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PubMed1989

Mathematical and philosophical reflections on motor control systems.

In line with the tradition of the Dutch school of functional morphology, an attempt is made to integrate numerical models of sarcomeres, muscle fibres, muscles, bone-connective-tissue systems, joints, muscle spindles and neural networks into one model simulating motor control. There are two purposes for this attempt. Firstly, to indicate whether numerical properties of the organs forming a system of motor control can be explained in terms of its motor functions. Secondly, to indicate properties that emerge from the integration of the organs into a system of motor control: how much more is an integrated motor system than the sum of its functional components. The motor control system of chewing has been taken as an example, particularly that in rats.

Animals↗

PubMed2003

Computational motor control and human factors: modeling movements in real and possible environments.

An aim of human factors research is to have models that allow for the advance design of user-friendly environments. This is still a distant dream because existing models are not yet sufficiently sophisticated. Models in the domain of motor control are a case in point, but recent developments in computational motor control suggest that the gap between the current state of modeling in this area and the desired state is shrinking. To illustrate this point, we review principles of motor control research that any model of motor control must accommodate. Then we describe a model that captures many of the capacities of actors in the everyday world, including the capacity to reach for objects in different ways depending on factors such as the ease with which different joints can rotate, the required speed of movement, and whether obstacles are present. The model relies on the ideas that goal postures are internally specified before movements are generated, that tasks are defined with flexibly ordered constraint hierarchies, and that movements can be shaped according to task demands. Actual or potential applications of this research include designing and testing possible environments where motor components play a key role.

Ergonomics↗

PubMed2001

Motor control of low-threshold motor units in the human trapezius muscle.

The firing pattern of low-threshold motor units was examined in the human trapezius and first dorsal interosseous (FDI) muscles during slowly augmenting, low-amplitude contractions that were intended to mimic contractile activity in postural muscles. The motor unit activity was detected with a special needle electrode and was analyzed with the assistance of computer algorithms. The surface electromyographic (EMG) signal was recorded. Its root-mean-square (RMS) value was calculated and presented to the subject who used it to regulate the muscle force level. In the trapezius, there was minimal, if any, firing rate modulation of early recruited motor units during slow contractions (< or =1% EMG(max)/s), and later recruited motor units consistently presented higher peak firing rates. As the force rate of the contraction increased (3% EMG(max)/s), the firing rates of the motor units in the trapezius approached an orderly hierarchical pattern with the earliest recruited motor units having the greatest firing rate. In contrast, and as reported previously, the firing rates of all motor units in the FDI always presented the previously reported hierarchical "onion-skin" pattern. We conclude that the low-threshold motor units in the postural trapezius muscle, that is the motor units that are most often called on to activate the muscle in postural activities, have different control features in slow and fast contractions. More detailed analysis revealed that, in the low force-rate contractions of the trapezius, recruitment of new motor units inhibited the firing rate of active motor units, providing an explanation for the depressed firing rate of the low-threshold motor units. We speculate that Renshaw cell inhibition contributes to the observed deviation of the low-threshold motor units from the hierarchical onion-skin pattern.

Adult↗

PubMedDate not supplied

Altered motor control and spasticity after spinal cord injury: subjective and objective assessment.

This study of measures of spasticity, or altered motor control, compares the clinically used Ashworth scale with a method based on surface electromyographic (sEMG) recordings called brain motor control assessment (BMCA) in a group of 97 subjects with spinal cord injury (SCI) and varying levels of motor dysfunction. In this paper, we describe how sEMG-derived scores relate to the severity of spasticity as judged clinically. When sEMG data from passive movements from the BMCA were analyzed by Ashworth category, we found that when the sEMG data were averaged for a limb, there was a significant difference between scores for those with Ashworth 0 vs. 2 and 3, and 1 vs. 2 and 3 (p<0.001), but not between 0 and 1. Analysis of the individual muscle scores improved the discrimination between Ashworth categories. Superiority of sEMG data over Ashworth category as an objective quantification of altered motor control ("spasticity") is argued.

Adult↗

PubMed2005

Residual motor control and cortical representations of function following hemispherectomy: effects of etiology.

