persistence and area were assessed in the first dorsal interosseous (FDI) muscle before titration, after 1 and 2h of hypoxic exposure, and at reoxygenation. The clamping protocols resulted in differing reductions in by 2h ( clamping protocol: 81.9±1.3%, clamping protocol: 90.6±2.5%). Although unconditioned MEP peak to peak amplitude and area did not differ between the protocols, SICI during clamping was significantly lower at 2h compared to clamping (P=0.011) and baseline (P<0.001), whereas ICF was higher throughout the clamping compared to clamping (P=0.005). Furthermore, a negative correlation between SICI and (rrm =-0.56, P=0.002) and a positive correlation between ICF and (rrm =0.69, P=0.001) were determined, where greater reductions in correlated with less inhibition and less facilitation of MEP responses. Although F-wave area progressively increased similarly throughout the protocols (P=0.037), persistence of responses was reduced at 2h and reoxygenation (P<0.01) during the clamping protocol compared to the clamping protocol. After 2h of hypoxic exposure, there is a reduction in the activity of intracortical circuits responsible for inhibiting motor output, as well as excitability of spinal motoneurones. However, these effects can be influenced by other physiological responses to hypoxia (i.e., hyperventilation and hypocapnia). NEW FINDINGS: What is the central question of this study? How do two common methods of acute hypoxic exposure influence the excitability of intracortical networks and spinal circuits responsible for motor output? What is the main finding and its importance? The excitability of spinal circuits and intracortical networks responsible for inhibition of motor output was reduced during severe acute exposure to hypoxia at 2 h, but this was not seen during less severe exposure. This provides insight into the potential cause of variance seen in motor evoked potential responses to transcranial magnetic stimulation (corticospinal excitability measures) when exposed to hypoxia.

Covariation of the amplitude and latency of motor evoked potentials elicited by transcranial magnetic stimulation in a resting hand muscle

Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation technique used to study human neurophysiology. A single TMS pulse delivered to the primary motor cortex can elicit a motor evoked potential (MEP) in a target muscle. MEP amplitude is a measure of corticospinal excitability and MEP latency is a measure of the time taken for intracortical processing, corticofugal conduction, spinal processing, and neuromuscular transmission. Although MEP amplitude is known to vary across trials with constant stimulus intensity, little is known about MEP latency variation. To investigate MEP amplitude and latency variation at the individual level, we scored single-pulse MEP amplitude and latency in a resting hand muscle from two datasets. MEP latency varied from trial to trial in individual participants with a median range of 3.9 ms. Shorter MEP latencies were associated with larger MEP amplitudes for most individuals (median r = − 0.47), showing that latency and amplitude are jointly determined by the excitability of the corticospinal system when TMS is delivered. TMS delivered during heightened excitability could discharge a greater number of cortico-cortical and corticospinal cells, increasing the amplitude and, by recurrent activation of corticospinal cells, the number of descending indirect waves. An increase in the amplitude and number of indirect waves would progressively recruit larger spinal motor neurons with large-diameter fast-conducting fibers, which would shorten MEP onset latency and increase MEP amplitude. In addition to MEP amplitude variability, understanding MEP latency variability is important given that these parameters are used to help characterize pathophysiology of movement disorders.

Dynamic motor practice improves movement accuracy, force control and leads to increased corticospinal excitability compared to isometric motor practice.

The central nervous system has a remarkable ability to plan motor actions, to predict and monitor the sensory consequences during and following motor actions and integrate these into future actions. Numerous studies investigating human motor learning have employed tasks involving either force control during isometric contractions or position control during dynamic tasks. To our knowledge, it remains to be elucidated how motor practice with an emphasis on position control influences force control and vice versa. Furthermore, it remains unexplored whether these distinct types of motor practice are accompanied by differential effects on corticospinal excitability. In this study, we tested motor accuracy and effects of motor practice in a force or position control task allowing wrist flexions of the non-dominant hand in the absence of online visual feedback. For each trial, motor performance was quantified as errors (pixels) between the displayed target and the movement endpoint. In the main experiment, 46 young adults were randomized into three groups: position control motor practice (PC), force control motor practice (FC), and a resting control group (CON). Following assessment of baseline motor performance in the position and force control tasks, intervention groups performed motor practice with, augmented visual feedback on performance. Motor performance in both tasks was assessed following motor practice. In a supplementary experiment, measures of corticospinal excitability were obtained in twenty additional participants by application of transcranial magnetic stimulation to the primary motor cortex hot spot of the flexor carpi radialis muscle before and following either position or force control motor practice. Following motor practice, accuracy in the position task improved significantly more for PC compared to FC and CON. For the force control task, both the PC and FC group improved more compared to CON. The two types of motor practice thus led to distinct effects including positive between-task transfer accompanying dynamic motor practice The results of the supplementary study demonstrated an increase in corticospinal excitability following dynamic motor practice compared to isometric motor practice. In conclusion, dynamic motor practice improves movement accuracy, and force control and leads to increased corticospinal excitability compared to isometric motor practice.

