During motor imagery, global inhibition and effector-specific inhibition contribute to prevent actual movements. We investigated the decay of inhibition using an action-mode switching paradigm. Participants switched between imagined and executed hand movements. Response-stimulus intervals (RSIs) were varied (200, 700, 1,300, and 2,000 ms). As inhibition (due to imagination) or activation (due to execution) in one trial affects performance in the subsequent trial, we analysed sequential effects. Evidence for the contribution of global inhibition (e.g., switch benefits in execution [E]-imagination [I] sequences compared with I-I sequences) and effector-specific inhibition (e.g., hand repetition costs after an imagination trial) was observed. Sequential effects decreased with increasing RSIs, indicating that both forms of inhibition are subject to decay. However, the decrease of sequential effects was less pronounced for global inhibition than for effector-specific inhibition. This indicates that global inhibition may decay slowly, whereas effector-specific inhibition decays rather quickly. In conclusion, global inhibition may be at least partly implemented in all contexts in which motor imagery has to be performed, whereas effector-specific inhibition may contribute to motor imagery only as soon as the exact movement parameters are known and may decay quickly after the imagined movement has been performed.
Keywords: Motor imagery; action switching; inhibition; passive decay; time course.