Fifteen posthemispherectomy children were examined to assess residual motor function of the paretic side using the 74-point Fugl-Meyer Assessment of Motor Recovery scale. The degree of residual motor control differed for upper and lower extremities, with hand function being most severely impaired. Posthemispherectomy motor outcomes also differed as a function of etiology: cortical dysplasia, perinatal infarct, and Rasmussen's encephalitis. Children whose intractable seizures resulted from perinatal middle cerebral artery stroke demonstrated the most spared motor function. To detect cortical areas that represented motor control of the hemiparetic side, we focused on voluntary control of the affected lower extremity. Seven of our patients were able to carry out a foot dorsiflexion paradigm during functional magnetic resonance imaging, and these results were compared with activations found in normal controls. All children showed activations in the sensorimotor network ipsilateral to the affected side. The perinatal infarct group demonstrated greater activity in the cingulate cortex, whereas the Rasmussen's encephalitis group had significant activations in the insula, suggesting etiology-specific differences in reorganization. These findings are discussed in the framework of our understanding of mechanisms of cortical plasticity in the injured brain and its relevance to neurologic rehabilitation. We suggest that imaging techniques are important tools in identifying cortical regions underlying functional reorganization. Furthermore, detection of such areas might become a basis for specific training promoting the optimal reorganization of cortical networks to enhance motor control.

Adolescent↗

PubMed2002

Therapeutic electrical stimulation to improve motor control and functional abilities of the upper extremity after stroke: a systematic review.

BACKGROUND: Therapeutic electrical stimulation (TES) is a therapeutic strategy aimed at improving impairments of the upper extremity in stroke. OBJECTIVE: Assessment of the available evidence on the effect of TES of the affected upper extremity in improving motor control and functional abilities after stroke. METHODS: A systematic literature search was performed to identify randomized controlled trials (RCTs) that have studied the effect of TES on motor control and functional abilities. The methodological quality of the studies was assessed systematically by two raters. The reported outcomes were examined to evaluate the effect of TES and to identify a possible relationship with patient characteristics, method of stimulation and methodological quality. When possible, effect sizes were calculated (Hedges' g). RESULTS: Six RCTs were included. The methodological scores ranged from 7 to 16 (maximum 19). All studies assessed the effect on motor control, and four reported a positive effect. Effect sizes calculated in three studies ranged from 0.55 to 1.46. Only two studies assessed the effect on functional ability, one reported a positive effect. Subgroup analyses in two studies suggest a better response to stimulation in less severely affected patients. Apart from this, no relationship between effect and patient characteristics, method of stimulation or methodological quality could be detected. CONCLUSIONS: The present review suggests a positive effect of electrical stimulation on motor control. No conclusions can be drawn with regard to the effect on functional abilities.

Arm↗

PubMed1983

[Development and training of monocular motor control].

Misalignment of the visual axes of the eyes observed in strabismus may result from sensory, motor, and/or central nervous system disorders. The functional properties of a technique designed to increase, through training, the monocular motor control of normal human subjects was evaluated, the ultimate goal being obviously to apply the technique to cases of minor strabismus. The subject is seated in front of a television screen. A diaphragm extending from the subject's head to the screen divides the picture into two visually separated half fields. A micro-computer was programmed to project two patterns on the screen, made up of vertical green and grey bars (spatial frequency, 3 deg.). Displacement of the two visually superposable half fields could be independently achieved. The subject's task was to fixate, with one eye, the corresponding half field maintained stationary and track, with the other eye, the motion of the second half field. Perfect fusion of the two half fields has to be preserved during movements of the mobile half field over 2 to 6 degrees at a frequency of 0.4 Hz. The results show that after a few training sessions, subjects developed a high gain monocular motor control. This observation suggests that the method may be used as therapy to correct minor strabismus with or without anomalous retinal correspondence, and offers the possibility to study static and dynamic characteristics of Panum's areas and particularly their modifications as a function of training of monocular motor control.

Adolescent↗

PubMed2003

Upper and lower extremity robotic devices for rehabilitation and for studying motor control.

PURPOSE OF REVIEW: The successful motor rehabilitation of stroke, traumatic brain-injured and spinal cord-injured patients requires an intensive and task-specific therapy approach. Budget constraints limit a hand-to-hand therapy approach, so that intelligent machines may offer a solution to promote motor recovery and obtain a better understanding of motor control. This new field of automated or robot-assisted motor rehabilitation has emerged since the 1990s. RECENT FINDINGS: This article will present clinically viable devices for upper and lower extremity rehabilitation. The MIT-Manus and the Mirror-Image Motion Enabler robot, which enable unrestricted unilateral or bilateral shoulder and elbow movement, consistently proved superior on the motor impairment level. The ARM guide, which assisted reaching in a straight-line trajectory, and the Bi-Manu-Track, which enabled the bilateral practice of a forearm and wrist movement, are currently being tested. For gait rehabilitation after stroke, the electromechanical gait trainer, GT I, has proved effective compared with treadmill training with body weight support. The Lokomat, consisting of a treadmill and a powered exoskeleton, lessened the therapeutic effort compared with manually assisted treadmill training in spinal cord-injured patients. Future developments will see more degrees of freedom, improved man-machine interaction and the implementation of virtual reality. SUMMARY: Technical possibilities are one aspect, but multi-centre trials and a consideration of the unsubstantiated fears among therapists of being replaced by machines will decide on the successful implementation of this most promising field to the benefit of patients.

