Changes in corticomotor excitability and inhibition after exercise are influenced by hand dominance and motor demand

Forearm Posture Affects the Corticospinal Excitability of Intrinsic and Extrinsic Hand Muscles in Dominant and Nondominant Sides

Different forearm postures can modulate corticospinal excitability. However, there is no consensus on whether handedness plays a role in such a mechanism. This study investigated the effects of 3 forearm postures (pronation, neutral, and supination) on the corticospinal excitability of muscles from the dominant and nondominant upper limbs. Surface electromyography was recorded from the abductor digiti minimi, flexor pollicis brevis, and flexor carpi radialis from both sides of 12 right-handed volunteers. Transcranial magnetic stimulation pulses were applied to each muscle's hotspot in both cerebral hemispheres. Motor-evoked potential peak-to-peak amplitude and latency and resting motor threshold were measured. The data were evaluated by analysis of variance. The level of significance was set at 5%. The resting motor threshold was similar for the 3 muscles and both sides. Motor-evoked potential peak-to-peak amplitude from flexor pollicis brevis was lower during supination, and the dominant upper limb latency was longer. The flexor carpi radialis presented lower motor-evoked potential peak-to-peak amplitudes for neutral and shorter latencies during supination. Abductor digiti minimi seemed not to be affected by posture or side. Different muscles from dominant and nondominant sides may undergo corticospinal modulation, even distally localized from a particular joint and under rest.

Upper extremity asymmetry due to nerve injuries or central neurologic conditions: a scoping review

BACKGROUND

Peripheral nerve injuries and central neurologic conditions can result in extensive disabilities. In cases with unilateral impairment, assessing the asymmetry between the upper extremity has been used to assess outcomes of treatment and severity of injury. A wide variety of validated and novel tests and sensors have been utilized to determine the upper extremity asymmetry. The purpose of this article is to review the literature and define the current state of the art for describing upper extremity asymmetry in patients with peripheral nerve injuries or central neurologic conditions.

METHOD

An electronic literature search of PubMed, Scopus, Web of Science, OVID was performed for publications between 2000 to 2022. Eligibility criteria were subjects with neurological conditions/injuries who were analyzed for dissimilarities in use between the upper extremities. Data related to study population, target condition/injury, types of tests performed, sensors used, real-world data collection, outcome measures of interest, and results of the study were extracted. Sackett's Level of Evidence was used to judge the quality of the articles.

RESULTS

Of the 7281 unique articles, 112 articles met the inclusion criteria for the review. Eight target conditions/injuries were identified (Brachial Plexus Injury, Cerebral Palsy, Multiple Sclerosis, Parkinson's Disease, Peripheral Nerve Injury, Spinal Cord Injury, Schizophrenia, and stroke). The tests performed were classified into thirteen categories based on the nature of the test and data collected. The general results related to upper extremity asymmetry were listed for all the reviewed articles. Stroke was the most studied condition, followed by cerebral palsy, with kinematics and strength measurement tests being the most frequently used tests. Studies with a level of evidence level II and III increased between 2000 and 2021. The use of real-world evidence-based data, and objective data collection tests also increased in the same period.

CONCLUSION

Adequately powered randomized controlled trials should be used to study upper extremity asymmetry. Neurological conditions other than stroke should be studied further. Upper extremity asymmetry should be measured using objective outcome measures like motion tracking and activity monitoring in the patient's daily living environment.

Participant attention on the intervention target during repetitive passive movement improved spinal reciprocal inhibition enhancement and joint movement function

