Exploring and Modeling Entrainment to Rhythm in the Motor System

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The human brain is constantly identifying regularity and patterns in the temporal dynamics of its environment and using them to predict what comes next and when. In many cases, the process of prediction over time involves key nodes of the brain system used for motor control, but our understanding of these motor regions and their roles in non-motor processes is very limited. Understanding the role of the motor system in temporal prediction is important to making sense of and treating the diverse symptoms of motor system disorders including Parkinson's and Huntington's disease, and also to building a deeper fundamental understanding of the relationship between our physical experience in the world and our cognition. Two components of the motor system, the supplementary motor area and the basal ganglia, have been conclusively shown to be activated by the task of following and anticipating auditory events in a cyclically-patterned rhythm (i.e., "entraining" to a beat). In my recent work, I have developed hypotheses detailing the roles of these "motor" structures in this perceptual process. These hypotheses illuminate physiological parallels between perceptual rhythm tracking and the selection and control of movement. I have further proposed a conceptual and computational framework in which this process can be formally understood and modeled as a process of optimal inference about the phase and tempo of an underlying cycle, taking a step toward unifying it with an increasingly influential inference-based theory of motor control. My next step is to experimentally validate these two theoretical frameworks. To test my neurophysiological theory, I plan to record fMRI as participants listen to identical rhythms with and without appropriate context or learning to recognize a beat, and use multivariate pattern analysis and Granger causality measures to look for evidence of predicted interactions between basal ganglia and supplementary motor area. To test my computational theory, I plan to design multiple parallel psychophysics and EEG rhythm-tracking tasks in multiple sensory modalities that will allow me to fit model parameters to individual participants and determine whether these parameters show consistency across tasks and modalities. These theories will be refined, extended, and/or overhauled as necessary to account for experimental data. By validating and further developing these theories, this proposal aims to further the long-term goal of developing a unified physiological and computational theory of the dynamic function of the motor system in both motor and non-motor processes.