Modeling motor learning in juggling: A Bayesian approach.

Motor learning is defined as the series of processes by which the performance of a task or skill is learned and refined through plastic reorganization within the nervous system. Although many studies have focused on deciphering the motor learning mechanisms within supraspinal structures, recent investigations have placed greater emphasis on understanding plastic responses at the spinal cord. The findings from these studies appear to suggest that reorganization at the spinal cord level is a unique response to skilled performance tasks as opposed to general motor activities and that the efficacy with which specificity is transferred may rely on a time component influenced by sleep or subsequent training sessions. In a recent study published in The Journal of Physiology, Giboin et al. (2020) further expand the motor learning literature by examining how the skill requirements of a balance task influence plastic changes at the spinal cord immediately and 24 h after practising the skill. Giboin et al. (2020) utilized a series of skill-graded balance performance tasks (i.e. sitting, unilateral standing, tilt board) to examine spinal cord plasticity via the Hoffmann reflex (H-reflex) amplitude relative to the M-wave of the soleus muscle. Eighteen healthy adults (10 women, eight men) underwent two assessment sessions separated by 24 h. During the first session, participants were tasked with learning how to perform a unilateral stance on a tilt board. Prior to practising the tilt board task (pre-acquisition), H-reflex amplitude was measured at rest, when standing unilaterally on the floor, and then when performing the tilt board task. Time to failure for the tilt board task was also assessed as a performance measure. Participants were then given 60 trials to practice the tilt board before H-reflex amplitude and performance were assessed across all three conditions again (post-acquisition). A second testing session, conducted 24 h later, was used to assess skill retention and determine any temporal effects of the skill acquisition (retention). Immediately following the skill acquisition session, H-reflex amplitude was decreased at rest. Interestingly, a similar decrease in H-reflex amplitude was observed during retention, but only during the tilt board task, despite no observed changes in performance from post-acquisition to retention. This provides compelling evidence that the plastic reorganization occurring within the spinal cord structures following skill training is probably both task- and time-dependent. This recent work by Giboin et al. (2020) brings to light several critical points for future investigations and interventions regarding motor learning. The findings of their study suggest that learning occurred at the motor neuron or spinal level as indicated by a down-regulation in H-reflex amplitude, potentially indicating a shift from a feedback-based motor command to feedforward. However, some issues regarding the validity of the H-reflex as a measure of plasticity at the spinal cord level are noted. Specifically, it was addressed that the H-reflex may not necessarily be indicative of plastic changes that occur exclusively at the spinal cord level and may reflect plastic changes that instead occur at supraspinal levels. Although it may be reasonable to hypothesize that changes in H-reflex amplitude observed at rest immediately after task acquisition may represent some short-term changes in plasticity at the spinal level, it may be argued that any conclusions drawn from these findings should be done so with caution. Prior studies have identified some limitations of the H-reflex. One such limitation is that the H-reflex is an electrically induced reflex that does not occur naturally in the human body, making it difficult to draw widely generalizable conclusions regarding dynamic muscle activity. Another limitation identified by prior studies is that the H-reflex may not accurately reflect motor neuron excitability considering synaptic connections between afferent and motor neurons may be subject to presynaptic modification. These limitations point towards the need for future research further investigating the validity of the H-reflex as an independent measure of plasticity at the spinal cord level. The decision by Giboin et al. (2020) to use a Bayesian linear mixed model in this investigation is prudent. When analysing data such as H-reflex amplitude, the inherent between-trial variability can present challenges determining where physiological phenomena actually occur. Linear mixed models will account for the high variability of the H-reflex and a Bayesian analysis will allow greater opportunity to discuss the credibility of results than frequentists statistics. The results of this analysis showed that H-reflex amplitude was higher during pre-acquisition than at retention with a strong evidence ratio during the tilt board task. Pre-acquisition H-reflex amplitude was also higher than post-acquisition but not retention during rest. This is interesting because there was an increase in performance from pre- to post-acquisition for the balance board task, yet no correlations were found between performance increases and changes in the H-reflex amplitude. To attempt to isolate H-reflex adaptations as a result of neural plasticity, Giboin et al. (2020) recorded M-wave and background electromyography (EMG) values. Background EMG values were higher during the floor and tilt board task than at rest, which is expected as a result of the increased muscle activity that occurs during task performance. Overall, the statistical approach used in this intervention was creative and appropriate. Bayesian approaches may prove to be an advantageous means of analysis in the fields of physiology or exercise science. Although no changes in performance on the tilt board task were observed, the decreased H-reflex amplitude during the balance task corresponds to a body of literature suggesting that motor learning and neuromuscular control is task-specific. The importance of task-specificity with respect to balance tasks has previously been emphasized by this group, reporting that slack-line training results in improved task-specific performance and neuromuscular control, without any improvements in general balance performance (Giboin et al. 2018; Ringhof et al. 2019). These findings may be clinically useful, especially in adults and children with neurological pathologies. Task-specific balance exercises, individualized to each patient's needs, may have more positive effects than general balance exercises on activities of daily living for post-stroke adults and children with neurological developmental disorders that affect coordination (Veerbeek et al. 2014). Task-specificity is also relevant in the context of strength-training adaptations and transferability. Among resistance-trained men, unstable variations of the chest-press exercise involving either dumbbells on a bench or a loaded barbell on a swiss ball resulted in greater task-specific strength gains compared to a stable variation of the chest-press using a Smith machine on a bench (Saeterbakken et al. 2016). This is probably because the unstable variations of the chest-press had greater potential for improvement in coordination compared to the fixed-path of a Smith machine. In the orthopaedic rehabilitation setting, one of the goals for common sports injuries, such as lateral ankle sprains, is to improve neuromuscular control of the muscles that help protect the joint. Based on the findings from Saeterbakken et al. (2016), it can be inferred that replicating similar, sport-specific scenarios and positions during rehabilitation with an added element of instability may help to improve neuromuscular control in a variety of unstable contexts. If applied appropriately, this approach may effectively lower the risk for re-injury and promote a safe return to sport. In addition to task-specificity, intensity of the practiced task contributes to motor learning. Although unmeasured, it is not unreasonable to suspect that the rate of perceived exertion was probably higher for the balance task on the tilt board compared to the balance task on the floor. Greater task intensity has been found to be associated with greater changes in neuroplasticity and corticospinal excitability, in agreement with the finding of Giboin et al. (2020) of decreased H-reflex amplitude for the balance tilt board task but not the floor balance task. Although conclusions cannot be drawn as to whether the down-regulated, task-specific H-reflex amplitude is resultant from adaptations at the spinal level or from supraspinal feedforward mechanisms, the findings support the use of task-specificity and intensity for addressing motor learning in both rehabilitation and performance settings. Clinicians who want to induce neuroplastic changes for improved motor learning in various populations (including neurological and orthopaedic) should consider individualizing the parameters that may affect neuroplasticity, including intensity and task-specificity. Although our current understanding of the exact mechanisms responsible for plastic reorganization at the spinal cord level during motor learning remains far from complete, the recent work by Giboin et al. (2020) presents valuable evidence regarding the specific task- and time-dependent nature of these adaptations. Furthermore, their investigation clarifies several avenues through which future studies can expand upon our understanding of spinal cord neuroplasticity at the same time as providing clinicians with several strategies to assist with improving motor performance. None. All authors have contributed towards and approved the final version. Each of the authors agree to be accountable for all aspects of the work. None. We thank Dr Matt S. Stock for his guidance in the preparation of this Journal Club submission.