Investigation of in-phase bilateral exercise effects on corticospinal plasticity in relapsing remitting multiple sclerosis: A registered report single-case concurrent multiple baseline design across five subjects.

Relapsing-remitting Multiple Sclerosis is the most common demyelinating neurodegenerative disease and is characterized by periods of relapses and generation of various motor symptoms. These symptoms are associated with the corticospinal tract integrity, which is quantified by means of corticospinal plasticity which can be probed via transcranial magnetic stimulation and assessed with corticospinal excitability measures. Several factors, such as exercise and interlimb coordination, can influence corticospinal plasticity. Previous work in healthy and in chronic stroke survivors showed that the greatest improvement in corticospinal plasticity occurred during in-phase bilateral exercises of the upper limbs. During in-phase bilateral movement, both upper limbs are moving simultaneously, activating the same muscle groups and triggering the same brain region respectively. Altered corticospinal plasticity due to bilateral cortical lesions is common in MS, yet, the impact of these type of exercises in this cohort is unclear. The aim of this concurrent multiple baseline design study is to investigate the effects of in-phase bilateral exercises on corticospinal plasticity and on clinical measures using transcranial magnetic stimulation and standardized clinical assessment in five people with relapsing-remitting MS. The intervention protocol will last for 12 consecutive weeks (30-60 minutes /session x 3 sessions/week) and include in-phase bilateral movements of the upper limbs, adapted to different sports activities and to functional training. To define functional relation between the intervention and the results on corticospinal plasticity (central motor conduction time, resting motor threshold, motor evoked potential amplitude and latency) and on clinical measures (balance, gait, bilateral hand dexterity and strength, cognitive function), we will perform a visual analysis and if there is a potential sizeable effect, we will perform statistical analysis. A possible effect from our study, will introduce a proof-of-concept for this type of exercise that will be effective during disease progression. Trial registration: ClinicalTrials.gov NCT05367947.

Perceived Muscle Soreness Does Not Modulate Corticospinal Excitability

Soreness due to exercise-induced muscle damage temporarily impairs motor performance. Transcranial magnetic stimulation (TMS) is often used to assess subtle changes in corticospinal excitability (CSE) and motor system input-output properties and demonstrates sensitivity to chronic pain. Nevertheless, the acute effects of muscle soreness on TMS-based measures of corticospinal excitability require further investigation. PURPOSE: To examine the relationship between perceived muscle soreness and CSE of postural and lower-extremity muscles. METHODS: 12 healthy adults (3 W, age: 27.2 ± 5.4 yr, ht: 175.6 ± 11.0 cm, wt: 72.6 ± 13.4 kg) completed three visits with maximal anaerobic lower extremity exercise. At the start of each visit, participants confirmed they abstained from any physical activity 24 hr prior, and rated their overall residual muscle soreness using a 100 mm visual analog scale. Visits were ranked based on muscle soreness with the highest and lowest soreness visits retained for analysis. To assess CSE, electromyographic motor-evoked potentials (MEPs) were recorded from the right rectus abdominis (RA) and vastus lateralis (VL). Active motor thresholds (AMT) were determined for each muscle during 15% of maximal voluntary isometric force using a biphasic stimulator and 96 mm curved double coil. To determine CSE, ten TMS pulses were applied to each M1 hotspot at 120% AMT with the resultant MEPs averaged based on peak-to-peak amplitude from 15-65 ms post-stimulus. Paired-samples t-test were used to assess mean differences in soreness, AMT, and MEP amplitudes. RESULTS: As expected, muscle soreness differed between visits (mean difference: 25.3 mm, t = 5.08, p < 0.01). Similar motor-thresholds were observed for the RA (mean difference: 0.3%, t = 0.26, p = 0.80) and VL (mean difference: 0.5%, t = 0.45, p = 0.66). MEP amplitudes were also similar for the RA (mean difference: 0.13 mV, t = 1.74, p = 0.12) and VL (mean difference: 0.01 mV, t = 0.30, p = 0.77). CONCLUSION: Day-to-day variation in CSE during lower extremity and axial contractions is not explained by differences in muscle soreness. Future work should examine CSE at multiple timepoints after acute exercise and use various submaximal intensities to further clarify whether CSE is responsive to muscle soreness.