This study aimed to evaluate the effects of the participant's attention target during repetitive passive movement (RPM) intervention on reciprocal inhibition (RI) and joint movement function. Twenty healthy adults participated in two experiments involving four attention conditions [control (forward attention with no RPM), forward attention (during RPM), monitor attention (monitor counting task during RPM), ankle joint attention (ankle movement counting task during RPM)] during 10-min RPM interventions on the ankle joint. Counting tasks were included to ensure the participant's attention remained on the target during the intervention. In Experiment 1, RI was measured before, immediately after, and 5, 10, 15, 20, and 30 min after the RPM intervention. In Experiment 2, we evaluated ankle joint movement function at the same time points before and after RPM intervention. The maximum ankle dorsiflexion movement (from 30° plantar flexion to 10° dorsiflexion) was measured, reflecting RI. In Experiment 1, the RI function reciprocal Ia inhibition was enhanced for 10 min after RPM under all attention conditions (excluding the control condition. D1 inhibition was enhanced for 20 min after RPM in the forward and monitor attention conditions and 30 min after RPM in the ankle joint attention condition. In Experiment 2, the joint movement function decreased under the forward and monitor attention conditions but improved under the ankle joint attention condition. This study is the first to demonstrate that the participant's attention target affected the intervention effect of the RI enhancement method, which has implications for improving the intervention effect of rehabilitation.

From thinking fast to moving fast: motor control of fast limb movements in healthy individuals

The ability to produce high movement speeds is a crucial factor in human motor performance, from the skilled athlete to someone avoiding a fall. Despite this relevance, there remains a lack of both an integrative brain-to-behavior analysis of these movements and applied studies linking the known dependence on open-loop, central control mechanisms of these movements to their real-world implications, whether in the sports, performance arts, or occupational setting. In this review, we cover factors associated with the planning and performance of fast limb movements, from the generation of the motor command in the brain to the observed motor output. At each level (supraspinal, peripheral, and motor output), the influencing factors are presented and the changes brought by training and fatigue are discussed. The existing evidence of more applied studies relevant to practical aspects of human performance is also discussed. Inconsistencies in the existing literature both in the definitions and findings are highlighted, along with suggestions for further studies on the topic of fast limb movement control. The current heterogeneity in what is considered a fast movement and in experimental protocols makes it difficult to compare findings in the existing literature. We identified the role of the cerebellum in movement prediction and of surround inhibition in motor slowing, as well as the effects of fatigue and training on central motor control, as possible avenues for further research, especially in performance-driven populations.

Hand dominance in the performance and perceptions of virtual reach control

PURPOSE

Efforts to optimize human-computer interactions are becoming increasingly prevalent, especially with virtual reality (VR) rehabilitation paradigms that utilize engaging interfaces. We hypothesized that motor and perceptional behaviors within a virtual environment are modulated uniquely through different modes of control of a hand avatar depending on limb dominance. This study investigated the effects of limb dominance on performance and concurrent changes in perceptions, such as time-based measures for intentional binding, during virtual reach-to-grasp.

METHODS

Participants (n = 16, healthy) controlled a virtual hand through their own hand motions with control adaptations in speed, noise, and automation.

RESULTS

A significant (p < 0.01) positive relationship between performance (reaching pathlength) and binding (time-interval estimation of beep-sound after grasp contact) was observed for the dominant hand. Unique changes in performance (p < 0.0001) and binding (p < 0.0001) were observed depending on handedness and which control mode was applied.

CONCLUSIONS

Developers of VR paradigms should consider limb dominance to optimize settings that facilitate better performance and perceptional engagement. Adapting VR rehabilitation for handedness may particularly benefit unilateral impairments, like hemiparesis or single-limb amputation.

Effect of Repetitive Passive Movement Before Motor Skill Training on Corticospinal Excitability and Motor Learning Depend on BDNF Polymorphisms

A decrease in cortical excitability tends to be easily followed by an increase induced by external stimuli via a mechanism aimed at restoring it; this phenomenon is called “homeostatic plasticity.” In recent years, although intervention methods aimed at promoting motor learning using this phenomenon have been studied, an optimal intervention method has not been established. In the present study, we examined whether subsequent motor learning can be promoted further by a repetitive passive movement, which reduces the excitability of the primary motor cortex (M1) before motor learning tasks. We also examined the relationship between motor learning and the brain-derived neurotrophic factor. Forty healthy subjects (Val/Val genotype, 17 subjects; Met carrier genotype, 23 subjects) participated. Subjects were divided into two groups of 20 individuals each. The first group was assigned to perform the motor learning task after an intervention consisting in the passive adduction–abduction movement of the right index finger at 5 Hz for 10 min (RPM condition), while the second group was assigned to perform the task without the passive movement (control condition). The motor learning task consisted in the visual tracking of the right index finger. The results showed that the corticospinal excitability was transiently reduced after the passive movement in the RPM condition, whereas it was increased to the level detected in the control condition after the motor learning task. Furthermore, the motor learning ability was decreased immediately after the passive movement; however, the motor performance finally improved to the level observed in the control condition. In individuals carrying the Val/Val genotype, higher motor learning was also found to be related to the more remarkable changes in corticospinal excitability caused by the RPM condition. This study revealed that the implementation of a passive movement before a motor learning tasks did not affect M1 excitatory changes and motor learning efficiency; in contrast, in subjects carrying the Val/Val polymorphism, the more significant excitatory changes in the M1 induced by the passive movement and motor learning task led to the improvement of motor learning efficiency. Our results also suggest that homeostatic plasticity occurring in the M1 is involved in this improvement.

