P300 assessment of anxiety effects on processing novel stimuli.

In the present experiment, event-related potentials (ERPs) were used to investigate the effect of anxiety on the attention to novel stimuli. A total of 16 healthy subjects participated in an experiment involving the anticipation of electric shocks. ERPs from 15 scalp sites were recorded in response to three types of auditory stimuli, and two attentional modes during threat and safe conditions. The three types of auditory stimuli were (1) frequent "standard" tones, (2) rare "target" tones, and (3) rare "novel" sounds. In the passive attentional mode, subjects passively listened to the stimuli. In the active attentional model, they had to Press a button in response to target tones. In each attentional mode, stimuli were presented under two conditions: threat (anticipation of shock) and safe (no-shock anticipation). P3 to the target stimuli was not affected by shock anticipation. The amplitude of P3 to the novel stimuli, however, was increased by the threat of shock in the passive but not in the active mode. The lack of impact of anxiety on P3 to the novel stimuli in the active mode is discussed.