Controlled movement processing: evidence for a common inhibitory control of finger, wrist, and arm movements

We used the behavioral task and theoretical construct of the countermanding paradigm to test whether there is any difference between the inhibitory control of the finger, wrist, and arm. Participants were instructed (primary task) to respond to a directional go signal presented at the fovea by pressing a button with either their index or middle fingers, moving a joystick with their wrists, or reaching to a stimulus on a touch screen with their arms. They were also instructed (secondary task) to withhold their responses when a stop signal was presented on 25% of trials. The participants' ability to inhibit each of the commanded movements was captured by their inhibition probability function, which describes how withholding is increasingly difficult as the delay between the go and stop signals increased. By modeling each participant's inhibition function, we estimated that the time needed to inhibit a commanded movement was about 240 ms, a variable that did not differ significantly between the three limb segments. Moreover, we found that the best-fit model of each segment's inhibition function could fit equally well the inhibition functions obtained with the other two segments. These results provide evidence that the upper limb segments share a common inhibitory control, which may facilitate the regulation of neuronal activity within the distributed motor cortical representations and thus simplify the voluntary control of multi-segmental movements.