Event-related brain responses as correlates of changes in predictive and affective values of conditioned stimuli

Previous evidence suggests that the judged predictive strength of one cue may be influenced by the predictive strengths of other pretrained cues (prediction errors). In the present study, we examined affective ratings and event-related brain responses from 18 healthy participants during an aversive conditioning task in which affective values of previously trained conditioned stimuli were modified through a blocking procedure. The task was divided into two phases. During the training phase, single stimulus A (e.g., red square) was always followed by aversive picture stimuli, while single stimulus B (e.g., yellow square) was signaling the absence of aversive stimulation. During the blocking phase, compound stimuli consisted of the combination of one single trained stimulus (A or B) and one new somatosensory stimulus were also followed by the presence of aversive stimulation. Results indicated that single stimulus A elicited greater ERP amplitudes and theta power, and was rated as more unpleasant than single stimulus B during the training phase. Moreover, single stimulus B elicited greater ERP amplitudes than stimulus A, as well as greater theta power and more unpleasant ratings during the blocking as compared with the training phase. By contrast, no changes in ERP amplitudes and theta power were observed for stimulus A. Our findings provide neurophysiological and behavioral evidence for an increased affective processing of conditioned stimuli when compound stimuli were introduced, but only if the target CS was previously trained to signal the absence of aversive stimulation.