Quadriceps motor evoked torque is a reliable measure of corticospinal excitability in individuals with anterior cruciate ligament reconstruction

This study comprehensively evaluated the test–retest reliability of raw and normalized quadriceps motor evoked responses elicited by transcranial magnetic stimulation (TMS) in individuals with anterior cruciate ligament (ACL) reconstruction. Fifteen participants were tested on three different days that were separated at least by 24 h. Motor evoked responses were collected during a small background contraction on the reconstructed leg across a range of TMS intensities using torque (MEPTORQUE) and electromyographic (MEPEMG) responses. MEPTORQUE and MEPEMG were evaluated using different normalization procedures (raw, normalized to maximum voluntary isometric contraction [MVIC], peak MEP, and background contraction). MEPTORQUE was also normalized to the magnetically-evoked peripheral resting twitch torque. The area under the recruitment curve was computed for both raw and normalized MEPs. Intraclass correlation coefficients (ICCs) were determined to assess test–retest reliability. Results indicated that MEPTORQUE generally showed greater reliability than MEPEMG for all normalization procedures. Vastus medialis MEPEMG generally showed greater reliability than rectus femoris MEPEMG. Finally, both MEPTORQUE and MEPEMG exhibited good reliability, even when not normalized. These findings indicate that MEPTORQUE and MEPEMG offer reliable measures of corticospinal function and suggest that MEPTORQUE is a suitable alternative to MEPEMG for measuring quadriceps corticospinal excitability in individuals with ACL reconstruction.

Effects of different modalities of afferent stimuli of the lumbo-sacral area on control of lumbar paravertebral muscles.

Somatosensory feedback to the central nervous system is essential to plan, perform and refine spine motor control. However, the influence of somatosensory afferent input from the trunk on the motor output to trunk muscles has received little attention. The objective was to compare the effects of distinct modalities of afferent stimulation on the net motoneuron and corticomotor excitability of paravertebral muscles. Fourteen individuals were recruited. Modulation of corticospinal excitability (motor-evoked potential [MEP]) of paravertebral muscles was measured when afferent stimuli (cutaneous noxious and non-noxious, muscle contraction) were delivered to the trunk at 10 intervals prior to transcranial magnetic stimulation. Each peripheral stimulation was applied alone, and subsequent electromyography (EMG) modulation was measured to control for net motoneuron excitability. MEP modulation and MEP/EMG ratio were used as measures of corticospinal excitability with and without control of net motoneuron excitability, respectively. MEP and EMG modulation were smaller after evoked muscle contraction than after cutaneous noxious and non-noxious stimuli. MEP/EMG ratio was not different between stimulation types. Both MEP and EMG amplitudes were reduced after evoked muscle contraction, but not when expressed as MEP/EMG ratio. Noxious and non-noxious stimulation had limited impact on all variables. Distinct modalities of peripheral afferent stimulation of the lumbo-sacral area differently modulated responses of paravertebral muscles, but without an influence on corticospinal excitability with control of net motoneuron excitability. Muscle stimulation reduced paravertebral activity and was best explained by spinal mechanisms. The impact of afferent stimulation on back muscles differs from the effects reported for limb muscles.

Within- and Between-Session Reliability of Corticospinal Excitability in the Upper Extremity

ABSTRACT Reliable techniques to assess centrally mediated function in healthy individuals are essential to understand the origins of neuromuscular dysfunction in pathologic populations. This study examined the test–retest reliability of corticospinal excitability in the upper extremity musculature of 21 healthy individuals using transcranial magnetic stimulation. Within-session reliability was assessed by comparing tests performed 120 minutes apart. Between-session reliability was assessed by comparing the second (24 hr), third (1-week), and forth (2-week) sessions to the first test. We recorded active motor threshold (AMT) and motor evoked potential (MEP) at 120% AMT of the upper trapezius (UT), middle deltoid (MD), and flexor carpi radialis (FCR) bilaterally. Intraclass correlation coefficients (3,1) were used to assess relative reliability, and minimal detectable changes at 95% confidence level were calculated to assess absolute reliability. Our results suggest that AMT of the MD and FCR demonstrated acceptable within-session and between-session reliability over 24 hours, with all muscles evaluated ranging from moderate to good over 2 weeks. In contrast, MEP amplitudes were less reliable for all muscles, with reliability point estimates ranging from poor to moderate. AMT appears to be a more consistent measure of corticospinal excitability in upper extremity musculature, which may be more appropriate in clinical outcomes research.