Artificial Limbs↗

PubMed1991

Synergism by caffeine and by cocaine of the motor control deficit produced by midazolam.

To evaluate the effects of caffeine and cocaine on the impairment of discriminative motor control produced by midazolam, rats were trained to hold a force transducer operated with a paw so that it remained between upper and lower limits of a force band for a continuous 1.5-s period to deliver each food pellet. Acute doses of 3 mg/kg midazolam SC impaired motor performance. Except for one animal, caffeine (10-40 mg/kg IP) had little or no effect on performance, while cocaine (3.75-22.5 mg/kg IP) produced dose-related impairment. When each dose of caffeine was combined with 3 mg/kg midazolam, a marked synergism in motor performance impairment occurred. Cocaine plus midazolam produced mainly an additive synergism. The conspicuous synergistic action of caffeine on the motor control deficit produced by midazolam contrasts with the typical antagonism found between the benzodiazepines and methylxanthines when performance is evaluated by psychomotor tests not requiring fine motor control.

Animals↗

PubMed2005

Reaching for visual cues to depth: the brain combines depth cues differently for motor control and perception.

Vision provides a number of cues about the three-dimensional (3D) layout of objects in a scene that could be used for planning and controlling goal-directed behaviors such as pointing, grasping, and placing objects. An emerging consensus from the perceptual work is that the visual brain is a near-optimal Bayesian estimator of object properties, for example, by integrating cues in a way that accounts for differences in their reliability. We measured how the visuomotor system integrates binocular and monocular cues to 3D surface orientation to guide the placement of objects on a slanted surface. Subjects showed qualitatively similar results to those found in perceptual studies--they gave more weight to binocular cues at low slants and more weight to monocular cues like texture at high slants. We compared subjects' performance in the visuomotor task with their performance on matched perceptual tasks that required an observer to estimate the same 3D surface properties needed to control the motor behavior. The relative influence of binocular and monocular cues changed in qualitatively the same way across stimulus conditions in the two types of task; however, subjects gave significantly more weight to binocular cues for controlling hand movements than for making explicit perceptual judgments in these tasks. Thus, the brain changes how it integrates visual cues based not only on the information content of stimuli, but also on the task for which the information is used.

Brain↗

PubMed1983

Motor control in man after partial or complete spinal cord injury.

The essential features of motor control in spinal man can be understood in terms of segmental reflexes interacting with, and controlled by, the influence of distant segments and even by the brainstem. Thus, overall motor control in patients with spinal cord lesions can be classified according to structure as: (1) simple segmental stretch and withdrawal reflexes; (2) plurisegmental gross reflex movement of paralyzed muscles; or (3) propriospinal processes with partial brain influence (i.e., severe spasticity and traces of position and postural control). Because of the variable nature of the injuries, there may be exceptions to this rule. However, the basic mechanisms can be understood by studying stretch reflex responses to various stimuli. The segmental reflexes are under a powerful influence of the propriospinal interneuron system which conducts impulses up and down the spinal cord. Finally, the apparently "isolated" spinal cord in which clinical signs indicate complete motor paralysis and lack of sensation below the lesion is not always isolated from supraspinal control of involuntary motor activity. In a significant proportion of the clinically complete spinal injuries we studied, it was possible to demonstrate the presence of preserved bulbospinal influences on spinal reflex responses.

Electromyography↗

PubMed1996

On the role of recurrent inhibitory feedback in motor control.

This article reviews presumed roles of recurrent inhibition in motor control, that have been proposed over the past five decades. The discussion is structured in an order of increasing complexity. It starts out with the simplest and earliest circuit, that is recurrent self-inhibition of skeleto-motoneurons, and related functions. It soon becomes clear that in order to understand recurrent inhibition, we must look beyond the simple self-inhibitory CNS circuit. First, recurrent inhibition must be seen in the context of other neural circuits. Second, some quantitative features appear to be correlated with features of the neuromusculo-skeletal periphery. Third, the aspect of lateral inhibition between different members of a motoneuron pool as well as between different motoneuron pools points to the essential multiple input-multiple output structure of recurrent inhibition that again can be understood only by correlating it with features of the neuromusculo-skeletal periphery. Another extension results from the discovery that recurrent inhibition affects not only skeleto-motoneurons, but also gamma-motoneurons, Ia inhibitory interneurons mediating reciprocal inhibition between antagonist motoneurons, other Renshaw cells and cells of origin of the ventral spinocerebellar tract (VSCT). Then the view broadens again, investigating the potential role that recurrent inhibition plays in two far-ranging theories of motor control, the inverse-dynamics approach and the equilibrium-point hypothesis. Finally, the present author tries to formulate, in broad strokes, a personal functional interpretation of recurrent inhibition. All the functional considerations, right or wrong, should yield ideas for new experiments, and this then is the last objective of this review.

