UC San Diego

Synchronizing our movements to rhythmic sounds is a complex behavior, but easy for many humans, whether in the form of playing an instrument, dancing, or simply nodding/ tapping along to a musical beat. How is this feat accomplished? A Hebbian hypothesis would argue that when sounds and movements co-occur, the systems become strongly associated, however many children exhibit a rhythmic sensitivity and do not seem to require training to move in time with music. An alternate explanation is that the motor system provides top down constraints to auditory processing (e.g. prediction and sequencing), such that the movement centers are already synchronized to external auditory cues prior to movement. In this dissertation I introduce three different electro-encephalography (EEG) studies that compare listening to, and moving along with rhythmic sounds, and explore the sensitivities of cortical motor rhythms to newly acquired action-sound pairings. In the first study I taught piano naive subjects to play a piano melody by ear and observed their motor rhythms showing preferential engagement when listening to the learned melodic sequence compared to unlearned melodies. In the second experiment, I compared the brainwave responses before and after subjects tapped or heard a tone and observed differences in motor rhythms in the time window before the events, but similarities in motor rhythm responses after sounds and after movements. In the third study, I introduce a novel EEG task - rhythmic hand drumming. I found that experienced drummers show greater engagement of motor rhythms while drumming than novice drummers, but across all subjects, motor rhythms were observed to modulate in time with drum rhythms regardless of whether subjects were just listening, or drumming themselves. Taken together, these three studies indicate that the motor system is sensitive to both rhythmic timing effects, and sequential effects of pitch order, and support a role for the motor system in auditory processing, when not otherwise engaged by movement