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How does the neural control of fine movements develop from childhood to adulthood? Here, we investigated developmental differences in functional corticomuscular connectivity using coherence analyses in 111 individuals from four different age groups covering the age range 8–30 y. EEG and EMG were recorded while participants performed a uni-manual force-tracing task requiring fine control of force in a precision grip with both the dominant and non-dominant hand. Using beamforming methods, we located and reconstructed source activity from EEG data displaying peak coherence with the EMG activity of an intrinsic hand muscle during the task. Coherent cortical sources were found anterior and posterior to the central sulcus in the contralateral hemisphere. Undirected and directed corticomuscular coherence was quantified and compared between age groups. Our results revealed that coherence was greater in adults (20–30 yo) than in children (8–10 yo) and that this difference was driven by greater magnitudes of descending (cortex-to-muscle), rather than ascending (muscle-to-cortex), coherence. We speculate that the age-related differences reflect maturation of corticomuscular networks leading to increased functional connectivity with age. We interpret the greater magnitude of descending oscillatory coupling as reflecting a greater degree of feedforward control in adults compared to children. The findings provide a detailed characterization of differences in functional sensorimotor connectivity for individuals at different stages of typical ontogenetic development that may be related to the maturational refinement of dexterous motor control.

Health and performance impairments provoked by thermal stress are societal challenges geographically spreading and intensifying with global warming. Yet, science may be underestimating the true impact, since no study has evaluated effects of sunlight exposure on human brain temperature and function. Accordingly, performance in cognitively dominated and combined motor-cognitive tasks and markers of rising brainstem temperature were evaluated during exposure to simulated sunlight (equal to ~1000 watt/m 2 ). Acute exposure did not affect any performance measures, whereas prolonged exposure of the head and neck provoked an elevation of the core temperature by 1 °C and significant impairments of cognitively dominated and motor task performances. Importantly, impairments emerged at considerably lower hyperthermia levels compared to previous experiments and to the trials in the presents study without radiant heating of the head. These findings highlight the importance of including the effect of sunlight radiative heating of the head and neck in future scientific evaluations of environmental heat stress impacts and specific protection of the head to minimize detrimental effects.

A central challenge in movement neuroscience is developing methods for non-invasive spatiotemporal imaging of brain activity during natural, whole-body movement. We test the utility of a new brain imaging modality, optically pumped magnetoencephalography (OP-MEG), as an instrument to study the spatiotemporal dynamics of human walking. Specifically, we ask whether known physiological signals can be recovered during discrete steps involving large-scale, whole-body translation. Our findings show that by using OP-MEG, we can image the brain during large-scale, natural movements. We provide proof-of-principle evidence for movement-related changes in beta band activity during stepping vs. standing, which are source-localized to the sensorimotor cortex. This work supports the significant potential of the OP-MEG modality for addressing fundamental questions in human gait research relevant to both the physiological and pathological mechanisms of walking.

Human dexterous motor control improves from childhood to adulthood, but little is known about the changes in cortico-cortical communication that support such ontogenetic refinement of motor skills. To investigate age-related differences in connectivity between cortical regions involved in dexterous control, we analyzed electroencephalographic data from 88 individuals (range 8-30 years) performing a visually guided precision grip task using dynamic causal modelling and parametric empirical Bayes. Our results demonstrate that bidirectional coupling in a canonical ‘grasping network’ is associated with precision grip performance across age groups. We further demonstrate greater backward coupling from higher-order to lower-order sensorimotor regions from late adolescence in addition to differential associations between connectivity strength in a premotor-prefrontal network and motor performance for different age groups. We interpret these findings as reflecting greater use of top-down and executive control processes with development. These results expand our understanding of the cortical mechanisms that support dexterous abilities through development.

