Inducing Amnesia for Unwanted Memories through Subliminal Reactivation

Traumatic memories contribute to psychological conditions such as post-traumatic stress disorder and phobias. Treatment of these disorders may benefit from techniques that reduce the accessibility of unwanted memories and their impact on cognition and emotion. Procedures such as retrieval suppression, associative interference, and reconsolidation disruption, though effective in inducing forgetting, involve exposure to the traumatic event, which is aversive and carries risks to the patient. But is explicit awareness of traumatic content truly necessary for effective voluntary forgetting? Recently, intentionally suppressing (i.e., stopping) retrieval of a memory in response to a reminder has been shown to temporarily interrupt hippocampal function. Disrupting hippocampal function through retrieval suppression induces an amnesic shadow that impairs the encoding and stabilization of unrelated “innocent bystander” memories that are activated near in time to people’s effort to suppress retrieval. Building on this mechanism, we successfully disrupted retention of unpleasant memories by subliminally reactivating them within this amnesic shadow window (on 88 participants across two experiments). Following the characteristics of retrieval suppression, the amnesic shadow disrupted memory for the subliminally reactivated events and induced forgetting that generalized across retrieval cues. Critically, whereas unconscious forgetting occurred on these affective “innocent bystander” memories, the amnesic shadow itself was induced by conscious suppression of unrelated and benign neutral memories, avoiding direct conscious re-exposure of unwelcome content. Combining the amnesic shadow with subliminal reactivation may offer a new approach to forgetting trauma that bypasses the unpleasantness in conscious exposure to unwanted memories.