Coupling online control and inhibitory systems in children with Developmental Coordination Disorder: Goal-directed reaching

For children with Developmental Coordination Disorder (DCD), the real-time coupling between frontal executive function and online motor control has not been explored despite reported deficits in each domain. The aim of the present study was to investigate how children with DCD enlist online control under task constraints that compel the need for inhibitory control. A total of 129 school children were sampled from mainstream primary schools. Forty-two children who met research criteria for DCD were compared with 87 typically developing controls on a modified double-jump reaching task. Children within each skill group were divided into three age bands: younger (6–7 years), mid-aged (8–9), and older (10–12). Online control was compared between groups as a function of trial type (non-jump, jump, anti-jump). Overall, results showed that while movement times were similar between skill groups under simple task constraints (non-jump), on perturbation (or jump) trials the DCD group were significantly slower than controls and corrected trajectories later. Critically, the DCD group was further disadvantaged by anti-jump trials where inhibitory control was required; however, this effect reduced with age. While coupling online control and executive systems is not well developed in younger and mid-aged children, there is evidence of age-appropriate coupling in older children. Longitudinal data are needed to clarify this intriguing finding. The theoretical and applied implications of these results are discussed.     

肝移植手术中的配合

自从 1 96 3年Starzl成功实施世界上第一例活体肝移植后 ,肝移植手术已经成为现代肝脏外科学领域里的一个比较实用、也比较时髦的手术及研究项目。结合我院已完成的 2例肝移植手术 ,简要介绍肝移植手术术前、术中及术后的相关问题 ,并介绍肝移植手术的主要步骤 ,叙述手术中的相关配合问题     

Changes in muscle recruitment patterns during skill acquisition

The control of movement is predicated upon a system of constraints of musculoskeletal and neural origin. The focus of the present study was upon the manner in which such constraints are adapted or superseded during the acquisition of motor skill. Individuals participated in five experimental sessions, in which they attempted to produce abduction-adduction movements of the index finger in time with an auditory metronome. During each trial, the metronome frequency was increased in eight steps from an individually determined base frequency. Electromyographic (EMG) activity was recorded from first dorsal interosseous (FDI), first volar interosseous (FVI), flexor digitorum superficialis (FDS), and extensor digitorum communis (EDC) muscles. The movements produced on the final day of acquisition more accurately matched the required profile, and exhibited greater spatial and temporal stability, than those generated during initial performance. In the early stages of skill acquisition, an alternating pattern of activation in FDI and FVI was maintained, even at the highest frequencies. In contrast, as the frequency of movement was increased, activity in FDS and EDC was either tonic or intermittent. As learning proceeded, alterations in recruitment patterns were expressed primarily in the extrinsic muscles (EDC and FDS). These changes took the form of increases in the postural role of these muscles, shifts to phasic patterns of activation, or selective disengagement of these muscles. These findings suggest that there is considerable flexibility in the composition of muscle synergies, which is exploited by individuals during the acquisition of coordination.     

The dynamics of isometric bimanual coordination

Eight right-handed subjects performed rhythmic isometric applications of torque in the directions of pronation and supination of the forearm, in single limb and bimanual conditions. Bimanual movements were executed in either in-phase (homologous muscles simultaneously active) or anti-phase (non-homologous muscles active simultaneously) modes of coordination, in self-paced and frequency-scaled conditions. In the inphase (frequency-scaled) condition, subjects were required to synchronise (applications of torque) with each beat of a metronome, either in the direction of pronation or supination. In the anti-phase (frequency-scaled) condition, subjects were required to synchronise (applications of torque) with each beat of the metronome, either to the left or to the right. Departures from the anti-phase mode of coordination were observed as pacing frequency was increased. However, these departures were of short duration and the anti-phase mode was always re-established. These findings are in marked contrast to those obtained when there is free motion of the limbs. There also existed systematic differences between the stability of the pronation and supination phases of torque application. These differences were, in turn, modified through coincidence with the pacing signal. These results are discussed with reference to the constraints imposed upon the coordination dynamics by the intrinsic properties of the neuromuscular-skeletal system.     

