Abstract: PURPOSE: Active forgetting is crucial for emotion regulation and psychological well-being. This could be achieved via two strategies: direct suppression (DS) and thought substitution (TS) yet their underlying neural mechanisms remain elusive.
METHODS: Here we recorded electroencephalography (EEG) activities on 49 human subjects while they were instructed to use DS or TS strategies in different trials to inhibit previously memorized word associations.
RESULTS: Behavioral results show that both DS and TS strategies efficiently disrupt memories, displaying gradual reductions in intrusive memories and decreased recall performance for both the trained and independent probe word cues. Most importantly, we demonstrate dissociated oscillatory neural mechanisms for DS and TS strategies. First, DS elicits stronger sustained alpha-band (8-11 Hz) activities in the parietal region while TS shows stronger theta-band (3-6 Hz) activities in the frontal region, indicating their respective inhibitory and excitatory characteristics. Second, the decrease of alpha-band power across blocks is accompanied by a similar decline in intrusive memories in the DS condition, suggesting alpha-band inhibition may be required to facilitate forgetting. Third, the theta-band power during TS condition is correlated to individual executive control function measured in independent ANT tasks and could also predict subsequent forgetting.
CONCLUSIONS: Taken together, we present new evidence for the dissociative neural mechanisms underlying different active forgetting strategies. While the DS strategy employs alpha-band inhibitory modulation to suppress intrusive memories, TS strategy relies heavily on theta-band frontal executive control activities to enable the formation and replacement of new and old memories, respectively.

Key words: direct suppression, thought substitution, intentional forgetting