Principles Of Motor Control Research Articles

An Analysis of Constraints on Access to Augmentative Communication in Cerebral Palsy

Effective use of augmentative communication requires an individual to manage its technical aspects. Motor-skill limitations in cerebral palsy (i.e., individual constraints) can influence this ability as can demands imposed by communication devices (i.e., task constraints). This paper emphasizes the importance of analyzing the confluence of task and individual constraints in promoting a functional fit between the individual with cerebral palsy and the communication device. We demonstrate the utility of current principles of motor control in analyzing this confluence. Task constraints imposed by target selection and individual constraints imposed by cerebral palsy are introduced prior to an analysis of their confluence using the degrees of freedom of the potential planes of limb motion. Occupational therapists should look beyond motor-skill assessment to the confluence of task and individual constraints when customizing target selection in augmentative communication.

Structured Variability of Muscle Activations Supports the Minimal Intervention Principle of Motor Control

Numerous observations of structured motor variability indicate that the sensorimotor system preferentially controls task-relevant parameters while allowing task-irrelevant ones to fluctuate. Optimality models show that controlling a redundant musculo-skeletal system in this manner meets task demands while minimizing control effort. Although this line of inquiry has been very productive, the data are mostly behavioral with no direct physiological evidence on the level of muscle or neural activity. Furthermore, biomechanical coupling, signal-dependent noise, and alternative causes of trial-to-trial variability confound behavioral studies. Here we address those confounds and present evidence that the nervous system preferentially controls task-relevant parameters on the muscle level. We asked subjects to produce vertical fingertip force vectors of prescribed constant or time-varying magnitudes while maintaining a constant finger posture. We recorded intramuscular electromyograms (EMGs) simultaneously from all seven index finger muscles during this task. The experiment design and selective fine-wire muscle recordings allowed us to account for a median of 91% of the variance of fingertip forces given the EMG signals. By analyzing muscle coordination in the seven-dimensional EMG signal space, we find that variance-per-dimension is consistently smaller in the task-relevant subspace than in the task-irrelevant subspace. This first direct physiological evidence on the muscle level for preferential control of task-relevant parameters strongly suggest the use of a neural control strategy compatible with the principle of minimal intervention. Additionally, variance is nonnegligible in all seven dimensions, which is at odds with the view that muscle activation patterns are composed from a small number of synergies.

Robotic neurorehabilitation: a computational motor learning perspective

Conventional neurorehabilitation appears to have little impact on impairment over and above that of spontaneous biological recovery. Robotic neurorehabilitation has the potential for a greater impact on impairment due to easy deployment, its applicability across of a wide range of motor impairment, its high measurement reliability, and the capacity to deliver high dosage and high intensity training protocols.We first describe current knowledge of the natural history of arm recovery after stroke and of outcome prediction in individual patients. Rehabilitation strategies and outcome measures for impairment versus function are compared. The topics of dosage, intensity, and time of rehabilitation are then discussed.Robots are particularly suitable for both rigorous testing and application of motor learning principles to neurorehabilitation. Computational motor control and learning principles derived from studies in healthy subjects are introduced in the context of robotic neurorehabilitation. Particular attention is paid to the idea of context, task generalization and training schedule. The assumptions that underlie the choice of both movement trajectory programmed into the robot and the degree of active participation required by subjects are examined. We consider rehabilitation as a general learning problem, and examine it from the perspective of theoretical learning frameworks such as supervised and unsupervised learning. We discuss the limitations of current robotic neurorehabilitation paradigms and suggest new research directions from the perspective of computational motor learning.

Epilogue: What We Know about Nonspeech Oral Motor Exercises

A great deal of information is available to help clinicians understand the principles of motor speech learning and control, and how to apply those principles to clinical practice. In addition, the results of many investigations have documented the differences between the motor movements for speech and nonspeech tasks. Finally, supporting evidence for using nonspeech tasks to improve speech is virtually nonexistent. All of that information, taken in concert, casts doubt on the use of nonspeech techniques for improving children's speaking skills. However, clinicians have available a variety of viable intervention techniques to help children improve speech productions. This article presents a summary of reasons not to use nonspeech remediation techniques along with suggestions clinicians should consider when choosing intervention procedures for children with speech sound errors.

V3 Spinal Neurons Establish a Robust and Balanced Locomotor Rhythm during Walking

A robust and well-organized rhythm is a key feature of many neuronal networks, including those that regulate essential behaviors such as circadian rhythmogenesis, breathing, and locomotion. Here we show that excitatory V3-derived neurons are necessary for a robust and organized locomotor rhythm during walking. When V3-mediated neurotransmission is selectively blocked by the expression of the tetanus toxin light chain subunit (TeNT), the regularity and robustness of the locomotor rhythm is severely perturbed. A similar degeneration in the locomotor rhythm occurs when the excitability of V3-derived neurons is reduced acutely by ligand-induced activation of the allatostatin receptor. The V3-derived neurons additionally function to balance the locomotor output between both halves of the spinal cord, thereby ensuring a symmetrical pattern of locomotor activity during walking. We propose that the V3 neurons establish a regular and balanced motor rhythm by distributing excitatory drive between both halves of the spinal cord.

