Targeted memory reactivation during sleep boosts intentional forgetting of spatial locations

Abstract

Although we experience thousands of distinct events on a daily basis, relatively few are committed to memory. the human capacity to intentionally control which events will be remembered has been demonstrated using learning procedures with instructions to purposely avoid committing specific items to memory. in this study, we used a variant of the item-based directed-forgetting procedure and instructed participants to memorize the location of some images but not others on a grid. these instructions were conveyed using a set of auditory cues. then, during an afternoon nap, we unobtrusively presented a cue that was used to instruct participant to avoid committing the locations of some images to memory. After sleep, memory was worse for to-be-forgotten image locations associated with the presented sound relative to those associated with a sound that was not presented during sleep. We conclude that memory processing during sleep can serve not only to secure memory storage but also to weaken it. Given that intentional suppression may be used to weaken unpleasant memories, such sleep-based strategies may help accelerate treatments for memory-related disorders such as post-traumatic stress disorder. Out of the multitude of events humans experience each day, relatively few are retained as declarative memories to support subsequent recall or recognition. Whereas forgetting has often been viewed as a negative, its adaptive role has gained prominence 1. Additionally, control over memory processes, including the retrieval of intrusive memories, has been hypothesized to support emotional regulation 2. Deficits in the capacity to actively suppress intrusive memories has been associated with disorders such as post-traumatic stress disorder 3. Forgetting involves the passive decay of memories 4,5 , but inhibitory neurocognitive mechanisms may also contribute to declining recollective abilities. This effect, termed active forgetting, is supported by adaptive, flexible processes that suppress memory-related brain networks 6-8. Possible mechanisms for active forgetting range from prefrontal inhibition 6 on the systems level to dopaminergic forgetting cells 7 and neurogenesis 8 on the cellular level. Most of these models are similar in that they involve a newly acquired, learning-like process that targets core memory structures or cells and suppresses them. An outstanding question is whether these inhibitory circuits, established through suppression learning, are strengthened during sleep, as is the case for declarative and nondeclarative memories generally 9. Several memory paradigms, such as extinction and "Think-No Think" 10 , have attempted to model active forgetting by using intentional, motivated suppression of memories. Another paradigm, item-based directed forgetting, involves exposure to remember-or forget-instructions directly after exposure to an item. To-be-forgotten (TBF) items are later recalled at lower rates relative to to-be-remembered (TBR) items 11 , an effect putatively mediated, in part, by active inhibitory proce...

Sleep reactivation did not boost suppression-induced forgetting

“…We next considered the effects of TMR on memory effects produced by the TNT procedure. Two main hypotheses were tested: (a) whether TMR can further enhance memory-suppression that was established via no-think instructions during wake (e.g., 21 ); and (b) whether memory suppression could be applied de-novo during sleep to impair subsequent retrieval (e.g., 20 ). Testing these hypotheses made use of the three word-sets used for cuing during NREM sleep.…”

“…The purpose of our study was to consider the effects of targeted reactivation on memory suppression. Two previous studies have successfully used TMR to enhance memory suppression using cues associated with suppression in the context of directed forgetting tasks (in which participants are instructed not to commit recently presented information to memory 20 , 21 ). The mechanism enabling this suppressive effect is unknown, but it may involve a reactivation of the suppressive context conjointly with a specific memory, thereby consolidating an inhibitory memory trace which counteracts its subsequent expression.…”

“…The mechanism enabling this suppressive effect is unknown, but it may involve a reactivation of the suppressive context conjointly with a specific memory, thereby consolidating an inhibitory memory trace which counteracts its subsequent expression. These two studies differ in several respects: Simon and colleagues 20 presented the suppressive memory cue in temporal proximity with a previously unrelated memory, effectively creating suppression de-novo during sleep; Schechtman and colleagues 21 associated a single sound with both the suppressive action and a set of individual, previously suppressed memories, thereby enhancing previously established suppression during sleep.…”

“…TMR is a technique involving the unobtrusive presentation of learning-related cues during sleep, thereby impacting memory consolidation 18 . This technique has repeatedly been shown to enhance prior learning 19 , and has also been used to weaken specific memories under some circumstances 20 , 21 . Importantly, a recent study showed that TNT-induced memory suppression can be achieved using unconsciously presented cues during wake, indirectly supporting our assumption that targeting suppression-related memories during sleep may selectively impact retrieval 22 .…”

Reward biases spontaneous neural reactivation during sleep

“…Previous studies using cueing procedures (or "targeted memory reactivation") have suggested that task-or stimulus-specific neural reactivation early in the sleep night or during a nap enhances memory consolidation 9,[20][21][22] . Although our participants did not spent a full night of sleep in the scanner, we tentatively sought to test for such an effect.…”