Consolidation of motor memory

Relationship between overall right pre-frontal cortex activity and learning and retention of a visuomotor adaptation task: A continuous analysis

Learning a visuomotor adaptation task (VMA) is typically assessed by describing the behavioral changes during adaption (early-fast and late-slow phases) and retention (consolidation) tests. Few studies have concurrently examined behavioral and brain activity during this type of learning and therefore their time-dependent dynamics is unknown. It has been proposed that two distinct strategies can be used during such learning: a model-free and a model-based, which distinctively involved explicit and implicit learning strategies. It has also been proposed that prefrontal cortex (PFC) is more implicated when explicit processes are more relevant as it was observed in the early adaptation (Taylor & Ivry, 2014; Wolpe et al., 2020). Additionally, an explicit model-based strategy has been inferred when prefrontal (PFC) activity increases. Therefore, the study's aims were: (1) to examine the continuous temporal dynamics of behavior and right PFC activity during adaptation and retention of a VMA, and (2) to infer the implication of explicit processes during the learning of a VMA derived from right PFC activity. Eighteen young adults (24.22 ± 3.12 years) took part in this study. Continuous measures of the performance (the initial directional error, IDE, and the root mean square error, RMSE) of a rotational visuomotor adaptation task during an adaptation (AD) and two retention sets at 1 h (RT1) and 24 h (RT24) were collected. Concurrently, measures of the right PFC activity (relative changes of the oxyhemoglobin concentration, [ΔO2Hb]) were registered via a three-channel functional near-infrared spectroscopy device. General linear mixed models were run to explore differences across adaptation and retentions. Also, cross-correlations between performance (IDE and RMSE) and PFC activity were conducted to observe their relation during sets. The main results indicated that (1) initial fast behavioral improvement (decrease of IDE and RMSE) did not occur simultaneously with the largest increase of the [ΔO2Hb] in the PFC during the AD, and (2) there was similar performance in the RT1 and RT24 but possibly involving the PFC differently. While in both retentions the errors improved after the first trials, in RT1, the [ΔO2Hb] decreased from the very beginning, whereas the PFC activity initially increased in RT24. Our observations would suggest that various cooperating learning strategies, including model-free (i.e., exploratory) and model-based explicit (i.e., strategy) and implicit (i.e., sensory prediction errors), are coordinated in different timings to cooperate during the sensorimotor adaptation and consolidation processes. Furthermore, the involvement of these strategies during the retention may depend on the time elapsed from the end of the adaptation to the re-introduction of the task.

Frontal midline theta power accounts for inter-individual differences in motor learning ability

Recent neurophysiological studies have demonstrated that frontal midline theta (FMT) activity plays a significant role in motor learning. One of the key challenges in motor learning is to understand the interindividual variability in learning proficiency rates, yet the underlying neural mechanisms remain unclear. To address this open question, this study recorded electroencephalogram activity from twenty-one healthy participants during a visuomotor tracking task to investigate whether modulation of FMT power and the theta phase synchronization across trials (theta phase consistency) during motor preparation could explain individual differences in learning proficiency. We found a significant positive correlation between increased FMT power during motor preparation and learning proficiency rates. Specifically, individuals with greater FMT power exhibited faster learning rates. In contrast, no significant correlation was observed between the consistency of the theta phase during motor preparation and learning proficiency. Together, these findings highlight that the FMT power, rather than phase synchrony, is closely associated with motor learning efficiency. This study provides a novel perspective for understanding the causes of individual differences in motor learning and further corroborates the previous evidence showing FMT power contributes to motor learning processes.

Long-Term Outcomes of Vagus Nerve Stimulation Paired With Upper Extremity Rehabilitation After Stroke

BACKGROUND

Persistent upper extremity (UE) impairment is common after stroke. Durable treatment benefits for chronic ischemic stroke are needed. The purpose of this report is to determine the long-term effects of vagus nerve stimulation paired with rehabilitation on impairment, activity, and participation in people with UE impairment after ischemic stroke.

METHODS

This is a post hoc analysis of data from the VNS-REHAB (A Pivotal Randomized Study Assessing Vagus Nerve Stimulation [VNS] During Rehabilitation for Improved Upper Limb Motor Function After Stroke) randomized clinical trial. Here, we report unblinded, partial crossover, and pooled 1-year outcomes. Initially, 108 participants across 19 sites with chronic ischemic stroke and moderate-to-severe UE impairment were enrolled in VNS-REHAB. Participants received 18 sessions of in-clinic intensive task-specific rehabilitation and 3 months of self-initiated home-based exercise with either real (active) or sham (control) vagus nerve stimulation. Thereafter, Control participants crossed over to receive in-clinic therapy paired with active stimulation. All participants performed home-based exercises paired with self-initiated active stimulation for 1 year. The Fugl-Meyer Assessment UE, Wolf Motor Function Test, and participation outcomes were assessed through 12 months.

RESULTS

Seventy-four participants (69%; 51 male; age, mean±SD, 59.6±8.9) completed 1-year follow-up and provided pooled data through 1 year. At 1 year, compared with baseline, there were improvements in impairment (Fugl-Meyer Assessment UE, 5.23 [95% CI, 4.08-6.39]; P<0.001) activity (Wolf Motor Function Test, 0.50 [95% CI, 0.41-0.59]; P<0.001) and patient-reported outcomes (Motor Activity Log-Quality of Movement: 0.64 [95% CI, 0.46-0.82], P<0.001; Motor Activity Log-Amount of Use: 0.64 [95% CI, 0.46-0.82], P<0.001; Stroke Impact Scale-Activities of Daily Living: 7.43 [95% CI, 5.09-9.77], P<0.001; Stroke Impact Scale-Hand: 17.89 [95% CI, 14.16-21.63], P<0.001; EQ-5D: 5.76 [95% CI, 2.08-9.45], P<0.05; and Stroke Specific-Quality of Life: 0.29 [95% CI, 0.19-0.39], P<0.001) compared with baseline.

CONCLUSIONS

People treated with paired vagus nerve stimulation maintained improvements in UE impairment, activity, participation, and quality-of-life measures at 1 year. Paired vagus nerve stimulation is a Food and Drug Administration-approved, beneficial treatment option for long-term benefit in individuals with chronic UE limitations after ischemic stroke.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT03131960.

Motor markers of congenital cerebellar hypoplasia

The Reach-to-Grasp (RtG) movement is a fundamental feature of human competence and a widely adopted model for the study of functional movements in both healthy and disease-affected individuals. In particular, 3-D kinematic analysis of RtG allows the study of fine hand movements and submovements, described as secondary fluctuations of the main movement. The aim of this study was to use a RtG movement to test upper limb motor performance in a patient with ataxic syndrome due to cerebellar hypoplasia. 3-D kinematical recording and MRI-based structural measures were combined to provide a comprehensive characterization of the movement and its neural underpinnings at the baseline and after a 2 years follow-up. In terms of kinematics, a dissociation between reaching and grasping performance was observed over time: while grasping appeared to be characterized by an improvement at the 2 years follow-up, reaching showed a significant increase of jerk submovements, suggesting a loss of functionality in feedback mechanisms allowing for smoothness of the movement. At the neural level, an increase of gray matter volume of the anterior right cerebellar hemisphere, alongside with an increased structural connectivity within the sensorimotor network were observed at the 2 years follow up, presumably mirroring the improvement observed for the grasping component. These results highlight the potential of the jerk submovements as a motor biomarker in contexts where feedback mechanisms may be compromised, such as in the case of cerebellar dysfunctions, contributing to the development of new methods for the motor assessment of patients in clinical settings.

Evidence of sensory error threshold in triggering locomotor adaptations in humans

Changing body biomechanics or external conditions trigger neural adaptations to optimize motor behavior. While the adaptations appear to be constantly minimizing movement errors, not all errors necessarily initiate sensorimotor adaptations. The locomotor control system may resist changes since exploratory modifications can lead to critical failures in walking. Theoretically, this implies the presence of an error threshold to trigger the adaptation mechanism. Here, kinematic and kinetic asymmetries were imposed as conditions on stepping using a passive orthosis (kinematic asymmetry) and real-time feedback about limb loading (kinetic asymmetry) to vary sensorimotor error during locomotion on a treadmill. Healthy participants adapted to asymmetric conditions while walking on a tied-belt treadmill. The asymmetry in leading and trailing double stance captured the presence of aftereffects, and consequently adaptation, in two conditions: i) only kinematic constraints, or ii) kinematic and kinetic constraints. We tested the hypothesis that the presence of adaptation depends on the magnitude of locomotor asymmetry. Kinematic asymmetry alone did not induce persistent locomotor adaptation; however, the addition of asymmetric interlimb loading triggered the expected adaptation. This result suggests that uninjured locomotor systems can cope with a range of kinematic asymmetries without initiating persistent adaptations, and that loading may be a key variable for triggering the adaptation. The error threshold within the adaptation mechanism may mitigate possible disruption of locomotion when adaptation is not necessary. These insights elucidate the mechanism of neural plasticity and have implications for rehabilitation.

