Computational motor control: feedback and accuracy

Movement trajectory smoothness is not associated with the endpoint accuracy of rapid multi-joint arm movements in young and older adults

The systematic observation and imagination of actions promotes acquisition of motor skills. Furthermore, studies demonstrated that early sleep after practice enhances motor learning through an offline stabilization process. Here, we investigated behavioral effects and neurodynamical correlates of early sleep after action observation and motor imagery training (AO + MI-training) on motor learning in terms of manual dexterity. Forty-five healthy participants were randomized into three groups receiving a 3 week intervention consisting of AO + MI-training immediately before sleeping or AO + MI-training at least 12 h before sleeping or a control stimulation. AO + MI-training implied the observation and motor imagery of transitive manual dexterity tasks, whereas the control stimulation consisted of landscape video-clips observation. Manual dexterity was assessed using functional tests, kinematic and neurophysiological outcomes before and after the training and at 1-month follow-up. AO + MI-training improved manual dexterity, but subjects performing AO + MI-training followed by early sleep had significantly larger improvements than those undergoing the same training at least 12 h before sleeping. Behavioral findings were supported by neurodynamical correlates during motor performance and additional sleep-dependent benefits were also detected at 1 month follow-up. These findings introduce a new approach to enhance the acquisition of new motor skills or facilitate recovery in patients with motor impairments.

Key pointsThe ability to learn new motor skills is supported by plasticity in the structural and functional organisation of the primary motor cortex in the human brain.Changes inhibitory to signalling by GABA are thought to be crucial in inducing motor cortex plasticity.This study used magnetic resonance spectroscopy (MRS) to quantify the concentration of GABA in human motor cortex during a period of motor learning, as well as during a period of movement and a period at rest.We report evidence for a reduction in the MRS‐measured concentration of GABA specific to learning. Further, the GABA concentration early in the learning task was strongly correlated with the magnitude of subsequent learning: higher GABA concentrations were associated with poorer learning.The results provide initial insight into the neurochemical correlates of cortical plasticity associated with motor learning, specifically relevant in therapeutic efforts to induce cortical plasticity during recovery from stroke.The ability to learn novel motor skills is a central part of our daily lives and can provide a model for rehabilitation after a stroke. However, there are still fundamental gaps in our understanding of the physiological mechanisms that underpin human motor plasticity. The acquisition of new motor skills is dependent on changes in local circuitry within the primary motor cortex (M1). This reorganisation has been hypothesised to be facilitated by a decrease in local inhibition via modulation of the neurotransmitter GABA, but this link has not been conclusively demonstrated in humans. Here, we used 7 T magnetic resonance spectroscopy to investigate the dynamics of GABA concentrations in human M1 during the learning of an explicit, serial reaction time task. We observed a significant reduction in GABA concentration during motor learning that was not seen in an equivalent motor task lacking a learnable sequence, nor during a passive resting task of the same duration. No change in glutamate was observed in any group. Furthermore, M1 GABA measured early in task performance was strongly correlated with the degree of subsequent learning, such that greater inhibition was associated with poorer subsequent learning. This result suggests that higher levels of cortical inhibition may present a barrier that must be surmounted in order to achieve an increase in M1 excitability, and hence encoding of a new motor skill. These results provide strong support for the mechanistic role of GABAergic inhibition in motor plasticity, raising questions regarding the link between population variability in motor learning and GABA metabolism in the brain.