Animals↗

PubMedDate not supplied

[Reliability of electrophysiological measurements of motor control].

OBJECTIVES: The aim of the study was the short term test-retest-reliability of electrophyisiological correlates of simple processes of the motor control, i.e. the execution (go) and the inhibition (no go) of a prepared motor response, evoked during the Continuous Performance Test (CPT). Our interest was centered in the reliability of the topographical P300-parameters described in previous studies, i.e. the localizations of the go and no go centroids and the no go anteriorization (NGA), which is the difference between the two centroid locations. A sufficient reliability is a basic requirement for the application of these new topographical parameters for the investigation of different psychiatric illnesses with suspected dysfunctions of prefrontal motor control, e.g. schizophrenias and affective illnesses, obsessive-compulsive disorders, personality disorders with deficits in impulse control, and in children with attention deficit hyperactivity disorder. PATIENTS AND METHODS: We examined 23 healthy subjects who executed two versions of the CPT with an interval of 30 minutes. After averaging the obtained evoked potentials of each subject, we determined the latencies, amplitudes and positive centroids, at the moment of the peak of the Global Field Power in a P300 time window. RESULTS: Statistical analysis revealed sufficient test-retest-reliabilities in comparison to other electrophysiological paradigms, mainly for the localizations of the go (r = 0.93; p = 10(-10)) and no go centroid (r = 0.85; p = 10(-4)), as well as for the no go anteriorization (r = 0.63; p = 10(-3)). CONCLUSION: These results are a prerequisite for the application of these topographical parameters as measures of the prefrontal motor control in different healthy and psychiatric populations.

Adult↗

PubMed2000

Patterns of motor control reorganization in a patient with mirror movements.

OBJECTIVE: To explore motor control reorganization in a 40-year-old, left-handed patient with perinatally acquired mirror movements. METHODS: We performed simultaneous bilateral recordings of motor evoked potentials (MEPs) following focal transcranial magnetic stimulation (fTMS) and of central silent period (cSP) during unilateral voluntary contraction in abductor pollicis brevis (APB) and abductor digiti minimi (ADM) muscles. RESULTS: For both muscles the MEP study showed bilateral fast-conducting corticospinal projections from the right undamaged hemisphere, and residual contralateral projections from the left hemisphere. The cSP findings differed in the two muscles: the mirror phenomenon was bilateral in the ADM, but present only on the right side in the APB muscles; the mirror activity of right ADM and APB muscles was inhibited only by fTMS of the ipsilateral right motor cortex; the mirror phenomenon in the left ADM muscle was inhibited only by fTMS of the contralateral right motor cortex. CONCLUSIONS: Mirror movements of right APB and ADM muscles were sustained by the ipsilateral connections from the undamaged motor cortex, while the mirror phenomenon in the left ADM muscle could be explained by hypothesizing a bilateral activation of motor cortices. This previously unreported electrophysiological picture demonstrates that different patterns of motor control may realize after perinatal cerebral lesions, even in different distal muscles of the same patient.

Adult↗

PubMed1996

Reaching to ipsilateral or contralateral targets: within-hemisphere visuomotor processing cannot explain hemispatial differences in motor control.

Aiming movements made to visual targets on the same side of the body as the reaching hand typically show advantages as compared to aiming movements made to targets on the opposite side of the body midline in the contralateral visual field. These advantages for ipsilateral reaches include shorter reaction time, higher peak velocity, shorter duration and greater endpoint accuracy. It is commonly hypothesized that such advantages are related to the efficiency of intrahemispheric processing, since, for example, a left-sided target would be initially processed in the visual cortex of the right hemisphere and that same hemisphere controls the motor output to the left hand. We tested this hypothesis by examining the kinematics of aiming movements made by 26 right-handed subjects to visual targets briefly presented in either the left or the right visual field. In one block of trials, the subjects aimed their finger directly towards the target; in the other block, subjects were required to aim their movement to the mirror symmetrical position on the opposite side of the fixation light from the target. For the three kinematic measures in which hemispatial differences were obtained (peak velocity, duration and percentage of movement time spent in deceleration), the advantages were related to the side to which the motor response was directed and not to the side where the target was presented. In addition, these effects tended to be larger in the right hand than in the left, particularly for the percentage of the movement time spent in deceleration. The results are interpreted in terms of models of biomechanical constraints on contralateral movements, which are independent of the hemispace of target presentation.

