Opposing Mechanisms Support the Voluntary Forgetting of Unwanted Memories

Reminders of the past can trigger the recollection of events that one would rather forget. Here, using fMRI, we demonstrate two distinct neural mechanisms that foster the intentional forgetting of such unwanted memories. Both mechanisms impair long-term retention by limiting momentary awareness of the memories, yet they operate in opposite ways. One mechanism, direct suppression, disengages episodic retrieval through the systemic inhibition of hippocampal processing that originates from right dorsolateral prefrontal cortex (PFC). The opposite mechanism, thought substitution, instead engages retrieval processes to occupy the limited focus of awareness with a substitute memory. It is mediated by interactions between left caudal and midventrolateral PFC that support the selective retrieval of substitutes in the context of prepotent, unwanted memories. These findings suggest that we are not at the mercy of passive forgetting; rather, our memories can be shaped by two opposite mechanisms of mnemonic control. º Voluntarily forgetting is mediated by two opposite mechanisms º These mechanisms recruit distinct PFC systems to either engage or disengage retrieval º DLPFC effectively inhibits retrieval processes supported by the hippocampus º A cPFC-mid-VLPFC circuit biases retrieval to supplant unwanted memories Suppressing awareness of an unwanted memory can cause forgetting. Benoit and Anderson show how this motivated forgetting can be achieved by opposite prefrontal mechanisms that either suppress hippocampal retrieval processes or engage retrieval to occupy awareness with a substitute memory.