Human motor fatigability as evoked by repetitive movements results from a gradual breakdown of surround inhibition

Motor fatigability emerges when demanding tasks are executed over an extended period of time. Here, we used repetitive low-force movements that cause a gradual reduction in movement speed (or 'motor slowing') to study the central component of fatigability in healthy adults. We show that motor slowing is associated with a gradual increase of net excitability in the motor network and, specifically, in primary motor cortex (M1), which results from overall disinhibition. Importantly, we link performance decrements to a breakdown of surround inhibition in M1, which is associated with high coactivation of antagonistic muscle groups. This is consistent with the model that a loss of inhibitory control might broaden the tuning of population vectors such that movement patterns become more variable, ill-timed and effortful. We propose that the release of inhibition in M1 is an important mechanism underpinning motor fatigability and, potentially, also pathological fatigue as frequently observed in patients with brain disorders.

Repetitive Passive Movement Modulates Corticospinal Excitability: Effect of Movement and Rest Cycles and Subject Attention

Repetitive passive movement (PM) affects corticospinal excitability; however, it is unknown whether a duty cycle which repeats movement and rest, or subjects’ conscious attention to movements, affects corticospinal excitability. We aimed to clarify the effect of the presence or absence of a duty cycle and subjects’ attention on corticospinal excitability. Three experiments were conducted. In Experiment 1, PM of the right index finger was performed for 10 min. Three conditions were used: (1) continuous PM (cPM) at a rate of 40°/s; (2) intermittent PM (iPM) with a duty cycle at 40°/s; and (3) iPM at 100°/s. In conditions 1 and 3, motor evoked potential (MEP) amplitude was significantly reduced. In Experiment 2, PM was performed for 30 min: condition 1 comprised cPM at a rate of 40°/s and Condition 2 comprised iPM at 40°/s. MEP amplitude significantly decreased in both conditions. In Experiment 3, PM was performed for 10 min: condition 1 comprised paying attention to the moving finger during iPM and Condition 2 was similar to Condition 1 but while counting images on a monitor without looking at the movement finger, and Condition 3 comprised counting images on a monitor without performing PM. MEP amplitude significantly increased only under Condition 1. Thus, afferent input from movements above a certain threshold may affect corticospinal excitability reduction. Furthermore, corticospinal excitability increases when paying attention to passive finger movement.

Cortical excitability following passive movement

In brain injury rehabilitation, passive movement exercises are frequently used to maintain or improve mobility and range of motion. They can also induce beneficial and sustained neuroplastic changes. Neuroimaging studies have revealed that passive movements without motor commands activate not only the primary somatosensory cortex but also the primary motor cortex, supplementary motor area, and posterior parietal cortex as well as the secondary somatosensory cortex (S2) in healthy subjects. Repetitive passive movement has also been reported to induce increases or decreases in cortical excitability. In this review, we focused on the following: cortical activity following passive movement; cortical excitability during passive movement; and changes in cortical excitability after repetitive passive movement.

Kinematics and muscle activation patterns during a maximal voluntary rate activity in healthy elderly and young adults

BACKGROUND

Maximal voluntary rate (MVR) performance tasks can provide important age-related information to the limiting factors associated with movement and the development of fatigue.

AIM

To determine whether kinematic and muscle activation patterns during an MVR task differ between young and older adults.

