Acute aerobic exercise modulates primary motor cortex inhibition

Determining the effects of transcranial alternating current stimulation on corticomotor excitability and motor performance: A sham-controlled comparison of four frequencies

Transcranial alternating current stimulation (tACS) modulates brain oscillations and corticomotor plasticity. We examined the effects of four tACS frequencies (20 Hz, 40 Hz, 60 Hz, and 80 Hz) on motor cortex (M1) excitability and motor performance. In a randomised crossover design, 12 adults received 20-minute tACS sessions, with Sham as control. Corticomotor and intracortical excitability was measured up to 60-minutes post-tACS. Motor performance was evaluated using the Grooved Pegboard Test (GPT) and sensorimotor assessments. Our findings demonstrated frequency-dependent modulation of corticomotor excitability based on MEP amplitude. 20 Hz and 40 Hz tACS reduced MEPs, while 60 Hz and 80 Hz increased MEPs. Inhibition (cortical silent period, SP) was reduced across all tACS frequencies compared to Sham, with 20 Hz and 40 Hz showing consistent reductions, 60 Hz showing effects at post-0 and post-30, and 80 Hz at post-60. Furthermore, 60 Hz tACS decreased intracortical inhibition at post-0, while intracortical facilitation increased with 20 Hz and 60 Hz at post-0, and 40 Hz at post-60. Motor performance remained unaffected across frequencies. Regression analyses revealed that shorter SP at 60 min post 60 Hz tACS predicted faster reaction times, while greater MEP amplitudes at 60 min following 80 Hz tACS predicted improved hand dexterity. Overall, beta and gamma tACS frequencies modulate M1 excitability, with consistent effects on SP, suggesting potential use in conditions involving SP elongation, such as stroke and Huntington's disease. These findings highlight 60 Hz tACS as a potential tool for motor rehabilitation therapies.

Post-exercise neural plasticity is augmented by adding blood flow restriction during low work rate arm cycling

Blood flow restriction (BFR) combined with low work rate exercise can enhance muscular and cardiovascular fitness. However, whether neural mechanisms mediate these enhancements remains unknown. This study examined changes in corticospinal excitability and motor cortical inhibition following arm cycle ergometry with and without BFR. Twelve healthy males (24 ± 4 years) completed four, randomized 15-min arm cycling conditions: high work rate (HW: 60% maximal power output), low work rate (LW: 30% maximal power output), low work rate with BFR (LW-BFR) and BFR without exercise (BFR-only). For BFR conditions, cuffs were applied around the upper arm and inflated to 70% of arterial occlusion pressure continuously during exercise. Single-pulse transcranial magnetic stimulation was delivered to left primary motor cortex (M1) to elicit motor-evoked potentials (MEP) in the right biceps brachii during a low-level isometric contraction. MEP amplitude and cortical silent period (cSP) duration were measured before and 1, 10 and 15 min post-exercise. MEP amplitude increased significantly from baseline to Post-10 and Post-15 for both the HW (both z < -7.07, both P < 0.001) and LW-BFR conditions (both z < -5.56, both P < 0.001). For the LW condition without BFR, MEP amplitude increased significantly from baseline to Post-10 (z = -3.53, P = 0.003) but not Post-15 (z = -1.85, P = 0.388). The current findings show that HW arm cycling and LW-BFR led to longer-lasting increases in corticospinal excitability than LW arm cycling alone. Future research should examine whether the increased corticospinal excitability is associated with the improvements in muscle strength observed with BFR exercise. A mechanistic understanding of BFR exercise improvement could guide BFR interventions in clinical populations.

Neurophysiological effects of acute aerobic exercise in young adults: a systematic review and meta-analysis

Evidence continues to accumulate that acute aerobic exercise (AAE) impacts neurophysiological excitability as measured by transcranial magnetic stimulation (TMS). Yet, uncertainty exists about which TMS measures are modulated after AAE in young adults. The influence of AAE intensity and duration of effects are also uncertain. This pre-registered meta-analysis (CRD42017065673) addressed these uncertainties by synthesizing data from 23 studies (including 474 participants) published until February 2024. Meta-analysis was run using a random-effects model and Hedge's g used as effect size. Our results demonstrated a decrease in short-interval intracortical inhibition (SICI) following AAE (g = 0.27; 95 % CI [0.16-0.38]; p <.0001), particularly for moderate (g = 0.18; 95 % CI [0.05-0.31]; p <.01) and high (g = 0.49; 95 % CI [0.27-0.71]; p <.0001) AAE intensities. These effects remained for 30 minutes after AAE. Additionally, increased corticospinal excitability was only observed for high intensity AAE (g = 0.28; 95 % CI, [0.07-0.48]; p <.01). Our results suggest potential mechanisms for inducing a more susceptible neuroplastic environment following AAE.

A systematic review and Bayesian meta-analysis provide evidence for an effect of acute physical activity on cognition in young adults

Physical exercise is a potential intervention for enhancing cognitive function across the lifespan. However, while studies employing long-term exercise interventions consistently show positive effects on cognition, studies using single acute bouts have produced mixed results. Here, a systematic review and meta-analysis was conducted to determine the impact of acute exercise on cognitive task performance in healthy young adults. A Bayesian hierarchical model quantified probabilistic evidence for a modulatory relationship by synthesizing 651 effect sizes from 113 studies from PsychInfo and Google Scholar representing 4,390 participants. Publication bias was mitigated using the trim-and-fill method. Acute exercise was found to have a small beneficial effect on cognition (g = 0.13 ± 0.04; BF = 3.67) and decrease reaction time. A meta-analysis restricted to executive function tasks revealed improvements in working memory and inhibition. Meta-analytic estimates were consistent across multiple priors and likelihood functions. Physical activities were categorized based on exercise type (e.g., cycling) because many activities have aerobic and anaerobic components, but this approach may limit comparison to studies that categorize activities based on metabolic demands. The current study provides an updated synthesis of the existing literature and insights into the robustness of acute exercise-induced effects on cognition. Funding provided by the United States Army Research Office.

Exercise-induced cortical disinhibition mediates the relationship between fitness and memory in older adults

Regular exercise benefits learning and memory in older adults, but the neural mechanisms mediating these effects remain unclear. Evidence in young adults indicates that acute exercise creates a favourable environment for synaptic plasticity by enhancing cortical disinhibition. As such, we investigated whether plasticity-related disinhibition mediated the relationship between cardiorespiratory fitness and memory function in healthy older adults (n = 16, mean age = 66.06). Participants completed a graded maximal exercise test and assessments of visual and verbal memory, followed by two counterbalanced sessions involving 20 min of either high-intensity interval training exercise or rest. Disinhibition was measured following intermittent theta burst stimulation via paired-pulse transcranial magnetic stimulation. In line with our hypotheses, we observed a positive correlation between cardiorespiratory fitness and verbal memory, which was mediated by plasticity-related cortical disinhibition. Our novel finding implicates cortical disinhibition as a mechanism through which the effects of acute bouts of exercise may translate to improved memory in older adults. This finding extends current understanding of the physiological mechanisms underlying the positive influence of cardiorespiratory fitness for memory function in older adults, and further highlights the importance of promoting exercise engagement to maintain cognitive health in later life. KEY POINTS: There are well established benefits of regular exercise for memory function in older adults, but the mechanisms are unclear. Cortical disinhibition is important for laying down new memories, and is enhanced following acute exercise in young adults, suggesting it is a potential mechanism underlying these benefits in ageing. Older adults completed a fitness test and assessments of memory, followed by two sessions involving either 20 min of exercise or rest. Disinhibition was measured following intermittent theta burst stimulation via paired-pulse transcranial magnetic stimulation. Cardiorespiratory fitness was positively associated with memory performance. Higher fitness was associated with enhanced cortical disinhibition following acute exercise. Cortical disinhibition completely mediated the relationship between fitness and memory. This novel finding provides a mechanistic account for the positive influence of cardiorespiratory fitness on memory in later life, and emphasises the importance of regular exercise for cognitive health in older populations.