A Lyapunov theory demonstrating a fundamental limit on the speed of systems consolidation

The nervous system reorganizes memories from an early site to a late site, a commonly observed feature of learning and memory systems known as systems consolidation. Previous work has suggested learning rules by which consolidation may occur. Here, we provide conditions under which such rules are guaranteed to lead to stable convergence of learning and consolidation. We use the theory of Lyapunov functions, which enforces stability by requiring learning rules to decrease an energy-like (Lyapunov) function. We present the theory in the context of a simple circuit architecture motivated by classic models of cerebellum-mediated learning and consolidation. Stability is only guaranteed if the learning rate in the late stage is not faster than the learning rate in the early stage. Further, the slower the learning rate at the late stage, the larger the perturbation the system can tolerate with a guarantee of stability. We provide intuition for this result by mapping a simple example consolidation model to a damped driven oscillator system and showing that the ratio of early- to late-stage learning rates in the consolidation model can be directly identified with the oscillator's damping ratio. We then apply the theory to modeling the tuning by the cerebellum of a well-characterized analog short-term memory system, the oculomotor neural integrator, and find similar stability conditions. This work suggests the power of the Lyapunov approach to provide constraints on nervous system function.

Probing sensorimotor memory through the human speech-audiomotor system

Our knowledge of human sensorimotor learning and memory is predominantly based on the visuospatial workspace and limb movements. Humans also have a remarkable ability to produce and perceive speech sounds. We asked whether the human speech-auditory system could serve as a model to characterize the retention of sensorimotor memory in a workspace that is functionally independent of the visuospatial one. Using adaptation to altered auditory feedback, we investigated the durability of a newly acquired speech-acoustical memory (8- and 24-h delay), its sensitivity to the manner of acquisition (abrupt vs. gradual perturbation), and factors affecting memory retrieval. We observed extensive retention of learning (∼70%) but found no evidence for offline gains. The speech-acoustical memory was insensitive to the manner of its acquisition. To assess factors affecting memory retrieval, tests were first done in the absence of auditory feedback (with masking noise). Under these conditions, it appeared there was no memory for prior learning as if after an overnight delay, speakers had returned to their habitual speech production modes. However, when speech was reintroduced, resulting in speech error feedback, speakers returned immediately to their fully adapted state. This rapid switch shows that the two modes of speech production (adapted and habitual) can coexist in parallel in sensorimotor memory. The findings demonstrate extensive persistence of speech-acoustical memory and reveal context-specific memory retrieval processes in speech-motor learning. We conclude that the human speech-auditory system can be used to characterize sensorimotor memory in a workspace that is distinct from the visuospatial workspace.NEW & NOTEWORTHY There is extensive retention of speech-motor learning. Two parallel modes exist in speech motor memory, one with access to everyday habitual speech and the other with access to newly learned speech-acoustical maps. The availability of speech error feedback triggers a switch between these two modes. Properties of sensorimotor memory in the human speech-auditory system are behaviorally similar to, but functionally independent of, their visuospatial counterparts.

The Effects of the Nocturnal Sleep on Learning of a Complex Motor Skill in Young and Older Adults

BACKGROUND/STUDY CONTEXT

Research on older adults has shown impairments in nocturnal sleep, impacting motor memory consolidation and learning. However, previous studies primarily focus on simple tasks, limiting generalization to complex motor activities. Moreover, no evidence exists on how sleep influences adaptability and relearning in older adults.

METHODS

Sixty older adults and 60 young adults practiced an underarm dart-throwing task. The participants were divided into 2 sub-groups: SLEEP, which practiced in the evening and was retested on the morning of the following day, and CONTROL, which practiced in the morning and was retested in the evening on the same day. The practice and retention phases were spaced 12 hours. We analyzed motor learning through persistence, adaptability and relearning rate.

RESULTS

Sleep did not enhance motor learning for any group. While young adults exhibited retention, older adults did not, especially after nocturnal sleep. There was no difference between sub-groups in adaptability. Older adults demonstrated inferior relearning compared to young adults, independently of sleep.

CONCLUSION

Nocturnal sleep did not influence memory consolidation in any group. On the contrary, our findings suggest that nocturnal sleep harms retention in older adults. Age-related characteristics induce a worse relearning rate regardless of sleep occurrence.

Aging, brain plasticity, and motor learning

Motor skill learning, the process of acquiring new motor skills, is critically important across the lifespan, from early development through adulthood and into older age, as well as in pathological conditions (i.e., rehabilitation). Extensive research has demonstrated that motor skill acquisition in young adults is accompanied by significant neuroplastic changes, including alterations in brain structure (gray and white matter), function (i.e., activity and connectivity), and neurochemistry (i.e., levels of neurotransmitters). In the aging population, motor performance typically declines, characterized by slower and less accurate movements. However, despite these age-related changes, older adults maintain the capacity for skill improvement through training. In this review, we explore the extent to which the aging brain retains the ability to adapt in response to motor learning, specifically whether skill acquisition is accompanied by neural changes. Furthermore, we discuss the associations between inter-individual variability in brain structure and function and the potential for future learning in older adults. Finally, we consider the use of non-invasive brain stimulation techniques aimed at optimizing motor learning in this population. Our review provides insights into the neurobiological underpinnings of motor learning in older adults and emphasizes strategies to enhance their motor skill acquisition.

Kernels of Motor Memory Formation: Temporal Generalization in Bimanual Adaptation

In daily life, we coordinate both simultaneous and sequential bimanual movements to manipulate objects. Our ability to rapidly account for different object dynamics suggests there are neural mechanisms to quickly deal with them. Here we investigate how actions of one arm can serve as a contextual cue for the other arm and facilitate adaptation. Specifically, we examine the temporal characteristics that underlie motor memory formation and recall, by testing the contextual effects of prior, simultaneous, and post contralateral arm movements in both male and female human participants. To do so, we measure their temporal generalization in three bimanual interference tasks. Importantly, the timing context of the learned action plays a pivotal role in the temporal generalization. While motor memories trained with post adaptation contextual movements generalize broadly, motor memories trained with prior contextual movements exhibit limited generalization, and motor memories trained with simultaneous contextual movements do not generalize to prior or post contextual timings. This highlights temporal tuning in sensorimotor plasticity: different training conditions yield substantially different temporal generalization characteristics. Since these generalizations extend far beyond any variability in training times, we suggest that the observed differences may stem from inherent differences in the use of prior, current, and post adaptation contextual information in the generation of natural behavior. This would imply differences in the underlying neural circuitry involved in learning and executing the corresponding coordinated bimanual movements.

The Unchanging Latency of Transcranial Motor-Evoked Potentials Among Various Age Groups

Background Human growth and development involve significant changes in bodily dimensions, yet motor learning appears to remain stable throughout life. This study investigates whether adjustments in motor velocity take place as individuals age by examining the latency of transcranial motor-evoked potentials (TcMEPs) across different age groups. Methods Data were collected from 100 patients who underwent surgery with intraoperative neuromonitoring at the All India Institute of Medical Sciences, New Delhi, between January 1, 2019, and January 1, 2020. TcMEP recordings were analyzed for 7 commonly monitored muscles across 7 distinct age groups: under 10 years, 10-19 years, 20-29 years, 30-39 years, 40-49 years, 50-59 years, and over 60 years. Results The analysis revealed no significant differences in motor-evoked potential (MEP) latency across the age groups, indicating that motor response latency remains stable despite the physical changes that occur with aging. Conclusion These findings enhance our understanding of motor learning, suggesting that motor response latency does not necessitate changes with age, highlighting the consistency of motor function over the human lifespan.

