Neural correlates of intrusion of emotion words in a modified Stroop task.

Behavioural studies have demonstrated that the emotional Stroop task is a valuable tool for investigating emotion-attention interactions in a variety of healthy and clinical populations, showing that participants are typically more distracted by negative stimuli as compared to neutral or positive stimuli. The main aim of this study was to find and examine the neural correlates of this greater intrusion from negative emotional stimuli. Reliable reaction time (RT) and event-related potential (ERP) data were collected from 23 participants who performed a manual emotional Stroop task with short (40 ms) and long (500 ms) inter-trial intervals. In the short interval condition, participants were found to produce longer RTs for negative than neutral words, suggesting that these stimuli were more difficult to ignore. This RT effect disappeared in the long interval condition, although larger P1 amplitudes were found for the negative words. This suggests that differences in early attention allocation may be unrelated to the degree of intrusion at the behavioural level. In addition, a larger negative slow wave around 300-700 ms post-stimulus was observed in the long interval condition, but only for those negative words that produced prolonged RTs as compared to their matched controls. This late and broadly distributed effect is believed to reflect suppression of meaning representations.