Fig. 5: Representation of individual actions in the SMA.

A, B Logic of analysis. Trials from the first Comparison Task were categorized as similar (Trial type 1) or dissimilar (Trial type 2) depending on whether the two action combinations of a pair shared the common action: in the current example of overlapping action plans, the common action would be moving the joystick to the right (A). Action could be shared between two action combinations by the same or different joysticks. We assumed that the shared motor information should elicit the modulation of BOLD response: a positive value would suggest activity suppression as a function of similarity (shown in B), while a negative value would indicate increased activity as a function of similarity. C Supplementary motor area (SMA) showed increased activity in the trials with similar action combinations (t(45)= -3.07; p = 0.005, Cohen’s d = -0.45, 95% CI= [-0.029, -0.006]; two-sided t-test). Dots represent data from n  =  46 participants. Box plots show median and upper/lower quartiles with whiskers extending to the most extreme data point within 1.5 interquartile ranges above/below the quartiles; black circles with error bars correspond to mean ± SEM; distributions depict probability density functions of data points. Source data are provided as a Source Data file. D The action similarity-dependent increase in activity in the SMA was confirmed on the whole-brain level (false discovery rate (FDR)-corrected using a voxel-level threshold of p < 0.01; MNI peak voxel coordinates: -6, 4, 67; peak voxel t(45) = −4.673; two-sided test). **p < 0.01; Bonferroni corrected for tests in two ROIs.