Acute aerobic exercise at different intensities modulates inhibitory control and cortical excitability in adults with attention-deficit hyperactivity disorder (ADHD)

BACKGROUND

This study aimed to investigate the effects of different aerobic exercise intensities on inhibitory control and cortical excitability in adults with attention-deficit/hyperactivity disorder (ADHD).

METHODS

The study was conducted in a within-subject design. Twenty-four adults with ADHD completed a stop signal task and received cortical excitability assessment by transcranial magnetic stimulation (TMS) before and after a single session of low-, moderate-, high-intensity aerobic exercise or a control intervention.

RESULTS

Acute moderate-, and high-intensity aerobic exercise improved inhibitory control in adults with ADHD. Moreover, the improving effect was similar between moderate-, and high-intensity aerobic exercise conditions. As shown by the brain physiology results, short interval intracortical inhibition was significantly increased following both, moderate- and high-intensity aerobic exercise intervention conditions. Additionally, the alteration of short interval intracortical inhibition and inhibitory control improvement were positively correlated.

CONCLUSIONS

The moderate-, and high-intensity aerobic exercise-dependent alterations of cortical excitability in adults with ADHD might partially explain the inhibitory control-improving effects of aerobic exercise in this population.

Associations of physical fitness with cortical inhibition and excitation in adolescents and young adults

Objective

We investigated the longitudinal associations of cumulative motor fitness, muscular strength, and cardiorespiratory fitness (CRF) from childhood to adolescence with cortical excitability and inhibition in adolescence. The other objective was to determine cross-sectional associations of motor fitness and muscular strength with brain function in adolescence.

Methods

In 45 healthy adolescents (25 girls and 20 boys) aged 16-19 years, we assessed cortical excitability and inhibition by navigated transcranial magnetic stimulation (nTMS), and motor fitness by 50-m shuttle run test and Box and block test, and muscular strength by standing long jump test. These measures of physical fitness and CRF by maximal exercise were assessed also at the ages 7-9, 9-11, and 15-17 years. Cumulative measures of physical measures were computed by summing up sample-specific z-scores at ages 7-9, 9-11, and 15-17 years.

Results

Higher cumulative motor fitness performance from childhood to adolescence was associated with lower right hemisphere resting motor threshold (rMT), lower silent period threshold (SPt), and lower motor evoked potential (MEP) amplitude in boys. Better childhood-to-adolescence cumulative CRF was also associated with longer silent period (SP) duration in boys and higher MEP amplitude in girls. Cross-sectionally in adolescence, better motor fitness and better muscular strength were associated with lower left and right rMT among boys and better motor fitness was associated with higher MEP amplitude and better muscular strength with lower SPt among girls.

Conclusion

Physical fitness from childhood to adolescence modifies cortical excitability and inhibition in adolescence. Motor fitness and muscular strength were associated with motor cortical excitability and inhibition. The associations were selective for specific TMS indices and findings were sex-dependent.

Aerobic Exercise Improves Cortical Inhibitory Function After Stroke: A Preliminary Investigation

BACKGROUND AND PURPOSE

Aerobic exercise can elicit positive effects on neuroplasticity and cognitive executive function but is poorly understood after stroke. We tested the effect of 4 weeks of aerobic exercise training on inhibitory and facilitatory elements of cognitive executive function and electroencephalography markers of cortical inhibition and facilitation. We investigated relationships between stimulus-evoked cortical responses, blood lactate levels during training, and aerobic fitness postintervention.

METHODS

Twelve individuals with chronic (>6 months) stroke completed an aerobic exercise intervention (40 minutes, 3×/wk). Electroencephalography and motor response times were assessed during congruent (response facilitation) and incongruent (response inhibition) stimuli of a Flanker task. Aerobic fitness capacity was assessed as o2peak during a treadmill test pre- and postintervention. Blood lactate was assessed acutely (<1 minute) after exercise each week. Cortical inhibition (N2) and facilitation (frontal P3) were quantified as peak amplitudes and latencies of stimulus-evoked electroencephalographic activity over the frontal cortical region.

RESULTS

Following exercise training, the response inhibition speed increased while response facilitation remained unchanged. A relationship between earlier cortical N2 response and faster response inhibition emerged postintervention. Individuals who produced higher lactate during exercise training achieved faster response inhibition and tended to show earlier cortical N2 responses postintervention. There were no associations between o2peak and metrics of behavioral or neurophysiologic function.

DISCUSSION AND CONCLUSIONS

These preliminary findings provide novel evidence for selective benefits of aerobic exercise on inhibitory control during the initial 4-week period after initiation of exercise training and implicate a potential therapeutic effect of lactate on poststroke inhibitory control.

Response to experimental cold-induced pain discloses a resistant category among endurance athletes, with a distinct profile of pain-related behavior and GABAergic EEG markers: a case-control preliminary study

Pain is a major public health problem worldwide, with a high rate of treatment failure. Among promising non-pharmacological therapies, physical exercise is an attractive, cheap, accessible and innocuous method; beyond other health benefits. However, its highly variable therapeutic effect and incompletely understood underlying mechanisms (plausibly involving the GABAergic neurotransmission) require further research. This case-control study aimed to investigate the impact of long-lasting intensive endurance sport practice (≥7 h/week for the last 6 months at the time of the experiment) on the response to experimental cold-induced pain (as a suitable chronic pain model), assuming that highly trained individual would better resist to pain, develop advantageous pain-copying strategies and enhance their GABAergic signaling. For this purpose, clinical pain-related data, response to a cold-pressor test and high-density EEG high (Hβ) and low beta (Lβ) oscillations were documented. Among 27 athletes and 27 age-adjusted non-trained controls (right-handed males), a category of highly pain-resistant participants (mostly athletes, 48.1%) was identified, displaying lower fear of pain, compared to non-resistant non-athletes. Furthermore, they tolerated longer cold-water immersion and perceived lower maximal sensory pain. However, while having similar Hβ and Lβ powers at baseline, they exhibited a reduction between cold and pain perceptions and between pain threshold and tolerance (respectively -60% and - 6.6%; -179.5% and - 5.9%; normalized differences), in contrast to the increase noticed in non-resistant non-athletes (+21% and + 14%; +23.3% and + 13.6% respectively). Our results suggest a beneficial effect of long-lasting physical exercise on resistance to pain and pain-related behaviors, and a modification in brain GABAergic signaling. In light of the current knowledge, we propose that the GABAergic neurotransmission could display multifaceted changes to be differently interpreted, depending on the training profile and on the homeostatic setting (e.g., in pain-free versus chronic pain conditions). Despite limitations related to the sample size and to absence of direct observations under acute physical exercise, this precursory study brings into light the unique profile of resistant individuals (probably favored by training) allowing highly informative observation on physical exercise-induced analgesia and paving the way for future clinical translation. Further characterizing pain-resistant individuals would open avenues for a targeted and physiologically informed pain management.

Ageing attenuates exercise-enhanced motor cortical plasticity

Cardiorespiratory exercise is known to modulate motor cortical plasticity in young adults, but the influence of ageing on this relationship is unknown. Here, we compared the effects of a single session of cardiorespiratory exercise on motor cortical plasticity in young and older adults. We acquired measures of cortical excitatory and inhibitory activity of the primary motor cortex using transcranial magnetic stimulation (TMS) from 20 young (mean ± SD = 25.30 ± 4.00 years, 14 females) and 20 older (mean ± SD = 64.10 ± 6.50 years, 11 females) healthy adults. Single- and paired-pulse TMS measurements were collected before and after a 20 min bout of high-intensity interval cycling exercise or an equivalent period of rest, and again after intermittent theta burst stimulation (iTBS). In both young (P = 0.027, Cohen's d = 0.87) and older adults (P = 0.006, Cohen's d = 0.85), there was an increase in glutamatergic excitation and a reduction in GABAergic inhibition from pre- to postexercise. However, in contrast to younger adults, older adults showed an attenuated plasticity response to iTBS following exercise (P = 0.011, Cohen's d = 0.85). These results demonstrate an age-dependent decline in cortical plasticity and indicate that a preceding bout of high-intensity interval exercise might be less effective for enhancing primary motor cortex plasticity in older adults. Our findings align with the hypothesis that the capacity for cortical plasticity is altered in older age. KEY POINTS: Exercise enhances motor cortical plasticity in young adults, but how ageing influences this effect is unknown. Here, we compared primary motor cortical plasticity responses in young and older adults before and after a bout of high-intensity interval exercise and again after a plasticity-inducing protocol, intermittent theta burst stimulation. In both young and older adults, exercise led to an increase in glutamatergic excitation and a reduction in GABAergic inhibition. Our key result was that older adults showed an attenuated plasticity response to theta burst stimulation following exercise, relative to younger adults. Our findings demonstrate an age-dependent decline in exercise-enhanced cortical plasticity and indicate that a preceding bout of high-intensity interval exercise might be less effective for enhancing primary motor cortex plasticity in older adults.

