The role of the preSMA and the rostral cingulate zone in internally selected actions.

In everyday life, one can differentiate between actions that are primarily internally guided and actions that are primarily guided by external events. FMRI studies investigating the neural correlates of internally guided actions usually report activation maxima in the rostral cingulate zone (RCZ) as well as the preSMA. However, the pertinent contrasts were often confounded by perceptual and motor differences between the different conditions. In the current study, we reinvestigated the neural correlates of internally vs. externally selected actions using a paradigm that avoids any such perceptual or motor confound. By doing so, we wanted to address the yet unsolved question which differential role the preSMA and RCZ play in internally guided actions. Subjects were required to make left or right key presses at the midpoint between isochronous pacing signals (a sequence of 'X's presented to the left or the right of the fixation point). In the internally selected condition, the location of the 'X' was determined by the location of the preceding key press that the subjects selected freely. In the externally selected condition, by contrast, the location of the 'X' prescribed the location of the subsequent key press response. We found that the RCZ was differentially activated by internally as compared to externally selected actions. In contrast to previous studies, the preSMA showed equal activity in both conditions and thus did not differentiate between the two modes of action selection. This suggests a primary role for the RCZ in internally selected actions.