Suppression weakens unwanted memories via a sustained reduction of neural reactivation

Abstract

Aversive events often turn into intrusive memories. However, prior evidence indicates that these memories can be forgotten via a mechanism of retrieval suppression. Here, we test the hypothesis that suppression weakens memories by deteriorating their neural representations. This deterioration, in turn, would hinder their subsequent reactivation and thus impoverish the vividness with which they can be recalled. In an fMRI study, participants repeatedly suppressed memories of aversive scenes. As predicted, this process rendered the memories less vivid. Using a pattern classifier, we observed that it did diminish the reactivation of scene information both globally across the grey matter and locally in the parahippocampal cortices. Moreover, in the right parahippocampal cortex, a stronger decline in vividness was associated with a greater reduction in generic reactivation of scene information and in the specific reinstatement of unique memory representations. These results support the hypothesis that suppression deteriorates memories by compromising their neural representations.