• Anticipatory task-related modifications in reach: age-related changes and implications for children with DCD

      Viswanathan, Priya; Whitall, Jill (2010)
      Reaching and grasping actions situated in the context of sequential actions can give useful knowledge pertaining to skillful acquisition of a task goal. The aim of this dissertation was to investigate the development of upper extremity skills in the performance of sequential actions in healthy young adults and typically developing (TD) children and apply this knowledge to determine the impairments of motor control in children with Developmental Coordination Disorder (DCD). A 6-camera Vicon system was used to record kinematics of upper limb actions when reaching-to-point, reaching-to-grasp, reaching-to-grasp-and-lift, and reaching-to-grasp-lift-and-place objects with either hand. In the first study, we investigated the control of sequential actions in adults to provide a baseline for `skillful' performance, with respect to feedforward control and reliance on online modifications to achieve the task goal. In addition, we also investigated performance differences attributable to manual asymmetry. We found that anticipatory modifications were present in both feedforward control and feedback elements of the reach and that the non-preferred hand was inferior only in feedback elements. In the first experiment of second study, we investigated the emergence of age-related differences in typically developing children (5-11 years) in their acquisition of improved control of sequential actions. In the TD children, all age groups of children showed task-specific changes in online modifications during the reach phase, but feedforward control was not adult-like at 11 years. The lateralization trajectory showed non-linear developmental trends and high within-group variability. In the second experiment of second study, we compared the performance of 9-11 year-old children with DCD in comparison with the profile of developmental landscape of TD children. Our results suggest that children with DCD are similar in performance to 6- and 8-year-olds, in their inability to plan and execute a movement sequence as a whole or to show asymmetry. The results point towards an inability to incorporate online modifications, and a possible developmental delay in coordination of sequential actions in children with DCD.
    • Auditory motor adaptation in children with and without developmental coordination disorder (DCD)

      Roche, Renuka; Whitall, Jill (2013)
      Tasks, such as dancing, require coordination between the various body segments and synchronization of the movement to auditory stimuli. Children with developmental coordination disorder (DCD), who have significant motor deficits, demonstrate impairments in bimanual self-paced tapping and tapping in synchrony to different frequencies of auditory cues. The purpose of this dissertation was to examine the ability of children with and without DCD to adapt to changing rhythms with constant frequency, under conditions where they could and could not perceive the change in the rhythm. First, we examined differences in the auditory phasing threshold, coordination and its stability in non-disabled children between 4 and 10 years. All children detected changes in rhythm however, the ability to detect more subtle changes increased with age. Children adapted to both perceptible and subliminal changes in rhythm and the developmental trajectories in both conditions were similar. However, variability in performance decreased across age. We, then, investigated the ability of children with DCD to adapt to perceptible and subliminal change and compared their performance to age- and gender- matched typically developing children (TDC). Children with DCD perceived changes in rhythm similar to TDC, and adapted to both perceptible and subliminal changes in rhythm but were more variable under all phasing conditions. The impairments in tapping may be a result of motor "noise" rather than a perceptual-motor coupling process. Finally, we investigated variability using linear measures to assess the amount and a non-linear measure to assess the structure of temporal/spatial variability. Children with DCD were more variable in their linear temporal variability compared to TDC and adults. Adults and TDC but not children with DCD had higher spatial variability in their non-dominant than their dominant finger, suggesting that children with DCD are delayed in lateralization. Children with and without DCD had lower non-linear structural variability than adults. This suggests that children with DCD freeze degrees of freedom to produce movements; however, they are not as effective as TDC. Our results can be interpreted within a neuro-anatomical computational model of motor control that may delineate potential areas of future investigation in children with DCD.
    • Biomechanical analysis of arm reaching in individual with stroke and non-disabled adults

      Liu, Wei; Whitall, Jill (2010)
      Upper extremity (UE) tasks such as arm reaching involve a variety of movement control strategies and unique specialization of function and lateralization in motor performance, namely handedness. UE dysfunction from stroke results in impairment in routine daily activities, including dressing, bathing, and writing. After stroke, movement patterns change to accommodate altered constraints; this is termed compensatory movement control strategy. The aim of this dissertation was to quantify the movement control strategies of arm reaching and identify the contributing biomechanical factors in motor lateralization and stroke. Better understanding of the control strategy of arm reaching could provide important insights for developing new interventions and promoting neural motor functional recovery. Early research findings on quantifying arm movement control strategies are limited to kinematic analysis or use a traditional inverse dynamics approach. The approach used in my research employs a newer quantification method called induced position analysis (IPA) that links both kinematic and kinetic domains. In the first study we developed and validated an IPA to address multijoint coordination of arm reaching in nondisabled individuals. We found that the shoulder and elbow act together in "overshoot" and "undershoot" patterns to move the arm forward to the final position. We termed this pattern as a directional control principle. In the second study we applied IPA to analyze lateralization and to test the current "hand dynamic dominance hypothesis" of arm reaching in nondisabled subjects. Both arms had similar multijoint dynamic patterns that showed movement asymmetry only at a fast speed, where the contribution of the shoulder and elbow was greater in the dominant vs. the nondominant arm. In the third study we did a post-hoc analysis of a bilateral arm training study and explored compensatory movement strategies in stroke survivors. We found that there were two different types of compensatory movement strategies associated with impairment levels ("mild to moderate" vs. "severe") and functional outcomes ("poor" vs. "good" outcomes). Shoulder moment contribution was a strong predictor of arm function change after bilateral arm training. In summary, using IPA provided new information about arm reaching in non-disabled adults and stroke survivors.
    • Interlimb Coordination and Neural Substrates of Complementary Bilateral Arm Movements in Young and Old Individuals