Acute Aerobic Exercise at Different Intensities Modulates Motor Learning Performance and Cortical Excitability in Sedentary Individuals

Converging evidence indicates the beneficial effects of aerobic exercise on motor learning performance. Underlying mechanisms might be an impact of aerobic exercise on neuroplasticity and cortical excitability. Evidence suggests that motor learning and cortical excitability alterations correlate with the intensity of aerobic exercise and the activity level of participants. Thus, this study aims to investigate the effects of different aerobic exercise intensities on motor learning and cortical excitability in sedentary individuals. The study was conducted in a crossover and double-blind design. Twenty-six healthy sedentary individuals (13 women and 13 men) performed a motor learning task and received a cortical excitability assessment before and after a single session of low-, moderate-, and high-intensity aerobic exercise or a control intervention. The study revealed that motor learning performance and cortical excitability were significantly enhanced in the moderate-intensity aerobic exercise, compared with the other conditions. These findings suggest aerobic exercise intensity-dependent effects on motor learning in sedentary adults. The underlying mechanism might be an exercised-induced alteration of cortical excitability, specifically a reduction of GABA activity.

Physiological, Anatomical and Metabolic Correlates of Aerobic Fitness in Human Primary Motor Cortex: A Multimodal Study

Physical activity (PA) has been shown to benefit various cognitive functions and promote neuroplasticity. Whereas the effects of PA on brain anatomy and function have been well documented in older individuals, data are scarce in young adults. Whether high levels of cardiorespiratory fitness (CRF) achieved through regular PA are associated with significant structural and functional changes in this age group remains largely unknown. In the present study, twenty young adults that engaged in at least 8 hours per week of aerobic exercise during the last 5 years were compared to twenty sedentary controls on measures of cortical excitability, white matter microstructure, cortical thickness and metabolite concentration. All measures were taken in the left primary motor cortex and CRF was assessed with VO_2max. Transcranial magnetic stimulation (TMS) revealed higher corticospinal excitability in high- compared to low-fit individuals reflected by greater input/output curve amplitude and slope. No group differences were found for other TMS (short-interval intracortical inhibition and intracortical facilitation), diffusion MRI (fractional anisotropy and apparent fiber density), structural MRI (cortical thickness) and magnetic resonance spectroscopy (NAA, GABA, Glx) measures. Taken together, the present data suggest that brain changes associated with increased CRF are relatively limited, at least in primary motor cortex, in contrast to what has been observed in older adults.

A single bout of moderate-intensity aerobic exercise improves motor learning in premanifest and early Huntington's disease

Introduction

Cardiorespiratory exercise has emerged as a promising candidate to modify disease progression in Huntington's disease (HD). In animal models, exercise has been found to alter biomarkers of neuroplasticity and delay evidence of disease, and some interventions-including exercise-have shown benefits in human HD patients. In healthy human populations, increasing evidence suggests that even a single bout of exercise can improve motor learning. In this pilot study, we investigated the effect of a single bout of moderate intensity aerobic exercise on motor skill learning in presymptomatic and early manifest HD patients.

Methods

Participants were allocated to either an exercise (n = 10) or control (n = 10) group. They performed either 20 min of moderate intensity cycling or rest before practicing a novel motor task, the sequential visual isometric pinch force task (SVIPT). After 1 week, the retention of the SVIPT was measured in both groups.

Results

We found that the exercise group performed significantly better during initial task acquisition. There were no significant differences in offline memory consolidation between groups, but total skill gain across both acquisition and retention sessions was greater in the group who exercised. The better performance of the exercise group was driven by improvements in accuracy, rather than speed.

Discussion

We have shown that a single bout of moderate intensity aerobic exercise can facilitate motor skill learning in people with HD gene-expansion. More research is needed to investigate the underlying neural mechanisms and to further explore the potential for neurocognitive and functional benefits of exercise for people with HD.

Exerkines and long-term synaptic potentiation: Mechanisms of exercise-induced neuroplasticity

Physical exercise may improve cognitive function by modulating molecular and cellular mechanisms within the brain. We propose that the facilitation of long-term synaptic potentiation (LTP)-related pathways, by products induced by physical exercise (i.e., exerkines), is a crucial aspect of the exercise-effect on the brain. This review summarizes synaptic pathways that are activated by exerkines and may potentiate LTP. For a total of 16 exerkines, we indicated how blood and brain exerkine levels are altered depending on the type of physical exercise (i.e., cardiovascular or resistance exercise) and how they respond to a single bout (i.e., acute exercise) or multiple bouts of physical exercise (i.e., chronic exercise). This information may be used for designing individualized physical exercise programs. Finally, this review may serve to direct future research towards fundamental gaps in our current knowledge regarding the biophysical interactions between muscle activity and the brain at both cellular and system levels.

The Combined Influences of Exercise, Diet and Sleep on Neuroplasticity

Neuroplasticity refers to the brain's ability to undergo structural and functional adaptations in response to experience, and this process is associated with learning, memory and improvements in cognitive function. The brain's propensity for neuroplasticity is influenced by lifestyle factors including exercise, diet and sleep. This review gathers evidence from molecular, systems and behavioral neuroscience to explain how these three key lifestyle factors influence neuroplasticity alone and in combination with one another. This review collected results from human studies as well as animal models. This information will have implications for research, educational, fitness and neurorehabilitation settings.

Motor cortex plasticity response to acute cardiorespiratory exercise and intermittent theta-burst stimulation is attenuated in premanifest and early Huntington’s disease

Huntington’s disease (HD) mouse models suggest that cardiovascular exercise may enhance neuroplasticity and delay disease signs, however, the effects of exercise on neuroplasticity in people with HD are unknown. Using a repeated-measures experimental design, we compared the effects of a single bout of high-intensity exercise, moderate-intensity exercise, or rest, on motor cortex synaptic plasticity in 14 HD CAG-expanded participants (9 premanifest and 5 early manifest) and 20 CAG-healthy control participants, using transcranial magnetic stimulation. Measures of cortico-motor excitability, short-interval intracortical inhibition and intracortical facilitation were obtained before and after a 20-min bout of either high-intensity interval exercise, moderate-intensity continuous exercise, or rest, and again after intermittent theta burst stimulation (iTBS). HD participants showed less inhibition at baseline compared to controls. Whereas the control group showed increased excitability and facilitation following high-intensity exercise and iTBS, the HD group showed no differences in neuroplasticity responses following either exercise intensity or rest, with follow-up Bayesian analyses providing consistent evidence that these effects were absent in the HD group. These findings indicate that exercise-induced synaptic plasticity mechanisms in response to acute exercise may be attenuated in HD, and demonstrate the need for future research to further investigate exercise and plasticity mechanisms in people with HD.

Acute High-Intensity Interval Exercise Modulates Corticospinal Excitability in Older Adults

INTRODUCTION

Acute exercise can modulate the excitability of the non-exercised upper-limb representation in the primary motor cortex (M1). Measures of M1 excitability using transcranial magnetic stimulation (TMS) are modulated following various forms of acute exercise in young adults, including high intensity interval training (HIIT). However, the impact of HIIT on M1 excitability in older adults is currently unknown. Therefore, the purpose of the current study was to investigate the effects of lower-limb cycling HIIT on bilateral upper-limb M1 excitability in older adults.