Proposed optimization criteria to explain human multijoint arm motion include smoothness criteria and a minimum-variance criterion based on motor command-dependent noise (signal-dependent noise). It is reported that each of these criteria can effectively reproduce the human trajectory. This paper investigates the possibility that the minimum-variance criterion is included in trajectory planning. First, the relation between the hand trajectory and the final point variance is investigated for motion in the sagittal plane by a numerical experiment. Next, the corresponding relation is investigated by a behavioral experiment. Then, noise is added to the motor command as a simulation, and a behavioral experiment is performed to investigate the relation between the change of the trajectory and the variance. The experimental result suggests the possibility that the minimum-variance criterion is used in trajectory planning. However, it is difficult to account for the human arm motion in the sagittal plane by using only the minimum-variance criterion. The above results seem to indicate that both the smoothness criterion and the minimum-variance criterion based on signal-dependent noise are used in human arm trajectory planning. © 2005 Wiley Periodicals, Inc. Syst Comp Jpn, 36(14): 32–43, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20365

Motor adaptation plays an important role in the acquisition of new motor skills. It has been reported that cognitive tasks can promote motor adaptation; however, which cognitive tasks effectively promote motor adaptation remains unknown. This study aimed to examine what factors of cognitive tasks contribute to promoting motor adaptation. Forty-two healthy young adults were randomly assigned to one of three groups: incongruent Stroop task group (iSTG), congruent Stroop task group (cSTG), and control group (CG). All participants underwent 20 blocks of a mouse-tracking task on the 1st and 2nd days. Before the mouse tracking task on the 1st day, the iSTG and cSTG completed the incongruent and congruent Stroop tasks, respectively. Participants in the CG did not perform any cognitive tasks. On the 28th day, all participants underwent 3 blocks of the mouse tracking task to evaluate their retention of motor adaptation. As a result, on the 1st day, the mouse tracking task performance improved equally for both groups. However, on the 2nd and 28th days, the mouse tracking task performance in the iSTG showed greater improvements for all blocks compared to those in the CG. These results suggest that the incongruent Stroop task promotes motor adaptation, but the congruent Stroop task does not. In addition, it is suggested that factors, which are primarily involved in the incongruent Stroop task, might promote motor adaptation.

Repetition of a cognitive task promotes motor learning

Motor skill acquisition inherently depends on the way one practices the motor task. The amount of motor task variability during practice has been shown to foster transfer of the learned skill to other similar motor tasks. In addition, variability in a learning schedule, in which a task and its variations are interweaved during practice, has been shown to help the transfer of learning in motor skill acquisition. However, there is little evidence on how motor task variations and variability schedules during practice act on the acquisition of complex motor skills such as music performance, in which a performer learns both the right movements (motor skill) and the right time to perform them (timing skill). This study investigated the impact of rate (tempo) variability and the schedule of tempo change during practice on timing and motor skill acquisition. Complete novices, with no musical training, practiced a simple musical sequence on a piano keyboard at different rates. Each novice was assigned to one of four learning conditions designed to manipulate the amount of tempo variability across trials (large or small tempo set) and the schedule of tempo change (randomized or non-randomized order) during practice. At test, the novices performed the same musical sequence at a familiar tempo and at novel tempi (testing tempo transfer), as well as two novel (but related) sequences at a familiar tempo (testing spatial transfer). We found that practice conditions had little effect on learning and transfer performance of timing skill. Interestingly, practice conditions influenced motor skill learning (reduction of movement variability): lower temporal variability during practice facilitated transfer to new tempi and new sequences; non-randomized learning schedule improved transfer to new tempi and new sequences. Tempo (rate) and the sequence difficulty (spatial manipulation) affected performance variability in both timing and movement. These findings suggest that there is a dissociable effect of practice variability on learning complex skills that involve both motor and timing constraints.

ERP evidence of adaptive changes in error processing and attentional control during rhythm synchronization learning

One of the predominant effects of PD is alteration of motor skills, which leads to compromised posture and physical balance. Aquatic physical therapy, performed in a heated pool, can serve as one of intervention alternatives for PD carriers. Aim: To analyze the effects of the Halliwick Concept hydrotherapy in acquisition of motor skills in Parkinson’s disease (PD) patients. Methods: A clinical, qualitative method was used to evaluate 7 volunteers (59.85 ± 7.92 years of age, both male and female), who were in II and III stages of PD according to the Hoehn & Yar Scale. The participants were evaluated in the start and end of the interventions phase, and then the evaluation was conducted interventions in a heated pool (32˚C - 34˚C) twice a week, each session lasting approximately 30 minutes, totaling 10 sessions. The Halliwick Principles’ 3phase 10-point methods were used for acquisition of aquatic motor skills. Results: They indicate an improvement in their ability to float in prone and supine positions (P = 0.04 * ) and longitudinal rotation in the bipedal position. Conclusion: The activation of motor control improved the motor skills of the participants.

