Probing motor cortical dynamics of movement preparation and execution

Abstract

Motor cortex is a crucial center for controlling movement, exhibiting complex dynamics in the orchestration of intentional movements. Over the span of several decades, electrophysiology studies have unveiled the motor cortex’s role in controlling the body by exploring the causal relationship between neural activities and kinematics. Furthermore, movement often proceeds through a preparatory phase before its execution. During this movement preparation phase, multiple computations occur concurrently as animals take into account contextual factors, engage in decision-making processes, and draw motivation. Thus, preparing and executing movement involve multiple computations to formulate these computations effectively. In this thesis, I address the neural mechanisms underlying the preparation of movement, with a specific focus on two critical factors in movement: the prediction of movement initiation timing and the decision-making process involved in planning movement. Also, I address how movement preparation and execution, which are distinct yet causally linked processes, are processed in the motor circuits. In Chapter 1, I introduce key concepts in the study of motor control, including our current understanding of how the motor cortex controls the body. Chapter 2 shifts the focus to an essential factor of movement preparation: time. I investigate how the prediction of movement initiation time influences the overall strategy in the movement preparation process. In Chapter 3, I address how the decision such as where to move is factored into motor cortical dynamics. In decision-making, animals often determine where to move based on the sensory cue. To understand the information processing during decision-making in movement preparation, I specifically focus on error cases where animals prepare to move toward the wrong direction. Chapter 4 explores the neural mechanisms of distinct stages in movement. During the movement preparation stage, neural activity undergoes a transition to a state capable of initiating the forthcoming movement while avoiding triggering overt movement. While mathematical models have provided insights into how distinct dynamics manifest depending on each phase, the biological circuit's mechanisms for executing these distinct stages remain elusive. I found distinct depth-specific involvement in each stage of movement, controlling the output node to the downstream region. Collectively, this dissertation provides a comprehensive exploration of movement preparation and execution, ranging from the behavioral strategy, decision-making, and the neural circuitry governing these essential behaviors of motor cortical dynamics. This dissertation elucidates the multifaceted role of the motor cortex, illustrating its significance beyond a mere output node and emphasizing its dynamic role in adapting to our surroundings.