Background Multiple sclerosis (MS) is characterized by impairment of physical function that is often linked to neuromuscular and cardiovascular deficits. However, the specific contributions of muscle strength and aerobic capacity to physical function in MS are not fully understood. Objective This study aimed to investigate the independent roles of maximal muscle strength (MVC) and aerobic capacity (VO2peak) on lower extremity physical function, as measured by the 6-minute walk test (6MWT) and five-time sit-to-stand test (5STS) in people with MS (pwMS). Methods In a cross-sectional study, 150 pwMS underwent assessment of VO2peak, maximal voluntary contraction (MVC), and physical function (6MWT and 5STS). Regression analyses were conducted to explore the associations between physiological parameters and physical function. Results MVC and VO2peak were moderately associated with (i.e., explained) 6MWT (R² = 0.40, p < 0.001), yet with VO2peak (β = 7.9, std. β = 0.45, p < 0.001) having a preferential influence compared to MVC (β = 48.2, std. β = 0.26, p < 0.001). MVC and VO2peak were weakly associated with (i.e., explained) 5STS (R² = 0.14, p < 0.001), yet with MVC (β = 0.06, std. β = 0.28, p = 0.004) having a preferential influence compared to VO2peak (β = 0.00, std. β = 0.16, p = 0.101). Conclusion Both maximal muscle strength and aerobic capacity to physical function in pwMS. Maximal muscle strength was preferentially linked to performance in the 5STS test, whereas aerobic capacity was preferentially linked to performance in the 6MWT. These findings support the need for tailored exercise interventions to target specific physiological deficits during MS rehabilitation.

Optimization of motor performance is of importance in daily life, in relation to recovery following injury as well as for elite sports performance. The present study investigated whether transcutaneous spinal direct current stimulation (tsDCS) may enhance voluntary ballistic activation of ankle muscles and descending activation of spinal motor neurons in able‐bodied adults. Forty‐one adults (21 men; 24.0 ± 3.2 years) participated in the study. The effect of tsDCS on ballistic motor performance and plantar flexor muscle activation was assessed in a double‐blinded sham‐controlled cross‐over experiment. In separate experiments, the underlying changes in excitability of corticospinal and spinal pathways were probed by evaluating soleus (SOL) motor evoked potentials (MEPs) following single‐pulse transcranial magnetic stimulation (TMS) over the primary motor cortex, SOL H‐reflexes elicited by tibial nerve stimulation and TMS‐conditioning of SOL H‐reflexes. Measures were obtained before and after cathodal tsDCS over the thoracic spine (T11‐T12) for 10 min at 2.5 mA. We found that cathodal tsDCS transiently facilitated peak acceleration in the ballistic motor task compared to sham tsDCS. Following tsDCS, SOL MEPs were increased without changes in H‐reflex amplitudes. The short‐latency facilitation of the H‐reflex by subthreshold TMS, which is assumed to be mediated by the fast conducting monosynaptic corticomotoneuronal pathway, was also enhanced by tsDCS. We argue that tsDCS briefly facilitates voluntary motor output by increasing descending drive from corticospinal neurones to spinal plantar flexor motor neurons. tsDCS can thus transiently promote within‐session CNS function and voluntary motor output and holds potential as a technique in the rehabilitation of motor function following central nervous lesions. We aimed to investigate the effects of transcutaneous spinal direct current stimulation (tsDCS) on descending activation of spinal motor neurons in healthy adults. Cathodal tsDCS facilitated peak torque and acceleration of a ballistic motor task and increased both the motor evoked potentials of the soleus, and the short‐latency facilitation of the soleus H‐reflex. Therefore, we argue that tsDCS may be a useful technique for facilitating descending drive and promoting motor function following central nervous lesions.

The use of touch screens, which require a high level of manual dexterity, has exploded since the development of smartphone and tablet technology. Manual dexterity relies on effective corticospinal control of finger muscles, and we therefore hypothesized that corticospinal drive to finger muscles can be optimized by tablet‐based motor practice. To investigate this, sixteen able‐bodied females practiced a tablet‐based game (3 × 10 min) with their nondominant hand requiring incrementally fast and precise pinching movements involving the thumb and index fingers. The study was designed as a semirandomized crossover study where the participants attended one practice‐ and one control session. Before and after each session electrophysiological recordings were obtained during three blocks of 50 precision pinch movements in a standardized setup resembling the practiced task. Data recorded during movements included electroencephalographic (EEG) activity from primary motor cortex and electromyographic (EMG) activity from first dorsal interosseous (FDI) and abductor pollicis brevis (APB) muscles. Changes in the corticospinal drive were evaluated from coupling in the frequency domain (coherence) between EEG–EMG and EMG–EMG activity. Following motor practice performance improved significantly and a significant increase in EEG‐EMGAPB and EMGAPB‐EMGFDI coherence in the beta band (15–30 Hz) was observed. No changes were observed after the control session. Our results show that tablet‐based motor practice is associated with changes in the common corticospinal drive to spinal motoneurons involved in manual dexterity. Tablet‐based motor practice may be a motivating training tool for stroke patients who struggle with loss of dexterity. Operation of touch screen devices requires manual dexterity that relies on effective corticospinal control of the finger muscles. Here we demonstrate that 30 minutes of tablet‐based motor practice with a specialized application improves performance and is accompanied by changes in the central nervous system, that is, in the coupling between the motor cortex and the spinal level that is the α‐motoneuronal activity.