Effects of Repetitive Motor Training on Movement Representations in Adult Squirrel Monkeys: Role of Use versus Learning

Determining how the human nervous system contends with neuro-motor noise is vital to understanding how humans achieve accurate goal-directed movements. Experimentally, people learning skilled tasks tend to reduce variability in distal joint movements more than in proximal joint movements. This suggests that they might be imposing greater control over distal joints than proximal joints. However, the reasons for this remain unclear, largely because it is not experimentally possible to directly manipulate either the noise or the control at each joint independently. Therefore, this study used a 2 degree-of-freedom torque driven arm model to determine how different combinations of noise and/or control independently applied at each joint affected the reaching accuracy and the total work required to make the movement. Signal-dependent noise was simultaneously and independently added to the shoulder and elbow torques to induce endpoint errors during planar reaching. Feedback control was then applied, independently and jointly, at each joint to reduce endpoint error due to the added neuromuscular noise. Movement direction and the inertia distribution along the arm were varied to quantify how these biomechanical variations affected the system performance. Endpoint error and total net work were computed as dependent measures. When each joint was independently subjected to noise in the absence of control, endpoint errors were more sensitive to distal (elbow) noise than to proximal (shoulder) noise for nearly all combinations of reaching direction and inertia ratio. The effects of distal noise on endpoint errors were more pronounced when inertia was distributed more toward the forearm. In contrast, the total net work decreased as mass was shifted to the upper arm for reaching movements in all directions. When noise was present at both joints and joint control was implemented, controlling the distal joint alone reduced endpoint errors more than controlling the proximal joint alone for nearly all combinations of reaching direction and inertia ratio. Applying control only at the distal joint was more effective at reducing endpoint errors when more of the mass was more proximally distributed. Likewise, controlling the distal joint alone required less total net work than controlling the proximal joint alone for nearly all combinations of reaching distance and inertia ratio. It is more efficient to reduce endpoint error and energetic cost by selectively applying control to reduce variability in the distal joint than the proximal joint. The reasons for this arise from the biomechanical configuration of the arm itself.

Neurorehabilitation that involves learning new motor skills is one of the promising clinical methods for motor recovery in people with multiple sclerosis (PwMS); therefore, factors that influence the acquisition of motor skills in PwMS need to be investigated. Sleep disturbances are common in PwMS; however, no study has investigated the effect of sleep and sleep-related biomarkers on skill acquisition in PwMS. This study aimed to examine the effect of sleep and sleep-related biomarkers on motor acquisition in PwMS. Forty participants with MS and 40 controls were recruited in this study. To assess motor acquisition, each participant was asked to perform a novel game through a virtual reality (VR) system 5 times (blocks). The main outcome measures for each block were the required time to complete the VR game and the recorded errors. The difference in scores between Block 5 and Block 1 for both outcomes were considered to represent motor skill acquisition. Sleep was assessed by self-report using the Pittsburgh Sleep Quality Index (PSQI) and objectively using sleep monitor technology. Serotonin level was assessed using means of enzyme-linked immunosorbent assay using plasma samples. There were significant positive correlations in both groups between motor skill acquisition and PSQI score. In PwMS, significant negative correlation between motor skill acquisition and sleep efficiency and significant positive correlation between motor skill acquisition and sleep latency were also observed. Interestingly, a significant negative correlation was observed between motor skill acquisition and the plasma serotonin level in both groups. Most of these correlations remained significant after controlling for disease severity, fatigue, baseline performance, and cognitive status. Sleep quality may influence motor skill acquisition in PwMS. Circulatory serotonin level might explain this relationship. Physical therapists are encouraged to be aware of sleep quality and sleep assessment. Sleep management strategies should be considered when treating PwMS.

