•Changes in H-reflexes between anticipatory conditions imply that spinal-level preparatory setting is perturbation-specific.•SICI was reduced before perturbations compared to static standing.•The ...cortically mediated LLR in anticipated perturbations was different to the LLR in non-anticipated perturbations.
Little is known about how the central nervous system prepares postural responses differently in anticipated compared to non-anticipated perturbations. To investigate this, participants were exposed to translational and rotational perturbations presented in a blocked (anticipated) and a random (non-anticipated) design. The preparatory setting (‘central set’) was measured by H-reflexes, motor-evoked potentials (MEPs), and short-interval intracortical inhibition (SICI) shortly before perturbation onset in the soleus of 15 healthy adults. Additionally, the behavioral consequences of differential preparatory settings were analyzed by comparing the short- (SLR), medium- (MLR), and long-latency response (LLR) of the soleus after anticipated and non-anticipated rotations and translations. H-reflexes elicited before perturbation were different between conditions (p=0.023) with larger amplitudes in anticipated translations compared to anticipated rotations (37.0%; p=0.048). Reduced SICI was found in the three conditions containing perturbations compared to static standing (p<0.001). Muscular responses assessed after perturbations remained unchanged for the SLR and MLR, whereas the LLR was decreased in anticipated rotations (−36.2%; p=0.002) and increased in anticipated translations (16.7%; p=0.046) compared to the corresponding non-anticipated perturbation. As the SLR and MLR are organized at the spinal and the LLR at the cortical level, the preparatory setting seems to mainly influence cortically mediated postural responses. However, the modulation of the H-reflex before anticipated perturbations indicates that supraspinal centers adjusted Ia-afferent transmission for the soleus in a perturbation-specific manner. Intracortical inhibition was also modulated but differentiates to a lesser extent only between perturbation conditions and unperturbed stance.
The aim of the present study was to compare the effects of countermovement jump (CMJ) and drop jump (DJ) training on the volleyball-specific jumping ability of non-professional female volleyball ...players. For that purpose, 26 female volleyball players (15-32 years) were assigned to either a CMJ (20.4 ± 3.1 years, 171.0 ± 3.0 cm) or a DJ training group (22.0 ± 4.4 years, 168.2 ± 5.0 cm), which performed a six-week jump training (two sessions per week, 60 jumps per session). Each group performed 20% of the jumps in the jump type of the other group in order to minimize the influence of enhanced motor coordination on the differences between groups regarding the improvements of jump performance. Before and after the training, jump height was assessed in four jump types, including the trained and volleyball-specific jump types. Although both training forms substantially improved jump height, the CMJ training was significantly more effective in all jump types (17 vs. 7% on average;
< 0.001). This suggests that, at least for non-professional female volleyball players and a training duration of six weeks, training with a high percentage of CMJs is more effective than one with a high percentage of DJs. We hypothesize that this might be related to the slower stretch-shortening cycle during CMJs, which seems to be more specific for these players and tasks. These findings should support volleyball coaches in designing optimal jump trainings.
Augmented feedback (aF) positively influences motor performance by enhancing motivation and/or by providing information about task execution. It was speculated that aF-induced performance increments ...that rely on motivation should also occur when providing incorrect aF, while performance increments that rely on guidance towards "successful executions" (i.e. improved performances) should only occur when aF is correct. We further hypothesised that the informational content of aF is more important in more complex motor tasks. Thus, 32 participants received two forms of aF (correct, incorrect) during maximal voluntary contractions (MVC's; maximise force without time constraints; less complex) and maximal explosive contractions (MEC's; maximise force in the shortest possible way; more complex) of the knee extensors. Peak torque (MVC), peak rate of torque development (MEC) and EMG signals of rectus femoris (RF) and vastus lateralis were recorded. Correct and incorrect aF significantly enhanced MVC performance, indicating that performance improvements resulted mainly from the motivational property of aF. The observed trend towards increased RF muscle activity supports this conclusion. In contrast, while correct aF positively impacted MEC performance, incorrect aF had a negative influence. This indicates that the informational property of aF guided participants towards movement executions resulting in improved (correct aF) or decreased (incorrect aF) performances. The observed simultaneous decrease in muscle activity suggests that participants changed motor strategy, supporting the guiding role of aF. Our results demonstrate that the motivational aspect of aF dominates in maximal tasks with lower complexity (MVC), while the informational aspect is used during more complex maximal tasks (MEC).