      Woytowicz, Elizabeth Jean; Whitall, Jill; Westlake, Kelly P. (2017)
      Understanding deficits in bilateral arm coordination with aging is essential given that everyday activities rely primarily on bilateral movements. A model of motor lateralization, based on unilateral movements, suggests that the left hemisphere is specialized for predicting task dynamics and the right hemisphere is specialized for impedance control. These arm-hemisphere specializations have been suggested to provide the mechanism for complementary bimanual coordination of the right (dominant) arm for reaching, and the left (non-dominant) arm for stabilizing. Aging has been shown to reduce lateralization of both cognitive and motor tasks. The overall objective of this thesis was to investigate the effect of hemispheric specializations during bilateral coordination in young and old non-disabled individuals. We hypothesized that these arm-hemisphere specializations would be expressed during complementary bilateral tasks in young adults and reduced in older adults. To test this hypothesis, young and old right-hand dominant individuals, completed a bilateral coordination paradigm in which one arm maintained its spatial position and the other arm performed a center-out reaching task with a spring affixed between the arms (conditions: right reach - left stabilize, right stabilize - left reach). Movement performance of reaching and stabilizing was compared across arms and age-group using both kinematic and dynamic variables. To identify the neural substrates underlying complementary bilateral coordination, effective connectivity of a bilateral motor network was investigated using fMRI. Subjects completed a modified version of the bilateral behavioral tasks and performed each task unimanually. In young adults, the right hand showed better reaching performance (less deviation from linearity) and the left hand stabilized better (less displacement). Movement performance of older adults illustrated a) reduced absolute performance; b) preserved asymmetry of reaching; and c) greater asymmetry of stabilizing, indicating an increase in motor lateralization. Finally, effective connectivity analyses illustrated a) greater intrahemispheric modulation for right reach - left stabilize bilateral task compared to greater interhemispheric modulation for the left reach - right stabilize bilateral task; b) reciprocal positive coupling between bilateral SMA for the right reach and left stabilize unilateral tasks; c) greater role for positive modulation from S1 to M1 for left vs. right stabilize tasks.
    • Locomotor Adaptation to a Novel Unilateral Swing Phase Perturbation in Nondisabled Individuals and Persons with Chronic Stroke and Hemiparesis

      Savin, Douglas N., Jr.; Morton, Susanne M.; Whitall, Jill (2011)
      Human walking must be flexible given the myriad of behavioral goals and conditions in which it occurs. Alterations to gait often occur after stroke and asymmetries of post-stroke gait such as step length and single limb support have shown little improvement with traditional therapeutic interventions. Contrasting gait's inherent flexibility with the resistance of hemiparetic gait asymmetries to intervention begs the question: to what extent are hemiparetic gait asymmetries alterable? Therefore, the purpose of this dissertation was to test a novel form of locomotor adaptation designed to specifically alter gait symmetry and determine mechanisms of adaptive interlimb coordination in nondisabled and subjects with stroke and hemiparesis. We recorded electromyography and spatiotemporal gait parameters during treadmill and overground walking as subjects adapted their gait to a novel unilateral swing phase perturbation. In study one we tested whether changes in the leg opposite the unilateral perturbation during treadmill walking were caused by practice-dependent adaptation or feedback corrective mechanisms. Nondisabled subjects demonstrated adaptations and aftereffects of multiple gait parameters and electromyography bilaterally. In study two we tested whether locomotor adaptation of spatial and temporal gait parameters was impaired in subjects with stroke and hemiparesis compared to nondisabled controls. Subjects with stroke had similar adaptations of spatial and temporal gait parameters regardless of which leg was perturbed compared to controls. After removal of the perturbation, negative aftereffects resulted in subjects with stroke initially walking with single limb support symmetry. In study three, we tested the extent to which step length symmetry adaptation during a 10-minute bout of treadmill walking generalized to overground. Both nondisabled and subjects with stroke generalized step length symmetry to overground walking. Negative aftereffects in subjects with stroke indicated they were capable of walking with step length symmetry overground. In summary, our results show feedforward changes in the leg opposite a unilateral perturbation, that locomotor adaptation is not impaired by stroke and hemiparesis and locomotor adaptation during treadmill walking is capable of generalizing to overground walking in nondisabled subjects and those with stroke and hemiparesis. These results suggest that motor adaptation may be beneficial in the rehabilitation of stroke-induced gait asymmetries.