Motor Control Research Research Articles

Control of redundant pointing movements involving the wrist and forearm.

The musculoskeletal system can move in more ways than are strictly necessary, allowing many tasks to be accomplished with a variety of limb configurations. Why some configurations are preferred has been a focus of motor control research, but most studies have focused on shoulder-elbow or whole arm movements. This study focuses on movements involving forearm pronation-supination (PS), wrist flexion-extension (FE), and wrist radial-ulnar deviation (RUD) and elucidates how these three degrees of freedom (DOF) combine to perform the common task of pointing, which only requires two DOF. Although pointing is more sensitive to FE and RUD than to PS and could be easily accomplished with FE and RUD alone, subjects tend to involve a small amount of PS. However, why we choose this behavior has been unknown and is the focus of this paper. With the use of a second-order model with lumped parameters, we tested a number of plausible control strategies involving minimization of work, potential energy, torque, and path length. None of these control schemes robustly predicted the observed behavior. However, an alternative control scheme, hypothesized to control the DOF that were most important to the task (FE and RUD) and ignore the less important DOF (PS), matched the observed behavior well. In particular, the behavior observed in PS appears to be a mechanical side effect caused by unopposed interaction torques. We conclude that moderately sized pointing movements involving the wrist and forearm are controlled by ignoring forearm rotation even though this strategy does not robustly minimize work, potential energy, torque, or path length. NEW & NOTEWORTHY Many activities require us to point our hands in a given direction using wrist and forearm rotations. Although there are infinitely many ways to do this, we tend to follow a stereotyped pattern. Why we choose this pattern has been unknown and is the focus of this paper. After testing a variety of hypotheses, we conclude that the pattern results from a simplifying strategy in which we focus on wrist rotations and ignore forearm rotation.

Catching the Integration Train: A Look Into the Next 10 Years of Motor-Control and Motor-Learning Research

This article explores the idea of integration as a common theme for the next decade of motor control and learning research. Theoretical advances coupled with advances in understanding individual differences and brain-imaging techniques will facilitate novel perspectives through an integrated understanding of sensory, cognitive, and emotional processing for motor control and learning. Through the support of fundamental research, discoveries that cannot be predicted today will create new insights into how motor control and learning can inform education, health care, and sport. An integrated approach is critical for designs of novel products and procedures, as many new designs are not subject to large-scale trials. To achieve the most effective integration with the public and wider scientific community, researchers should explore novel methods for sharing our findings efficiently, ethically, and effectively.

Muscarinic modulation of the Xenopus laevis tadpole spinal mechanosensory pathway

Muscarinic acetylcholine receptors (mAChRs) mediate effects of acetylcholine (ACh) in many systems, including those involved in spinal functions like locomotion. In Xenopus laevis tadpoles at two days old, a model vertebrate for motor control research, we investigated the role of mAChRs in the skin mechanosensory pathway. We found that mAChR activation by carbachol did not affect the sensory Rohon-Beard neuron properties. However, carbachol could hyperpolarise sensory interneurons and decrease their voltage responses to outward currents. Carbachol could increase the threshold for the mechanosensory pathway to start swimming, preventing the initiation of swimming at higher concentrations altogether. Recording from the sensory interneurons in carbachol showed that their spiking after skin stimulation was depressed. However, the general muscarinic antagonist atropine did not have a clear effect on the swimming threshold or the modulation of sensory interneuron membrane conductance. Our results suggest the skin mechanosensory pathway may be subject to muscarinic modulation in this simple vertebrate system.

Motion control research of underwater spherical robot

ABSTRACTUnderwater spherical robot motion control can be used to simulate satellite motion control under weightlessness. In this paper, firstly the motion equation of spherical robot is established by force analysis. Then, to solve the nonlinear and control channel coupling problems, the CMAC-PID control algorithm with neural network decoupling and genetic algorithm optimization is proposed. In the algorithm, CMAC-PID compound control is designed to generate control signals, and neural network decoupler is designed to decouple multi-channel control into single-channel control, and genetic algorithm is adopted to obtain the best PID parameters. The simulation results show that the GA can obtain the appropriate parameters quickly, and the decoupler can adapt to the change of the attitude of the controlled object. Compared with conventional PID control method, the proposed algorithm shows fast dynamic response and high steady-state accuracy, which can be used for reference of neutral buoyancy experimental object motion control.