Control issues in adjustable speed drives

Adjustable-speed electric motor/generator drives (ASDs) are used to save electric energy and increase productivity in variable-output work processes of all new and well-established industries such as: digital information gadgets, digital home appliances, automotive and robotics electric actuators, pump compressors, other vehicles, industrial processes, and distributed and renewable energy system electric generators. With power levels that go from less than 1 W to hundreds of megawatts, ASDs have become in the last 20 years a very dynamic worldwide industry/market. The recent advances in electric/magnetic materials, modeling tools, design and fabrication of electric machines for ASDs, corroborated with matched progress in ASD power electronics with power quality control, DSP menu based control, novel sensors and interfacing, field orientation and direct torque control (FOC and DTC), and advanced state observers for motion or current sensorless control, has prompted us to do this selective review. This article selects a few control issues in ASD, such as performance indices, three-phase ac motor control principles, wide constant power speed control, motion-sensorless control of ac drives, variable-speed ac generator control, and linear motor drives control, and discusses their basics, recent progress, and a few directions of ASD research and industrial development for the near future.

Temporal and spatial control following bilateral versus unilateral training

Principles of motor control and learning such as bilateral coordination and task-specificity, are increasingly incorporated in the design of upper extremity rehabilitation protocols for stroke survivors. Yet most studies investigating the efficacy of new protocols report composite scores of standardized tests, such as the Fugl-Meyer Upper Extremity test (FM) and the Wolf Motor Arm Test, rather than determining how the motor control and coordination of arm movements has changed. Here we present a sub-study of a larger randomized controlled trial comparing a bilateral and unilateral training protocol where participants were assessed on bilateral and unilateral arm reaching. Eligible participants for the arm reaching analysis were 9 (FM=37) and 9 (FM=34) in Bilateral Arm Training with Rhythmic Auditory Cueing (BATRAC) and Dose Matched Therapeutic Exercises (DMTE), respectively. Participants undertook 18 sessions of training for 6 weeks with 20min of active training per session. For bilateral arm reaching, participants after BATRAC were faster, with increased peak acceleration, fewer movement units, and smoother hand paths for each arm. The BATRAC training group showed greater improvements with training than the DMTE group during bilateral reaching for parameters of movement units and smoothness of hand path. For unilateral arm reaching, participants were faster after DMTE for paretic arm reaching; however, this group did not improve to a greater extent than the BATRAC training group. Within group functional gains were seen after BATRAC on FM, Wolf Motor Arm Test (time and weight) and after DMTE on FM and Wolf Weight. There was a positive correlation between movement units and the time component of the Wolf Motor Arm Test. The reaching analysis demonstrates task-specificity in training since BATRAC improves performance in bilateral reaching and DMTE improves performance in unilateral reaching. Temporal/spatial control outcomes in studies of post-stroke interventions can identify functionally relevant motor control changes that are not captured by traditional standardized tests.

PARALLEL `PHASIC' AND `TONIC' MOTOR SYSTEMS OF THE CRAYFISH ABDOMEN

![Figure][1] The ground-breaking papers of Donald Kennedy and Kimihisa Takeda ([Kennedy and Takeda, 1965b][2]; [Kennedy and Takeda, 1965a][3]) on crustacean motor systems established a general principle of motor control: there is a division of labour among available motor neurons and muscle

Hb9 Versus Type 2 Interneurons

to the editor: In a recent issue of the Journal of Neurophysiology , [Wilson, Cowan, and Brownstone (2007)][1] investigated the incidence of electrical coupling between different spinal interneurons. Both Wilson et al. and our group use the Hb9:GFP transgenic mouse line that was generated in the

Repeated-Slip Training: An Emerging Paradigm for Prevention of Slip-Related Falls Among Older Adults

Falls frequently cause injury-related hospitalization or death among older adults. This article reviews a new conceptual framework on dynamic stability and weight support in reducing the risk for falls resulting from a forward slip, based on the principles of motor control and learning, in the context of adaptation and longer-term retention induced by repeated-slip training. Although an unexpected slip is severely destabilizing, a recovery step often is adequate for regaining stability, regardless of age. Consequently, poor weight support (quantified by reduction in hip height), rather than instability, is the major determinant of slip-related fall risk. Promisingly, a single session of repeated-slip training can enhance neuromechanical control of dynamic stability and weight support to prevent falls, which can be retained for several months or longer. These principles provide the theoretical basis for establishing task-specific adaptive training that facilitates the development of protective strategies to reduce falls among older adults.

