Biomedical subjects

Susan V Duff

Publications and source records attributed to Susan V Duff.

7 recordsLinked to original sources

PubMed2006

Lateralization of motor adaptation reveals independence in control of trajectory and steady-state position.

We recently provided evidence that the dominant and nondominant arms are specialized for controlling different aspects of reaching movements. In this study, we test whether these specializations lead to qualitatively different adaptive mechanisms, when exposed to novel inertial dynamics. Two groups of six right-handed adults performed a reaching task toward a single target with either the dominant or nondominant arm. After 39 trials of task familiarization without a load, subjects performed 180 trials with a 1.5 kg mass, positioned 25 cm lateral to the forearm. To assess the time course of adaptation, we quantified changes in movement direction and linearity, and to assess the quality of adaptation, we randomly interspersed aftereffect trials and generalization trials. The former were assessed by removing the mass and the latter by changing the location of the movement in the workspace. Whereas, final position accuracy improved to the same extent for both arms, initial movement direction improved only for the dominant arm. In contrast, nondominant arm adaptation occurred mainly by making more effective corrections for persistent errors in initial direction. Consistent with these findings, aftereffect trials, an indicator of feedforward control processes, showed progressive increases in error for only the dominant arm. In addition, substantial generalization only occurred for the dominant arm. These results support our hypothesis that interlimb differences in control mechanisms produce different patterns of adaptation to novel inertial dynamics.

Adaptation, Physiological↗

PubMed2004

Enhancing prehension in infants and children: fostering neuromotor strategies.

Learning to reach for and manipulate objects requires considerable neuromotor control and flexibility. Through environmental and object exploration individual neuromotor strategies expand, and prehensile skills improve, as infants and children overcome constraints. Infants and children with prehensile deficits often have difficulty exploring objects and the environment, thus, may not sufficiently develop the strategies needed to expand their prehensile skills. This article reviews neuromotor factors that influence prehension development, discusses limitations to prehensile function and provides guidelines that can be used to examine and enhance prehensile behaviors in infants and young children based on a task-oriented approach addressing impairments, motor strategies and function.

Adaptation, Physiological↗

PubMed2003

Object release under varying task constraints in children with hemiplegic cerebral palsy.

Considerable attention has been given in recent years to fingertip force coordination during grasping and lifting small objects in children with cerebral palsy (CP). However, little is known about the children's ability to replace and release an object from grasp. The present study examined the coordination of fingertip forces during replacement and release of an object from grasp under varying task constraints in the involved hand of 15 children (10 males, five females, age range 7 to 14 years) with hemiplegic CP and in the non-dominant hand of 15 age-matched, typically-developing children (seven males, eight females). Participants released an object, instrumented with force transducers and held with a precision grip, onto a stable surface and onto an unstable surface (requiring higher accuracy) at self-paced and fast-as-possible speeds. Temporal and force measures were recorded and the dependent measures were tested using analyses of variance. Results showed that force coordination was impaired in children with hemiplegia, resulting in prolonged and uncoordinated replacement and release of the object (p<0.05). Differences between controls and children with hemiplegia were greater when speed and accuracy constraints were imposed (i.e. task performance was affected by these constraints to a greater extent in the children with CP, p<0.05). Impairments in temporal coordination of object release were also observed in the non-involved hand under all conditions (p<0.05). These results provide additional information about impaired hand function in children with hemiplegic CP. Clinical implications of these findings are discussed.

Adolescent↗

PubMed2003

Learning of grasp control in children with hemiplegic cerebral palsy.

This study examined whether children with hemiplegic cerebral palsy (CP) have anticipatory control of fingertip forces during lifts of familiar objects, and what type of practice (blocked or random) best enhances the retention of anticipatory control during lifts of novel objects. Eighteen children with hemiplegic CP (7 females, 11 males; 7 to 14 years of age, mean age 10 years, SD 1.8) and 18 age-matched typically developing children (8 males, 10 females; mean age 10.4 years, SD 1.7) participated in the study. In the first experiment the children lifted familiar objects of various weights and sizes five times each, while the vertical lifting (load) force was measured. Most participants demonstrated higher rates of load force increase for heavier (and larger) objects already during the first lift, indicating anticipatory control. Furthermore, the load force rates generally were similar across the five lifts for each object, suggesting that they had stable representations of the objects' properties. In the second experiment children lifted three novel objects varying in weight (but identical in volume) 27 times each, in either a blocked or a random order, followed by nine immediate and nine delayed (24 hours) retention trials. Blocked practice resulted in greater differentiation of the force rates between objects during acquisition than did random practice. Both practice schedules resulted in similar retention. These findings suggest that children with hemiplegic CP have a priori internal representations used for anticipatory force scaling with familiar objects. Furthermore, the results indicate that these children can form and retain internal representations of novel objects for anticipatory control, irrespective of the type of practice schedule employed. Thus, clinically based practice sessions that incorporate lifts with novel objects may enhance anticipatory force scaling and related prehensile function in children with hemiplegic CP.

Adolescent↗

PubMedDate not supplied

Impact of peripheral nerve injury on sensorimotor control.

Deficits in sensorimotor control are experienced immediately after nerve injury due to changes in the periphery and central nervous system. Muscle denervation and sensory loss often disrupt prehensile coordination requiring the use of alternative strategies. To effectively foster coordination postinjury clinicians should address not only impairments and function but motor control issues through the prescription of specific sensory and motor experiences. Engagement in carefully planned, therapeutic activity can take advantage of the nervous systems' ability to regenerate and reorganize following nerve lesions. This article reviews motor control issues and neural reorganization concepts that may influence the recovery of skilled prehension following upper limb nerve injury. It also provides clinical guidelines for examining and enhancing coordination.

Adaptation, Physiological↗

PubMedDate not supplied

Does motor lateralization have implications for stroke rehabilitation?

Recent findings on motor lateralization have revealed consistent differences in the control strategies of the dominant and nondominant hemisphere/limb systems that could have implications for hemiplegic stroke patients. Studies in stroke patients have demonstrated deficiencies in the ipsilesional arm that reflect these distinctions; patients with right-hemisphere damage tend to show deficits in positional accuracy, and patients with left-hemisphere damage show deficits in trajectory control. Such deficits have been shown to impede functional performance; yet patients with severe dominant-side hemiplegia must often use the nondominant arm as the primary manipulator for activities of daily living. Nevertheless, the nondominant arm may not spontaneously become efficient as a dominant manipulator, as indicated by the persistence of deficits in chronic stroke patients. More research is necessary to determine whether motor therapy can facilitate a more effective transition of this arm from a nondominant to a dominant controller.

Functional Laterality↗

PubMedDate not supplied

Manual asymmetry during object release under varying task constraints.

OBJECTIVE: This study examined differences between the dominant and nondominant hands of children during an object release task under various accuracy and speed constraints. METHOD: Fifteen children 7 to 14 years of age who were typically developing released an instrumented object held with a precision grip onto a stable or unstable surface at a self-paced or quick speed while temporal and force measures were recorded. RESULTS: Few differences were found between the two hands under stable, self-paced conditions. However, given accuracy constraints, object replacement with the nondominant hand took longer than the dominant hand. The nondominant hand exhibited different force coordination patterns than the dominant hand when both accuracy and speed constraints were imposed. CONCLUSION: Task constraints differentially affected the performance of the dominant and nondominant hands during this object release task. The results suggest that clinicians should incorporate various task constraints into hand preference evaluations and during "dominance retraining".

Adolescent↗