METHODS

We assessed the impact of acute lower-limb HIIT or rest on bilateral corticospinal excitability, intracortical inhibition and facilitation, and interhemispheric inhibition of the non-exercised upper-limb muscle in healthy older adults (aged 66 ± 8). We used single and paired-pulse TMS to assess motor evoked potentials (MEPs), short-interval intracortical inhibition (SICI), intracortical facilitation (ICF) and the ipsilateral silent period (iSP). Two groups of healthy older adults completed either HIIT exercise or seated rest for 23 min, with TMS measures performed pre (T0), immediately post (T1) and 30 min post (T2) HIIT/rest.

RESULTS

MEPs were significantly increased after HIIT exercise at T2 compared to T0 in the dominant upper-limb. Contrary to our hypothesis we did not find any significant change in SICI, ICF or iSP following HIIT.

CONCLUSIONS

Our findings demonstrate that corticospinal excitability of the non-exercised upper-limb is increased following HIIT in healthy older adults. Our results indicate that acute HIIT exercise impacts corticospinal excitability in older adults, without affecting intracortical or interhemispheric circuitry. These findings have implications for the development of exercise strategies to potentiate neuroplasticity in healthy older and clinical populations.

Acute Exercise Modulates the Excitability of Specific Interneurons in Human Motor Cortex

Acute exercise can modulate the excitability of the non-exercised upper-limb representation in the primary motor cortex (M1). Accumulating evidence demonstrates acute exercise affects measures of M1 intracortical excitability, with some studies also showing altered corticospinal excitability. However, the influence of distinct M1 interneuron populations on the modulation of intracortical and corticospinal excitability following acute exercise is currently unknown. We assessed the impact of an acute bout of leg cycling exercise on unique M1 interneuron excitability of a non-exercised intrinsic hand muscle using transcranial magnetic stimulation (TMS) in young adults. Specifically, posterior-to-anterior (PA) and anterior-to-posterior (AP) TMS current directions were used to measure the excitability of distinct populations of interneurons before and after an acute bout of exercise or rest. Motor evoked potentials (MEPs) and short-interval intracortical inhibition (SICI) were measured in the PA and AP current directions in M1 at two time points separated by 25 min of rest, as well as immediately and 30 min after a 25-minute bout of moderate-intensity cycling exercise. Thirty minutes after exercise, MEP amplitudes were significantly larger than other timepoints when measured with AP current, whereas MEP amplitudes derived from PA current did not show this effect. Similarly, SICI was significantly decreased immediately following acute exercise measured with AP but not PA current. Our findings suggest that the excitability of unique M1 interneurons are differentially modulated by acute exercise. These results indicate that M1 interneurons preferentially activated by AP current may play an important role in the exercise-induced modulation of intracortical and corticospinal excitability.

Physical activity, motor performance and skill learning: a focus on primary motor cortex in healthy aging

Participation in physical activity benefits brain health and function. Cognitive function generally demonstrates a noticeable effect of physical activity, but much less is known about areas responsible for controlling movement, such as primary motor cortex (M1). While more physical activity may support M1 plasticity in older adults, the neural mechanisms underlying this beneficial effect remain poorly understood. Aging is inevitably accompanied by diminished motor performance, and the extent of plasticity may also be less in older adults compared with young. Motor complications with aging may, perhaps unsurprisingly, contribute to reduced physical activity in older adults. While the development of non-invasive brain stimulation techniques have identified that human M1 is a crucial site for learning motor skills and recovery of motor function after injury, a considerable lack of knowledge remains about how physical activity impacts M1 with healthy aging. Reducing impaired neural activity in older adults may have important implications after neurological insult, such as stroke, which is more common with advancing age. Therefore, a better understanding about the effects of physical activity on M1 processes and motor learning in older adults may promote healthy aging, but also allow us to facilitate recovery of motor function after neurological injury. This article will initially provide a brief overview of the neurophysiology of M1 in the context of learning motor skills, with a focus on healthy aging in humans. This information will then be proceeded by a more detailed assessment that focuses on whether physical activity benefits motor function and human M1 processes.

The Effects of Combined Physical and Cognitive Training on Inhibitory Control: A Systematic Review and Meta-Analysis

While strong inhibitory control is critical for health and wellbeing, there are no broadly applicable effective behavioural interventions that enhance it. This meta-analysis examined the neurocognitive rationale for combined physical and cognitive training and synthesised the rapidly growing body of evidence examining combined paradigms to enhance inhibitory control. Across the research to date, there was a small positive effect (n studies = 16, n participants = 832) of combined training on improving inhibitory control. Sub-group analyses showed small-moderate positive effects when the physical component of the combined training was moderately intense, as opposed to low or vigorous intensities; moderate positive effects were found in older adults, as compared to adolescents and adults; and healthy individuals and those with vascular cognitive impairment, as compared to ADHD, ASD, mild cognitive impairment and cancer survivors. This is the first meta-analysis to provide evidence that combined physical, specifically when moderately intense, and cognitive training has the capacity to improve inhibitory control, particularly when delivered to healthy individuals and those experiencing age-related decline.

Transcranial Magnetic Stimulation to Assess Exercise-Induced Neuroplasticity

Aerobic exercise facilitates neuroplasticity and has been linked to improvements in cognitive and motor function. Transcranial magnetic stimulation (TMS) is a non-invasive technique that can be used to quantify changes in neurophysiology induced by exercise. The present review summarizes the single- and paired-pulse TMS paradigms that can be used to probe exercise-induced neuroplasticity, the optimal stimulation parameters and the current understanding of the neurophysiology underlying each paradigm. Further, this review amalgamates previous research exploring the modulation of these paradigms with exercise-induced neuroplasticity in healthy and clinical populations and highlights important considerations for future TMS-exercise research.

A Single Bout of High-intensity Interval Exercise Increases Corticospinal Excitability, Brain-derived Neurotrophic Factor, and Uncarboxylated Osteolcalcin in Sedentary, Healthy Males

Exercise induces neuroplasticity in descending motor pathways facilitating motor learning, and as such it could be utilized as an intervention in neurorehabilitation, for example when re-learning motor skills after stroke. To date, however, the neurophysiological and molecular mechanisms underlying exercise-induced neuroplasticity remain largely unknown impeding the potential utilization of exercise protocols as 'motor learning boosters' in clinical and non-clinical settings. Here, we assessed corticospinal excitability, intracortical facilitation (ICF) and short-interval intracortical inhibition (SICI) using transcranial magnetic stimulation (TMS) and serum biochemical markers including brain-derived neurotrophic factor (BDNF), total and precursor cathepsin B (tCTSB, proCTSB), uncarboxylated and carboxylated osteocalcin (unOCN, cOCN) and irisin using ELISA. Measurements were carried out in sedentary, healthy males before and after a single session of high-intensity interval exercise (HIIE) or in individuals who rested and did not perform exercise (No Exercise). We found that HIIE increased corticospinal excitability, BDNF and unOCN, and decreased cOCN. We also determined that greater increases in BDNF were associated with increases in unOCN and irisin and decreases in cOCN only in participants who underwent HIIE, suggesting that unOCN and irisin may contribute to exercise-induced BDNF increases. Conversely, no changes other than a decrease in serum unOCN/tOCN were found in No Exercise participants. The present findings show that a single session of HIIE is sufficient to modulate corticospinal excitability and to increase BDNF and unOCN in sedentary, healthy males.

