It's not too late: the onset of the frontocentral P3 indexes successful response inhibition in the stop-signal paradigm.

The frontocentral P3 event-related potential has been proposed as a neural marker of response inhibition. However, this association is disputed: some argue that P3 latency is too late relative to the timing of action stopping (stop-signal reaction time; SSRT) to index response inhibition. We tested whether P3 onset latency is a marker of response inhibition, and whether it coincides with the timing predicted by neurocomputational models. We measured EEG in 62 participants during the stop-signal task, and used independent component analysis and permutation statistics to measure the P3 onset in each participant. We show that P3 onset latency is shorter when stopping is successful, that it is highly correlated with SSRT, and that it coincides with the purported timing of the inhibition process (towards the end of SSRT). These results demonstrate the utility of P3 onset latency as a noninvasive, temporally precise neural marker of the response inhibition process.