The cerebellum acts as the analog to the medial temporal lobe for sensorimotor memory

The cerebellum is critical for sensorimotor learning. The specific contribution that it makes, however, remains unclear. Inspired by the classic finding that for declarative memories, medial temporal lobe (MTL) structures provide a gateway to the formation of long-term memory but are not required for short-term memory, we hypothesized that for sensorimotor memories, the cerebellum may play an analogous role. Here, we studied the sensorimotor learning of individuals with severe ataxia from cerebellar degeneration. We dissected the memories they formed during sensorimotor learning into a short-term temporally-volatile component, that decays rapidly with a time constant of just 15 to 20 s and thus cannot lead to long-term retention, and a longer-term temporally-persistent component that is stable for 60 s or more and leads to long-term retention. Remarkably, we find that these individuals display dramatically reduced levels of temporally-persistent sensorimotor memory, despite spared and even elevated levels of temporally-volatile sensorimotor memory. In particular, we find both impairment that systematically worsens with memory window duration over shorter memory windows (<12 s) and near-complete impairment of memory maintenance over longer memory windows (>25 s). This dissociation uncovers a unique role for the cerebellum as a gateway for the formation of long-term but not short-term sensorimotor memories, mirroring the role of the MTL for declarative memories. It thus reveals the existence of distinct neural substrates for short-term and long-term sensorimotor memory, and it explains both the trial-to-trial differences identified in this study and long-standing study-to-study differences in the effects of cerebellar damage on sensorimotor learning ability.

Synaptic weight dynamics underlying memory consolidation: Implications for learning rules, circuit organization, and circuit function

Systems consolidation is a common feature of learning and memory systems, in which a long-term memory initially stored in one brain region becomes persistently stored in another region. We studied the dynamics of systems consolidation in simple circuit architectures with two sites of plasticity, one in an early-learning and one in a late-learning brain area. We show that the synaptic dynamics of the circuit during consolidation of an analog memory can be understood as a temporal integration process, by which transient changes in activity driven by plasticity in the early-learning area are accumulated into persistent synaptic changes at the late-learning site. This simple principle naturally leads to a speed-accuracy tradeoff in systems consolidation and provides insight into how the circuit mitigates the stability-plasticity dilemma of storing new memories while preserving core features of older ones. Furthermore, it imposes two constraints on the circuit. First, the plasticity rule at the late-learning site must stably support a continuum of possible outputs for a given input. We show that this is readily achieved by heterosynaptic but not standard Hebbian rules. Second, to turn off the consolidation process and prevent erroneous changes at the late-learning site, neural activity in the early-learning area must be reset to its baseline activity. We provide two biologically plausible implementations for this reset that propose functional roles in stabilizing consolidation for core elements of the cerebellar circuit.

Unraveling the time-of-day influences on motor consolidation through the motor-declarative memory conflict

Competition between motor and declarative memory systems, both involved simultaneously in motor learning, has been shown to reduce motor consolidation. Here, we investigated this conflict during the learning of a sequential finger-tapping task (SFTT) scheduled for either the morning or the afternoon. Sixty participants, divided into four groups, trained on SFTT at either 10 a.m. or 3 p.m., and retested five hours later. To disrupt the conflict between the two memories, two groups underwent declarative learning immediately after SFTT training, involving word list training (G10DL and G3DL), while the two other groups (G10CTR and G3CTR) experienced no additional learning. The results revealed that after morning training without additional learning (C10CTR), skill consolidation deteriorated, while the addition of declarative learning (G10DL) significantly attenuated this decay, stabilizing consolidation. Afternoon training showed skill stabilization for both groups (G3CTR and G3DL). These results suggest that weaker consolidation after morning training may be due to an important competition between motor and declarative memories within the same motor task.

The cerebellum and the Mirror Neuron System: A matter of inhibition? From neurophysiological evidence to neuromodulatory implications. A narrative review

Mirror neurons show activity during both the execution (AE) and observation of actions (AO). The Mirror Neuron System (MNS) could be involved during motor imagery (MI) as well. Extensive research suggests that the cerebellum is interconnected with the MNS and may be critically involved in its activities. We gathered evidence on the cerebellum's role in MNS functions, both theoretically and experimentally. Evidence shows that the cerebellum plays a major role during AO and MI and that its lesions impair MNS functions likely because, by modulating the activity of cortical inhibitory interneurons with mirror properties, the cerebellum may contribute to visuomotor matching, which is fundamental for shaping mirror properties. Indeed, the cerebellum may strengthen sensory-motor patterns that minimise the discrepancy between predicted and actual outcome, both during AE and AO. Furthermore, through its connections with the hippocampus, the cerebellum might be involved in internal simulations of motor programs during MI. Finally, as cerebellar neuromodulation might improve its impact on MNS activity, we explored its potential neurophysiological and neurorehabilitation implications.

Motor interference on lateral pelvis shifting towards the paretic leg during walking and its cortical mechanisms in persons with stroke

Motor interference, where new skill acquisition disrupts the performance of a previously learned skill, is a critical yet underexplored factor in gait rehabilitation post-stroke. This study investigates the interference effects of two different practice schedules, applying interleaved (ABA condition) and intermittent (A-A condition) pulling force to the pelvis during treadmill walking, on lateral pelvis shifting towards the paretic leg in individuals with stroke. Task A involved applying resistive pelvis force (pulling towards the non-paretic side), and Task B applied assistive force (pulling towards the paretic side) at the stance phase of the paretic leg during walking. Sixteen individuals with chronic stroke were tested for gait pattern changes, including lateral pelvis shifting and spatiotemporal gait parameters, and neurophysiological changes, including muscle activity in the paretic leg and beta band absolute power in the lesioned cortical areas. A-A condition demonstrated increased lateral pelvis shifting towards the paretic side, extended paretic stance time and longer non-paretic step length after force release while ABA condition did not show any changes. These changes in gait pattern after A-A condition were accompanied by increased muscle activities of the ankle plantarflexors, and hip adductors/abductors. A-A condition demonstrated greater changes in beta band power in the sensorimotor regions compared to ABA condition. These findings suggest that while walking practice with external force to the pelvis can improve lateral pelvis shifting towards the paretic leg post-stroke, practicing a new pelvis shifting task in close succession may hinder the performance of a previously obtained lateral pelvis shifting pattern during walking.

Parallel signatures of cognitive maturation in primate antisaccade performance and prefrontal activity

The ability to suppress inappropriate actions and respond rapidly to appropriate ones matures late in life, after puberty. We investigated the development of this capability in monkeys trained to look away from a lone, bright stimulus (antisaccade task). We evaluated behavioral performance and recorded neural activity in the prefrontal cortex both before and after the transition from puberty to adulthood. Compared to when young, adult monkeys processed the stimulus more rapidly, resisted more effectively the involuntary urge to look at it, and adhered to the task rule more consistently. The spatially selective visuomotor neurons in the prefrontal cortex provided neural correlates of these behavioral changes indicative of a faster transition from stimulus-driven (exogenous) to goal-driven (endogenous) control within the time course of each trial. The results reveal parallel signatures of cognitive maturation in behavior and prefrontal activity that are consistent with improvements in attentional allocation after adolescence.

Synaptic weight dynamics underlying memory consolidation: implications for learning rules, circuit organization, and circuit function

Systems consolidation is a common feature of learning and memory systems, in which a long-term memory initially stored in one brain region becomes persistently stored in another region. We studied the dynamics of systems consolidation in simple circuit architectures with two sites of plasticity, one in an early-learning and one in a late-learning brain area. We show that the synaptic dynamics of the circuit during consolidation of an analog memory can be understood as a temporal integration process, by which transient changes in activity driven by plasticity in the early-learning area are accumulated into persistent synaptic changes at the late-learning site. This simple principle naturally leads to a speed-accuracy tradeoff in systems consolidation and provides insight into how the circuit mitigates the stability-plasticity dilemma of storing new memories while preserving core features of older ones. Furthermore, it imposes two constraints on the circuit. First, the plasticity rule at the late-learning site must stably support a continuum of possible outputs for a given input. We show that this is readily achieved by heterosynaptic but not standard Hebbian rules. Second, to turn off the consolidation process and prevent erroneous changes at the late-learning site, neural activity in the early-learning area must be reset to its baseline activity. We propose two biologically plausible implementations for this reset that suggest novel roles for core elements of the cerebellar circuit.

