Repetition priming in the stop signal task: The electrophysiology of sequential effects of stopping

Inhibition of a response affects the processing of subsequent stimuli. When a response has to be made to a stimulus to which a response was previously inhibited, response time increases. In this study, we investigated the neurophysiological underpinnings of this repetition priming phenomenon. We aimed at distinguishing between two possible mechanisms. Firstly, it could be that slowing after a successful inhibition trial originates at the response execution level and is due to the reactivation of the system responsible for motor inhibition interfering with execution of the go response. The second possibility is that interference occurs at the more abstract level of conflicting action goals or plans (i.e. "stop" and "go") that are activated prior to response execution. We analyzed activity over primary motor cortices and the parietal cortex in a stop signal task. Stimulus repetition led to a decrease in activity over primary motor cortices but irrespective of history of stopping. Stopping on the previous trial did affect the stimulus-locked parietal P300 only on repetition of the stimulus, mimicking the behavioral pattern. Furthermore, the P300 was lateralized and affected by both stimulus onset and response time, suggesting that the interference caused by inhibition priming is situated between stimulus perception and response execution. Taken together, these findings show that the prolonged response times to a stimulus that was previously successfully inhibited to, do not originate from reactivated suppression of motor output, but are caused by interference between a stop and a go goal in parietal cortex that hampers translation from stimulus to response.