It has also been demonstrated that the premotor–motor interactions are very sensitive to ISIs and stimulus intensity (Civardi et al., 2001; Davare et al., 2008, 2009). It is thus possible that the PMv–M1 interactions might be shifted towards different components (latencies, activation threshold) in patients with FHD. As our study focused on investigating the role of the premotor–motor
interactions in SI at various phases of movement, the experiment even with one ISI took about 2 h. Hence, we could not test more ISIs. We decided to test the ISI that exerted the most efficient premotor–motor influence (6 ms), as shown by Davare et al. Entinostat (2008). In order to fully define the importance of the impairment of the premotor–motor interactions in patients with FHD, more ISIs should be tested in future studies. Looking at the synergistic muscle, the current study shows that MEP amplitudes in the FDI are not modulated by stimulation of the PMv. This is probably due to the fact that PMv–M1 interactions are muscle specific (Davare et al., 2009) and are extremely sensitive this website to the parameters of stimulation. Indeed, small variations of the conditioning stimulus intensity greatly influence the outcome (Civardi et al., 2001). As the stimulation intensities used in the current study were adjusted to RMTAPB, we cannot make clear conclusions about the effects of the paired
stimulations over the FDI. Indeed, although the FDI and APB hotspots and RMT are very close to each other, we showed that, at rest, MEPFDI was higher than MEPAPB in both groups. This difference is probably explained by a Interleukin-3 receptor difference in the input–output curve. Thus, a stimulation set at 80% RMTAPB might correspond to approximately 90% RMTFDI. It is then reasonable to expect significant differences in results between the FDI and APB, as it has been demonstrated that a stimulation at 90% AMTFDI over the dorsal premotor cortex could inhibit M1, whereas a stimulation set at 80 or 100% AMTFDI had no effect on the M1 (Civardi et al., 2001). As a consequence, we can only make conclusions about significant premotor–motor interactions regarding the APB muscle, a surrounding muscle, not involved in the task. Although the APB is not recruited
during this task, it is probable that this latter muscle might be under the influence of the PMv. Indeed, it has been shown that the PMv exerts an important role in hand posture and fingertip position, and elaborates the appropriate pattern of activation of intrinsic hand muscles (Ceballos-Baumann et al., 1997; Ibanez et al., 1999; Davare et al., 2006). It has also been described that the PMv plays a relevant role in visually-cued finger movements (Pollok et al., 2009; Ruspantini et al., 2011). PMv might thus play a key role in finger positioning in our task. Patients with FHD suffer from an abnormal activation pattern of the hand muscles during writing or music playing, with abnormal overflow of agonist and antagonist muscles (van der Kamp et al., 1989).