Significance Statement

How are memories transformed over time? We propose a simple organizing principle for how long term memories are moved from an initial to a final site of storage. We show that successful transfer occurs when the late site of memory storage is endowed with synaptic plasticity rules that stably accumulate changes in activity occurring at the early site of memory storage. We instantiate this principle in a simple computational model that is representative of brain circuits underlying a variety of behaviors. The model suggests how a neural circuit can store new memories while preserving core features of older ones, and suggests novel roles for core elements of the cerebellar circuit.

Sleep benefits perceptual but not movement-based learning of locomotor sequences

Practicing complex locomotor skills, such as those involving a step sequence engages distinct perceptual and motor mechanisms that support the recall of learning under new conditions (i.e., skill transfer). While sleep has been shown to enhance learning of sequences of fine movements (i.e., sleep-dependent consolidation), here we examined whether this benefit extends to learning of a locomotor pattern. Specifically, we tested the perceptual and motor learning of a locomotor sequence following sleep compared to wake. We hypothesized that post-practice sleep would increase locomotor sequence learning in the perceptual, but not in the motor domain. In this study, healthy young adult participants (n = 48; 18-33 years) practiced a step length sequence on a treadmill cued by visual stimuli displayed on a screen during training. Participants were then tested in a perceptual condition (backward walking with the same visual stimuli), or a motor condition (forward walking but with an inverted screen). Skill was assessed immediately, and again after a 12-h delay following overnight sleep or daytime wake (n = 12 for each interval/condition). Off-line learning improved following sleep compared to wake, but only for the perceptual condition. Our results suggest that perceptual and motor sequence learning are processed separately after locomotor training, and further points to a benefit of sleep that is rooted in the perceptual as opposed to the motor aspects of motor learning.

Finding Pattern in the Noise: Persistent Implicit Statistical Knowledge Impacts the Processing of Unpredictable Stimuli

Humans can extract statistical regularities of the environment to predict upcoming events. Previous research recognized that implicitly acquired statistical knowledge remained persistent and continued to influence behavior even when the regularities were no longer present in the environment. Here, in an fMRI experiment, we investigated how the persistence of statistical knowledge is represented in the brain. Participants (n = 32) completed a visual, four-choice, RT task consisting of statistical regularities. Two types of blocks constantly alternated with one another throughout the task: predictable statistical regularities in one block type and unpredictable ones in the other. Participants were unaware of the statistical regularities and their changing distribution across the blocks. Yet, they acquired the statistical regularities and showed significant statistical knowledge at the behavioral level not only in the predictable blocks but also in the unpredictable ones, albeit to a smaller extent. Brain activity in a range of cortical and subcortical areas, including early visual cortex, the insula, the right inferior frontal gyrus, and the right globus pallidus/putamen contributed to the acquisition of statistical regularities. The right insula, inferior frontal gyrus, and hippocampus as well as the bilateral angular gyrus seemed to play a role in maintaining this statistical knowledge. The results altogether suggest that statistical knowledge could be exploited in a relevant, predictable context as well as transmitted to and retrieved in an irrelevant context without a predictable structure.

The Effectiveness of Paired Associative Stimulation on Motor Recovery after Stroke: A Scoping Review

Paired associative stimulation (PAS) is a non-invasive brain stimulation technique combining transcranial magnetic stimulation and peripheral nerve stimulation. PAS allows connections between cortical areas and peripheral nerves (C/P PAS) or between cortical regions (C/C PAS) to be strengthened or weakened by spike-timing-dependent neural plasticity mechanisms. Since PAS modulates both neurophysiological features and motor performance, there is growing interest in its application in neurorehabilitation. We aimed to synthesize evidence on the motor rehabilitation role of PAS in stroke patients. We performed a literature search following the PRISMA Extension for Scoping Reviews Framework. Eight studies were included: one investigated C/C PAS between the cerebellum and the affected primary motor area (M1), seven applied C/P PAS over the lesional, contralesional, or both M1. Seven studies evaluated the outcome on upper limb and one on lower limb motor recovery. Although several studies omit crucial methodological details, PAS highlighted effects mainly on corticospinal excitability, and, more rarely, an improvement in motor performance. However, most studies failed to prove a correlation between neurophysiological changes and motor improvement. Although current studies seem to suggest a role of PAS in post-stroke rehabilitation, their heterogeneity and limited number do not yet allow definitive conclusions to be drawn.

The cerebellum acts as the analog to the medial temporal lobe for sensorimotor memory

The cerebellum is critical for sensorimotor learning. The specific contribution that it makes, however, remains unclear. Inspired by the classic finding that, for declarative memories, medial temporal lobe structures provide a gateway to the formation of long-term memory but are not required for short-term memory, we hypothesized that, for sensorimotor memories, the cerebellum may play an analogous role. Here we studied the sensorimotor learning of individuals with severe ataxia from cerebellar degeneration. We dissected the memories they formed during sensorimotor learning into a short-term temporally-volatile component, that decays rapidly with a time constant of just 15-20sec and thus cannot lead to long-term retention, and a longer-term temporally-persistent component that is stable for 60 sec or more and leads to long-term retention. Remarkably, we find that these individuals display dramatically reduced levels of temporally-persistent sensorimotor memory, despite spared and even elevated levels of temporally-volatile sensorimotor memory. In particular, we find both impairment that systematically increases with memory window duration over shorter memory windows (<12 sec) and near-complete impairment of memory maintenance over longer memory windows (>25 sec). This dissociation uncovers a new role for the cerebellum as a gateway for the formation of long-term but not short-term sensorimotor memories, mirroring the role of the medial temporal lobe for declarative memories. It thus reveals the existence of distinct neural substrates for short-term and long-term sensorimotor memory, and it explains both newly-identified trial-to-trial differences and long-standing study-to-study differences in the effects of cerebellar damage on sensorimotor learning ability.

Significance Statement

A key discovery about the neural underpinnings of memory, made more than half a century ago, is that long-term, but not short-term, memory formation depends on neural structures in the brain's medial temporal lobe (MTL). However, this dichotomy holds only for declarative memories - memories for explicit facts such as names and dates - as long-term procedural memories - memories for implicit knowledge such as sensorimotor skills - are largely unaffected even with substantial MTL damage. Here we demonstrate that the formation of long-term, but not short-term, sensorimotor memory depends on a neural structure known as the cerebellum, and we show that this finding explains the variability previously reported in the extent to which cerebellar damage affects sensorimotor learning.

Dyad motor learning in a wrist-robotic environment: Learning together is better than learning alone

OBJECTIVE

Dyad motor practice is characterized by two learners alternating between physical and observational practice, which can lead to better motor outcomes and reduce practice time compared to physical practice alone. Robot-assisted therapy has become an established neurorehabilitation tool but is limited by high therapy cost and access. Implementing dyad practice in robot-assisted rehabilitation has the potential to improve therapeutic outcomes and/or to achieve them faster. This study aims to determine the effects of dyad practice on motor performance in a wrist-robotic environment to evaluate its potential use in robotic rehabilitation settings.

METHODS

Forty-two healthy participants (18-35 years) were randomized into three groups (n = 14): Dyad practice, physical practice with rest and physical practice without rest. Participants practiced a 2 degree-of-freedom gamified wrist movement task for 20 trials using a custom-made wrist robotic device. A motor performance score (MPS) that captured temporal and spatial time-series kinematics was computed at baseline, the end of training and 24 h later to assess retention.

RESULTS

MPS did not differ between groups at baseline. All groups revealed significant performance gains by the end of training. However, dyads outperformed the other groups at the end of training (p < 0.001) and showed higher retention after 24-h (p = 0.02). Median MPS improved by 46.5% in dyads, 25.3% in physical practice-rest, and 33.6% in physical practice-no rest at the end of training compared to baseline.

CONCLUSION

Compared to physical practice alone, dyad practice leads to superior motor outcomes in a robot-assisted motor learning task. Dyads still outperformed their counterparts 24-h after practice.

IMPACT STATEMENT

Improving motor function in complex motor tasks without increasing required practice time, dyad practice can optimize therapeutic resources. This is particularly impactful in robot-assisted rehabilitation regimens as it would help to improve patients' outcomes and increase care efficiency.

Neural correlates of fine motor grasping skills: Longitudinal insights into motor cortex activation using fNIRS

BACKGROUND

Motor learning is essential for performing specific tasks and progresses through distinct stages, including the rapid learning phase (initial skill acquisition), the consolidation phase (skill refinement), and the stable performance phase (skill mastery and maintenance). Understanding the cortical activation dynamics during these stages can guide targeted rehabilitation interventions.

