Is post error slowing a post error inhibition? A transcranial magnetic stimulation approach

The commission of an error triggers cognitive control processes which help to avoid similar errors in the future. An example of such processes is post-error slowing, a delay in correct responses in trials following an error. Two hypotheses have been proposed to explain this phenomenon. The inhibitory account (Ridderinkhof, 2002) holds that, after an erroneous response, an increase of selective inhibition of motor planning occurs. Alternatively, the conflict monitoring account (Botvinick et al, 2001) suggests that the detection of an error triggers the activation of a system monitoring network reducing the excitatory input at the motor plan. In the present study, single pulse transcranial magnetic stimulation (TMS) was applied to the motor cortex ipsilateral to the responding hand, while participants were performing a modified Eriksen Flanker Task. A robotic arm with a movement compensation system (Mathaus et al., 2008) was used to maintain the TMS coil in the correct position during the experiment. A magnetic pulse was delivered at different times (150, 300, 450 ms) after correct and erroneous responses, and the motor evoked potentials (MEP) of the contralateral first dorsal interosseous muscle (FDI) were recorded. Results show an increase of the peak-to-peak post-error MEP amplitude, produced by the magnetic pulse delivered 450 ms post-response which might correspond to a decrease in the excitability of the contralateral motor cortex occurring by transcallosal inhibition. Present data are in agreement with the inhibition account and thus contribute to our understanding of compensatory mechanisms after error commission.