Intensity Matters: High-intensity Interval Exercise Enhances Motor Cortex Plasticity More Than Moderate Exercise

A single bout of cardiovascular exercise can enhance plasticity in human cortex; however, the intensity required for optimal enhancement is debated. We investigated the effect of exercise intensity on motor cortex synaptic plasticity, using transcranial magnetic stimulation. Twenty healthy adults (Mage = 35.10 ± 13.25 years) completed three sessions. Measures of cortico-motor excitability (CME) and inhibition were obtained before and after a 20-min bout of either high-intensity interval exercise, moderate-intensity continuous exercise, or rest, and again after intermittent theta burst stimulation (iTBS). Results showed that high-intensity interval exercise enhanced iTBS plasticity more than rest, evidenced by increased CME and intracortical facilitation, and reduced intracortical inhibition. In comparison, the effect of moderate-intensity exercise was intermediate between high-intensity exercise and rest. Importantly, analysis of each participant's plasticity response profile indicated that high-intensity exercise increased the likelihood of a facilitatory response to iTBS. We also established that the brain-derived neurotrophic factor Val66Met polymorphism attenuated plasticity responses following high-intensity exercise. These findings suggest that high-intensity interval exercise should be considered not only when planning exercise interventions designed to enhance neuroplasticity, but also to maximize the therapeutic potential of non-invasive brain stimulation. Additionally, genetic profiling may enhance efficacy of exercise interventions for brain health.

Determining the Intracortical Responses After a Single Session of Aerobic Exercise in Young Healthy Individuals: A Systematic Review and Best Evidence Synthesis

ABSTRACT

Alibazi, RJ, Pearce, AJ, Rostami, M, Frazer, AK, Brownstein, C, and Kidgell, DJ. Determining the intracortical responses after a single session of aerobic exercise in young healthy individuals: a systematic review and best evidence synthesis. J Strength Cond Res 35(2): 562-575, 2021-A single bout of aerobic exercise (AE) may induce changes in the excitability of the intracortical circuits of the primary motor cortex (M1). Similar to noninvasive brain stimulation techniques, such as transcranial direct current stimulation, AE could be used as a priming technique to facilitate motor learning. This review examined the effect of AE on modulating intracortical excitability and inhibition in human subjects. A systematic review, according to PRISMA guidelines, identified studies by database searching, hand searching, and citation tracking between inception and the last week of February 2020. Methodological quality of included studies was determined using the Downs and Black quality index and Cochrane Collaboration of risk of bias tool. Data were synthesized and analyzed using best-evidence synthesis. There was strong evidence for AE not to change corticospinal excitability and conflicting evidence for increasing intracortical facilitation and reducing silent period and long-interval cortical inhibition. Aerobic exercise did reduce short-interval cortical inhibition, which suggests AE modulates the excitability of the short-latency inhibitory circuits within the M1; however, given the small number of included studies, it remains unclear how AE affects all circuits. In light of the above, AE may have important implications during periods of rehabilitation, whereby priming AE could be used to facilitate motor learning.

Behavioral and Neurophysiological Aspects of Inhibition-The Effects of Acute Cardiovascular Exercise

This review summarizes behavioral and neurophysiological aspects of inhibitory control affected by a single bout of cardiovascular exercise. The review also examines the effect of a single bout of cardiovascular exercise on these processes in young adults with a focus on the functioning of prefrontal pathways (including the left dorsolateral prefrontal cortex (DLPFC) and elements of the prefrontal-basal ganglia pathways). Finally, the review offers an overview on the potential effects of cardiovascular exercise on GABA-ergic and glutamatergic neurotransmission in the adult brain and propose mechanisms or processes that may mediate these effects. The main findings show that a single bout of cardiovascular exercise can enhance inhibitory control. In addition, acute exercise appears to facilitate activation of prefrontal brain regions that regulate excitatory and inhibitory pathways (specifically but not exclusively the prefrontal-basal-ganglia pathways) which appear to be impaired in older age. Based on the reviewed studies, we suggest that future work examine the beneficial effects of exercise on the inhibitory networks in the aging brain.

Understanding the Neurophysiological and Molecular Mechanisms of Exercise-Induced Neuroplasticity in Cortical and Descending Motor Pathways: Where Do We Stand?

Exercise is a promising, cost-effective intervention to augment successful aging and neurorehabilitation. Decline of gray and white matter accompanies physiological aging and contributes to motor deficits in older adults. Exercise is believed to reduce atrophy within the motor system and induce neuroplasticity which, in turn, helps preserve motor function during aging and promote re-learning of motor skills, for example after stroke. To fully exploit the benefits of exercise, it is crucial to gain a greater understanding of the neurophysiological and molecular mechanisms underlying exercise-induced brain changes that prime neuroplasticity and thus contribute to postponing, slowing, and ameliorating age- and disease-related impairments in motor function. This knowledge will allow us to develop more effective, personalized exercise protocols that meet individual needs, thereby increasing the utility of exercise strategies in clinical and non-clinical settings. Here, we review findings from studies that investigated neurophysiological and molecular changes associated with acute or long-term exercise in healthy, young adults and in healthy, postmenopausal women.

Combining transcranial direct current stimulation with aerobic exercise to optimize cortical priming in stroke

Aerobic exercise (AE) and transcranial direct current stimulation (tDCS) are priming techniques that have been studied for their potential neuromodulatory effects on corticomotor excitability (CME); however, the synergistic effects of AE and tDCS are not explored in stroke. Here we investigated the synergistic effects of AE and tDCS on CME, intracortical and transcallosal inhibition, and motor control for the lower limb in stroke. Twenty-six stroke survivors participated in 3 sessions: tDCS, AE, and AE+tDCS. AE included moderate-intensity exercise and tDCS included 1 mA of anodal tDCS to the lower limb motor cortex with or without AE. Outcomes included measures of CME, short-interval intracortical inhibition (SICI), ipsilateral silent period (iSP) (an index of transcallosal inhibition) for the tibialis anterior, and ankle reaction time. Ipsilesional CME significantly decreased for AE compared with AE+tDCS and tDCS. No differences were noted in SICI, iSP measures, or reaction time between all 3 sessions. Our findings suggest that a combination of exercise and tDCS, and tDCS demonstrate greater excitability of the ipsilesional hemisphere compared with exercise only; however, these effects were specific to the descending corticomotor pathways. No additive priming effects of exercise and tDCS over tDCS was observed. Novelty: An exercise and tDCS paradigm upregulated the descending motor pathways from the ipsilesional lower limb primary motor cortex compared with exercise. Exercise or tDCS administered alone or in combination did not affect intracortical or transcallosal inhibition or reaction time.

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.

The influence of an acute bout of moderate-intensity cycling exercise on sensorimotor integration

Acute cycling exercise can modulate motor cortical circuitry in the non-exercised upper-limb. Within the primary motor cortex, measures of intracortical inhibition are reduced and intracortical facilitation is enhanced following acute exercise. Further, acute cycling exercise decreases interhemispheric inhibition between the motor cortices and lowers cerebellar-to-motor cortex inhibition. Yet, investigations into the effects of acute exercise on sensorimotor integration, referring to the transfer of incoming afferent information from the primary somatosensory cortex to motor cortex, are lacking. The current work addresses this gap in knowledge with two experimental sessions. In the first session, we tested the exercise-induced changes in somatosensory and motor excitability by assessing somatosensory (SEP) and motor evoked potentials (MEPs). In the second session, we explored the effects of acute cycling exercise on short- (SAI) and long-latency afferent inhibition (LAI), and afferent facilitation. In both experimental sessions, neurophysiological measures were obtained from the non-exercised upper-limb muscle, tested at two time points pre-exercise separated by a 25-min period of rest. Next, a 25-min bout of moderate-intensity lower-limb cycling was performed with measures assessed at two time points post-exercise. Acute lower-limb cycling increased LAI, without modulation of SAI or afferent facilitation. Further, there were no exercise-induced changes to SEP or MEP amplitudes. Together, these results suggest that acute exercise has unique effects on sensorimotor integration, which are not accompanied by concurrent changes in somatosensory or motor cortical excitability.

Comparative study of the effectiveness of a low-pressure hyperbaric oxygen treatment and physical exercise in women with fibromyalgia: randomized clinical trial

Background

Fibromyalgia (FM) is characterized by chronic pain and fatigue, among other manifestations, thus advising interventions that do not aggravate these symptoms. The main purpose of this study is to analyse the effect of low-pressure hyperbaric oxygen therapy (HBOT) on induced fatigue, pain, endurance and functional capacity, physical performance and cortical excitability when compared with a physical exercise program in women with FM.