The Contribution of Different Cortical Regions to the Control of Spatially Decoupled Eye–Hand Coordination

Our brain's ability to flexibly control the communication between the eyes and the hand allows for our successful interaction with the objects located within our environment. This flexibility has been observed in the pattern of neural responses within key regions of the frontoparietal reach network. More specifically, our group has shown how single-unit and oscillatory activity within the dorsal premotor cortex (PMd) and the superior parietal lobule (SPL) change contingent on the level of visuomotor compatibility between the eyes and hand. Reaches that involve a coupling between the eyes and hand toward a common spatial target display a pattern of neural responses that differ from reaches that require eye-hand decoupling. Although previous work examined the altered spiking and oscillatory activity that occurs during different types of eye-hand compatibilities, they did not address how each of these measures of neurological activity interacts with one another. Thus, in an effort to fully characterize the relationship between oscillatory and single-unit activity during different types of eye-hand coordination, we measured the spike-field coherence (SFC) within regions of macaque SPL and PMd. We observed stronger SFC within PMdr and superficial regions of SPL (areas 5/PEc) during decoupled reaches, whereas PMdc and regions within SPL surrounding medial intrapareital sulcus had stronger SFC during coupled reaches. These results were supported by meta-analysis on human fMRI data. Our results support the proposal of altered cortical control during complex eye-hand coordination and highlight the necessity to account for the different eye-hand compatibilities in motor control research.

Response to Tendon Vibration Questions the Underlying Rationale of Proprioceptive Training.

Proprioceptive training on compliant surfaces is used to rehabilitate and prevent ankle sprains. The ability to improve proprioceptive function via such training has been questioned. Achilles tendon vibration is used in motor-control research as a form of proprioceptive stimulus. Using measures of postural steadiness with nonlinear measures to elucidate control mechanisms, tendon vibration can be applied to investigate the underlying rationale of proprioceptive training. To test whether the effect of vibration on young adults' postural control depended on the support surface. Descriptive laboratory study. Research laboratory. Thirty healthy adults and 10 adults with chronic ankle instability (CAI; age range = 18-40 years). With eyes open, participants stood in bilateral stance on a rigid plate (floor), memory foam, and a Both Sides Up (BOSU) ball covering a force platform. We applied bilateral Achilles tendon vibration for the middle 20 seconds in a series of 60-second trials and analyzed participants' responses from previbration to vibration (pre-vib) and from vibration to postvibration (vib-post). We calculated anterior-posterior excursion of the center of pressure and complexity index derived from the area under multiscale entropy curves. The excursion response to vibration differed by surface, as indicated by a significant interaction of P < .001 for the healthy group at both time points and for the CAI group vib-post. Although both groups demonstrated increased excursion from pre-vib and from vib-post, a decrease was observed on the BOSU. The complexity response to vibration differed by surface for the healthy group (pre-vib, P < .001). The pattern for the CAI group was similar but not significant. Complexity changes vib-post were the same on all surfaces for both groups. Participants reacted less to ankle vibration when standing on the BOSU as compared with the floor, suggesting that proprioceptive training may not be occurring. Different balance-training paradigms to target proprioception, including tendon vibration, should be explored.

Temporal prediction abilities are mediated by motor effector and rhythmic expertise.

Motor synchronization is a critical part of musical performance and listening. Recently, motor control research has described how movements that contain more available degrees of freedom are more accurately timed. Previously, we demonstrated that stick tapping improves perception in a timing detection task, where percussionists greatly outperformed non-percussionists only when tapping along. Since most synchronization studies implement finger tapping to examine simple motor synchronization, here we completed a similar task where percussionists and non-percussionistssynchronized using finger tapping; movement with fewer degrees of freedom than stick tapping. Percussionists and non-percussionists listened to an isochronous beat sequence and identified the timing of a probe tone. On half of the trials, they tapped along with their index finger, and on the other half of the trials, they listened without moving prior to making timing judgments. We found that both groups benefited from tapping overall. Interestingly, percussionists performed only marginally better than did non-percussionists when finger tapping and no different when listening alone, differing from past studies reporting highly superior timing abilities in percussionists. Additionally, we found that percussionist finger tapping was less variable and less asynchronous than was non-percussionist tapping. Moreover, in both groups finger tapping was more variable and more asynchronous than stick tapping in our previous study. This study demonstrates that the motor effector implemented in tapping studies affects not only synchronization abilities, but also subsequent prediction abilities. We discuss these findings in light of effector-specific training and degrees of freedom in motor timing, both of which impact timing abilities to different extents.

New Developments in Understanding the Complexity of Human Speech Production.

