Cortical processing during table tennis - an fNIRS study in experts and novices.

Among the many factors that determine top athletic performance, little is known about the contribution of the brain. With the present study, we aimed to uncover aspects of this role by examining modulatory differences in brain processing as a function of expertise and task complexity in table tennis. For this purpose, 28 right-handed volunteers (14 experts and 14 novices) performed two table tennis strokes in a standardized manner. Hemodynamic response alterations reflecting neuronal activation were recorded during task execution using functional near-infrared spectroscopy (fNIRS) and analyzed within and between groups. Our results showed localized activation patterns in motor areas (primary motor cortex (M1), premotor cortex (PMC), and inferior parietal cortex (IPC)) for experts and novices. Compared to novices, experts completed more table tennis strokes and showed a significant increase in hemodynamic response alterations in channels corresponding to motor areas. Furthermore, we found significant correlations between the number of strokes and hemodynamic response magnitudes in individual channels of M1, PMC, and IPC. Taken together, our findings show that table tennis performance is accompanied by extensive activation of M1, PMC, and IPC. Furthermore, the observed difference in behavioral performance between experts and novices was associated with increased activation in M1, PMC, and IPC. We postulate that these differences in brain processing between experts and novices potentially imply modulatory distinctions related to increased movement speed or frequency but may also reflect an increased task familiarity of the experts.

Intermuscular coherence between homologous muscles during dynamic and static movement periods of bipedal squatting.

Coordination of functionally coupled muscles is a key aspect of movement execution. Demands on coordinative control increase with the number of involved muscles and joints, as well as with differing movement periods within a given motor sequence. While previous research has provided evidence concerning inter- and intramuscular synchrony in isolated movements, compound movements remain largely unexplored. With this study, we aimed to uncover neural mechanisms of bilateral coordination through intermuscular coherence (IMC) analyses between principal homologous muscles during bipedal squatting (BpS) at multiple frequency bands (alpha, beta, and gamma). For this purpose, participants performed bipedal squats without additional load, which were divided into three distinct movement periods (eccentric, isometric, and concentric). Surface electromyography (EMG) was recorded from four homologous muscle pairs representing prime movers during bipedal squatting. We provide novel evidence that IMC magnitudes differ between movement periods in beta and gamma bands, as well as between homologous muscle pairs across all frequency bands. IMC was greater in the muscle pairs involved in postural and bipedal stability compared with those involved in muscular force during BpS. Furthermore, beta and gamma IMC magnitudes were highest during eccentric movement periods, whereas we did not find movement-related modulations for alpha IMC magnitudes. This finding thus indicates increased integration of afferent information during eccentric movement periods. Collectively, our results shed light on intermuscular synchronization during bipedal squatting, as we provide evidence that central nervous processing of bilateral intermuscular functioning is achieved through task-dependent modulations of common neural input to homologous muscles.NEW & NOTEWORTHY It is largely unexplored how the central nervous system achieves coordination of homologous muscles of the upper and lower body within a compound whole body movement, and to what extent this neural drive is modulated between different movement periods and muscles. Using intermuscular coherence analysis, we show that homologous muscle functions are mediated through common oscillatory input that extends over alpha, beta, and gamma frequencies with different synchronization patterns at different movement periods.

Cerebellar Transcranial Direct Current Stimulation Improves Maximum Isometric Force Production during Isometric Barbell Squats.

Maximum contraction force (MVC) is an important predictor of athletic performance as well as physical fitness throughout life. Many everyday life activities involve multi-joint or whole-body movements that are determined in part through optimized muscle strength. Transcranial direct current stimulation (tDCS) has been reported to enhance muscle strength parameters in single-joint movements after its application to motor cortical areas, although tDCS effects on MIVC in compound movements remain to be investigated. Here, we tested whether anodal tDCS and/or sham stimulation over primary motor cortex (M1) and cerebellum (CB) improves maximum isometric contraction force (MIVC) during isometric barbell squats (iBS). Our results provide novel evidence that CB stimulation enhances MIVC during iBS. Although this indicates that parameters relating to muscle strength can be modulated through anodal tDCS of the cerebellum, our results serve as an initial reference point and need to be extended. Therefore, further studies are necessary to expand knowledge in this area of research through the inclusion of different tDCS paradigms, for example investigating dynamic barbell squats, as well as testing other whole-body movements.

Corticomuscular interactions during different movement periods in a multi-joint compound movement.

