published_or_final_version / Psychology / Master / Master of Philosophy

Motor skill learning underlies much of what we do, be it hitting a tennis serve, playing the piano, or simply brushing our teeth. Yet despite its importance, little is known about the neural circuits that implement the learning process or how the motor program is represented in the brain. Here I explore the role of motor cortex through lesion studies in rats trained on a motor skill. First, I interrogate whether motor cortex is necessary for the production of a complex motor sequence by training animals to produce temporally precise self-initiated movement sequences on a lever-pressing task. The movement sequences that emerged over months of training were remarkably complex, yet very precise. This motor skill, once mastered, survives large bilateral motor cortex lesions, suggesting that motor cortex is not required for generating movement sequences after consolidation. Next, I explored the role of motor cortex in motor skills that require dexterous manipulations. Animals trained to make constrained spatially precise movements using a joystick were impaired after motor cortex lesions. The role of motor cortex thus depends on the nature of the movements involved but not on the sequencing of movements. Third, I explored the function of motor cortex in sensorimotor transformations by training animals on the same lever-pressing task but with external cues instead of self-initiated movement. Surprisingly, these animals were also not impaired after lesions, suggesting that the method of learning the motor sequence has no consequence once the motor sequences are consolidated. Lastly, I explored the role of motor cortex in learning motor skills. Animals that were lesioned after being exposed to the lever-pressing task could learn to adjust the timing of their movements, indicating that motor cortex is not required for adapting a previously-acquired motor sequence. Lesions of motor cortex prior to any training, however, severely disrupted learning. Even with extended training, animals were unable to fully master the task, demonstrating that motor cortex is necessary for the acquisition of new motor skills even when it is not required for their execution.

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A size-weight illusion (SWI) occurs when a large object and small object of equal mass but different volume are lifted and the small object is perceived as heavier than the large object. All previous studies of the SWI used similar coloured objects and found that individuals initially use more force to lift the large object, compared to the small object but then use similar forces for the two objects on subsequent lifts. In contrast to the change in lifting forces over trials, the perceptual illusion stays consistent across all trials. The goal of the current study was to determine if introducing different colours for the SWI stimuli could alter participants’ expectations about the masses of the two objects and therefore modify the perceptual SWI. Participants lifted SWI stimuli that were either identical in colour or stimuli of different colour.

A recent theory of motor control, based on optimal feedback control, posits that voluntary motor behaviour involves the sophisticated manipulation of sensory feedback. Although this theory can explain how people move in the world, it does not specifically describe how this control process is implemented by the nervous system. In this thesis, we propose and explore one physiological implication of this theory. Specifically, we hypothesize that rapid feedback responses should possess the key functional attributes of voluntary control because these two systems share a common neural pathway through motor areas of cerebral cortex. Our first four studies were designed to elaborate the functional attributes of the long-latency stretch reflex, a fast feedback response which occurs 50-100ms following the mechanical stretch of a muscle. Consistent with our hypothesis, we found that the long-latency response possesses many attributes commonly reserved for voluntary control: the long-latency response is continuously modulated by subject intent (Chapter 2), it compensates for the size-recruitment principle of the motoneuron pool (Chapter 3) and it accounts for the mechanical properties of the upper-limb (Chapter 5). Further investigation revealed that the long-latency response can be decomposed into two functionally-independent processes (Chapter 4), and that one of these components contributes all of the sophistication observed in Chapters 2 and 3. The goal of our fifth study was to investigate the neural basis of the long-latency response (Chapter 6). Our results provide strong evidence from both single-neuron recordings in non-human primates and transcranial magnetic stimulation in humans that primary motor cortex, which is known to be a critical node for voluntary control, also contributes to the sophistication of the long-latency response. Taken together, the studies presented in this thesis demonstrate that the long- latency response possesses several functional attributes typically reserved for voluntary control and that this sophistication likely arises via a transcortical pathway through primary motor cortex. / Thesis (Ph.D, Neuroscience Studies) -- Queen's University, 2011-01-18 09:19:24.579

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The classification of vehicle types and their attributes for various traffic modelling exercises is a common occurrence. The increasing use of microsimulation packages, which are based on modelling individual vehicles through the road network, points to the importance of having proper vehicle attributes specified in order to achieve the modelling results that match real-life conditions. / The use of a customised vehicle fleet instead of the default types that are usually built into microsimulation software will allow more accurate estimation of traffic performance indicators, such as speeds, travel times, capacity, fuel consumption etc. Most notably the accurate classification of vehicles is essential for reliable vehicle emissions modelling to occur, since the type and fuel used by vehicles has a significant effect on their emissions performance. To this end there are a number of databases that can be used for vehicle classification, these include but are not limited to: Australian Bureau of Statistics Motor Vehicle Census Data; Austroads Vehicle Classifications; Fleet composition models produced by Bureau of Transport Economics. / This thesis describes the development of the customised vehicle fleet to be used in Paramics microsimulation modelling package by Quadstone in the UK. Vehicle fleet profiles were developed for South Australian urban and rural conditions based on Australian Bureau of Statistics Motor Vehicle Census data and supplemented with other sources of vehicle kinematics and physical characteristics. / Thesis (MEng(TransportSystemsEng))--University of South Australia, 2005

Thesis (MAppSc in Physiotherapy) -- University of South Australia, 1994