Figure 2.

Representative UCM data during bimanual force control across three tDCS protocols. (A) Bi-AA stimulation (i.e., bilateral dual-anodal stimulation), (B) Bi-AC stimulation (i.e., bilateral anodal-cathodal stimulation), and (C) Sham stimulation. UCM analysis focuses on 10 pairs of normalized elemental variables (i.e., raw force produced by left and right hands and represented as black circles) from each trial. Blue circles indicated elemental variables projected to UCM sub-space (i.e., blue dotted line) and red circles denote elemental variables projected to ORT sub-space (i.e., red dotted line orthogonal to blue dotted line). The variance of blue circles (i.e., V_UCM: good variability) does not change bimanual force control performances whereas the variance of red circles (i.e., V_ORT: bad variability) interferes with bimanual force control performances.