Mapping Musical Rhythm in the Brain: Causality, Connectivity, and Individual Differences

Rhythm is not only something we perceive but also something we internalize and feel. In music, humans have a remarkable ability to extract a regular beat from complex auditory patterns. Unlike many sensory phenomena, rhythmic processing does not rely on a direct mapping between sound features and the resulting percept. Instead, it is driven by internal, top-down mechanisms that generate and sustain a sense of temporal regularity. The motor system, particularly the premotor cortex (PMC), is hypothesized to orchestrate these processes, not only during overt synchronization but also during passive listening and imagery. Despite this, the causal role, topographical specificity, and connectivity of the PMC in beat-based timing remain poorly understood, and little is known about how individual traits and contextual factors shape rhythmic processing. This thesis addresses these gaps by combining behavioral and neurophysiological approaches to examine the causality, topography, excitability, and connectivity of the PMC in rhythm perception and imagery, while also considering the influence of individual and contextual factors in driving rhythmic processing. In Study 1, online TMS revealed that stimulation of the right caudal dorsal PMC (dPMC), compared to SMA, pre-SMA, and left dPMC, selectively disrupted beat perception. This provided causal evidence for a functional specialization of the right dPMC in endogenous beat generation, with individual differences in musical reward sensitivity further predicting perception performance. Study 2 extended these findings to imagery: right dPMC stimulation impaired beat imagery, particularly in individuals with lower auditory imagery skills, supporting its predictive role in internally guided beat processing and showing that the neural response to TMS is shaped by individual functional states. Again, musical reward sensitivity modulated rhythmic imagery performance. In Study 3, we combined TMS with electroencephalography (EEG) to investigate dPMC excitability and connectivity. Preliminary results indicated that neural excitability in the dPMC increased when perceived or imagined metric expectations were stronger, highlighting dPMC role in generating top-down predictive signals. Extending beyond perception and imagery, Study 4 investigated interpersonal rhythm production. We observed that synchronization between pairs was closer in time when they jointly produced consonant chords, with stronger consonance effect in dyads who reported lower social closeness prior to the experiment. Together, these studies provide converging evidence for the critical role of the right dPMC in beat perception and imagery, clarify its functional interactions with auditory regions, and demonstrate that rhythmic abilities are shaped not only by stable traits (e.g., reward sensitivity, imagery ability) but also by transient contextual factors (e.g., musical consonance, social closeness). More broadly, this work advances our understanding of the neural foundations of rhythm and offers insights into how predictive motor–auditory mechanisms may have supported the evolution of human musicality and its social functions.