Methods

A total of 49 women with FM took part in this randomized controlled trial. They were randomly allocated to three groups: physical exercise group (PEG, n = 16), low-pressure hyperbaric oxygen therapy group (HBG, n = 17) and control group (CG, n = 16). Induced fatigue, perceived pain, pressure pain threshold, endurance and functional capacity, physical performance and cortical excitability were assessed. To analyse the effect of the interventions, two assessments, that is, pre and post intervention, were carried out. Analyses of the data were performed using two-way mixed multivariate analysis of variance.

Results

The perceived pain and induced fatigue significantly improved only in the HBG (p < 0.05) as opposed to PEG and CG. Pressure pain threshold, endurance and functional capacity, and physical performance significantly improved for both interventions (p < 0.05). The cortical excitability (measured with the resting motor threshold) did not improve in any of the treatments (p > 0.05).

Conclusions

Low-pressure HBOT and physical exercise improve pressure pain threshold, endurance and functional capacity, as well as physical performance. Induced fatigue and perceived pain at rest significantly improved only with low-pressure HBOT.

Trial registration

ClinicalTrials.gov identifier NCT03801109.

Light aerobic exercise modulates executive function and cortical excitability

Single bouts of aerobic exercise can modulate cortical excitability and executive cognitive function, but less is known about the effect of light-intensity exercise, an intensity of exercise more achievable for certain clinical populations. Fourteen healthy adults (aged 22 to 30) completed the following study procedures twice (≥7 days apart) before and after 30 min of either light aerobic exercise (cycling) or seated rest: neurocognitive battery (multitasking performance, inhibitory control and spatial working memory), paired-pulse TMS measures of cortical excitability. Significant improvements in response times during multitasking performance and increases in intracortical facilitation (ICF) were seen following light aerobic exercise. Light aerobic exercise can modulate cortical excitability and some executive function tasks. Populations with deficits in multitasking ability may benefit from this intervention.

Neurophysiology of motor skill learning in chronic stroke

OBJECTIVE

Motor learning is relevant in chronic stroke for acquiring compensatory strategies to motor control deficits. However, the neurophysiological mechanisms underlying motor skill acquisition with the paretic upper limb have received little systematic investigation. The aim of this study was to assess the modulation of corticomotor excitability and intracortical inhibition within ipsilesional primary motor cortex (M1) during motor skill learning.

METHODS

Ten people at the chronic stage after stroke and twelve healthy controls trained on a sequential visuomotor isometric wrist extension task. Skill was quantified before, immediately after, 24 hours and 7 days post-training. Transcranial magnetic stimulation was used to examine corticomotor excitability and short- and long-interval intracortical inhibition (SICI and LICI) pre- and post-training.

RESULTS

The patient group exhibited successful skill acquisition and retention, although absolute skill level was lower compared with controls. In contrast to controls, patients' ipsilesional corticomotor excitability was not modulated during skill acquisition, which may be attributed to excessive ipsilesional LICI relative to controls. SICI decreased after training for both patient and control groups.

CONCLUSIONS

Our findings indicate distinct inhibitory networks within M1 that may be relevant for motor learning after stroke.

SIGNIFICANCE

These findings have potential clinical relevance for neurorehabilitation adjuvants aimed at augmenting the recovery of motor function.

The Influence of Primary Motor Cortex Inhibition on Upper Limb Impairment and Function in Chronic Stroke: A Multimodal Study

BACKGROUND

Stroke is a leading cause of adult disability owing largely to motor impairment and loss of function. After stroke, there may be abnormalities in γ-aminobutyric acid (GABA)-mediated inhibitory function within primary motor cortex (M1), which may have implications for residual motor impairment and the potential for functional improvements at the chronic stage.

OBJECTIVE

To quantify GABA neurotransmission and concentration within ipsilesional and contralesional M1 and determine if they relate to upper limb impairment and function at the chronic stage of stroke.

METHODS

Twelve chronic stroke patients and 16 age-similar controls were recruited for the study. Upper limb impairment and function were assessed with the Fugl-Meyer Upper Extremity Scale and Action Research Arm Test. Threshold tracking paired-pulse transcranial magnetic stimulation protocols were used to examine short- and long-interval intracortical inhibition and late cortical disinhibition. Magnetic resonance spectroscopy was used to evaluate GABA concentration.

RESULTS

Short-interval intracortical inhibition was similar between patients and controls ( P = .10). Long-interval intracortical inhibition was greater in ipsilesional M1 compared with controls ( P < .001). Patients who did not exhibit late cortical disinhibition in ipsilesional M1 were those with greater upper limb impairment and worse function ( P = .002 and P = .017). GABA concentration was lower within ipsilesional ( P = .009) and contralesional ( P = .021) M1 compared with controls, resulting in an elevated excitation-inhibition ratio for patients.

CONCLUSION

These findings indicate that ipsilesional and contralesional M1 GABAergic inhibition are altered in this small cohort of chronic stroke patients. Further study is warranted to determine how M1 inhibitory networks might be targeted to improve motor function.

Acute Low-Intensity Aerobic Exercise Modulates Intracortical Inhibitory and Excitatory Circuits in an Exercised and a Non-exercised Muscle in the Primary Motor Cortex

Recent studies have reported that acute aerobic exercise modulates intracortical excitability in the primary motor cortex (M1). However, whether acute low-intensity aerobic exercise can also modulate M1 intracortical excitability, particularly intracortical excitatory circuits, remains unclear. In addition, no previous studies have investigated the effect of acute aerobic exercise on short-latency afferent inhibition (SAI). The aim of this study was to investigate whether acute low-intensity aerobic exercise modulates intracortical circuits in the M1 hand and leg areas. Intracortical excitability of M1 (Experiments 1, 2) and spinal excitability (Experiment 3) were measured before and after acute low-intensity aerobic exercise. In Experiment 3, skin temperature was also measured throughout the experiment. Transcranial magnetic stimulation was applied over the M1 non-exercised hand and exercised leg areas in Experiments 1, 2, respectively. Participants performed 30 min of low-intensity pedaling exercise or rested while sitting on the ergometer. Short- and long-interval intracortical inhibition (SICI and LICI), and SAI were measured to assess M1 inhibitory circuits. Intracortical facilitation (ICF) and short-interval intracortical facilitation (SICF) were measured to assess M1 excitatory circuits. We found that acute low-intensity aerobic exercise decreased SICI and SAI in the M1 hand and leg areas. After exercise, ICF in the M1 hand area was lower than in the control experiment, but was not significantly different to baseline. The single motor-evoked potential, resting motor threshold, LICI, SICF, and spinal excitability did not change following exercise. In conclusion, acute low-intensity pedaling modulates M1 intracortical circuits of both exercised and non-exercised areas, without affecting corticospinal and spinal excitability.

Modulation of inhibitory function in the primary somatosensory cortex and temporal discrimination threshold induced by acute aerobic exercise

Acute aerobic exercise beneficially affects brain function. The effect of acute aerobic exercise on the inhibitory mechanism of the primary somatosensory cortex (S1) and somatosensory function remains unclear. We investigated whether acute aerobic exercise modulates S1 inhibitory function and somatosensory function. In Experiment 1, we measured somatosensory evoked potentials (SEP) and paired-pulse inhibition (PPI) in 15 healthy right-handed participants. The right median nerve underwent electrical stimulation (ES). Interstimulus intervals were 5 ms, 30 ms, and 100 ms. In Experiment 2, we assessed the somatosensory function by using a somatosensory temporal discrimination task. Single or paired ES was applied to the distal phalanx of the right index finger. Both the experiments involved three sessions: 20 min of moderate-intensity exercise, 30 min of low-intensity exercise, and 30 min of seated rest. Before and after each session, PPI and somatosensory temporal discrimination task performance were measured. The N20 latency was significantly shortened immediately after moderate exercise. The SEP amplitude was not modulated in any session. The PPI at 30 ms (PPI_30ms) significantly decreased 20 min after moderate exercise, whereas the PPI at 5 ms (PPI_5ms) and PPI at 100 ms (PPI_100ms) did not change. The 50% and 75% thresholds and reaction time did not improve in any session. We found negative relationships between the change in PPI_5ms and the change in the 75% threshold under low-intensity exercise condition. Thus, acute aerobic exercise modulated S1 inhibitory function depending on exercise intensity. The exercise-induced change in PPI was associated with the change in temporal discrimination.