METHODS

We continuously measured frequency, amplitude, peak velocity, index of co-contraction and median frequencies of the index finger flexors and extensors during a 20-s MVR task in 10 young and 10 older subjects.

RESULTS

Index finger amplitude and peak velocity in flexion and extension were significantly lower in the older group. During the MVR, amplitude was maintained in the old (1-4 s, 53.2° ± 2.8° vs. 15-19 s, 48.6° ± 3.2°, ns) but not in the younger group (1-4 s, 64.9° ± 4.9° vs. 15-19 s, 59.4° ± 3.3°; p = 0.001). Frequency declined in the young (1-4 s, 5.2 ± 0.24 Hz vs. 15-19 s, 4.4 ± 0.25 Hz; p = 0.001) and old (1-4 s, 4.6 ± 0.17 Hz vs. 15-19 s, 4.0 ± 0.15 Hz; p = 0.01). Similarly, peak flexion velocity of the young (1-4 s, 1.77 ± 0.07 × 10³ °/s vs. 15-19 s, 1.01 ± 0.07 × 10³ °/s, p = 0.01) and older groups (1-4 s, 1.04 ± 0.07 × 10³ °/s vs. 15-19 s, 0.78 ± 0.06 × 10³ °/s; p = 0.016) as well as peak extension velocity of the young (1-4 s, 1.01 ± 0.053 × 10³ °/s vs. 15-19 s, 0.78 ± 0.06 × 10³ °/s, p = 0.01) and older groups (1-4 s, 0.72 ± 0.04 × 10³ °/s vs. 15-19 s, 0.58 ± 0.05 × 10³ °/s, p = 0.012) significantly decreased throughout the MVR. Median frequency of the flexors and extensors were maintained and were not different between groups. Only the older group experienced an increase in the index of co-contraction.

CONCLUSION

The changes in kinematics over time are not a result of a decrease in pre-post test force or velocity, but rather central factors affecting movement coordination.

Regulation of primary motor cortex excitability by repetitive passive finger movement frequency

Somatosensory input induced by passive movement activates primary motor cortex (M1). We applied repetitive passive movement (RPM) of different frequencies to test if modulation of M1 excitability depends on RPM frequency. Twenty-seven healthy subjects participated in this study. Motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) to left M1 were recorded from the right first dorsal interosseous muscle (FDI) to assess corticospinal excitability (experiment 1: n=15), and F-waves were measured from the right FDI as an index of spinal motoneuron excitability (experiment 2: n=15). Passive abduction/adduction of the right index finger was applied for 10min at 0.5, 1.0, 3.0, and 5.0Hz. Both 0.5Hz-RPM and 1.0Hz-RPM decreased MEPs for 2min (p<0.05), and 5.0Hz-RPM decreased MEPs for 15min compared with baseline (p<0.05); however, there was no difference in MEPs after 3.0Hz-RPM. No F-wave changes were observed following any RPM intervention. Based on the results of experiments 1 and 2, we investigated whether RPM modulates cortical inhibitory circuit using the paired-pulse TMS technique (experiment 3: n=12). Short-interval intracortical inhibition (SICI) was measured using paired-pulse TMS (inter-stimulus interval of 3ms) before and after 1.0, 3.0, and 5.0Hz-RPM. Both 1.0 and 5.0Hz-RPM increased SICI compared with baseline (p<0.05). These experiments suggest that M1 excitability decreases after RPM depending on movement frequency, possibly through frequency-dependent enhancement of cortical inhibitory circuit in M1.

Evidence of altered corticomotor excitability following targeted activation of gluteus maximus training in healthy individuals

It has been proposed that strengthening and skill training of gluteus maximus (GM) may be beneficial in treating various knee injuries. Given the redundancy of the hip musculature and the small representational area of GM in the primary motor cortex (M1), learning to activate this muscle before prescribing strength exercises and modifying movement strategy would appear to be important. This study aimed to determine whether a short-term activation training program targeting the GM results in neuroplastic changes in M1. Using transcranial magnetic stimulation, motor evoked potentials (MEPs) were obtained in 12 healthy individuals at different stimulation intensities while they performed a double-leg bridge. Participants then completed a home exercise program for ∼1 h/day for 6 days that consisted of a single exercise designed to selectively target the GM. Baseline and post-training input-output curves (IOCs) were generated by graphing average MEP amplitudes and cortical silent period durations against corresponding stimulation intensities. Following the GM activation training, the linear slope of both the MEP IOC and cortical silent period IOC increased significantly. Short-term GM activation training resulted in a significant increase in corticomotor excitability as well as changes in inhibitory processes of the GM. We propose that the observed corticomotor plasticity will enable better utilization of the GM in the more advanced stages of a rehabilitation/training program.