METHODS

In this longitudinal randomized controlled trial, functional near-infrared spectroscopy was used to explore the temporal dynamics of cortical activation in hand-related motor learning. Thirty-one healthy right-handed individuals were randomly assigned to perform either easy or intricate motor tasks with their non-dominant hand over 10 days. We conducted 10 monitoring sessions to track cortical activation in the right hemisphere (according to lateralization principles, the primary hemisphere for motor control) and evaluated motor proficiency concurrently.

RESULTS

The study delineated three stages of nondominant hand motor learning: rapid learning (days 1 and 2), consolidation (days 3-7), and stable performance (days 8-10). There was a power-law enhancement of motor skills correlated with learning progression. Sustained activation was observed in the supplementary motor area (SMA) and parietal lobe (PL), whereas activation in the right primary motor cortex (M1R) and dorsolateral prefrontal cortex (PFCR) decreased. These cortical activation patterns exhibited a high correlation with the augmentation of motor proficiency.

CONCLUSIONS

The findings suggest that early rehabilitation interventions, such as transcranial magnetic stimulation and transcranial direct current stimulation (tDCS), could be optimally directed at M1 and PFC in the initial stages. In contrast, SMA and PL can be targeted throughout the motor learning process. This research illuminates the path for developing tailored motor rehabilitation interventions based on specific stages of motor learning.

NEW AND NOTEWORTHY

In an innovative approach, our study uniquely combines a longitudinal design with the robustness of generalized estimating equations (GEEs). With the synergy of functional near-infrared spectroscopy (fNIRS) and the Minnesota Manual Dexterity Test (MMDT) paradigm, we precisely trace the evolution of neural resources during complex, real-world fine-motor task learning. Centering on right-handed participants using their nondominant hand magnifies the intricacies of right hemisphere spatial motor processing. We unravel the brain's dynamic response throughout motor learning stages and its potent link to motor skill enhancement. Significantly, our data point toward the early-phase rehabilitation potential of TMS and transcranial direct current stimulation on the M1 and PFC regions. Concurrently, SMA and PL appear poised to benefit from ongoing interventions during the entire learning curve. Our findings carve a path for refined motor rehabilitation strategies, underscoring the importance of timely noninvasive brain stimulation treatments.

Hippocampal motor memory network reorganization depends on familiarity, not time

There is debate as to whether a time-dependent transformation of the episodic-like memory network is observed for nonepisodic tasks, including procedural motor memory. To determine how motor memory networks reorganize with time and practice, mice performed a motor task in a straight alley maze for 1 d (recent), 20 d of continuous training (continuous), or testing 20 d after the original training (remote), and then regional c-Fos expression was assessed. Elevated hippocampal c-Fos accompanied remote, but not continuous, motor task retrieval after 20 d, suggesting that the hippocampus remains engaged for nonhabitual remote motor memory retrieval.

Conscious awareness of others' actions during observational learning does not benefit motor skill performance

The conscious awareness of motor success during motor learning has recently been revealed as a learning factor. In these studies, participants had to learn a motor sequence and to detect when they assumed the execution had reached a maximal fluidity. The consciousness groups showed better motor performance during a delayed post-training test than the non-consciousness control groups. Based on the "similar mechanism" hypothesis between observational and physical practice, we tested this beneficial effect of the conscious awareness of action in an observational learning context. In the present study, two groups learned a motor sequence task by observing a videotaped human model performing the task. However, only the consciousness group had to detect the maximal fluidity of the learning human model during observational practice. Unpredictably, no difference was detected between groups during the post-training test. However, the consciousness group outperformed the non-consciousness control group for tests that assessed the motor knowledges.

Moderate-intensity cardiovascular exercise performed before motor practice attenuates offline implicit motor learning in stroke survivors but not age-matched neurotypical adults

The acute impact of cardiovascular exercise on implicit motor learning of stroke survivors is still unknown. We investigated the effects of cardiovascular exercise on implicit motor learning of mild-moderately impaired chronic stroke survivors and neurotypical adults. We addressed whether exercise priming effects are time-dependent (e.g., exercise before or after practice) in the encoding (acquisition) and recall (retention) phases. Forty-five stroke survivors and 45 age-matched neurotypical adults were randomized into three sub-groups: BEFORE (exercise, then motor practice), AFTER (motor practice, then exercise), and No-EX (motor practice alone). All sub-groups practiced a serial reaction time task (five repeated and two pseudorandom sequences per day) on three consecutive days, followed 7 days later by a retention test (one repeated sequence). Exercise was performed on a stationary bike, (one 20-min bout per day) at 50% to 70% heart rate reserve. Implicit motor learning was measured as a difference score (repeated-pseudorandom sequence response time) during practice (acquisition) and recall (delayed retention). Separate analyses were performed on the stroke and neurotypical groups using linear mixed-effects models (participant ID was a random effect). There was no exercise-induced benefit on implicit motor learning for any sub-group. However, exercise performed before practice impaired encoding in neurotypical adults and attenuated retention performance of stroke survivors. There is no benefit to implicit motor learning of moderately intense cardiovascular exercise for stroke survivors or age-matched neurotypical adults, regardless of timing. Practice under a high arousal state and exercise-induced fatigue may have attenuated offline learning in stroke survivors.

Visual cortex: How mice learn to detect entirely novel inputs

A new study has revealed that neural amplification in mouse primary visual cortex substantially increases between training sessions as mice learn to detect novel optogenetic input directly into visual cortex, suggesting consolidation and recurrent network plasticity contribute to learning the behavior.

Amplified cortical neural responses as animals learn to use novel activity patterns

Cerebral cortex supports representations of the world in patterns of neural activity, used by the brain to make decisions and guide behavior. Past work has found diverse, or limited, changes in the primary sensory cortex in response to learning, suggesting that the key computations might occur in downstream regions. Alternatively, sensory cortical changes may be central to learning. We studied cortical learning by using controlled inputs we insert: we trained mice to recognize entirely novel, non-sensory patterns of cortical activity in the primary visual cortex (V1) created by optogenetic stimulation. As animals learned to use these novel patterns, we found that their detection abilities improved by an order of magnitude or more. The behavioral change was accompanied by large increases in V1 neural responses to fixed optogenetic input. Neural response amplification to novel optogenetic inputs had little effect on existing visual sensory responses. A recurrent cortical model shows that this amplification can be achieved by a small mean shift in recurrent network synaptic strength. Amplification would seem to be desirable to improve decision-making in a detection task; therefore, these results suggest that adult recurrent cortical plasticity plays a significant role in improving behavioral performance during learning.

Effective practice and instruction: A skill acquisition framework for excellence

We revisit an agenda that was outlined in a previous paper in this journal focusing on the importance of skill acquisition research in enhancing practice and instruction in sport. In this current narrative review, we reflect on progress made since our original attempt to highlight several potential myths that appeared to exist in coaching, implying the existence of a theory-practice divide. Most notably, we present five action points that would impact positively on coaches and practitioners working to improve skill learning across sports, as well as suggesting directions for research. We discuss the importance of practice quality in enhancing learning and relate this concept to notions of optimising challenge. We discuss how best to assess learning, the right balance between repetition and practice that is specific to competition, the relationship between practice conditions, instructions, and individual differences, and why a more "hands-off" approach to instruction may have advantages over more "hands-on" methods. These action points are considered as a broad framework for advancing skill acquisition for excellence (SAFE) in applied practice. We conclude by arguing the need for increased collaboration between researchers, coaches, and other sport practitioners.

Evidence that anterograde learning interference depends on the stage of learning of the interferer: blocked versus interleaved training

Training on one task (task A) can disrupt learning on a subsequently trained task (task B), illustrating anterograde learning interference. We asked whether the induction of anterograde learning interference depends on the learning stage that task A has reached when the training on task B begins. To do so, we drew on previous observations in perceptual learning in which completing all training on one task before beginning training on another task (blocked training) yielded markedly different learning outcomes than alternating training between the same two tasks for the same total number of trials (interleaved training). Those blocked versus interleaved contrasts suggest that there is a transition between two differentially vulnerable learning stages that is related to the number of consecutive training trials on each task, with interleaved training presumably tapping acquisition, and blocked training tapping consolidation. Here, we used the blocked versus interleaved paradigm in auditory perceptual learning in a case in which blocked training generated anterograde-but not its converse, retrograde-learning interference (A→B, not B←A). We report that anterograde learning interference of training on task A (interaural time difference discrimination) on learning on task B (interaural level difference discrimination) occurred with blocked training and diminished with interleaved training, with faster rates of interleaving leading to less interference. This pattern held for across-day, within-session, and offline learning. Thus, anterograde learning interference only occurred when the number of consecutive training trials on task A surpassed some critical value, consistent with other recent evidence that anterograde learning interference only arises when learning on task A has entered the consolidation stage.

