Humans have the unique ability to produce highly coordinated movements, especially while using both hands to achieve a shared goal. The purpose of this dissertation was to investigate the factors influencing a natural consequence of our motor system - bimanual interference. While the word 'interference' often has a negative connotation, interference in the motor system naturally arises from the complex interaction of brain circuitry and anatomical connections and allows motor researchers to explore these systems in detail to provide understanding of how motor information is shared across the brain. In a series of three aims, I investigate possible neural and anatomical mechanisms for interference and frame my interpretation in contemporary theories of volitional motor control.Previous research has demonstrated that as the force demands for movement increases, interference between the upper extremities during movement increases. This interference likely occurs by neurons communicating across the hemispheres through a process called neural crosstalk. While this is a well-established understanding of how interference arises, it is currently not known whether and to what extent interference is affected by motor adaptation, or short-term learning of new movements. I designed two experiments to test the hypothesis that if interference is mediated by neural crosstalk, and that adaptation increases sensitivity to sensory information, interference will be more robust in participants engaging in an adaptation task in one hand while moving the other hand without visual feedback. I found that participants who adapted did indeed show more interference, and this increase is likely due to a shared representation of sensory-motor processes between hemispheres.While the first aim shows adaptation can affect interference via sensory upregulation, my second and third aims attempted to directly test the role adaptation plays in this process. In Aim 2, I designed an experiment to test whether learning can transfer from one hand to the other. Specifically, half of participants performed a reaching task where visual feedback was randomly rotated so that what they saw no longer matched where they reached while the other participants reached normally. Following this, both groups made reaches to a target where visual feedback was rotated by a fixed amount, and I show that participants who previously experienced the random rotations adapted faster. Importantly, my results show that measures targeting feedback processing are transferred more robustly than measures targeting movement planning. Since results from Aim 1 suggest that interference is increased by an upregulation in sensitivity to sensory information, and Aim 2 shows it is mostly the feedback information processing that is shared between limbs, this led me to determine if learning random rotations prior to our interference task can increasing bimanual interference.Aim 3 addressed this question by first having half of our participants engage in random rotation training, while the others reached normally. We then exposed both groups to the interference task used in Aim 1. We found that participants who learned the random rotation had more interference than those reaching with normal visual feedback during training, especially early in the adaptation process. Taken together, these experiments extend our understanding of bimanual coordination to highlight the importance of learning and adaptation in the communication of motor information between the hemispheres and may help to promote their use in future research and clinical applications.
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