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Everyday movements, such as reaching for a drink of water or typing on a keyboard highlight the relative ease with which we move and interact with our surroundings. However, the success of these skilled movements depends on the motor system’s ability to consider a variety of factors, such as the goal of the behavioral task, the surrounding environment and the physical properties of the musculoskeletal system. Recent theories of voluntary motor control, namely optimal feedback control, suggest that such skilled motor behavior is achieved through sophisticated feedback control. This thesis investigates one physiological implication of this theory. Specifically, we hypothesize that rapid feedback responses following mechanical perturbations possess many of the functional attributes thought to be reserved for voluntary control because these two systems have contributions from similar neural substrates (eg. motor areas in cortex). Our studies were specifically designed to investigate rapid feedback responses during the long-latency epoch, which occurs between 50-100ms following a mechanical perturbation. Consistent with our hypothesis, we found that the sophistication of the long-latency response rivals that of voluntary control. In our first study (Chapter 2) we examined if rapid feedback responses were sensitive to features of the end target. We found that muscle activity during the long-latency epoch was modulated by the size/shape of the end. In our second study (Chapter 3) we observed flexible responses in muscle activity during the long-latency epoch that reflected rapid ‘decisions’ during online control regarding how to navigate around obstacles in the environment as well as how to select amongst multiple potential goals. In our final study (Chapter 4) we examined if rapid feedback responses in the shortened muscle parallel the sophisticated responses observed in the lengthened muscle. We found that unloading a pre-excited muscle elicited sophisticated inhibitory responses, including knowledge of limb mechanics and rapid target selection, during the long-latency epoch that are comparable to the excitatory responses observed during loading. Taken together, the studies presented in this thesis demonstrate that the responses in the long-latency epoch reflect several functional attributes typically reserved for voluntary control. / Thesis (Ph.D, Neuroscience Studies) -- Queen's University, 2014-04-29 16:54:12.489

Following lower-limb amputation, patients suffer from sensory loss within the prosthesis/residuum complex leading to diminished proprioception and balance. Artificial sensory systems have the potential to improve rehabilitation outcomes including better functional usage of lower-limb prostheses to achieve a higher quality of life for the prosthetic users. The purpose of this work was to develop and test the e fficacy of a vibrotactile feedback system for lower-limb amputees that may augment feedback during complex balance and movement tasks. Responses to different vibrotactile stimuli frequencies, locations, and physical conditions were assessed. Key outcome measures for this work were the response time and response accuracy of the subjects to the different stimulator configurations. Frequencies closer to 250 Hz applied to the anterior portion of the thigh resulted in the quickest reaction times. When multitasking, reaction times increased. These preliminary results indicate that vibrotactile sensory feedback may be viable to use by lower-limb amputees.

Following lower-limb amputation, patients suffer from sensory loss within the prosthesis/residuum complex leading to diminished proprioception and balance. Artificial sensory systems have the potential to improve rehabilitation outcomes including better functional usage of lower-limb prostheses to achieve a higher quality of life for the prosthetic users. The purpose of this work was to develop and test the e fficacy of a vibrotactile feedback system for lower-limb amputees that may augment feedback during complex balance and movement tasks. Responses to different vibrotactile stimuli frequencies, locations, and physical conditions were assessed. Key outcome measures for this work were the response time and response accuracy of the subjects to the different stimulator configurations. Frequencies closer to 250 Hz applied to the anterior portion of the thigh resulted in the quickest reaction times. When multitasking, reaction times increased. These preliminary results indicate that vibrotactile sensory feedback may be viable to use by lower-limb amputees.

Recent research has found that perceptual deficits exist in Parkinson???s disease (PD), yet the link between perception and movement impairments is not well understood. Inaccurate estimation of distance has the potential to be an underlying cause of movement impairments. Alternatively, those with PD may not be able to perceive their own movements accurately. The main objective of this thesis was to evaluate (1) whether distance estimation is influenced by static perception compared to perception during movement in PD, (2) how visual motion processing contributes to distance estimation during movement, and (3) how dopaminergic medication contributes to these distance estimation deficits. Thirty-seven participants (19 individuals with PD, 18 age-matched healthy control participants (HC) estimated distance to a remembered target in a total of 48 trials, in 4 randomized blocks. Estimation conditions included: (i) no motion: participants pointed with a laser, (ii) motion: participants walked to the estimated position, (iii) visual motion (wheelchair): participants were pushed in a wheelchair while they gave their estimate, (iv) visual motion (VR): participants completed their distance estimate while seated and viewed themselves (as if they were walking) in VR. PD patients completed this protocol twice; once OFF and once ON dopaminergic medication. Participants were matched for age, distance acuity, Modified Mini Mental State Exam (3MS), spatial working memory and motor planning ability. In Study 1 (no motion vs. motion), individuals with PD and healthy control participants did not differ in judgment accuracy during the no motion condition. However, those with PD did have greater amounts of error compared to healthy control participants while estimating distance during the motion condition. Similarly, those with PD significantly underestimated the target position compared to healthy control participants during the motion condition only. Individuals with PD demonstrated greater variability overall. In Study 2, error did not differ between PD and HC groups during visual motion perception (wheelchair). Interestingly, the HC group tended to perform significantly worse than those with PD in the VR condition. Overall, across both studies there was no significant influence of dopaminergic medication in any of the conditions. Individuals with PD demonstrated distance estimation deficits only when required to move through their environment. In contrast to estimations made with movement, neither static estimation nor estimations made with visual motion revealed significant differences between the two groups. Thus perceptual estimation deficits appear to occur only during movement, which may be suggestive of an underlying sensory processing deficit which leads to a problem integrating vision and self-motion information.

