, 2010). Therefore, it is likely that degraded TCI may be beneficial for improving spatiotemporal bimanual coordination, even if the bimanual action is carried out asymmetrically. Another interpretation is that the decrease in TCI is a manifestation of the general suppression of the absolute impact of transcallosal interference. It

was proposed that the gain control of excitatory CHIR-99021 order and inhibitory transcallosal discharges countervails the neural interference between the motor cortices (Rokni et al., 2003). This allows each motor cortex to work independently without any interference from the contralateral cortex. Regarding this notion, callosotomy patients reportedly acquire a high degree of independence for movements on each side during bimanual movements at the expense of their Selleck Akt inhibitor ability to coordinate bimanual movements (Eliassen et al., 1999). Thus, when movements on each side have their own respective task goals, it should be beneficial that the movements on each side are organized individually and that they do not interfere with each other. Recent

behavioral studies reported that such motor organization was implemented depending on the task requirement (Diedrichsen et al., 2004; Diedrichsen, 2007; Mutha & Sainburg, 2009). Given these reports, our findings might provide a good perspective of the CC circuit as a key structure influencing task-dependent bimanual interactions, even though the observed modulation of TCI did not demonstrate directly the extent of interhemispheric connectivity. Although we demonstrated that the symmetric condition exhibited larger TCI than the asymmetric condition, it could be claimed that the transcallosal

inhibitory circuit was occluded during asymmetric condition. A relatively high intensity of TMS is required to elicit TCI. Therefore, if the transcallosal circuit is highly activated during the asymmetric condition, Ureohydrolase such high TMS intensity might produce some effects that give rise to the underestimation of TCI. We cannot completely rule out this possibility from a physiological point of view, even though we confirmed that TCI was further increased as TMS intensity was > 150% RMT during static muscle contraction (Supporting Information Fig. S1). In addition, we need to consider the data-processing methods for both force and EMG averaging. The present study adopted a signal averaging approach to increase the signal-to-noise ratio of the TMS-induced response on the ongoing EMG activity. It is true that the temporal profile of averaged force trace may not be representative of any single trial. However, it is also true that a single trial was not enough to properly detect TCI onset and offset. To obtain reliable data, we averaged more than 20 signals for all experiments, which improved our ability to assess TCI.