The Posterior Parietal Cortex Subserves Precise Motor Timing in Professional Drummers

Abstract

The synchronization task is a well-established paradigm for the investigation of motor timing with respect to an external pacing signal. It requires subjects to synchronize their finger taps in synchrony with a regular metronome. A specific significance of the posterior parietal cortex (PPC) for superior synchronization in professional drummers has been suggested. In non-musicians, modulation of the excitability of the left PPC by means of transcranial direct current stimulation (tDCS) modulates synchronization performance of the right hand. In order to determine the significance of the left PPC for superior synchronization in drummers, we here investigate the effects of cathodal and anodal tDCS in 20 professional drummers on auditory-motor synchronization of the right hand. A continuation and a reaction time task served as control conditions. Moreover, the interaction between baseline performance and tDCS polarity was estimated in precise as compared to less precise synchronizers according to median split. Previously published data from 16 non-musicians were re-analyzed accordingly in order to highlight possible differences of tDCS effects in drummers and non-musicians. TDCS was applied for 10 min with an intensity of 0.25 mA over the left PPC. Behavioral measures were determined prior to and immediately after tDCS. In drummers the overall analysis of synchronization performance revealed significantly larger tap-to-tone asynchronies following anodal tDCS with the tap preceding the tone replicating findings in non-musicians. No significant effects were found on control tasks. The analysis for participants with large as compared to small baseline asynchronies revealed that only in drummers with small asynchronies tDCS interfered with synchronization performance. The re-analysis of the data from non-musicians indicated the reversed pattern. The data support the hypothesis that the PPC is involved in auditory-motor synchronization and extend previous findings by showing that its functional significance varies with musical expertise.

Keywords: anticipation; brain plasticity; musicians; synchronization; transcranial direct current stimulation (tDCS).

Figure 1

Application of transcranial direct current stimulation (tDCS). The target area was set to Talairach coordinates (x, y, z) −25, −46, 62 corresponding to Brodmann area (BA) 7 (left). The right part of the figure schematically illustrates the electrode montage over the left posterior parietal cortex (PPC). Please note that the reference electrode was placed over the contralateral orbit.

Figure 2

Results from the overall analysis in drummers. The analysis revealed a significant increase of the tap-to-tone asynchrony following anodal tDCS while no significant effects occurred following cathodal tDCS. Error bars indicate the standard error of the mean (SEM).

Figure 3

Analysis of tDCS effects on synchronization accuracy depending on baseline performance in drummers. Data were split according to group median of the tap-to-tone asynchrony during baseline. In drummers with large tap-to-tone asynchronies (A) no significant effects depending on tDCS polarity were observed while in participants with small asynchronies (B) anodal tDCS significantly modulated the tap-to-tone asynchrony. Error bars indicate the SEM.

Figure 4

Analysis of tDCS effects on synchronization accuracy depending on baseline performance in non-musicians. Data were split according to group median of the tap-to-tone asynchrony during baseline. In non-musicians with large tap-to-tone asynchronies (A) anodal tDCS resulted in significantly larger asynchronies, while in subjects with small baseline asynchronies (B) no significant tDCS effects were found. Error bars indicate the SEM.