Event-related changes in neuromagnetic activity associated with syncopation and synchronization timing tasks

For low rhythmic rates (1.0 to similar to2.0 Hz), subjects are able to succ essfully coordinate finger flexion with an external metronome in either a s yncopated (between the beats) or synchronized (on each beat) fashion. Beyon d this rate, however, syncopation becomes unstable and subjects spontaneous ly switch to synchronization to maintain a 1:1 stimulus/response relationsh ip. We used a whole-head magnetometer to investigate the spatiotemporal dyn amics of neuromagnetic activity (MEG) associated with both coordinative pat terns at eight different rates spanning the range 1.0-2.75 Hz. Timing chang es in the event-related fields accompanied transitions from syncopation to synchronization and followed the placement of the motor response within eac h stimulus/response cycle. Decomposition of event-related fields into compo nent auditory and motor brain responses revealed that the amplitude of the former decreased with increasing coordination rate whereas the motor contri bution remained approximately constant across all rates. Such an interactio n may contribute to changes in auditory-motor integration that cause syncop ation to become unstable. Examination of event-related changes in high freq uency bands revealed that MEG signal power in the beta band (15-30 liz) was significantly lower during syncopated coordination in sensors covering the contralateral sensorimotor area suggesting a dependence of beta rhythm amp litude on task difficulty. Suppression of beta rhythms was also stronger du ring synchronization preceded by syncopation, e.g., after subjects had swit ched, when compared with a control condition in which subjects synchronized throughout the entire range of rates.