There was a significant correlation between changes in EMG mirroring and the individual maximal s-IHI at baseline (r = 0.65, P = 0.0019; Fig. 6), indicating that the greatest reduction in EMG Sotrastaurin nmr mirroring was associated with the most effective individual maximal s-IHI. The correlation between changes in EMG mirroring and the average baseline l-IHI was not significant (r = 0.25, P = 0.27; Fig. 6). There was no correlation between overall changes in either s-IHI or l-IHI and practice-related changes in EMG mirroring (r = 0.36,

P = 0.11; r = 0.11, P = 0.63). As outlined in the Materials and methods, we also tested whether the practice-related changes in EMG mirroring were related to the changes in acceleration of the ballistic movement or to the changes of the average corticospinal excitability of the trained hemisphere. There was no correlation between changes in EMG mirroring and acceleration peak (r = 0.32, P = 0.16). Similarly, there was no correlation between changes in EMG mirroring and average corticospinal excitability of the trained hemisphere (r = −0.0081,

P = 0.97). In the present study we found that, as reported by others (Classen et al., 1998; Muellbacher et al., 2001; Agostino et al., 2007, 2008), subjects improved performance in the trained task. Furthermore, this happened even though there was no overall change in EMG mirroring, and even a tendency for it to decline. Physiologically there was an increase in the excitability of corticospinal PS-341 output from the trained hemisphere, but there was no change in IHI from Acetophenone the trained to the contralateral hemisphere. However, individual changes in EMG mirroring did relate to the basal amount of s-IHI, i.e. the greater the basal levels of s-IHI the greater the reduction in EMG mirroring. The conclusions from this are: (i) that corticospinal excitability and cortico-cortical (interhemispheric) excitability can be modulated independently

by motor training, even though they may share some of the same circuitry (Avanzino et al., 2007); and (ii) basal physiology measures of s-IHI give an indication of the overall extent to which EMG mirroring modification is possible, i.e. that the baseline s-IHI is a key factor that determines how successfully participants can learn to focus their motor commands on the task being trained and prevent overflow to the opposite hemisphere. The reduction in EMG mirroring we observed during motor training in individuals with greater baseline s-IHI was not explained by a change in the level of background EMG activity in the tonically contracting FDIMIRROR as this was constant. Nor is it likely to reflect any fatigue that might have been caused by training as fatigue is known to increase rather than decrease EMG mirroring (Cincotta & Ziemann, 2008). There was also no correlation between the reduced amount of EMG mirroring and the improvement in motor performance, i.e.