Adult↗

PubMed1990

[A new concept of the role of the cerebellum in operative motor control and the shaping of motor automatism].

A new theory of the cerebellum work is presented. It explains all the experimental data now accumulated.

Animals↗

PubMed2004

Fine motor control in adults with and without chronic hemiparesis: baseline comparison to nondisabled adults and effects of bilateral arm training.

OBJECTIVES: To characterize fine motor control through finger tapping in both arms of 10 patients with chronic stroke, to make baseline comparisons with matched controls, and to examine the responsiveness of deficits seen in stroke patients after 6 weeks of bilateral arm-based training. DESIGN: Nonrandomized controlled, cohort before-after trial. SETTING: Research institution. PARTICIPANTS: Ten people from the community with chronic unilateral ischemic stroke and 10 age- and sex-matched healthy controls. Participants with hemiparesis had completed all conventional care and were more than 6 month poststroke. Inclusion criteria were at least 6 months since a unilateral stroke, ability to follow simple instructions and 2-step commands, volitional control of the nonparetic arm, and at least minimal antigravity movement in the shoulder of the paretic arm. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Measurements included rate and timing consistency of unilateral tapping at a preferred and a maximal rate and the accuracy and stability of interlimb coordination in bilateral simultaneous (inphase) and alternating (antiphase) tapping at a preferred rate. RESULTS: Nonparetic finger control was similar to that of the nondisabled participants except under bilateral conditions, where it was less consistent. A subgroup with residual paretic finger function, had slower and less consistent paretic finger tapping, as well as less accurate and more variable interlimb coordination; however, basic bilateral coupling relationships were preserved. Bilateral arm-based training improved bilateral nonparetic consistency but slowed unilateral preferred tapping. Training also improved paretic fine motor control in 2 of 4 participants with mild stroke severity. The 2 responders, with dominant hemisphere lesions, indicated a possible recovery advantage with bilateral training for such lesions. CONCLUSIONS: In general, nonparetic finger control for tapping was preserved but paretic finger control was compromised. Disruption of nonparetic control of tapping, particularly consistency of tapping, occurred during bilateral tapping tasks but was responsive to 6 weeks of bilateral arm-based training. Despite the apparent lack of training specificity, the generalizable effects of bilateral arm training to fine motor interlimb coordination may reflect central motor control mechanisms for upper-extremity coordination, which may be accessed and may influence the recovery of arm function after stroke.

Chronic Disease↗

PubMed1996

Modification of motor control of wrist extension by mesh-glove electrical afferent stimulation in stroke patients.

OBJECTIVE: To study the effect of mesh-glove afferent stimulation on motor control of voluntary wrist movement in stroke patients who have chronic neurological deficits. DESIGN: Case series. Motor control was evaluated by surface EMG of the arm muscles and kinematics of voluntary wrist movements on 3 occasions: before and immediately after the initial session of mesh-glove stimulation, and then after a daily mesh-glove stimulation program conducted over several months. SETTING: Tertiary care center. PATIENTS: The inclusion criteria were: a history of stroke lasting longer than 6 months; completion of a rehabilitation program during early recovery; and preserved cognitive and communicative ability. Fourteen referred patients (age 63 +/- 9yr; time since stroke 31 +/- 22mo) fulfilled the criteria and completed the daily stimulation program. INTERVENTION: A single initial and then daily mesh-glove electrical afferent stimulation was applied to the hand of the involved upper limb for 20 to 30min. MAIN OUTCOME MEASURES: Surface EMGs from the affected biceps brachii and wrist extensor muscles and amplitudes of wrist movements were analyzed. RESULTS: The single, initial mesh-glove application had no effect on outcome measures. Following a daily mesh-glove stimulation program, however, both the amplitude of wrist extension movement and wrist extensor integrated EMG were significantly increased while coactivation of biceps brachii decreased. These findings were most prominent in subjects with partially preserved voluntary wrist movements. CONCLUSION: We conclude that daily mesh-glove stimulation can modify altered motor control and improve voluntary wrist extension movement in stroke subjects with chronic neurological deficits.

Afferent Pathways↗