Previous history of activity and learning modulates synaptic plasticity and can lead to saturation of synaptic connections. According to the synaptic homeostasis hypothesis, neural oscillations during slow-wave sleep play an important role in restoring plasticity within a functional range. However, it is not known whether slow-wave oscillations—without the concomitant requirement of sleep—play a causal role in human synaptic homeostasis. Here, we aimed to answer this question using transcranial alternating current stimulation (tACS) to induce slow-oscillatory activity in awake human participants. tACS was interleaved between two plasticity-inducing interventions: motor learning, and paired associative stimulation (PAS). The hypothesis tested was that slow-oscillatory tACS would prevent homeostatic interference between motor learning and PAS, and facilitate plasticity from these successive interventions. Thirty-six participants received sham and active fronto-motor tACS in two separate sessions, along with electroencephalography (EEG) recordings, while a further 38 participants received tACS through a control montage. Motor evoked potentials (MEPs) were recorded throughout the session to quantify plasticity changes after the different interventions, and the data were analysed with Bayesian statistics. As expected, there was converging evidence that motor training led to excitatory plasticity. Importantly, we found moderate evidence against an effect of active tACS in restoring PAS plasticity, and no evidence of lasting entrainment of slow oscillations in the EEG. This suggests that, under the conditions tested here, slow-oscillatory tACS does not modulate synaptic homeostasis in the motor system of awake humans.