Augmented feedback (aF) can influence performance by enhancing the motivation and/or by providing information about the execution of a task.
Our results demonstrate that over the short-term, the motivational aspect of aF dominates in maximal tasks with lower complexity (maximal voluntary contractions). In contrast, the informational aspect will predominantly be used during more complex maximal tasks (maximal explosive contractions).
This is the first study distinguishing between the motivational and informational aspects of aF during maximal motor tasks. Future research should focus on the long-term effects of these two separate aspects of aF.
Introduction
The evidence for changes in intracortical inhibition when executing two tasks simultaneously (i.e., dual tasking) is ambiguous as decreased (Corp et al., 2014) and increased (Corp et ...al., 2016) inhibition were reported. One way to bring more light into this question is to tests the effect of a single task training (STT) and a dual task training (DTT) on the short interval intracortical inhibition (SICI) during a single balancing task and two different dual tasks in healthy young adults.
Methods
Twenty-nine healthy young adults were randomly separated into two groups participating in STT (n = 15) or DTT (n = 14) consisting of 6 training sessions within 3 weeks. Before and after the training, a single task (balancing on a rocker board) was performed at two resistance levels (easy and hard). Additionally to the single task, either a cognitive (2-back number recall) or a motor (balancing a ball on a hand-held tray) dual task was executed simultaneously. During execution of these three tasks, SICI was measured with transcranial magnetic stimulation over the motor cortical area representing the right tibialis anterior.
Results
Training improvements in balance performance were group and task-specific over time (p = .018). While the STT group improved more in the single balance task (12.3% vs. 6.6% DTT), the DTT group had more sway reductions in the motor dual task condition (13.7% vs. 4.5% STT). Similar statistical outcome (p = .034) was observed for the dual task costs (DTC). There was a tendence for SICI (p = .075), mainly indicating higher increase in SICI for the DTT group in the motor dual task (16.0% vs. 5.8% STT). During the execution of the single balance task, the group-specific adaptations in SICI were less pronounced (13.7% DTT vs. 16.2% STT). When analyzing the SICI dual task difference (Δ) from single to dual task, SICI is altered group and task specific (p = .011). The DTT group could increase the dual task difference in SICI in the dual motor condition (Δ 3.2%), whereas the STT group had a decrease (Δ -9.6%).
Discussion/Conclusion
The results of this study show that DTT causes gains in balance performance and increases in SICI when the secondary task is also a motor task, but not when the second task is a cognitive one. STT is particularly beneficial in the single task. It is therefore assumed that intracortical inhibition is important during the simultaneous performance of two motor tasks, while intracortical inhibition was not modulated in a group-specific manner by the additional cognitive task.
References
Corp, D. T., Lum, J. A. G., Tooley, G. A., & Pearce, A. J. (2014). Corticospinal activity during dual tasking: A systematic review and meta-analysis of TMS literature from 1995 to 2013. Neuroscience & Biobehavioral Reviews, 43, 74-87. https://doi.org/10.1016/j.neubiorev.2014.03.017
Corp, D. T., Rogers, M. A., Youssef, G. J., & Pearce, A. J. (2016). The effect of dual-task difficulty on the inhibition of the motor cortex. Experimental Brain Research, 234, 443-452. https://doi.org/10.1007/s00221-015-4479-2
Introduction
Recent findings have demonstrated that low-frequency repetitive magnetic stimulations (rTMS) over the primary motor cortex (M1) impaired short-term consolidation of a balance task, ...underscoring the causal connection between M1 and the consolidation of balancing skills (Egger et al., 2023). However, the underlying neural mechanisms induced by rTMS and whether these adaptations endure over an extended period, encompassing multiple acquisition sessions, remain insufficiently elucidated (Censor & Cohen, 2011). So far, its is widely acknowledged that GABAergic processes play an important role for consolidation (Sanes & Donoghue, 2000), at the same time, are affected by learning balance skills (Mouthon & Taube, 2019; Taube et al., 2020). Therefore, the present study aimed to investigate the impact of rTMS on GABA-mediated short-interval intracortical inhibition (SICI) and to explore the role of M1 in the long-term consolidation of a balance task (i.e., across multiple acquisition sessions).