Speech is one of the most unique features of human communication. Our ability to articulate our thoughts by means of speech production depends critically on the integrity of the motor cortex. Long thought to be a low-order brain region, exciting work in the past years is overturning this notion. Here, we highlight some of major experimental advances in speech motor control research and discuss the emerging findings about the complexity of speech motocortical organization and its large-scale networks. This review summarizes the talks presented at a symposium at the Annual Meeting of the Society of Neuroscience; it does not represent a comprehensive review of contemporary literature in the broader field of speech motor control.

Geometrical Invariance and Smoothness Maximization for Task-Space Movement Generation

In human motor control studies, end-effector (e.g., hand) trajectories have been successfully modeled using optimization principles. Yet, it remains unclear how such trajectories are updated when the end-effector or task goals are perturbed. Here, we present an approach to human and robotic task-level trajectory planning and modification using geometrical invariance and optimization, allowing to adapt learned movements to a priori unknown boundary conditions. The optimization criterion represents a tradeoff between smoothness (minimum jerk) and accuracy (jerk–accuracy model). We show that planning maximally smooth movements allows recovery from perturbations by superimposing specific affine orbits on maximally smooth preplanned trajectories. The generated trajectories are compared with those resulting from other recent approaches used in robotics. Finally, we discuss conditions for affine invariance of maximally smooth task-space trajectories. Possible applications of this study to both human motor control and robotics research studies are discussed.

Intersegment Dynamics In Multi-joint Control Of The Lower Limb During Walking

PURPOSE: To fully understand the control and regulation of multi-joint movements, the biomechanical properties of the moving subject, specifically intersegment dynamics, must be considered in the motor control research. This study was to understand the multi-joint control of the lower limbs during walking, by studying the intersegment dynamics of the hip, knee and ankle. METHODS: Subjects (n=16, male) performed over-ground walking at 2 different speeds (1.5m/s, 2m/s). Three-dimensional kinematic data were collected via 16 high-resolution cameras (200 Hz). The Ground reaction forces were collected by 2 recessed forceplates (1000 Hz). Data from the right lower extremity in the sagittal plane were used for the intersegmental dynamics analysis. Torques at each joint were separated into five categories: net torque (NET), gravitational torque (GRA), interactive torque (INT), external contact torque (EXT), and muscle torque (MUS). NET is the sum of the other four components. An impulse analysis was used to evaluate the contribution of each component to the NET. All the torques were normalized by the product of body weight (N) and height (m). RESULTS: During the stance phase, the dominant joint torques which provided the positive contribution to the joint movement were all MUS at the hip, knee and ankle (e.g. 2.0m/s, 2.0±0.5, 1.2±0.6, 2.5±0.4). However, during the swing phase of walking, the dominant joint torques which provided the positive contribution to the joint movement were GRA at the hip (e.g. 0.4±0.1); GRA at the knee during 1.5m/s walking (0.4±0.01), MUS at the knee during 2.0 m/s walking (0.6±0.02); INT at the ankle (0.02±0.01). Speed was significantly associated with the impulse of each torque, especially INT (e.g. INT at knee in swing phase: 0.5±0.01 vs 0.7±0.01, p<.01). CONCLUSIONS: During the stance phase of walking, the joint motion was mainly generated by the muscle strength at each joint. However, during the swing phase, interactive forces and the gravity were exploited to generate the joint motion. The control strategy also changed as the movement speed increased. The central nervous system not only exploits the muscle strength, but the passive torques to perform effective and economical limb movement.

Physiology in Perspective: Pursuing the Enchanted Loom of Motor Control.

Sir Charles Sherrington was a pioneer in spinal cord and motor control research, and much of the conceptual framework that now underlies motor control research can be attributed to him. Sherrington clearly identified the motor unit, which he defined as an alpha motoneuron and the group of muscle

It's in the eyes: Planning precise manual actions before execution.

It is well-known that our eyes typically fixate those objects in a scene, with which interactions are about to unfold. During manual interactions, our eyes usually anticipate the next subgoal and thus serve top-down, goal-driven information extraction requirements, probably driven by a schema-based task representation. On the other hand, motor control research concerning object manipulations has extensively demonstrated how grasping choices are often influenced by deeper considerations about the final goal of manual interactions. Here we show that also these deeper considerations are reflected in early eye fixation behavior, significantly before the hand makes contact with the object. In this study, subjects were asked to either pretend to drink out of the presented object or to hand it over to the experimenter. The objects were presented upright or upside down, thus affording a thumb-up (prone) or a thumb-down (supine) grasp. Eye fixation data show a clear anticipatory preference for the region where the index finger is going to be placed. Indeed, fixations highly correlate with the final index finger position, thus subserving the planning of the actual manual action. Moreover, eye fixations reveal several orders of manual planning: Fixation distributions do not only depend on the object orientation but also on the interaction task. These results suggest a fully embodied, bidirectional sensorimotor coupling of eye-hand coordination: The eyes help in planning and determining the actual manual object interaction, considering where to grasp the presented object in the light of the orientation and type of the presented object and the actual manual task to be accomplished with the object.