While much is known about motor control during simple movements, corticomuscular communication profiles during compound movement control remain largely unexplored. Here, we aimed at examining frequency band related interactions between brain and muscles during different movement periods of a bipedal squat (BpS) task utilizing regression corticomuscular coherence (rCMC), as well as partial directed coherence (PDC) analyses. Participants performed 40 squats, divided into three successive movement periods (Eccentric (ECC), Isometric (ISO) and Concentric (CON)) in a standardized manner. EEG was recorded from 32 channels specifically-tailored to cover bilateral sensorimotor areas while bilateral EMG was recorded from four main muscles of BpS. We found both significant CMC and PDC (in beta and gamma bands) during BpS execution, where CMC was significantly elevated during ECC and CON when compared to ISO. Further, the dominant direction of information flow (DIF) was most prominent in EEG-EMG direction for CON and EMG-EEG direction for ECC. Collectively, we provide novel evidence that motor control during BpS is potentially achieved through central motor commands driven by a combination of directed inputs spanning across multiple frequency bands. These results serve as an important step toward a better understanding of brain-muscle relationships during multi joint compound movements.

Structural connectivity prior to whole-body sensorimotor skill learning associates with changes in resting state functional connectivity.

Changes in resting state functional connectivity are induced by sensorimotor training and assumed to be concomitant of motor learning, although a potential relationship between functional and structural connectivity associated with sensorimotor sequence learning remains elusive. To investigate whether initial structural connectivity relates to changes in functional connectivity, we evaluated resting state functional connectivity (rs-FC), white matter fibre density (FD), fibre-bundle cross-section (FC), and gray matter volume (GMV) in healthy human participants before and after two days of performing a complex whole-body serial reaction time task (CWB-SRTT). As CWB-SRTT was implicit, participants were not told about the presence of any sequence. Since the lateral prefrontal cortex (PFC) plays an important role in sequence learning, we hypothesized that structural connectivity within the PFC prior to learning is associated with changes in rs-FC involving the lateral PFC. Sequence specific improvements, as assessed by the time difference between the last random and the last sequence blocks, were observed for reaction times, suggesting that sensorimotor sequence memory was acquired. Rs-FC between the right lateral PFC and bilateral striatum increased significantly in the learning group, when compared to a control group who performed only random blocks. This indicated that rs-FC changes are related to sequence memory but not to exercise itself. In addition, changes in rs-FC between the right lateral PFC and the left striatum were correlated with sequence specific improvements in individual reaction times. Furthermore, changes in rs-FC between right lateral PFC and left striatum were positively correlated with FC in the right anterior corona radiata measured before the task. We did not find any structural changes or significant correlations in FD or GMV. These findings suggest that an early phase of sensorimotor sequence learning in complex whole-body movements is associated with an increase in rs-FC between prefrontal and subcortical regions. Furthermore, we provide novel evidence that CWB-SRTT-induced changes in rs-FC were correlated with FC within the PFC.

Inverse relationship between amplitude and latency of physiological mirror activity during repetitive isometric contractions.

Mirror Activity (MA) is a phenomenon that is characterized by involuntarily occurring muscular activity in homologous contralateral limbs during unilateral movements. Even in neurologically healthy humans, MA of a small extent has been described, which does not directly lead to visible movements, but nonetheless, it is still detectable with surface electromyography (EMG) and therefore defined as physiological MA (pMA). The present study investigated latency- and amplitude-characteristics of pMA during repetitive unimanual isometric contractions with high but constant force requirements (80% maximum force). Here, we show for the first time that pMA is not time-locked to the muscle onset of voluntarily contracting hand muscles but starts with varying and dynamically changing latencies. Following consecutive isometric unilateral contractions, the latency of pMA progressively decreases accompanied by a progressive linear increase in its amplitude possibly as a result of changes in inhibitory mechanisms involved in suppressing involuntarily occurring muscular activity. Overall, the latency and amplitude of pMA show a strong inverse relationship. Furthermore, based on the previously proposed hypothesis of motor overflow, we explored the possibility of pMA modulation through anodal and cathodal transcranial direct current stimulation (tDCS) applied to the ipsilateral primary motor cortex (M1), relative to a voluntarily contracting hand. Neither anodal nor cathodal tDCS is able to modulate amplitude or latency of pMA compared to sham tDCS. In conclusion, our results extend the existing knowledge of pMA occurring due to high-effort unilateral contractions with constant force requirements to the aspect of its latency and the inverse association with its amplitude.