The “inhibitory” N2 is understood to tap response inhibition, particularly when prepotent response tendencies (Go responses) are present. The N2 peak is observed at frontal electrode sites about 200-350 ms post-stimulus, and its amplitude is greater on successful NoGo trials, when subjects withhold a learned response (Bokura et al., 2001; Eimer, 1993; Falkenstein et al., 1999; Jodo and Kayama, 1992; Lavric et al., 2004). However, robust frontal N2 peaks have been reported on “Go” trials as well (e.g., Davis et al., 2003; Nieuwenhuis et al., 2003). Studies evaluating trial-type frequency have reported enhanced N2 amplitude for stimuli occurring at low frequency, irrespective of whether the stimuli were associated with generating (Go) or suppressing (NoGo) a response (e.g., Nieuwenhuis et al., 2003). These authors have argued that their results are consistent with the view that the Go/NoGo N2 represents an index of response conflict monitoring on correct trials that arises from competition between execution and inhibition of a single response (Botvinick et al., 2001; Braver et al., 2001; Nieuwenhuis et al., 2003). Although few studies have interpreted the NoGo N2 “effect”