Design and Evaluation of a Fiber-Optic Grip Force Sensor with Compliant 3D-Printable Structure for (f)MRI Applications

Grip force sensors compatible with magnetic resonance imaging (MRI) are used in human motor control and decision-making research, providing objective and sensitive behavioral outcome measures. Commercial sensors are expensive, cover limited force ranges, rely on pneumatic force transmission that cannot detect fast force changes, or are electrically active, which increases the risk of electromagnetic interference. We present the design and evaluation of a low-cost, 3D-printed, inherently MRI-compatible grip force sensor based on a commercial intensity-based fiber-optic sensor. A compliant monobloc structure with flexible hinges transduces grip force to a linear displacement captured by the fiber-optic sensor. The structure can easily be adapted for different force ranges by changing the hinge thickness. A prototype designed for forces up to 800 N was manufactured and showed a highly linear behavior (nonlinearity of 2.37%) and an accuracy of 1.57% in a range between zero and 500 N. It can be printed and assembled within one day and for less than $300. Accurate performance was confirmed, both inside and outside a 3 T MRI scanner within a pilot study. Given its simple design allowing for customization of sensing properties and ergonomics for different applications and requirements, the proposed grip force handle offers researchers a valuable scientific tool.

Selection and coordination: The articulatory basis for the emergence of phonological structure

Phonological theories commonly analyze speech utterances as composed of hierarchically organized units, such as features/gestures, segments, moras, and syllables, but it is not well understood why this hierarchical organization is observed. Moreover, current phonological theories and speech production models fail to explain cross-linguistic and developmental variation in the organization of units. This paper presents the selection-coordination theory of speech production, which attempts to unify our understanding of developmental and cross-linguistic variation in phonological structure. The theory holds that hierarchical organization emerges from a recurring trend in speech development whereby children acquire coordinative regimes of control over articulatory gestures that were previously competitively selected. In this framework, segments, moras, and syllables are understood as differently-sized instantiations of the same type of motor planning unit, and cross-linguistic and developmental phonological patterns are derived from distinguishing competitive and coordinative regimes of articulatory control. Evidence for the theory is drawn from research in motor control, speech development, and phonological and phonetic patterns in speech.

Training-related changes in the EMG–moment relationship during isometric contractions: Further evidence of improved control of muscle activation in strength-trained men?

The possibility of using electromyography (EMG) to track muscle activity has raised the question of its relationship with the effort exerted by the muscles around the joints. However, the EMG–moment relationship is yet to be fully defined, and increasing knowledge of this topic could contribute to research in motor control and to the development of EMG-based algorithms and devices. With regards the training-related adaptations at the peripheral and central level, the present study investigated the effect of strength training on EMG–moment relationship. Our aim was to clarify its nature and gain further understanding of how morphological and neural factors may affect its form. The EMG–moment relationship was determined during knee flexion and extension isometric contractions performed by strength-trained male athletes and untrained male participants. The results showed that strength training induced linearity of the EMG–moment relationship concomitantly with enhanced maximum force production capacity and decreased co-activation of knee agonist–antagonist muscle pair. These results clarified discordant results regarding the linear or curved nature of the EMG–moment in isometric conditions and suggested that the remarkable linearity of the EMG–moment found in trained participants could indicate improved control of muscle activation.

Nonequilibrium Thermodynamic State Variables of Human Self-Paced Rhythmic Motions: Canonical-Dissipative Approach, Augmented Langevin Equation, and Entropy Maximization

Nonequilibrium thermodynamic state variables are derived for a stochastic limit-cycle oscillator model that has been used in motor control research to describe human rhythmic limb movements. The nonequilibrium thermodynamic state variables are regarded as counterparts to the thermodynamic state variables entropy, internal energy, and free energy of equilibrium systems. The derivation of the state variables is based on maximum entropy distributions of the Hamiltonian energy of the stochastic limit-cycle oscillators. The limit-cycle oscillator model belongs to the class of canonical-dissipative systems, on the one hand, and, on the other hand, can be cast into the form of an augmented Langevin equation. Both concepts are known as physical models for open systems. Experimental data from paced and self-paced pendulum swinging experiments are presented and estimates for the nonequilibrium thermodynamic state variables are given. Entropy and internal energy increased with increasing oscillation frequency both for the paced and self-paced conditions. Interestingly, the nonequilibrium free energy decayed when oscillation frequency was increased, which is akin to the decay of the Landau free energy when the control parameter is scaled further away from its critical value.

