Movement Preparation and Execution Under Uncertain Conditions

Abstract

The primary focus of my research is on movement preparation and execution under uncertain conditions. This dissertation will present two main research projects. The first is a human behavioral study that examines the flexibility of a movement plan to make changes under different levels of uncertainty. In general, the term uncertainty implies situations where the information needed to make a decision or perform a task is unreliable or incomplete. Hence, as the level of uncertainty about the movement goal increases, the chances of needing to re-prepare a movement increases as well. Under such situations, we were interested in observing if a movement plan would be more flexible to make changes when presented with new information about the goal. Indeed, we observed that human subjects were able to re-prepare movements at a faster rate when the initial movement plan was formed under greater levels of uncertainty. The results from this study will be presented in detail in Chapter 2. The second project is a non-human primate study where we investigate the influence of uncertainty on motor cortical activity during movement preparation and execution. In this study we trained a rhesus macaque on a reaching task that also manipulated the level of uncertainty by providing partial information about the movement goal using potential targets. The colors of the potential targets were associated with the probability of where the final target would appear. Similar to human behavior, we observed that flexibility in updating movement plans was dependent on the degree of uncertainty about the original movement plan. We evaluated whether this behavior could be explained by a reduction in the distance between neural states associated with preparing movements to uncertain targets. These results will be presented in chapter 3. Before presenting the main research findings from the two projects, I will first review previous studies that have examined the concepts of uncertainty and its relationship to motor behavior in various contexts. Additionally, I will also review the various anatomical and functional features of the motor cortex, specifically, focusing on the primary motor cortex and the dorsal premotor cortex, two brain regions that are strongly involved in goal directed movement preparation and execution. In the fourth and final chapter, I will summarize the main findings and provide a list of future studies that will help extend the findings from the two projects highlighted in chapters 2 and 3.