An acute bout of aerobic exercise reduces movement time in a Fitts' task

Movement time (MT) is one of the most important variables influencing the way we control our movements. A few previous studies have generally found that MT reduces with reaction time testing during exercise. However, limited evidence exists concerning change in MT following an acute bout of exercise. Our purpose was to investigate the effect of an acute bout of aerobic exercise on movement time as assessed by a Fitts’ Law task. We also sought to determine if exercise would further lower MT during the more difficult task conditions compared with rest. Nineteen (12 male, 7 female) volunteers (19–28 yrs) completed a computerized paired serial pointing task to measure movement time before and after rest (R) and an acute bout of moderate aerobic exercise (E) using a within subjects crossover design. Comparisons between exercise and rest conditions were made to determine if there were differences in movement time. Exercise significantly reduced MT compared with rest. Movement time was reduced by an average of 208 ms following exercise compared with 108 ms following rest. Exercise did not further lower MT during the more difficult task conditions. These results suggest that an acute bout of aerobic exercise reduces movement time which is an important component of motor control. Further studies are needed to determine the duration of the effect as well as the optimum duration and intensity of exercise.

Feasibility, reliability, and validity of using accelerometers to measure physical activities of patients with stroke during inpatient rehabilitation

Promoting physical activities is important for medical and functional recovery after stroke. Therefore, an accurate and convenient measurement of physical activities is necessary to provide feedback on functional status and effects of rehabilitative interventions. We assessed the feasibility, reliability, and validity of wearing accelerometers to monitor physical activities of stroke patients by estimating energy expenditure. This was a prospective observational quantitative study conducted in an inpatient rehabilitation unit. Twenty-four patients with subacute stroke were enrolled. They wore accelerometers on wrists and ankles for three consecutive weekdays. The feasibility was evaluated by daily wear-time. The test-retest reliability was determined by intra-class correlation coefficient. The validity was evaluated by comparing accelerometeric data to behavior mappings using Mann-Whitney U test, Spearman’s rho correlation coefficient (r) and Bland-Altman plots. Average wearing time for four accelerometers was 20.99 ± 3.28 hours per day. The 3-day accelerometer recording showed excellent test-retest reliability. For sedentary activities, wrist accelerometers showed higher correlation with direct observation than ankle accelerometers. For light to moderate activities, ankle accelerometers showed higher correlation with direct observation than wrist accelerometers. Overall, combined models of accelerometers showed higher correlation with direct observation than separate ones. Wearing accelerometers for 24 h may be useful for measuring physical activities in subjects with subacute stroke in an inpatient rehabilitation unit.

Exercise intensity affects acute neurotrophic and neurophysiological responses poststroke

Aerobic exercise may acutely prime the brain to be more responsive to rehabilitation, thus facilitating neurologic recovery from conditions like stroke. This aerobic priming effect could occur through multiple mechanisms, including upregulation of circulating brain-derived neurotrophic factor (BDNF), increased corticospinal excitability, and decreased intracortical inhibition. However, optimal exercise parameters for targeting these mechanisms are poorly understood. This study tested the effects of exercise intensity on acute BDNF and neurophysiological responses. Sixteen ambulatory persons >6 mo poststroke performed three different 20-min exercise protocols in random order, approximately 1 wk apart, including the following: 1) treadmill high-intensity interval training (HIT-treadmill); 2) seated-stepper HIT (HIT-stepper); and 3) treadmill moderate-intensity continuous exercise (MCT-treadmill). Serum BDNF and transcranial magnetic stimulation measures of paretic lower limb excitability and inhibition were assessed at multiple time points during each session. Compared with MCT-treadmill, HIT-treadmill elicited significantly greater acute increases in circulating BDNF and corticospinal excitability. HIT-stepper initially showed BDNF responses similar to HIT-treadmill but was no longer significantly different from MCT-treadmill after decreasing the intensity in reaction to two hypotensive events. Additional regression analyses showed that an intensity sufficient to accumulate blood lactate appeared to be important for eliciting BDNF responses, that the interval training approach may have facilitated the corticospinal excitability increases, and that the circulating BDNF response was (negatively) related to intracortical inhibition. These findings further elucidate neurologic mechanisms of aerobic exercise and inform selection of optimal exercise-dosing parameters for enhancing acute neurologic effects. NEW & NOTEWORTHY Acute exercise-related increases in circulating BDNF and corticospinal excitability are thought to prime the brain for learning. Our data suggest that these responses can be obtained among persons with stroke using short-interval treadmill high-intensity interval training, that a vigorous aerobic intensity sufficient to generate lactate accumulation is needed to increase BDNF, that interval training facilitates increases in paretic quadriceps corticospinal excitability, and that greater BDNF response is associated with lesser intracortical inhibition response.

Developing an optimized strategy with transcranial direct current stimulation to enhance the endogenous pain control system in fibromyalgia

INTRODUCTION

Fibromyalgia affects more than 5 million people in the United States and has a detrimental impact on individuals' quality of life. Current pharmacological treatments provide limited benefits to relieve the pain of fibromyalgia, along with a risk of adverse effects; a scenario that explains the increasing interest for multimodal approaches. A tailored strategy to focus on this dysfunctional endogenous pain inhibitory system is transcranial direct current stimulation (tDCS) of the primary motor cortex. By combining tDCS with aerobic exercise, the effects can be optimized. Areas covered: The relevant literature was reviewed and discussed the methodological issues for designing a mechanistic clinical trial to test this combined intervention. Also, we reviewed the neural control of different pathways that integrate the endogenous pain inhibitory system, as well as the effects of tDCS and aerobic exercise both alone and combined. In addition, potential neurophysiological assessments are addressed: conditioned pain modulation, temporal slow pain summation, transcranial magnetic stimulation, and electroencephalography in the context of fibromyalgia. Expert commentary: By understanding the neural mechanisms underlying pain processing and potential optimized interventions in fibromyalgia with higher accuracy, the field has an evident potential of advancement in the direction of new neuromarkers and tailored therapies.

High-intensity exhaustive exercise reduces long-interval intracortical inhibition

The development of fatigue during single-joint isolated muscle contractions is accompanied by an increase in long-interval intracortical inhibition (LICI). However, the effect of whole-body locomotor endurance exercise on LICI is unknown. Eighteen healthy men completed three exercise trials on a cycle ergometer. The first trial was completed to determine the lactate threshold (LT) and maximal oxygen uptake ([Formula: see text]). The remaining two trials (familiarisation and experimental) involved cycling to volitional exhaustion at an intensity equivalent to halfway between the LT and [Formula: see text] (50%Δ). Responses to stimulation of the femoral nerve [motor nerve stimulation (MNS)] and motor cortex [transcranial magnetic stimulation (TMS)] were determined pre- and post-exercise to determine the level of peripheral fatigue [potentiated quadriceps twitch (Q_tw,pot)] and central fatigue [voluntary activation measured by MNS and TMS (VA_MNS and VA_TMS, respectively)]. Corticospinal excitability (motor evoked potentials) and intracortical inhibition [LICI and corticospinal silent period (SP)] were also measured from electromyography recordings on the vastus lateralis. There were exercise-induced reductions in maximal voluntary contraction torque (- 21 ± 10%), Q_tw,pot (- 37 ± 18%), VA_MNS (- 7 ± 7%) and VA_TMS (- 8 ± 10) (all P < 0.01). There were increases in the LICI ratio and reductions in SP duration from pre- to post-exercise (mean absolute change of 16 ± 14% and - 31 ± 28 s, respectively) (both P < 0.01). The pre- and post-exercise MEP amplitudes were not different (P = 0.86). The neural inhibitory circuits that mediate the LICI and SP became less excitable with fatigue following high-intensity exhaustive cycling, which could be important in the aetiology of central fatigue during whole-body locomotor endurance exercise.