Upper extremity function: What's posture got to do with it?

This perspective paper reviews the linkage between developing postural control and upper extremity function. We suggest updated principles for guiding clinical practice, based on current views from motor learning, motor development, and motor control research. Using three clinical examples, we illustrate principles focusing on the use of variability, the importance of errors in learning movement, task specific exploration and practice, and the critical timing necessary to build skill of the upper extremity in a variety of postures. These principles differ from historic approaches in therapeutic exercise, which treated posture as a separate system and a precursor for extremity skill building. We maintain that current movement science supports the tight interaction of posture and upper extremity function through developmental time and in real time, such that one system cannot be considered separate from the other. Specific suggestions for clinical practice flow from the guiding principles outlined in this paper.

Improving performance in golf: current research and implications from a clinical perspective.

Golf, a global sport enjoyed by people of all ages and abilities, involves relatively long periods of low intensity exercise interspersed with short bursts of high intensity activity. To meet the physical demands of full swing shots and the mental and physical demands of putting and walking the course, it is frequently recommended that golfers undertake golf-specific exercise programs. Biomechanics, motor learning, and motor control research has increased the understanding of the physical requirements of the game, and using this knowledge, exercise programs aimed at improving golf performance have been developed. However, while it is generally accepted that an exercise program can improve a golfer's physical measurements and some golf performance variables, translating the findings from research into clinical practice to optimise an individual golfer's performance remains challenging. This paper discusses how biomechanical and motor control research has informed current practice and discusses how emerging sophisticated tools and research designs may better assist golfers improve their performance.

Should the Equilibrium Point Hypothesis (EPH) be Considered a Scientific Theory?

The purpose of this commentary is to discuss factors that limit consideration of the equilibrium point hypothesis as a scientific theory. The EPH describes control of motor neuron threshold through the variable lambda, which corresponds to a unique referent configuration for a muscle, joint, or combination of joints. One of the most compelling features of the equilibrium point hypothesis is the integration of posture and movement control into a single mechanism. While the essential core of the hypothesis is based upon spinal circuitry interacting with peripheral mechanics, the proponents have extended the theory to include the higher-level processes that generate lambda, and in doing so, imposed an injunction against the supraspinal nervous system modeling, computing, or predicting dynamics. This limitation contradicts evidence that humans take account of body and environmental dynamics in motor selection, motor control, and motor adaptation processes. A number of unresolved limitations to the EPH have been debated in the literature for many years, including whether muscle resistance to displacement, measured during movement, is adequate to support this form of control, violations in equifinality predictions, spinal circuits that alter the proposed invariant characteristic for muscles, and limitations in the description of how the complexity of spinal circuitry might be integrated to yield a unique and stable equilibrium position for a given motor neuron threshold. In addition, an important empirical limitation of EPH is the measurement of the invariant characteristic, which needs to be done under a constant central state. While there is no question that the EPH is an elegant and generative hypothesis for motor control research, the claim that this hypothesis has reached the status of a scientific theory is premature.

Impaired Executive Function Can Predict Recurrent Falls in Parkinson's Disease

ObjectiveTo examine whether impairment in executive function independently predicts recurrent falls in people with Parkinson's disease (PD). DesignProspective cohort study. SettingUniversity motor control research laboratory. ParticipantsA convenience sample of community-dwelling people with PD (N=144) was recruited from a patient self-help group and movement disorders clinics. InterventionsNot applicable. Main Outcome MeasuresExecutive function was assessed with the Mattis Dementia Rating Scale Initiation/Perseveration (MDRS-IP) subtest, and fear of falling (FoF) with the Activities-specific Balance Confidence (ABC) Scale. All participants were followed up for 12 months to record the number of monthly fall events. ResultsForty-two people with PD had at least 2 falls during the follow-up period and were classified as recurrent fallers. After accounting for demographic variables and fall history (P=.001), multiple logistic regression analysis showed that the ABC scores (P=.014) and MDRS-IP scores (P=.006) were significantly associated with future recurrent falls among people with PD. The overall accuracy of the prediction was 85.9%. With the use of the significant predictors identified in multiple logistic regression analysis, a prediction model determined by the logistic function was generated: Z = 1.544 + .378 (fall history) − .045 (ABC) − .145 (MDRS-IP). ConclusionsImpaired executive function is a significant predictor of future recurrent falls in people with PD. Participants with executive dysfunction and greater FoF at baseline had a significantly greater risk of sustaining a recurrent fall within the subsequent 12 months.