The goal of this thesis is to explore different control strategies to execute rhythmic movements. This issue is covered both with design perspectives (implementation in a robot) and analysis perspectives. Indeed we aim at analyzing both our robot behavior, and the behavior of human subjects executing the same task. Interesting parallels between these data sets are raised, illustrating for instance the ubiquitous trade-off of control theory between performance and robustness. / L'objectif de cette thèse est d'explorer différentes stratégies d'exécution des mouvements rythmiques. Cet objectif est couvert à la fois dans des perspectives d'implémentation (sur un robot) et d'analyse. En effet, nous souhaitons analyser à la fois le comportement de notre robot, et le comportement de sujets humains exécutant la même tâche. Des parallèles intéressants, entre les deux ensemble de données, sont proposés et illustrent, par exemple, le compromis entre la robustesse et la performance, souvent utilisé dans la thèorie du contrôle.

Recent research has found that perceptual deficits exist in Parkinson’s disease (PD), yet the link between perception and movement impairments is not well understood. Inaccurate estimation of distance has the potential to be an underlying cause of movement impairments. Alternatively, those with PD may not be able to perceive their own movements accurately. The main objective of this thesis was to evaluate (1) whether distance estimation is influenced by static perception compared to perception during movement in PD, (2) how visual motion processing contributes to distance estimation during movement, and (3) how dopaminergic medication contributes to these distance estimation deficits. Thirty-seven participants (19 individuals with PD, 18 age-matched healthy control participants (HC) estimated distance to a remembered target in a total of 48 trials, in 4 randomized blocks. Estimation conditions included: (i) no motion: participants pointed with a laser, (ii) motion: participants walked to the estimated position, (iii) visual motion (wheelchair): participants were pushed in a wheelchair while they gave their estimate, (iv) visual motion (VR): participants completed their distance estimate while seated and viewed themselves (as if they were walking) in VR. PD patients completed this protocol twice; once OFF and once ON dopaminergic medication. Participants were matched for age, distance acuity, Modified Mini Mental State Exam (3MS), spatial working memory and motor planning ability. In Study 1 (no motion vs. motion), individuals with PD and healthy control participants did not differ in judgment accuracy during the no motion condition. However, those with PD did have greater amounts of error compared to healthy control participants while estimating distance during the motion condition. Similarly, those with PD significantly underestimated the target position compared to healthy control participants during the motion condition only. Individuals with PD demonstrated greater variability overall. In Study 2, error did not differ between PD and HC groups during visual motion perception (wheelchair). Interestingly, the HC group tended to perform significantly worse than those with PD in the VR condition. Overall, across both studies there was no significant influence of dopaminergic medication in any of the conditions. Individuals with PD demonstrated distance estimation deficits only when required to move through their environment. In contrast to estimations made with movement, neither static estimation nor estimations made with visual motion revealed significant differences between the two groups. Thus perceptual estimation deficits appear to occur only during movement, which may be suggestive of an underlying sensory processing deficit which leads to a problem integrating vision and self-motion information.

Locomotion is an integral part of a whole range of animal behaviours. The basic rhythm for locomotion in vertebrates has been shown to arise from local networks residing in the spinal cord and these networks are known as central pattern generators (CPG). However, during the locomotion, these centres are constantly interacting with the sensory feedback signals coming from muscles, joints and peripheral skin receptors in order to adapt the stepping or swimming to varying environmental conditions. Conceptual models of vertebrate locomotion have been constructed using mathematical models of locomotor subsystems based on the neurophysiological evidence obtained primarily in the cat and the salamander, an amphibian with a sprawling posture. Such models provide opportunity for studying the key elements in the transition from aquatic to terrestrial locomotion. Several aspects of locomotor control using the cat or the salamander as an animal model have been investigated employing computer simulations and here we use the same approach to address a number of questions or/and hypotheses related to rhythmic locomotion in quadrupeds. Some of the involved questions are, the role of mechanical linkage during deafferented walking, finding inherent stabilities/instabilities of muscle-joint interactions during normal walking and estimating phase dependent controlability of muscle action over joints. Also we investigate limb and body coordination for different gaits, use of side-stepping in front limbs for turning and the role of sensory feedback in gait generation and transitions in salamanders.      This thesis presents the basics of the biologically realistic models of cat and salamander locomotion and summarizes computational methods in modeling quadruped locomotor subsystems such as CPG, limb muscles and sensory pathways. In the case of cat hind limb, we conclude that the mechanical linkages between the legs play a major role in producing the alternating gait. In another experiment we use the model to identify open-loop linear transfer functions between muscle activations and joint angles while ongoing locomotion. We hypothesize that the musculo-skeletal system for locomotion in animals, at least in cats, operates under critically damped condition.      The 3D model of the salamander is successfully used to mimic locomotion on level ground and in water. We compare the walking gait with the trotting gait in simulations. We also found that for turning, the use of side-stepping alone or in combination with trunk bending is more effective than the use of trunk bending alone. The same model together with a more realistic CPG composed of spiking neurons was used to investigate the role of sensory feedback in gait generation and transition. We found that the proprioceptive sensory inputs are essential in obtaining the walking gait, whereas the trotting gait is more under central (CPG) influence compared to that of the peripheral or sensory feedback.      This thesis work sheds light on understanding the neural control mechanisms behind vertebrate locomotion. Additionally, both neuro-mechanical models can be used for further investigations in finding new control algorithms which give robust, adaptive, efficient and realistic stepping in each leg, which would be advantageous since it can be implemented on a controller of a quadruped-robotic device. / This work is Funded by Swedish International Development cooperation Agency (SIDA). QC 20111110

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