Acute aerobic exercise modulates primary motor cortex inhibition

Aerobic exercise can enhance neuroplasticity although presently the neural mechanisms underpinning these benefits remain unclear. One possible mechanism is through effects on primary motor cortex (M1) function via down-regulation of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). The aim of the present study was to examine how corticomotor excitability (CME) and M1 intracortical inhibition are modulated in response to a single bout of moderate intensity aerobic exercise. Ten healthy right-handed adults were participants. Single- and paired-pulse transcranial magnetic stimulation was applied over left M1 to obtain motor-evoked potentials in the right flexor pollicis brevis. We examined CME, cortical silent period (SP) duration, short- and long-interval intracortical inhibition (SICI, LICI), and late cortical disinhibition (LCD), before and after acute aerobic exercise (exercise session) or an equivalent duration without exercise (control session). Aerobic exercise was performed on a cycle ergometer for 30 min at a workload equivalent to 60 % of maximal cardiorespiratory fitness (VO₂ peak; heart rate reserve = 75 ± 3 %, perceived exertion = 13.5 ± 0.7). LICI was reduced at 10 (52 ± 17 %, P = 0.03) and 20 min (27 ± 8 %, P = 0.03) post-exercise compared to baseline (13 ± 4 %). No significant changes in CME, SP duration, SICI or LCD were observed. The present study shows that GABA_B-mediated intracortical inhibition may be down-regulated after acute aerobic exercise. The potential effects this may have on M1 plasticity remain to be determined.

Do Differences in Levels, Types, and Duration of Muscle Contraction Have an Effect on the Degree of Post-exercise Depression?

We conducted two experiments to determine how differences in muscle contraction levels, muscle contraction types, and movement duration affect degree of post-exercise depression (PED) after non-exhaustive, repetitive finger movement. Twelve healthy participants performed repetitive abduction movements of the right index finger at 2 Hz. In experiment 1, we examined the effects of muscle contraction levels at 10, 20, and 30% maximum voluntary contraction and the effects of muscle contraction types at isotonic and isometric contraction. In experiment 2, we examined the effects of movement duration at 2 and 6 min. Motor-evoked potentials (MEPs) were recorded from the right first dorsal interosseous muscle before movement tasks and 1–10 min after movement tasks. MEP amplitudes after isotonic contraction tasks were significantly smaller than those after isometric contraction tasks and decreased with increasing contraction levels, but were independent of movement duration. This study demonstrated that the degree of PED after non-exhaustive repetitive finger movement depended on muscle contraction levels and types. Thus, the degree of PED may depend on the levels of activity in the motor cortex during a movement task. This knowledge will aid in the design of rehabilitation protocols.

Assessing vibratory stimulation-induced cortical activity during a motor task--A randomized clinical study

Effects of vibratory stimulation on motor performance have been widely investigated. Many theories have been applied, in order to evaluate its influence on individuals; however, very few studies have researched vibratory stimulation-induced cortical behavior. The aim of the present study is to investigate behavioral changes, such as reaction time and index finger movements, as well as electrophysiological changes, using beta band absolute power, in subjects submitted to vibratory stimulation. For this study, 30 healthy subjects were randomly selected and divided into two groups, experimental and control, and were submitted to a right index finger task, before and after vibratory stimulation, which was applied to the right upper limb, while their standard cerebral activity was recorded through electroencephalogram. No significant difference was found among behavioral variables. On the other hand, beta band absolute power significantly increased in the experimental group for the C3, C4 and P4 derivations, while it decreased at P3. The results suggest that electrophysiological changes were induced by vibratory stimulation, while reaction time and task-related movements were not affected by it.