A double dissociation between savings and long-term memory in motor learning

Memories are easier to relearn than learn from scratch. This advantage, known as savings, has been widely assumed to result from the reemergence of stable long-term memories. In fact, the presence of savings has often been used as a marker for whether a memory has been consolidated. However, recent findings have demonstrated that motor learning rates can be systematically controlled, providing a mechanistic alternative to the reemergence of a stable long-term memory. Moreover, recent work has reported conflicting results about whether implicit contributions to savings in motor learning are present, absent, or inverted, suggesting a limited understanding of the underlying mechanisms. To elucidate these mechanisms, we investigate the relationship between savings and long-term memory by experimentally dissecting the underlying memories based on short-term (60-s) temporal persistence. Components of motor memory that are temporally-persistent at 60 s might go on to contribute to stable, consolidated long-term memory, whereas temporally-volatile components that have already decayed away by 60 s cannot. Surprisingly, we find that temporally-volatile implicit learning leads to savings, whereas temporally-persistent learning does not, but that temporally-persistent learning leads to long-term memory at 24 h, whereas temporally-volatile learning does not. This double dissociation between the mechanisms for savings and long-term memory formation challenges widespread assumptions about the connection between savings and memory consolidation. Moreover, we find that temporally-persistent implicit learning not only fails to contribute to savings, but also that it produces an opposite, anti-savings effect, and that the interplay between this temporally-persistent anti-savings and temporally-volatile savings provides an explanation for several seemingly conflicting recent reports about whether implicit contributions to savings are present, absent, or inverted. Finally, the learning curves we observed for the acquisition of temporally-volatile and temporally-persistent implicit memories demonstrate the coexistence of implicit memories with distinct time courses, challenging the assertion that models of context-based learning and estimation should supplant models of adaptive processes with different learning rates. Together, these findings provide new insight into the mechanisms for savings and long-term memory formation.

Action observation and motor learning: The role of action observation in learning judo techniques

Within the theoretical framework of embodied cognition, several experiments have shown the existence of links between action observation and motor learning. Our aim was to assess the effectiveness of an observational learning protocol (action observation training: AOT) of point-light-display (PLD) in judoka. Twenty participants were given 7 days to learn Go-No-Sen. During this time period, all of the participants received conventional kata training consisting of Uchi-komi and Nage-komi (repetition of techniques) on tatami. In addition to this conventional learning, the experimental group watched 5 min of PLD video representing the different kata techniques, whereas the control group watched neutral videos during the same time period. After the learning period, both the qualitative and biomechanical performances on the kata and the transfer abilities were assessed. The results showed better biomechanical performance and transfer ability in the experimental group than in the control group. Therefore, this first experiment suggests that observational learning of PLD may be beneficial for the acquisition of judo techniques. Future experiments will be needed to specify the mechanisms that are involved in this effect.

Gestures-enhanced anatomy teaching: A literature review of an educational strategy with promising outcomes

PURPOSE

The educational use of gestures has resulted in positive outcomes in several fields. We performed a literature review to investigate the outcomes of the use of gestures to enhance the existing anatomy education methods.

METHODS

PubMed, SCOPUS, ERIC and Cochrane databases were searched for papers with purpose to investigate the outcomes of the use of gestures (either seeing or performing them or both) as adjuncts to existing anatomy education methods.

RESULTS

Six articles were included. Three studies comprised both seeing and performing gestures by the students, while the remaining three studies only comprised either seeing or performing gestures by the students. Most studies evaluated the acquisition of anatomical knowledge after the educational intervention and demonstrated that the addition of gestures resulted in significant benefit compared to control groups, while positive students' perceptions were recorded. It was not clarified whether seeing or performing gestures by the students leads to better educational outcomes.

CONCLUSION

Gestures-enhanced anatomy education seems to be a promising teaching strategy, given that it has led to significantly increased acquisition of anatomical knowledge compared to no gestures-enhanced modalities. The addition of gestures to existing anatomy education modalities seems able to increase their potential without increasing their cost. Further research is needed to determine if seeing or performing gestures by the students is more effective.

Extended Poststroke Rehabilitation Combined with Cerebrolysin Promotes Upper Limb Motor Recovery in Early Subacute Phase of Rehabilitation: A Randomized Clinical Study

Background and Objectives: The recovery of stroke patients with severe impairment is usually poor and limited and, unfortunately, under-investigated in clinical studies. In order to support neuroplasticity and modulate motor recovery, Cerebrolysin combined with rehabilitation treatment has proven effective in the acute stroke phase in moderate to severe motor impairment. The aim of this study was to determine the efficacy of extended poststroke rehabilitation combined with Cerebrolysin on upper limb motor recovery in subacute stroke patients with severe upper limb motor impairment. Materials and Methods: A randomized, double-blind, placebo-controlled study was conducted. Sixty patients at the early stage of severe sub-acute stroke who fulfilled all eligibility criteria were randomly assigned to the Cerebrolysin group or placebo group (𝑛 = 30 each). Both groups, after conducting three weeks of conventional rehabilitation treatment five days per week, continued to perform conventional rehabilitation treatment three times per week until 90 days of rehabilitation treatment. The primary outcome measure was the Action Research Arm Test (ARAT), and the secondary outcomes were the Fugl-Meyer Assessment-Upper Extremity (FMA-UE) motor score, Barthel index (BI), and the National Institutes of Health Stroke Scale (NIHSS). The outcome data were evaluated before, after three weeks of treatment, and on the 90th day of rehabilitation treatment, and compared within groups and between the two groups. There were no adverse events. Results: Both groups showed a significant improvement (p < 0.001) over time in BI, FMA-UE, ARAT, and NIHSS scores. Patients receiving Cerebrolysin showed more significant improvement in post-stroke upper limb motor impairment and functioning compared to the placebo group after only three weeks, and the trend was maintained after 90 days of follow up. Conclusion: Cerebrolysin delivered in the early subacute post-stroke phase added to extended conventional rehabilitation treatment is beneficial and improves motor functional recovery in patients with severe motor impairment, especially on the paretic upper extremity.

Motor Memory Consolidation Deficits in Parkinson's Disease: A Systematic Review with Meta-Analysis

BACKGROUND

The ability to encode and consolidate motor memories is essential for persons with Parkinson's disease (PD), who usually experience a progressive loss of motor function. Deficits in memory encoding, usually expressed as poorer rates of skill improvement during motor practice, have been reported in these patients. Whether motor memory consolidation (i.e., motor skill retention) is also impaired is unknown.

OBJECTIVE

To determine whether motor memory consolidation is impaired in PD compared to neurologically intact individuals.

METHODS

We conducted a pre-registered systematic review (PROSPERO: CRD42020222433) following PRISMA guidelines that included 46 studies.

RESULTS

Meta-analyses revealed that persons with PD have deficits in retaining motor skills (SMD = -0.17; 95% CI = -0.32, -0.02; p = 0.0225). However, these deficits are task-specific, affecting sensory motor (SMD = -0.31; 95% CI -0.47, -0.15; p = 0.0002) and visuomotor adaptation (SMD = -1.55; 95% CI = -2.32, -0.79; p = 0.0001) tasks, but not sequential fine motor (SMD = 0.17; 95% CI = -0.05, 0.39; p = 0.1292) and gross motor tasks (SMD = 0.04; 95% CI = -0.25, 0.33; p = 0.7771). Importantly, deficits became non-significant when augmented feedback during practice was provided, and additional motor practice sessions reduced deficits in sensory motor tasks. Meta-regression analyses confirmed that deficits were independent of performance during encoding, as well as disease duration and severity.

CONCLUSION

Our results align with the neurodegenerative models of PD progression and motor learning frameworks and emphasize the importance of developing targeted interventions to enhance motor memory consolidation in PD.

