The effect of rTMS over left and right dorsolateral premotor cortex on movement timing of either hand

It has been suggested that the left dorsolateral premotor cortex (dPMC) controls timing abilities of either hand. To further clarify its functional significance for movement timing, low-frequency repetitive transcranial magnetic stimulation (rTMS) was applied over the left and right dPMC, respectively, while subjects performed an auditorily paced finger-tapping task with each hand. rTMS over the left dPMC decreased tapping accuracy of both hands, whereas no behavioural effects occurred following right dPMC stimulation. To elucidate the time window in which left dPMC TMS disturbs synchronization abilities, pairs of TMS pulses were applied over the left dPMC and the left anterior parietal cortex serving as control condition. TMS pulses were applied randomly at 40 ms, 80 ms, 120 ms, 160 ms, 200 ms and 240 ms before pacer onset, as taps precede the pacing signal for about 20-60 ms. Again, the analysis revealed that TMS over the left dPMC disturbed synchronization abilities of either hand; however, this effect was shown at different times suggesting that the left dPMC affects the right M1 via at least one additional relay station. The present data support the hypothesis that the left dPMC is crucial for accurate timing of either hand. Additionally, they reveal a piece of evidence that the left dPMC affects the left hand not via a direct left dPMC-right M1 connection.