Methods
Thirty-one volunteers underwent six balance acquisition sessions on a rocker-board, each followed by either rTMS or sham rTMS based on group affiliation. During the first and last training session, SICI was measured twice; before the balance acquisition and after the application of rTMS or sham-rTMS to investigate potential short- and long-term adaptations in intracortical inhibition. Adaptations were assessed during the execution of the learned balance task and in a non-learning postural control task (i.e., stable upright stance).
Results
Regardless of group affiliation, all participants achieved comparable improvements within the balance acquisition sessions. However, consolidation varied between groups. In particular, between the third and the fourth acquisition session, as Tukey corrected post-hoc tests showed a significant decline in performance for the rTMS group (p = 0.006). Both short- (p = 0.014) and long-term (p = 0.038) adaptations in SICI were affected by rTMS: while the sham rTMS group upregulated SICI, rTMS led to reduced levels of inhibition. No neurophysiological effects were observed in the non-learning control task (upright stance).
Discussion/Conclusion
The interfering effect of rTMS on balance consolidation and on upregulation of SICI indicates that increased intracortical inhibition is an important mechanism to protect and engrave newly acquired motor memory. Importantly, adaptations in SICI were only apparent during the execution of the learned task.
References
Censor, N., & Cohen, L. G. (2011). Using repetitive transcranial magnetic stimulation to study the underlying neural mechanisms of human motor learning and memory. The Journal of Physiology, 589(1), 21-28. https://doi.org/10.1113/jphysiol.2010.198077
Egger, S., Wälchli, M., Rüeger, E., & Taube, W. (2023). Short-term balance consolidation relies on the primary motor cortex: A rTMS study. Scientific Reports, 13, Article 5169. https://doi.org/10.1038/s41598-023-32065-x
Mouthon, A., & Taube, W. (2019). Intracortical inhibition increases during postural task execution in response to balance training. Neuroscience, 401, 35-42. https://doi.org/10.1016/j.neuroscience.2019.01.007
Sanes, J. N., & Donoghue, J. P. (2000). Plasticity and primary motor cortex. Annual Review of Neuroscience, 23, 393-415. https://doi.org/10.1146/annurev.neuro.23.1.393
Taube, W., Gollhofer, A., & Lauber, B. (2020). Training-, muscle- and task-specific up- and downregulation of cortical inhibitory processes. The European Journal of Neuroscience, 51(6), 1428-1440. https://doi.org/10.1111/ejn.14538
Different approaches like providing augmented feedback (aF), applying an external focus of attention (EF), or rewarding participants with money (RE) have been shown to instantly enhance motor ...performance. So far, these approaches have been tested either in separate studies or directly against each other. However, there is no study that combined aF, EF, and/or RE to test whether this provokes additional benefits. The aim of the present study was therefore to identify the most powerful combination.
Eighteen participants performed maximal countermovement jumps in six different conditions: neutral (NE), aF, RE, aF + EF, aF + RE, and aF + EF + RE.
Participants demonstrated the highest jump heights with aF + EF, followed by aF + EF + RE, aF + RE, aF, RE, and finally, NE. Activity of the M. rectus femoris differed significantly between conditions resulting in lower muscular activity in aF + EF and aF + EF + RE compared with NE. All other parameters, such as ground reaction forces and joint angles, were comparable across conditions.
This is the first study showing superior performance when combining aF with EF. As reduced muscular activity was found only in conditions with EF, it is argued in line with the constrained action hypothesis that adopting an EF improves movement efficiency. In contrast, aF seems to rather enhance (intrinsic) motivation. However, monetary reward did not further amplify performance.
