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The Neural and Behavioral Processes Underlying Limb Selection

Abstract

In the process of planning a reaching movement, people have two principle decisions: where to reach and which limb to reach with. Recent investigations have shed light on how the brain integrates value information about different stimulus-outcome pairs in order to make this first decision. However, recent work in neuroeconomics, while abundant, has almost exclusively focused on how we decided between stimuli external to the body and ignored how we decide between our two limbs.

In this dissertation, I explore the psychological processes and neural correlates of hand choice in three experiments, all of which involve an unconstrained reaching task. The first study demonstrates that hand choice is influenced by recent reinforcement history: People increase the use of the non-dominant hand when the likelihood of hitting the target with the non-dominant hand is increased and/or the likelihood of missing the target with the dominant hand is decreased. In the second study, I use functional neuroimaging to explore the neural correlates of hand choice, comparing conditions in which people are either directed to use the left or right hand or free to choose between the two hands. The free choice condition led to increased hemodynamic activity in a network of cortical and subcortical areas, including the medial prefrontal cortex, posterior parietal area, basal ganglia, and cerebellum. In the third experiment, I lay the groundwork for a full characterization of the neural regions involved in value-based decision making between two targets and two limbs.

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