Exercise-Induced Neuroplasticity: A Mechanistic Model and Prospects for Promoting Plasticity

Aerobic exercise improves cognitive and motor function by inducing neural changes detected using molecular, cellular, and systems level neuroscience techniques. This review unifies the knowledge gained across various neuroscience techniques to provide a comprehensive profile of the neural mechanisms that mediate exercise-induced neuroplasticity. Using a model of exercise-induced neuroplasticity, this review emphasizes the sequence of neural events that accompany exercise, and ultimately promote changes in human performance. This is achieved by differentiating between neuroplasticity induced by acute versus chronic aerobic exercise. Furthermore, this review emphasizes experimental considerations that influence the opportunity to observe exercise-induced neuroplasticity in humans. These include modifiable factors associated with the exercise intervention and nonmodifiable factors such as biological sex, ovarian hormones, genetic variations, and fitness level. To maximize the beneficial effects of exercise in health, disease, and following injury, future research should continue to explore the mechanisms that mediate exercise-induced neuroplasticity. This review identifies some fundamental gaps in knowledge that may serve to guide future research in this area.

GABA concentration in sensorimotor cortex following high-intensity exercise and relationship to lactate levels

KEY POINTS

Magnetic resonance spectroscopy was conducted before and after high-intensity interval exercise. Sensorimotor cortex GABA concentration increased by 20%. The increase was positively correlated with the increase in blood lactate. There was no change in dorsolateral prefrontal cortex. There were no changes in the glutamate-glutamine-glutathione peak.

ABSTRACT

High-intensity exercise increases the concentration of circulating lactate. Cortical uptake of blood borne lactate increases during and after exercise; however, the potential relationship with changes in the concentration of neurometabolites remains unclear. Although changes in neurometabolite concentration have previously been demonstrated in primary visual cortex after exercise, it remains unknown whether these changes extend to regions such as the sensorimotor cortex (SM) or executive regions such as the dorsolateral prefrontal cortex (DLPFC). In the present study, we explored the acute after-effects of high-intensity interval training (HIIT) on the concentration of gamma-Aminobutyric acid (GABA) and the combined glutamate-glutamine-glutathione (Glx) spectral peak in the SM and DLPFC, as well as the relationship with blood lactate levels. Following HIIT, there was a robust increase in GABA concentration in the SM, as evident across the majority of participants. This change was not observed in the DLPFC. Furthermore, the increase in SM GABA was positively correlated with an increase in blood lactate. There were no changes in Glx concentration in either region. The observed increase in SM GABA concentration implies functional relevance, whereas the correlation with lactate levels may relate to the metabolic fate of exercise-derived lactate that crosses the blood-brain barrier.

Effects of regular aerobic exercise on visual perceptual learning

This study investigated the influence of five days of moderate intensity aerobic exercise on the acquisition and consolidation of visual perceptual learning using a motion direction discrimination (MDD) task. The timing of exercise relative to learning was manipulated by administering exercise either before or after perceptual training. Within a matched-subjects design, twenty-seven healthy participants (n = 9 per group) completed five consecutive days of perceptual training on a MDD task under one of three interventions: no exercise, exercise before the MDD task, or exercise after the MDD task. MDD task accuracy improved in all groups over the five-day period, but there was a trend for impaired learning when exercise was performed before visual perceptual training. MDD task accuracy (mean ± SD) increased in exercise before by 4.5 ± 6.5%; exercise after by 11.8 ± 6.4%; and no exercise by 11.3 ± 7.2%. All intervention groups displayed similar MDD threshold reductions for the trained and untrained motion axes after training. These findings suggest that moderate daily exercise does not enhance the rate of visual perceptual learning for an MDD task or the transfer of learning to an untrained motion axis. Furthermore, exercise performed immediately prior to a visual perceptual learning task may impair learning. Further research with larger groups is required in order to better understand these effects.

Combining aerobic exercise and repetitive transcranial magnetic stimulation to improve brain function in health and disease

The aetiology of various psychiatric and neurological disorders may be partially attributable to impairments in neuroplasticity. Developing novel methods of stimulating neuroplasticity is a promising treatment approach to counterbalance these maladaptive influences and alleviate symptomologies. Two non-pharmacological approaches with significant and direct impacts on neuroplasticity are aerobic exercise and repetitive transcranial magnetic stimulation. Aerobic exercise is associated with the promotion of numerous neurotrophic mechanisms at a molecular and cellular level, which have a broad influence on neuroplasticity. Transcranial magnetic stimulation is a form of non-invasive brain stimulation with the capacity to modulate the synaptic efficacy and connectivity of particular brain networks. This review synthesises extant literature to explore the complementary physiological mechanisms targeted by aerobic exercise and repetitive transcranial magnetic stimulation, and to substantiate the hypothesis that the use of these techniques in tandem may result in synergistic impact on neural mechanisms to achieve a more efficacious therapeutic approach for mental disorders.

Physical activity modulates corticospinal excitability of the lower limb in young and old adults

Aging is associated with reduced neuromuscular function, which may be due in part to altered corticospinal excitability. Regular physical activity (PA) may ameliorate these age-related declines, but the influence of PA on corticospinal excitability is unknown. The purpose of this study was to determine the influence of age, sex, and PA on corticospinal excitability by comparing the stimulus-response curves of motor evoked potentials (MEP) in 28 young (22.4 ± 2.2 yr; 14 women and 14 men) and 50 old adults (70.2 ± 6.1 yr; 22 women and 28 men) who varied in activity levels. Transcranial magnetic stimulation was used to elicit MEPs in the active vastus lateralis muscle (10% maximal voluntary contraction) with 5% increments in stimulator intensity until the maximum MEP amplitude. Stimulus-response curves of MEP amplitudes were fit with a four-parameter sigmoidal curve and the maximal slope calculated (slopemax). Habitual PA was assessed with tri-axial accelerometry and participants categorized into either those meeting the recommended PA guidelines for optimal health benefits (>10,000 steps/day, high-PA; n = 21) or those not meeting the guidelines (<10,000 steps/day, low-PA; n = 41). The MEP amplitudes and slopemax were greater in the low-PA compared with the high-PA group (P < 0.05). Neither age nor sex influenced the stimulus-response curve parameters (P > 0.05), suggesting that habitual PA influenced the excitability of the corticospinal tract projecting to the lower limb similarly in both young and old adults. These findings provide evidence that achieving the recommended PA guidelines for optimal health may mediate its effects on the nervous system by decreasing corticospinal excitability.NEW & NOTEWORTHY Transcranial magnetic stimulation was used to determine whether achieving the recommended 10,000 steps/day for optimal health influenced the excitability of the corticospinal tract projecting to the knee extensor muscles. Irrespective of age and sex, individuals who achieved >10,000 steps/day had lower corticospinal excitability than those who performed <10,000 steps/day, possibly representing greater control of inhibitory and excitatory networks. Physical activity involving >10,000 steps/day may mediate its effects on the nervous system by decreasing corticospinal excitability.

High-intensity Interval Exercise Promotes Motor Cortex Disinhibition and Early Motor Skill Consolidation

Gamma-aminobutyric acid (GABA) inhibition shapes motor cortex output, gates synaptic plasticity in the form of long-term potentiation, and plays an important role in motor learning. Remarkably, recent studies have shown that acute cardiovascular exercise can improve motor memory, but the cortical mechanisms are not completely understood. We investigated whether an acute bout of lower-limb high-intensity interval (HIT) exercise could promote motor memory formation in humans through changes in cortical inhibition within the hand region of the primary motor cortex. We used TMS to assess the input–output relationship, along with inhibition involving GABAA and GABAB receptors. Measures were obtained before and after a 20-min session of HIT cycling (exercise group) or rest (control group). We then had the same participants learn a new visuomotor skill and perform a retention test 5 hr later in the absence of sleep. No differences were found in corticomotor excitability or GABAB inhibition; however, synaptic GABAA inhibition was significantly reduced for the exercise group but not the control group. HIT exercise was found to enhance motor skill consolidation. These findings link modification of GABA to improved motor memory consolidation after HIT exercise and suggest that the beneficial effects of exercise on consolidation might not be dependent on sleep.