Learning New Movements Depends on the Statistics of Your Prior Actions

Acute cardiovascular exercise (aCE) seems to be a promising strategy to improve motor performance and learning. However, results are heterogeneous, and the related neurophysiological mechanisms are not well understood. Oscillatory brain activitiy, such as task-related power (TRPow) in the alpha and beta frequencies, are known neural signatures of motor activity. Here, we tested the effects of aCE on motor performance and learning, along with corresponding modulations in EEG TRPow over the sensorimotor cortex. Forty-five right-handed participants (aged 18–34 years) practiced a visuomotor force-matching (FM) task after either high-intensity (HEG), low-intensity (LEG), or no exercise (control group, CG). Motor performance was assessed immediately, 15 min, 30 min, and 24 h after aCE/control. EEG was measured during the FM task. Results of frequentist and Bayesian statistics revealed that high- and low-intensity aCE had no effect at the behavioral level, adding to the previous mixed results. Interestingly, EEG analyses showed an effect of aCE on the ipsilateral sensorimotor cortex, with a stronger decrease in β-TRPow 15 min after exercise in both groups compared to the CG. Overall, aCE applied before motor practice increased ipsilateral sensorimotor activity, while motor learning was not affected; it remains to be seen whether aCE might affect motor learning in the long run.

Atypical motor learning has been suggested to underpin the development of motoric challenges (e.g., handwriting difficulties) in autism. Bayesian accounts of autistic cognition propose a mechanistic explanation for differences in the learning process in autism. Specifically, that autistic individuals overweight incoming, at the expense of prior, information and are thus less likely to (a) build stable expectations of upcoming events and (b) react to statistically surprising events. Although Bayesian accounts have been suggested to explain differences in learning across a range of domains, to date, such accounts have not been extended to motor learning. 28 autistic and 35 non-autistic controls (IQ > 70) completed a computerised task in which they learned sequences of actions. On occasional “surprising” trials, an expected action had to be replaced with an unexpected action. Sequence learning was indexed as the reaction time difference between blocks which featured a predictable sequence and those that did not. Surprise-related slowing was indexed as the reaction time difference between surprising and unsurprising trials. No differences in sequence-learning or surprise-related slowing were observed between the groups. Bayesian statistics provided anecdotal to moderate evidence to support the conclusion that sequence learning and surprise-related slowing were comparable between the two groups. We conclude that individuals with autism do not show atypicalities in response to surprising events in the context of motor sequence-learning. These data demand careful consideration of the way in which Bayesian accounts of autism can (and cannot) be extended to the domain of motor learning.

Bayesian models have been applied to many areas of cognitive science including vision, language, and motor learning. We discuss the implications of this framework for cognitive development. We first present a brief introduction to the Bayesian framework. Bayesian models make assumptions about representation explicit, and provide a detailed account of learning. Furthermore, they can provide an account of developmental transitions and other phenomena in development, such as curiosity and exploration. Drawing on recent work bridging empirical developmental data and modeling, we show that these features of the Bayesian approach provide solutions to problems that elude traditional accounts of learning and raise new areas of investigation.

Skill training aims to improve the performance of the task at hand and aims to transfer the acquired skill to related tasks. Both skill training and skill transfer are part of our everyday lives, and essential for survival, and their importance is reflected in years of research. Despite these enormous efforts, however, the complex relationship between skill training and skill transfer is not yet portrayed completely. Building upon two theories, we probed this relationship through the example of bimanual learning with a large cross-sectional design (N = 450) using an online framework. We designed five training tasks which differed in the variance of the training material (schema theory) and three transfer tasks differing in their similarity to the training task (identical elements theory). Theoretically, the five training tasks and the three transfer tasks varied approximately linearly from each other. Empirical data, however, suggested merely the presence of three statistically different training tasks and two significantly different transfer tasks, indicating a nonlinear relationship. Against our expectation, Bayesian statistics suggested that the type of skill training was not related to the type of skill transfer. However, the amount of skill training was positively related to the amount of skill transfer. Together, we showed that motor learning studies can be conducted online. Further, our results shed light on the complex relationship between skill training and skill transfer. Understanding this relationship has wide-ranging practical implications for the general population, particularly for musicians, athletes and patients recovering from injury.

BackgroundDespite the low rate of neurological deficits following the SARS-COV-2 infection in the pediatric population, children and adolescents who develop multisystem inflammatory syndrome (MIS-C) after being infected with SARS-COV-2 are...

WITHDRAWN: A test of the variability vs. specificity hypotheses in the retention of a motor skill.