Predictive validity of event-related potentials (ERPs) in relation to the directed forgetting effects

OBJECTIVE A directed forgetting paradigm (word method) was used to assess the relationships between the event-related potentials (ERPs) recorded during the study phase and the subsequent forgetting effects. METHODS In the study phase 100 words were presented each followed by either an instruction to remember (R) or to forget (F). Then these 100 words, together with another 100 new words, were presented and subjects had to perform an old/new decision task. The forgetting effect was considered as the difference between the rate of R- and F-words correctly recognised. Based on this difference, the whole sample was divided into two 10-subject groups with high and low forgetting effect. RESULTS From 300 to 600 msec post-instruction differences in ERPs between R and F instructions were similar in both groups. In contrast, in the 100-300 msec epoch, ERP differences only appeared in the high-effect group and consisted of an enhanced positive activity elicited by F instruction at frontal and prefrontal areas and a larger positivity associated to R instruction at parietal area. CONCLUSIONS The findings suggest that the processing of the word is kept on stand-by until the instruction is provided. Instruction to remember would reactivate this processing, which would mainly involve the parietal area, whereas instruction to forget appears to trigger frontal and prefrontal mechanisms trying to inhibit such processing.