CAN WE EVALUATE KANSEI BY PHYSIOLOGICAL MEASUREMENT?

Kansei, a kind of sensitivity and mental reaction specific to humans, is thought to be generated by a highly advanced function of the human brain, although natural science has hardly explained it yet. In this review, we propose a model of neural mechanisms for kansei from a physiological viewpoint and discuss its applicability to feelings of a car driver. After introducing our model, based on the principles of motor control by the central nervous system (CNS), we point out that it is similar to a driver model that describes interactions of a driver's behavior and vehicle dynamics. We examine physiological responses of a driver in a moving vehicle and correlate these responses with vehicle dynamics. Attention is directed to muscle activity, the final motor output of the CNS that reflects a command signal originating from the higher motor center. Our study shows that the sternocleidomastoid muscle in the neck contributes to maintaining the head position in the pitch and roll planes against backward and lateral inertial forces during driving. The research may potentially pave the way for a challenging approach to objective evaluation of a driver's feelings. Finally, we discuss possible future directions of this approach. Objective analysis of physiological data, combined with appropriate subjective evaluation of a driver's feelings, may provide an insight into the neural mechanisms of kansei. Such a cross-disciplinary research that covers neuroscience, information science and kansei engineering is expected to clarify this advanced function of the brain and to create a new research field of ‘kansei science’.

Stability in Dance Training

Stability training has become a recognized component of dance training in the past decade. Drawing on knowledge applied in sports and spinal rehabilitation, dancers are now able to enhance their performance by applying similar principles in their training. The main issue with stability training is one of being able to recognize the difference between muscle strength training and muscle skill acquisition. Motor control principles underlie stability training as it is the long-term, learned, skill of effective muscle recruitment that is desired rather than short-term strengthening of these muscles. We know that the musculoskeletal system is not an inherently stable structure and ultimately relies on muscle activity to maintain its integrity. This article explores both local and global stability muscle systems, the processes of skill acquisition, and highlight the differences between stability and rigidity.

On the complex nature of speech kinematics

Studying kinematic behavior in speech production is an indispensable and fruitful methodology in order to describe for instance phonemic contrasts, allophonic variations, prosodic effects in articulatory movements. More intriguingly, it is also interpreted with respect to its underlying control mechanisms. Several interpretations have been borrowed from motor control studies of arm, eye, and limb movements. They do either explain kinematics with respect to a fine tuned control by the Central Nervous System (CNS) or they take into account a combination of influences arising from motor control strategies at the CNS level and from the complex physical properties of the peripheral speech apparatus. We assume that the latter is more realistic and ecological. The aims of this article are: first, to show, via a literature review related to the so called '1/3 power law' in human arm motor control, that this debate is of first importance in human motor control research in general. Second, to study a number of speech specific examples offering a fruitful framework to address this issue. However, it is also suggested that speech motor control differs from general motor control principles in the sense that it uses specific physical properties such as vocal tract limitations, aerodynamics and biomechanics in order to produce the relevant sounds. Third, experimental and modelling results are described supporting the idea that the three properties are crucial in shaping speech kinematics for selected speech phenomena. Hence, caution should be taken when interpreting kinematic results based on experimental data alone.

Development and application of virtual reality technology to improve hand use and gait of individuals post-stroke

Development and application of virtual reality (VR) systems for rehabilitation is an iterative process produced by collaboration of an inter-disciplinary team of engineers, neuroscientists and clinician-scientists. In this paper the use of virtual reality technology for the rehabilitation of individuals post-stroke is described. The development of the hardware is based on principles of motor control. Development of the software uses findings from the enrichment and motor plasticity and training literatures as well as principles of motor learning. Virtual environments are created to afford individuals post-stroke opportunities to practice tasks for which they require rehabilitation. These tasks, related to hand function and gait, are trained both at the impairment and functional level. The training engages users to allow for the repetitive intensive practice required for behavioral motor plasticity. Results from a series of upper and lower extremity studies indicate that use of VR technology to augment rehabilitation of individuals post-stroke merits further study.

Control strategies for initiation of human gait are influenced by accuracy constraints

The accuracy of placement of swing limb heel-strike was used to determine strategies of motor control of the stance limb during gait initiation (GI). Subjects initiated gait as fast as possible with the swing limb heel-strike landing on either a small or large target. Stance limb ground reaction forces, electromyogram duration and temporal data for GI were measured. It was hypothesized that accuracy would affect movement speed and the rate of rise, or the slope, of the ground reaction forces that control GI. The slopes of the stance limb forces that coincide with swing limb toe-off remained invariant. However, the slopes of forces and peak forces related to swing limb heel-strike were significantly less for the small target. These initial data suggest that principles of upper extremity motor control may be generalized to the initiation of movement from upright stance.