Regular physical activity has a positive impact on cognition and brain function. Here we investigated if a single bout of exercise can improve motor memory and motor skill learning. We also explored if the timing of the exercise bout in relation to the timing of practice has any impact on the acquisition and retention of a motor skill. Forty-eight young subjects were randomly allocated into three groups, which practiced a visuomotor accuracy-tracking task either before or after a bout of intense cycling or after rest. Motor skill acquisition was assessed during practice and retention was measured 1 hour, 24 hours and 7 days after practice. Differences among groups in the rate of motor skill acquisition were not significant. In contrast, both exercise groups showed a significantly better retention of the motor skill 24 hours and 7 days after practice. Furthermore, compared to the subjects that exercised before practice, the subjects that exercised after practice showed a better retention of the motor skill 7 days after practice. These findings indicate that one bout of intense exercise performed immediately before or after practicing a motor task is sufficient to improve the long-term retention of a motor skill. The positive effects of acute exercise on motor memory are maximized when exercise is performed immediately after practice, during the early stages of memory consolidation. Thus, the timing of exercise in relation to practice is possibly an important factor regulating the effects of acute exercise on long-term motor memory.

•We studied how motor skill learning affects CNS communication across development.•Performance and coherence were assessed in participants (8–30y) pre/post motor practice.•Performance and coherence increased most in 16–18y and 20–30y.•Control experiments suggested that changes were related to motor practice.•Network adaptations accompanied by motor practice are age dependent. Learning a new motor skill relies on functional reorganization of the human central nervous system (CNS). Plasticity may shape the transmission and communication between cortical regions and between cortical and spinal networks involved in sensorimotor control, but little is known about the influence of age on these adaptations. In a series of experiments, we investigated whether changes in cortical and corticospinal functional connectivity following motor practice differ among individuals at different stages of development (age range 8–30 years old). One hundred and one individuals practiced a visuomotor tracking task in a single experimental session. Functional cortico-cortical and cortico-muscular connectivity were quantified before and after motor training using non-zero lagged coherence estimated from source-reconstructed electroencephalographic (EEG) and electromyographic (EMG) time series. For cortico-cortical coherence, the focus was on sources in a pre-specified cortical network consistently implicated in motor learning. For cortico-muscular coherence, analyses were restricted to the contralateral primary motor cortex. The results showed that upregulation of connectivity in cortical and corticospinal networks, and improvements in motor performance following practice were more pronounced in adults compared to children. Control experiments demonstrated that these changes were dependent on motor practice rather than extended use and on changes in motor performance rather than absolute performance levels. We propose that the reported age-related differences reflect that the mature CNS is tuned to engage in adaptive processes, leading to increased sensorimotor connectivity and improvements in skilled performance during early motor learning. Our results contribute to a better understanding of age-related differences in the network adaptations underlying successful skill learning during human development.

Motor learning relies on experience-dependent plasticity in relevant neural circuits. In four experiments, we provide initial evidence and a double-blinded, sham-controlled replication (Experiment I-II) demonstrating that motor learning involving ballistic index finger movements is improved by preceding paired corticospinal-motoneuronal stimulation (PCMS), a human model for exogenous induction of spike-timing-dependent plasticity. Behavioral effects of PCMS targeting corticomotoneuronal (CM) synapses are order- and timing-specific and partially bidirectional (Experiment III). PCMS with a 2 ms inter-arrival interval at CM-synapses enhances learning and increases corticospinal excitability compared to control protocols. Unpaired stimulations did not increase corticospinal excitability (Experiment IV). Our findings demonstrate that non-invasively induced plasticity interacts positively with experience-dependent plasticity to promote motor learning. The effects of PCMS on motor learning approximate Hebbian learning rules, while the effects on corticospinal excitability demonstrate timing-specificity but not bidirectionality. These findings offer a mechanistic rationale to enhance motor practice effects by priming sensorimotor training with individualized PCMS. Whether paired corticospinal-motoneuronal stimulation (PCMS)-protocols can promote motor learning and how PCMS protocols interact with mechanisms of experience-dependent plasticity is not fully understood. Here authors show that non-invasively induced plasticity targeting corticomotoneuronal synapses promotes motor learning by interacting positively with experience-dependent plasticity.