Timing, kinematics, and the cerebellum: Tapping into differences between musicians and non-musicians

Musical performance relies on basic processes such as timing, and the synchronization of motor responses with environmental stimuli. The study of the effects of musical training on behaviour and the brain provides an opportunity to understand these processes and their neural correlates, particularly in relation to the cerebellum, a brain region implicated in timing. The first study presented here compared musicians and non-musicians on the standard sensorimotor synchronization task of finger tapping to a metronome, with and without tactile feedback. The results indicated that musicians differed from non-musicians in their use of kinematics and sensory information for synchronization. The second study focused on how musical training affects event-based and emergent timing in repetitive rhythmic tapping and drawing. Event-based timing has been shown to rely on an internal clock-like process that is independent of the motor response. Conversely, emergent timing establishes regular rhythmic movement by stabilizing kinematic parameters without reference to an explicit internal representation of time intervals. Musical training was associated with improved precision in event-based timing but not in emergent timing. For musicians only, the kinematic parameter of movement jerk was decoupled from timing variability in both event-based and emergent timing. These results support the dissociability of the two timing modes, iv highlight the limits of musical training, and show that the relationship between kinematics and timing is affected by musical expertise. The third study examined differences between musicians and non-musicians in a finger-tapping task, and in regional cerebellar volumes measured from magnetic resonance imaging data. Smaller volumes were associated with an earlier age of start of musical training, and with better timing performance. These findings are evidence for a sensitive period, before seven years, for initiation of musical training. Timing variability was associated with the volume of right Lobule VI, indicating localization of event-based timing to this region. The overall pattern of results suggests that musicians may be using sensory information to maintain timing in a more efficient and parsimonious manner compared to non-musicians. This is interpreted as evidence that musicians are using a top-down approach for many music-related tasks, in contrast to the bottom-up approach of non-musicians. v In memory of my parents, Evelyn and Lucian Baer. vi Acknowledgements