Coordination of multiple muscles in two degree of freedom elbow movements

The present study quantifies electromyographic (EMG) magnitude, timing, and duration in one and two degree of freedom elbow movements involving combinations of flexion-extension and pronation-supination. The aim is to understand the organization of commands subserving motion in individual and multiple degrees of freedom. The muscles tested in this study fell into two categories with respect to agonist burst magnitude: those whose burst magnitude varied with motion in a second degree of freedom at the elbow, and those whose burst magnitude depended on motion in one degree of freedom only. In multiarticular muscles contributing to motion in two degrees of freedom at the elbow, we found that the magnitude of the agonist burst was greatest for movements in which a muscle acted as agonist in both degrees of freedom. The burst magnitudes for one degree of freedom movements were, in turn, greater than for movements in which the muscle was agonist in one degree of freedom and antagonist in the other. It was also found that, for movements in which a muscle acted as agonist in two degrees of freedom, the burst magnitude was, in the majority of cases, not different from the sum of the burst magnitudes in the component movements. When differences occurred, the burst magnitude for the combined movement was greater than the sum of the components. Other measures of EMG activity such as burst onset time and duration were not found to vary in a systematic manner with motion in these two degrees of freedom. It was also seen that several muscles which produced motion in one degree of freedom at the elbow, including triceps brachii (long head), triceps brachii (lateral head), and pronator quadratus displayed first agonist bursts whose magnitude did not vary with motion in a second degree of freedom. However, for the monoarticular elbow flexors brachialis and brachioradialis, agonist burst magnitude was affected by pronation or supination. Lastly, it was observed that during elbow movements in which muscles acted as agonist in one degree of freedom and antagonist in the other, the muscle activity often displayed both agonist and antagonist components in the same movement. It was found that, for pronator teres and biceps brachii, the timing of the bursts was such that there was activity in these muscles concurrent with activity in both pure agonists and pure antagonists. The empirical summation of EMG burst magnitudes and the presence in a single muscle of both agonist and antagonist bursts within a movement suggest that central commands associated with motion in individual degrees of freedom at the elbow may be superimposed to produce elbow movements in two degrees of freedom.     

Cerebellar involvement in the coordination control of the oculo-manual tracking system: effects of cerebellar dentate nucleus lesion

Summary When the hand of the observer is used as a visual target, oculomotor performance evaluated in terms of tracking accuracy, delay and maximal ocular velocity is higher than when the subject tracks a visual target presented on a screen. The coordination control exerted by the motor system of the arm on the oculomotor system has two sources: the transfer of kinaesthetic information originating in the arm which increases the mutual coupling between the arm and the eyes and information from the arm movement efferent copy which synchronizes the motor activities of both subsystems (Gauthier et al. 1988; Gauthier and Mussa-Ivaldi 1988). We investigated the involvement of the cerebellum in coordination control during a visuo-oculo-manual tracking task. Experiments were conducted on baboons trained to track visual targets with the eyes and/or the hand. The role of the cerebellum was determined by comparing tracking performance defined in terms of delay, accuracy (position or velocity tracking errors) and maximal velocity, before and after lesioning the cerebellar dentate nucleus. Results showed that in the intact animal, ocular tracking was more saccadic when the monkey followed an external target than when it moved the target with its hand. After lesioning, eye-alone tracking of a visual target as well as eye-and-hand-tracking with the hand contralateral to the lesion was little if at all affected. Conversely, ocular tracking of the hand ipsilateral to the lesion side became more saccadic and the correlation between eye and hand movement decreased considerably while the delay between target and eyes increased. In normal animals, the delay between the eyes and the hand was close to zero, and maximal smooth pursuit velocity was around 100 degrees per second with close to unity gain; in eye-alone tracking the delay and maximal smooth pursuit velocity were 200 ms and 50 deg per second, respectively. After lesioning, delay and maximum velocity were respecttively around 210 ms and 40 deg per second, that is close to the values measured in eye-alone tracking. Thus, after dentate lesioning, the oculomotor system was unable to use information from the motor system of the arm to enhance its performance. We conclude that the cerebellum is involved in the coordination control between the oculomotor and manual motor systems in visuo-oculo-manual tracking tasks.     

Compensation for distal impairments of grasping in adults with hemiparesis

Previous studies have shown that patients with arm and hand paresis following stroke recruit an additional degree of freedom (the trunk) to transport the hand during reaching and use alternative strategies for grasping. The few studies of grasping parameters of the impaired hand have been case studies mainly focusing on describing grasping in the presence of particular impairments such as hemi-neglect or optic ataxia and have not focussed on the role of the trunk in prehension. We hypothesized that the trunk movement not only ensures the transport of the hand to the object, but it also assists in orienting the hand for grasping when distal deficits are present. Nineteen patients with chronic hemiparesis and seven healthy subjects participated in the study. Patients had sustained a stroke of non-traumatic origin 6–82 months previously (31±22 months) and had mild or moderate to severe arm paresis. Using a whole hand grasp, subjects reached and grasped a cylinder (35 mm) that was placed sagittally (T1) or at a 45° angle to the sagittal midline in the ipsilateral workspace (T2), both at about 90% arms length (10 trials per target). Eight infrared emitting diodes were placed on bony landmarks of the hand, arm and trunk and kinematic data were recorded by an optical motion analysis system (Optotrak) for 2–5 s at 120 Hz. Hand position and orientation were recorded by a Fastrack Polhemus system. Our results show that during goal-directed prehension tasks, individuals with hemiparesis oriented the hand more frontally for grasping and used more trunk anterior displacement or rotation to transport the hand to the target compared to healthy subjects. Despite these changes, the major characteristics of reaching and grasping such as grip aperture size, temporal coordination between hand transport and aperture formation and the relative timing of grip aperture were largely preserved. For patients with more severe distal impairments, the amount of trunk displacement was also correlated with a more frontal hand orientation for grasping. Furthermore, in healthy subjects and patients without distal impairments, the trunk movement was mostly related to proximal arm movements while in those with distal impairments, trunk movement was related to both proximal and distal arm movements. Data support the hypothesis that the trunk movement is used to assist both arm transport and hand orientation for grasping when distal deficits are present.     