Anosmia in COVID-19 could be associated with long-term deficits in the consolidation of procedural and verbal declarative memories

Background and purpose

Long-COVID describes the long-term effects of the coronavirus disease 2019 (COVID-19). In long-COVID patients, neuropsychological alterations are frequently reported symptoms. Research points to medial temporal lobe dysfunction and its association with anosmia in long-COVID patients. This study aims to investigate the acquisition and consolidation of declarative and procedural memory in long-COVID patients and to explore whether anosmia is related to these dissociated memory functions.

Methods

Forty-two long-COVID participants and 30 controls (C) were recruited. The sample of long-COVID patients was divided into two groups based on the presence or absence of anosmia, group A and group NA, respectively. Objective performance in verbal declarative memory (Paired-Associate Learning, PAL), procedural memory (Mirror Tracing Test, MTT), general cognitive function (Montreal Cognitive Assessment scale), psychomotor speed, and incidental learning (Digit Symbol Substitution Test) were assessed and compared among the A, NA, and C groups. Long-term retention of PAL and MTT were assessed 24 h after acquisition.

Results

Lower scores in general cognition, psychomotor speed, and sustained attention were found in A and NA compared with C. However, incidental learning, both cue-guided and free-recalled, was diminished in group A compared with C, with no differences with group NA. General cognition and incidental learning were related to declarative memory function exclusively in long-COVID groups. Long-COVID groups presented lower long-term retention of verbal declarative memory than controls in recall tests but no differences in recognition tests. No group differences were found in the acquisition of procedural memory. However, long-term retention of this memory was worse in group A as compared to the NA and C groups, respectively, when errors and time of execution were considered.

Conclusion

Findings support that consolidation of both procedural and declarative memories is more affected than the acquisition of these memories in long-COVID patients, who are also more vulnerable to deficits in delayed recall than in recognition of declarative memories. Deficits in the consolidation of procedural memory and immediate recall of declarative information are especially relevant in long-COVID participants with anosmia. This indicates that anosmia in COVID-19 could be associated with a long-term dysfunction of the limbic system.

Long-term stability of single neuron activity in the motor system

How an established behavior is retained and consistently produced by a nervous system in constant flux remains a mystery. One possible solution to ensure long-term stability in motor output is to fix the activity patterns of single neurons in the relevant circuits. Alternatively, activity in single cells could drift over time provided that the population dynamics are constrained to produce the same behavior. To arbitrate between these possibilities, we recorded single-unit activity in motor cortex and striatum continuously for several weeks as rats performed stereotyped motor behaviors-both learned and innate. We found long-term stability in single neuron activity patterns across both brain regions. A small amount of drift in neural activity, observed over weeks of recording, could be explained by concomitant changes in task-irrelevant aspects of the behavior. These results suggest that long-term stable behaviors are generated by single neuron activity patterns that are themselves highly stable.

Memory decay and generalization following distinct motor learning mechanisms

Motor skill learning is considered to arise out of contributions from multiple learning mechanisms, including error-based learning (EBL), use-dependent learning (UDL), and reinforcement learning (RL). These learning mechanisms exhibit dissociable roles and engage different neural circuits during skill acquisition. However, it remains largely unknown how a newly formed motor memory acquired through each learning mechanism decays over time and whether distinct learning mechanisms produce different generalization patterns. Here, we used variants of reaching paradigms that dissociated these learning mechanisms to examine the time course of memory decay following each learning and the generalization patterns of each learning. We found that motor memories acquired through these learning mechanisms decayed as a function of time. Notably, 15 min, 6 h, and 24 h after acquisition, the memory of EBL decayed much greater than that of RL. The memory acquired through UDL faded away within a few minutes. Motor memories formed through EBL and RL for given movement directions generalized to untrained movement directions, with the generalization of EBL being greater than that of RL. In contrast, motor memory of UDL could not generalize to untrained movement directions. These results suggest that distinct learning mechanisms exhibit different patterns of memory decay and generalization.NEW & NOTEWORTHY Motor skill learning is likely to involve error-based learning, use-dependent plasticity, and operant reinforcement. Here, we showed that these dissociable learning mechanisms exhibited distinct patterns of memory decay and generalization. With a better understanding of the characteristics of these learning mechanisms, it becomes possible to regulate each learning process separately to improve neurological rehabilitation.

Separability of Human Motor Memories during reaching adaptation with force cues

Judging by the breadth of our motor repertoire during daily activities, it is clear that learning different tasks is a hallmark of the human motor system. However, for reaching adaptation to different force fields, the conditions under which this is possible in laboratory settings have remained a challenging question. Previous work has shown that independent movement representations or goals enabled dual adaptation. Considering the importance of force feedback during limb control, here we hypothesised that independent cues delivered by means of background loads could support simultaneous adaptation to various velocity-dependent force fields, for identical kinematic plan and movement goal. We demonstrate in a series of experiments that indeed healthy adults can adapt to opposite force fields, independently of the direction of the background force cue. However, when the cue and force field were in the same direction but differed by heir magnitude, the formation of different motor representations was still observed but the associated mechanism was subject to increased interference. Finally, we highlight that this paradigm allows dissociating trial-by-trial adaptation from online feedback adaptation, as these two mechanisms are associated with different time scales that can be identified reliably and reproduced in a computational model.

Exploring pain interference with motor skill learning in humans: A systematic review

Motor learning underpins successful motor skill acquisition. Although it is well known that pain changes the way we move, it’s impact on motor learning is less clear. The aim of this systematic review was to synthesize evidence on the impact of experimental and clinical pain on task performance and activity-dependent plasticity measures across learning and explore these findings in relation to different pain and motor learning paradigms. Five databases were searched: Web of Science, Scopus, MEDLINE, Embase and CINAHL. Two reviewers independently screened the studies, extracted data, and assessed risk of bias using the Cochrane ROB2 and ROBIN-I. The overall strength of evidence was rated using the GRADE guidelines. Due to the heterogeneity of study methodologies a narrative synthesis was employed. Twenty studies were included in the review: fifteen experimental pain and five clinical pain studies, covering multiple motor paradigms. GRADE scores for all outcome measures suggested limited confidence in the reported effect for experimental pain and clinical pain, on motor learning. There was no impact of pain on any of the task performance measures following acquisition except for ‘accuracy’ during a tongue protrusion visuomotor task and ‘timing of errors’ during a motor adaptation locomotion task. Task performance measures at retention, and activity dependent measures at both acquisition and retention showed conflicting results. This review delivers a detailed synthesis of research studies exploring the impact of pain on motor learning. This is despite the challenges provided by the heterogeneity of motor learning paradigms, outcome measures and pain paradigms employed in these studies. The results highlight important questions for further research with the goal of strengthening the confidence of findings in this area.

Visuomotor performance at high altitude in COPD patients. Randomized placebo-controlled trial of acetazolamide

Introduction: We evaluated whether exposure to high altitude impairs visuomotor learning in lowlanders with chronic obstructive pulmonary disease (COPD) and whether this can be prevented by acetazolamide treatment. Methods: 45 patients with COPD, living <800 m, FEV1 ≥40 to <80%predicted, were randomized to acetazolamide (375 mg/d) or placebo, administered 24h before and during a 2-day stay in a clinic at 3100 m. Visuomotor performance was evaluated with a validated, computer-assisted test (Motor-Task-Manager) at 760 m above sea level (baseline, before starting the study drug), within 4h after arrival at 3100 m and in the morning after one night at 3100 m. Main outcome was the directional error (DE) of cursor movements controlled by the participant via mouse on a computer screen during a target tracking task. Effects of high altitude and acetazolamide on DE during an adaptation phase, immediate recall and post-sleep recall were evaluated by regression analyses. www.ClinicalTrials.gov NCT03165890. Results: In 22 patients receiving placebo, DE at 3100 m increased during adaptation by mean 2.5°, 95%CI 2.2° to 2.7° (p < 0.001), during immediate recall by 5.3°, 4.6° to 6.1° (p < 0.001), and post-sleep recall by 5.8°, 5.0 to 6.7° (p < 0.001), vs. corresponding values at 760 m. In 23 participants receiving acetazolamide, corresponding DE were reduced by -0.3° (-0.6° to 0.1°, p = 0.120), -2.7° (-3.7° to -1.6°, p < 0.001) and -3.1° (-4.3° to -2.0°, p < 0.001), compared to placebo at 3100 m. Conclusion: Lowlanders with COPD travelling to 3100 m experienced altitude-induced impairments in immediate and post-sleep recall of a visuomotor task. Preventive acetazolamide treatment mitigated these undesirable effects.