Modulation of corticomotor excitability after maximal or sustainable-rate repetitive finger movement is impaired in Parkinson's disease and is reversed by levodopa

OBJECTIVES

In healthy subjects, fatiguing exercises induce a period of post-exercise corticomotor depression (PECD) that is absent in Parkinson's disease (PD). Our objective is to determine the time-course of corticomotor excitability changes following a 10-s repetitive index finger flexion-extension task performed at maximal voluntary rate (MVR) and a slower sustainable rate (MSR) in PD patients OFF and ON levodopa.

METHODS

In 11 PD patients and 10 healthy age-matched controls, motor evoked potentials (MEPs) were recorded from the extensor indicis proprius (EIP) and first dorsal interosseous (FDI) muscles of the dominant arm immediately after the two tasks and at 2-min intervals for 10 min.

RESULTS

In the OFF condition the PECD was absent in the two test muscles after both the MVR and MSR tasks. In the ON condition finger movement kinematics improved and a period of PECD comparable to that in controls was present after both tasks.

CONCLUSION

The absence of PECD in PD subjects off medication indicates a persisting increase in corticomotor excitability after non-fatiguing repetitive finger movement that is reversed by levodopa.

SIGNIFICANCE

Dopamine depletion is associated with impaired modulation of corticomotor excitability after non-fatiguing repetitive finger movement.

Effects of interocclusal distance on bite force and masseter EMG in healthy participants

The aim of this study was to investigate effects of interocclusal distance (IOD) on bite force and masseter electromyographic (EMG) activity during different isometric contraction tasks. Thirty-one healthy participants (14 women and 17 men, 21·2 ± 1·8 years) were recruited. Maximal Voluntary Occlusal Bite Force (MVOBF) between the first molars and masseter EMG activity during all the isometric-biting tasks were measured. The participants were asked to bite at submaximal levels of 20%, 40%, 60% and 80% MVOBF with the use of visual feedback. The thickness of the force transducer was set at 8, 12, 16 and 20 mm (= IOD), and sides were tested in random sequence. MVOBF was significantly higher at 8 mm compared with all other IODs (P < 0·001). Only in women, IOD always had significant influence on the corresponding root-mean-square (RMS) value of EMG (P < 0·011). When biting was performed on the ipsilateral side to the dominant hand, the working side consistently showed higher masseter EMG activity compared with the balancing side (P < 0·020). On the contralateral side, there was no difference between the masseter EMG at any IODs. The results replicated the finding that higher occlusal forces can be generated between the first molars at shorter IODs. The new finding in this study was that an effect of hand dominance could be found on masseter muscle activity during isometric biting. This may suggest that there can be a general dominant side effect on human jaw muscles possibly reflecting differences in motor unit recruitment strategies.

Comparing kinematic changes between a finger-tapping task and unconstrained finger flexion-extension task in patients with Parkinson's disease

Repetitive finger tapping is a well-established clinical test for the evaluation of parkinsonian bradykinesia, but few studies have investigated other finger movement modalities. We compared the kinematic changes (movement rate and amplitude) and response to levodopa during a conventional index finger-thumb-tapping task and an unconstrained index finger flexion-extension task performed at maximal voluntary rate (MVR) for 20 s in 11 individuals with levodopa-responsive Parkinson's disease (OFF and ON) and 10 healthy age-matched controls. Between-task comparisons showed that for all conditions, the initial movement rate was greater for the unconstrained flexion-extension task than the tapping task. Movement rate in the OFF state was slower than in controls for both tasks and normalized in the ON state. The movement amplitude was also reduced for both tasks in OFF and increased in the ON state but did not reach control levels. The rate and amplitude of movement declined significantly for both tasks under all conditions (OFF/ON and controls). The time course of rate decline was comparable for both tasks and was similar in OFF/ON and controls, whereas the tapping task was associated with a greater decline in MA, both in controls and ON, but not OFF. The findings indicate that both finger movement tasks show similar kinematic changes during a 20-s sustained MVR, but that movement amplitude is less well sustained during the tapping task than the unconstrained finger movement task. Both movement rate and amplitude improved with levodopa; however, movement rate was more levodopa responsive than amplitude.