Disinhibition in the gamma motoneuron circuitry: a neglected mechanism for understanding myofascial pain syndromes?

Dysregulation in the gamma motoneuron circuitry is proposed as one mechanism to explain the development of trigger point activity in myofascial pain syndrome. Dysregulation in this context is defined operationally as significantly (and functionally) different levels of electrical activity detected in the same muscle on the left and right sides of the body that is persistently present with movement of that muscle. Neurophysiological concepts as they pertain to muscles and motor control principles are reviewed. Research is integrated that ties together material from diverse fields of psychology and medicine. Dysregulation in the gamma motoneuron circuitry may lead to disinhibition of muscle that causes it to remain hyperactive after contraction, generate excessive electrical activity during movement, and/or inappropriately coactivate with other muscles during movement. Any or all of these phenomena may occur with dysregulation. Such dysregulation may be corrected by learning. Immediate clinical implications are discussed, including the addition of specifically targeted neuromuscular retraining procedures via surface electromyography, as well as some conceptual and research issues that require further clarification.

Intermuscular co-ordination during fast contact control leg tasks in man

From previous inverse dynamic analyses of human leg extensions, it was hypothesized that the underlying processes for the activation of mono- and biarticular muscles are different; the mono-articular muscles being activated when they shortened, whereas the biarticular muscles appeared responsible for the control of the external force direction. In the present study, experiments were performed on a dynamometer which was especially developed to test this hypothesis. Subjects had to exert different prescribed force vectors on a moving force-plate during leg extension, which they had intensively practised prior to the actual experiments. Of each trial, position, force and EMG activity were recorded. Net joint torques were calculated by the method of inverse dynamics and related to the EMG-patterns of the mono- and biarticular upper leg muscles to reveal whether the previously observed different roles in contact tasks might constitute a general principle in motor control. The results showed that although the action of the biarticular m. rectus femoris and hamstrings muscles was consistent in controlling the direction of the external force, the actions of the mono-articular muscles did not agree with their hypothesized role as simple work generators. The generalizability of a different control for mono-and biarticular muscles could thus not be confirmed for these tasks. They might rather reflect one out of more available strategies the CNS can use to control different contact control tasks.

Variation in speech movement kinematics and temporal patterns of coarticulation with changes in clarity and rate

It is hypothesized that segmental speech movements are programmed to achieve perceptual objectives, by realizing articulatory and acoustic goals. As demands for clarity and rate change, movement kinematics and coarticulation will be adjusted in a trade-off between clarity and economy of effort. In a preliminary test of these ideas, articulatory and acoustic signals have been recorded from two speakers under different conditions of clarity and rate. Effort-related measures are calculated from kinematic data on the tongue body, tongue blade and lips; degrees of labial and lingual coarticulation are measured from timing data, and correlates of clarity are calculated from acoustic data. Initial results indicate a complicated picture, with differences among articulators and between the two subjects. In general, one mediating factor seems to be the influence of basic principles of motor control, reflected in such relationships as duration versus movement distance and velocity versus distance. The results will be discussed in relation to the idea that speakers use an internal representation of relations between articulatory and perceptual domains to help manage the trade-off between listener-oriented perceptual requirements and a speaker-oriented objective to conserve effort. [Work supported by NIDCD.]

The use of functional activities in therapy: An integration of the principles of motor control and the learning process

The successful rehabilitation of a patient following a CVA is largely dependent on the effective relearning of previous motor skills or the learning of new skills. An understanding of the components of motor function and control and the principles of the learning process is therefore essential. Functional activities may be used as an optimal means of combining these principles so as to improve the efficacy of physiotherapy treatment. Two case studies are used to illustrate this approach.

A New Theory of Cerebellar Function

A new theory of cerebellar function is proposed. It is suggested that the cerebellum works according to a hitherto unknown principle of motor control. A simple learning process in the cerebellum, the 'coupling operation', seems powerful enough to explain the role of this brain part in training and performance ofcomplex motor skills. The coupling operation greatly enhances the capability to perform fast, accurate and highly coordinated motions. These motions can be executed by many different paths, while being well adapted to changing intentions and situations. However, the cerebellar 'coupling machine' does not control movements by itself ; rather, it is a supportive device. In the case of skilled motions, for instance, the control is always left to the forebrain. A network model of the cerebellum demonstrates how the coupling operation might be carried out in cellular detail in a biologically plausible way. According to the theory, the cerebellum only influences complex voluntary movements, and not simple ones. This theory explains a great deal of physiological, anatomical and clinical data, producing a coherent picture.