•Old (12.0 years) outperformed young children (6.7 years) in perturbed postural responses.•Balance training improved postural responses to external perturbations.•Trained old children improved more ...in anticipated than non-anticipated situations.
Postural control undergoes rapid changes during child development. However, the influence of balance training (BT) on the compensation of perturbations has not yet been investigated in children. For this purpose, young (6.7 ± 0.6 years) and old children (12.0 ± 0.4 years) were exposed to externally induced anticipated (direction known) and non-anticipated (direction unknown) perturbations on a free swinging platform before and after either child-oriented BT (INT; young: n = 12, old: n = 18) or regular physical education (CON; young: n = 9, old: n = 9). At baseline, old children exhibited less platform sway after perturbations than young children (p = .004; η2p = 0.17). However, no differences were found between anticipated and non-anticipated perturbations. After training, INT reduced the platform sway path while CON remained stable (−11.1% vs. +2.7%; p < .001; η2p = 0.26). Furthermore, the young INT group adapted statistically similarly in anticipated and non-anticipated situations (−7.9% vs. −12.6%; p = .556; r = 0.33), whereas the old INT group tended to improve more in anticipated perturbations (−15.1% vs. −8.2%; p = .052; r = 0.51). Thus, the maturity of the postural system seems to influence the extent of training adaptations in anticipated perturbations. Furthermore, this study provides evidence that BT can improve postural responses to external perturbations in children and may represent a useful intervention to prevent falls.
While the positive effect of balance training on age-related impairments in postural stability is well-documented, the neural correlates of such training adaptations in older adults remain poorly ...understood. This study therefore aimed to shed more light on neural adaptations in response to balance training in older adults.
Postural stability as well as spinal reflex and cortical excitability was measured in older adults (65-80 years) before and after 5 weeks of balance training (n = 15) or habitual activity (n = 13). Postural stability was assessed during one- and two-legged quiet standing on a force plate (static task) and a free-swinging platform (dynamic task). The total sway path was calculated for all tasks. Additionally, the number of errors was counted for the one-legged tasks. To investigate changes in spinal reflex excitability, the H-reflex was assessed in the soleus muscle during quiet upright stance. Cortical excitability was assessed during an antero-posterior perturbation by conditioning the H-reflex with single-pulse transcranial magnetic stimulation.
A significant training effect in favor of the training group was found for the number of errors conducted during one-legged standing (p = .050 for the static and p = .042 for the dynamic task) but not for the sway parameters in any task. In contrast, no significant effect was found for cortical excitability (p = 0.703). For spinal excitability, an effect of session (p < .001) as well as an interaction of session and group (p = .009) was found; however, these effects were mainly due to a reduced excitability in the control group.
In line with previous results, older adults' postural stability was improved after balance training. However, these improvements were not accompanied by significant neural adaptations. Since almost identical studies in young adults found significant behavioral and neural adaptations after four weeks of training, we assume that age has an influence on the time course of such adaptations to balance training and/or the ability to transfer them from a trained to an untrained task.
The target of rapamycin (TOR), discovered 30 years ago, is a highly conserved serine/threonine protein kinase that plays a central role in regulating cell growth and metabolism. It is activated by ...nutrients, growth factors, and cellular energy. TOR forms two structurally and functionally distinct complexes, TORC1 and TORC2. TOR signaling activates cell growth, defined as an increase in biomass, by stimulating anabolic metabolism while inhibiting catabolic processes. With emphasis on mammalian TOR (mTOR), we comprehensively reviewed the literature and identified all reported direct substrates. In the context of recent structural information, we discuss how mTORC1 and mTORC2, despite having a common catalytic subunit, phosphorylate distinct substrates. We conclude that the two complexes recruit different substrates to phosphorylate a common, minimal motif.
mTOR is a central growth regulatory kinase whose function has been intensively studied, revealing a bevy of downstream effects, many of which are indirect. Here, Hall and colleagues discern which targets are validated direct substrates of its two complexes, mTORC1 and mTORC2, and propose a target motif.
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