Joint angle variability in 3D bimanual pointing: uncontrolled manifold analysis

The structure of joint angle variability and its changes with practice were investigated using the uncontrolled manifold (UCM) computational approach. Subjects performed fast and accurate bimanual pointing movements in 3D space, trying to match the tip of a pointer, held in the right hand, with the tip of one of three different targets, held in the left hand during a pre-test, several practice sessions and a post-test. The prediction of the UCM approach about the structuring of joint angle variance for selective stabilization of important task variables was tested with respect to selective stabilization of time series of the vectorial distance between the pointer and aimed target tips (bimanual control hypothesis) and with respect to selective stabilization of the endpoint trajectory of each arm (unimanual control hypothesis). The components of the total joint angle variance not affecting (V_COMP) and affecting (V_UN) the value of a selected task variable were computed for each 10% of the normalized movement time. The ratio of these two components R_V=V_COMP/V_UN served as a quantitative index of selective stabilization. Both the bimanual and unimanual control hypotheses were supported, however the R_V values for the bimanual hypothesis were significantly higher than those for the unimanual hypothesis applied to the left and right arm both prior to and after practice. This suggests that the CNS stabilizes the relative trajectory of one endpoint with respect to the other more than it stabilizes the trajectories of each of the endpoints in the external space. Practice-associated improvement in both movement speed and accuracy was accompanied by counter-intuitive lack of changes in R_V. Both V_COMP and V_UN variance components decreased such that their ratio remained constant prior to and after practice. We conclude that the UCM approach offers a unique and under-explored opportunity to track changes in the organization of multi-effector systems with practice and allows quantitative assessment of the degree of stabilization of selected performance variables.     

Variant and invariant characteristics of speech movements

Summary Upper lip, lower lip, and jaw kinematics during select speech behaviors were studied in an attempt to identify potential invariant characteristics associated with this highly skilled motor behavior. Data indicated that speech motor actions are executed and planned presumably in terms of relatively invariant combined multimovement gestures. In contrast, the individual upper lip, lower lip, and jaw movements and their moment-to-moment coordination were executed in a variable manner, demonstrating substantial motor equivalence. Based on the trial-to-trial variability in the movement amplitudes, absolute positions, and velocities of the upper lip, lower lip, and jaw, it appears that speech motor planning is not formulated in terms of spatial coordinates. Seemingly, object-level planning for speech may be encoded in relation to the acoustic consequences of the movements and ultimately with regard to listener's auditory perceptions. In addition, certain temporal parameters among the three movements (relative times of movement onsets and velocity peaks) were related stereotypically, reflecting invariances characteristic of more automatic motor behaviors such as chewing and locomotion. These data thus appear to provide some additional insights into the hierarchy of multimovement control. At the top of the motor control hierarchy, the overall plan appears to be generated with explicit specification of certain temporal parameters. Subsequently, based upon the plan and within that stereotypic temporal framework, covariable adjustments among the individual movements are implemented. Given the results of previous perturbation studies, it is hypothesized that these covariable velocity and amplitude adjustments reflect the action of sensorimptor mechanisms.     

Timing of onset of afferent responses and of use of kinesthetic information for control of movement in normal and cerebellar-impaired subjects

A coordinated triggering task requiring use of kinesthetic information was employed to assess the timing of use of kinesthetic information in normal subjects and patients with cerebellar dysfunction. Passive movements of varying velocity were imposed in the flexor direction about the metacarpophalangeal joint of the right index finger. Subjects attempted to depress a switch with their left thumb when the index finger moved, past a specified angle that was learned during a training session. The velocities ranged from 10°/s to 88°/s in 2°/s increments. After 200 trials, subjects were then instructed instead to react as quickly as possible (reaction-time task) to the onset of movement for an additional 200 trials. For the same movements, the timing of onset of responses of muscle spindle afferents and cutaneous mechanoreceptors was determined by recording the responses of these afferents using microneurography. For slow velocities, patients were able to perform similarly to normals but at faster velocities patients triggered too late compared with normals. Patients required more time to use kinesthetic information than did normal subjects. An estimate of kinesthetic processing was not longer in patients. The chief explanation for the prolonged time required to use kinesthetic information in patients was that their reaction times were prolonged by 93 ms. In addition, the movement time was also prolonged, but this accounted for only 23 ms. Impaired motor performance in tasks requiring the use of kinesthetic information in cerebellar patients can be explained largely by their prolonged reaction times. Muscle spindle afferents responded on average much sooner than cutaneous mechanoreceptors. Because of the limited time available to perfomr the kinesthetic triggering task, the role for cutaneous mechanoreceptors, to provide singals for on-line coordination of movement appears limited compared with muscle spindle afferents.