MeCP2 deficiency impairs motor cortical circuit flexibility associated with motor learning

Loss of function mutations in the X-linked gene encoding methyl-CpG binding protein 2 (MECP2) cause Rett syndrome (RTT), a postnatal neurological disorder. The loss of motor function is an important clinical feature of RTT that manifests early during the course of the disease. RTT mouse models with mutations in the murine orthologous Mecp2 gene replicate many human phenotypes, including progressive motor impairments. However, relatively little is known about the changes in circuit function during the progression of motor deficit in this model. As the motor cortex is the key node in the motor system for the control of voluntary movement, we measured firing activity in populations of motor cortical neurons during locomotion on a motorized wheel-treadmill. Different populations of neurons intermingled in the motor cortex signal different aspects of the locomotor state of the animal. The proportion of running selective neurons whose activity positively correlates with locomotion speed gradually decreases with weekly training in wild-type mice, but not in Mecp2-null mice. The fraction of rest-selective neurons whose activity negatively correlates with locomotion speed does not change with training in wild-type mice, but is higher and increases with the progression of locomotion deficit in mutant mice. The synchronization of population activity that occurs in WT mice with training did not occur in Mecp2-null mice, a phenotype most clear during locomotion and observable across all functional cell types. Our results could represent circuit-level biomarkers for motor regression in Rett syndrome.

The benefits of learning movement sequences in social interactions

Although we frequently acquire knowledge and skills through social interactions, the focus of most research on learning is on individual learning. Here we characterize Interaction Based Learning (IBL), which represents the acquisition of knowledge or skill through social interactions, and compare it to Observational Learning (OL)—learning by observation. To that end, we designed a movement synchronization paradigm whereby participants learned Tai-Chi inspired movement sequences from trained teachers in two separated sessions. We used a motion capture system to track the movement of 40 dyads comprised of a teacher and learner, who were randomly divided into OL or IBL groups, and calculated time-varying synchrony of three-dimensional movement velocity. While in the IBL group both the learner and the teacher could see each other through a transparent glass, in the OL group dyads interacted through a one-way mirror, such that the learners observed the teacher, but the teacher could not see the learners. Results show that although the number of movements recalled was not different between groups, we found improved movement smoothness in the IBL compared to the OL group, indicating movement acquisition was better in the IBL group. In addition, we found that motor synchronization levels in dyads improved over time, indicating that movement synchronization can be learned and retained. In the first session, the IBL group, but not the OL group, showed a significant improvement in synchronization. This suggests that dyadic interaction is important for learning movement sequences, and that bidirectional communication of signals and mutual feedback are essential for the consolidation of motor learning.

Differences in implicit motor learning between adults who do and do not stutter

Implicit learning allows us to acquire complex motor skills through repeated exposure to sensory cues and repetition of motor behaviours, without awareness or effort. Implicit learning is also critical to the incremental fine-tuning of the perceptual-motor system. To understand how implicit learning and associated domain-general learning processes may contribute to motor learning differences in people who stutter, we investigated implicit finger-sequencing skills in adults who do (AWS) and do not stutter (ANS) on an Alternating Serial Reaction Time task. Our results demonstrated that, while all participants showed evidence of significant sequence-specific learning in their speed of performance, male AWS were slower and made fewer sequence-specific learning gains than their ANS counterparts. Although there were no learning gains evident in accuracy of performance, AWS performed the implicit learning task more accurately than ANS, overall. These findings may have implications for sex-based differences in the experience of developmental stuttering, for the successful acquisition of complex motor skills during development by individuals who stutter, and for the updating and automatization of speech motor plans during the therapeutic process.

Motor training is improved by concurrent application of slow oscillating transcranial alternating current stimulation to motor cortex

Physical exercise and neurorehabilitation involve repetitive training that can induce changes in motor performance arising from neuroplasticity. Retention of these motor changes occurs via an encoding process, during which rapid neuroplastic changes occur in response to training. Previous studies show that transcranial alternating current stimulation (tACS), a form of non-invasive brain stimulation, can enhance encoding of a cognitive learning task during wakefulness. However, the effect of tACS on motor processes in the awake brain is unknown. In this study, forty-two healthy 18–35 year old participants received either 0.75 Hz (active) tACS (or sham stimulation) for 30 min during a ballistic thumb abduction motor training task. Training-related behavioural effects were quantified by assessing changes in thumb abduction acceleration, and neuroplastic changes were quantified by measuring motor evoked potential (MEP) amplitude of the abductor pollicis brevis muscle. These measures were reassessed immediately after the motor training task to quantify short-term changes, and then 24 h later to assess longer-term changes. Thumb abduction acceleration in both active and sham stimulation conditions increased immediately after the motor learning, consistent with effective training. Critically, participants in the active group maintained significantly higher thumb acceleration 24 h later (t₄₀ = 2.810, P = 0.044). There were no significant changes or inter-group differences in MEPs for both conditions. The results suggest that 0.75 Hz tACS applied during motor training enhances the effectiveness of motor training, which manifests as enhancement in longer-term task benefits.

Repeated adaptation and de-adaptation to the pelvis resistance force facilitate retention of motor learning in stroke survivors

Locomotor adaptation to novel walking patterns induced by external perturbation has been tested to enhance motor learning for improving gait parameters in individuals post-stroke. However, little is known regarding whether repeated adaptation and de-adaptation to the externally perturbed walking pattern may facilitate or degrade the retention of locomotor learning. In this study, we examined whether the intermittent adaptation to novel walking patterns elicited by external perturbation induces greater retention of the adapted locomotion in stroke survivors, compared with effects of the continuous adaptation. Fifteen individuals post-stroke participated in two experimental conditions consisting of 1) treadmill walking with intermittent (i.e., interspersed 2 intervals of no perturbation) or continuous (no interval) adaptation to externally perturbed walking patterns and 2) overground walking before, immediately, and 10 min after treadmill walking. During the treadmill walking, we applied a laterally pulling force to the pelvis toward the non-paretic side during the stance phase of the paretic leg to disturb weight shifts toward the paretic side. Participants showed improved weight shift toward the paretic side and enhanced muscle activation of hip abductor/adductors immediately after the removal of the pelvis perturbation for both intermittent and continuous conditions (P<0.05), and showed longer retention of the improved weight shift and enhanced muscle activation for the intermittent condition, which transferred from treadmill to overground walking (P<0.05). In conclusion, repeated motor adaptation and de-adaptation to the pelvis resistance force during walking may promote the retention of error-based motor learning for improving weight shift toward the paretic side in individuals post-stroke.

Efficacy of Virtual Reality-Based Rehabilitation Interventions to Improve Balance Function in Patients with Cerebral Palsy: A Systematic Review and Meta-analysis of RCTs

Context: Cerebral palsy (CP) results from damage to the central nervous system, leading to disturbances of motor and sensory functions, especially the balance. Virtual reality exercise intervention (VRI) is a promising technique to improve motor function in children with CP by engaging such individuals in real-like world events through simulations. This review study examines the effects of VRI on static and functional balances and summarizes the effective protocols of virtual reality-based rehabilitation interventions for the CP patients. Methods: A comprehensive search was performed using the following databases: Medline/PubMed, Scopus, Cochrane Library, PEDro, EBSCOhost, and the Online Library of the University of London. The PEDro scale was used to assess the methodological quality. The data extracted from the reviewed studies were coded according to Cooper and Hedges’ guidelines considering the following criteria: (I) Patients' characteristics, (II) intervention protocols, (III) outcomes, and (IV) results. To this end, twelve RCTs with 248 patients aged 4 - 20 years old were analyzed and assessed as "fair" to "good" methodological quality according to Pedro’s scale (4 to 8). VRI alone or in combination with a standard physiotherapy program or with other tools such as tDCS was applied. Results: Twelve RCTs met the inclusion criteria. The meta-analysis showed the good effect of VRI on the static and functional balances of patients with CP (Cohen’s d = 0.66). The funnel plot revealed no significant asymmetry or heterogeneity among the studies (P = 0.271, I2 = 19.71%), reflecting the absence of publication biases. Conclusions: This review reports four major perspectives of the VRI applications: (1) VRI settings, (2) selection of exercises, (3) outcome measures, and (4) long-term effects. Moreover, this review summarizes the specific effects of VRI on balance improvement in patients with CP from different perspectives. However, considering the limited number of well-conducted RCTs in this field, a large homogeneous samples size is still needed for future RCTs.