The role of error-based learning in movement and stillness

When people and other animals perform a movement that produces an unexpected outcome, they learn from the resulting error and retain a portion of this learning over time. Curiously, for reaching movements of the arm, errors that occur solely during periods of movement cause changes to both the way we move and also the way we hold the arm still. Here, we explore the way the brain corrects for error after a single occurrence, how this response to error changes with experience, and finally, how these responses to error change the way we maintain stillness of the arm. In Chapter 2, we consider mechanisms that guide learning after a single error. Here we provide evidence that the brain uses its past corrections as a model for its future movement plans. This learning response does not remain fixed over time, but is augmented with experience. In Chapter 3, we describe a new algorithm that can be used to extract mathematical properties of adaptation. With this tool, we show that savings (faster rate of re-learning) is caused by an increase in the brain’s sensitivity to error, specifically within fast motor learning processes. Next, we show that reemergence of earlier memories is caused by the decay of fast learning processes. In Chapter 4, we show that anterograde interference (slower rate of re-learning) is caused by a reduction in one’s sensitivity to error, that recovers over time. Finally, in Chapter 5, we demonstrate that modulation of error sensitivity not only changes the rate at which we acquire motor memories, but also the point at which the learning process saturates. Lastly, in Chapter 6, we revisit our initial observation, that adaptation changes not only the way we move, but also the way we hold still. In a series of experiments in human and non-human primates, we report a surprising relationship between movement and posture: on a within-trial basis, the commands that hold the arm and finger at a target location depend in part on the mathematical integration of the commands that moved the limb to that location