ERP components in Go Nogo tasks and their relation to inhibition

In visual Go/Nogo tasks the ERP usually shows a frontal negativity after No go stimuli ("Nogo-N2"), which possibly reflects an inhibition process. Howe ver, the Nogo-N2 appears to be very small after auditory stimuli, which is evidence against the inhibition hypothesis. In the present study we tested this hypothesis by evaluating performance differences between subjects. Ass uming that for Ss with a high false alarm rate the inhibition process is we akened and/ or delayed, they should reveal a smaller and/or later Nogo-N2 t han Ss with a low false alarm rate. This prediction was confirmed, which su pports the inhibition hypothesis. However, the Nogo-N2 was again much small er and had a different topography after auditory than after visual stimuli despite similar performance in both modalities. This modality asymmetry was explained by assuming that the inhibitory mechanism reflected in the Nogo- N2 is located at a pre-motor rather than at the motor level. In the second part of the study we compared the Nogo-N2 with a similar phenomenon, the er ror negativity (N-e), which occurs in trials with commission errors (false alarms). Earlier work suggests that the N-e is a correlate of error detecti on or inhibition. This raises the possibility that the N-e is a delayed Nog o-N2, i.e., the N-e may reflect a late and hence unsuccessful attempt to in hibit the response after a nontarget. However, the N-e amplitude showed no difference between performance groups and stimulus modalities, as found for the Nogo-N2. Moreover, N-e and Nogo-N2 had different scalp topographies. T his suggests that different mechanisms and generators underlie the N-e and the Nogo-N2. (C) 1999 Elsevier Science B.V. All rights reserved. PsycINFO c lassification: 2530.