Intellectual disability (ID) and autism spectrum disorder (ASD) are associated with impairments in motor development, attention, and behavior. Physical activity (PA) has been demonstrated to improve these conditions. However, many individuals with ID and ASD are not motivated to persist at performing PA tasks for an extended period of time. Therefore, there is a great need to find forms of PA that could motivate individuals to stay at performing PA. One such form of PA is Drums-Alive, which involves movement, drumming, and music to increase enjoyment motivation. While it is speculated the Drums-Alive could have an effect on motor skills, attention, and behavior, this concept has not been examined in persons with ID and ASD. Therefore, this study aimed to explore the effect of Drums-Alive on motor skills, attention, and behavior for individuals with ID and ASD. Nine adolescents diagnosed with ID or ASD participated in an eight-week Drums-Alive program intervention. Motor skills, attention, and behavior were measured before and after the intervention. Paired-samples t-tests were used, and the statistical significance was established at p ≤ 0.05. The results suggested no significant differences in motor skills, attention, and behavior before and after the Drums-Alive intervention (p > 0.05). Though no statistical significance was found, improvements were observed from the pretest and posttest means, and all participants expressed their enjoyment of participating in the Drum-Alive program. More extended intervention and more participants will be needed in future research.

This paper studies the constellation optimization approach for multiple-input multiple-output (MIMO) visible light communication (VLC) systems with signal-dependent noise (SDN). We propose a constellation optimization method aiming at minimizing the system pairwise error probability. In order to obtain the transmitter constellation, we design the demapping rules from the perspective of energy efficiency and illumination uniformity. For the scenario where receiver randomly moves, the constellation lookup table is proposed to transform real-time optimization into table lookup operation, which effectively reduces the real-time computational complexity. Simulation results show that the optimized constellation leads to lower symbol error rate (SER) than the method of maximizing minimum Euclidean distance. In addition, the constellation lookup table operation shows negligible SER performance degradation.

BackgroundIndividuals with autism spectrum disorder (ASD) show deficits processing sensory feedback to reactively adjust ongoing motor behaviors. Atypical reliance on visual and somatosensory feedback each have been reported during motor behaviors in ASD suggesting that impairments are not specific to one sensory domain but may instead reflect a deficit in multisensory processing, resulting in reliance on unimodal feedback. The present study tested this hypothesis by examining motor behavior across different visual and somatosensory feedback conditions during a visually guided precision grip force test.MethodsParticipants with ASD (N = 43) and age-matched typically developing (TD) controls (N = 23), ages 10–20 years, completed a test of precision gripping. They pressed on force transducers with their index finger and thumb while receiving visual feedback on a computer screen in the form of a horizontal bar that moved upwards with increased force. They were instructed to press so that the bar reached the level of a static target bar and then to hold their grip force as steadily as possible. Visual feedback was manipulated by changing the gain of the force bar. Somatosensory feedback was manipulated by applying 80 Hz tendon vibration at the wrist to disrupt the somatosensory percept. Force variability (standard deviation) and irregularity (sample entropy) were examined using multilevel linear models.ResultsWhile TD controls showed increased force variability with the tendon vibration on compared to off, individuals with ASD showed similar levels of force variability across tendon vibration conditions. Individuals with ASD showed stronger age-associated reductions in force variability relative to controls across conditions. The ASD group also showed greater age-associated increases in force irregularity relative to controls, especially at higher gain levels and when the tendon vibrator was turned on.ConclusionsOur findings that disrupting somatosensory feedback did not contribute to changes in force variability or regularity among individuals with ASD suggests a reduced ability to integrate somatosensory feedback information to guide ongoing precision manual motor behavior. We also document stronger age-associated gains in force control in ASD relative to TD suggesting delayed development of multisensory feedback control of motor behavior.