Most people have memories they wish to forget – painful experiences, embarrassing moments, or traumatic events. For some individuals, aversive memories become overwhelming, intruding into awareness and affecting mental health. Scientists have long sought methods to help manage troubling memories, particularly for conditions like post-traumatic stress disorder.
Researchers have made significant progress toward addressing this challenge. A new study published in the Proceedings of the National Academy of Sciences shows promising results for weakening negative memories by reinforcing positive ones during sleep.
Sleep May Hold Key to Memory Modification
Memory formation and emotional processing both occur during sleep. Scientists have discovered that memories from daily experiences are spontaneously reactivated during sleep, contributing to memory consolidation.
An international research team developed a novel procedure spanning multiple days to test how sleep might be used to modify aversive memories. “We found that this procedure weakened recall of aversive memories and also increased involuntary intrusions of positive memories,” write researchers in their published paper.
Scientists call this approach “targeted memory reactivation,” where sensory cues associated with specific memories are replayed during sleep to influence memory consolidation. While previous research has used this technique to strengthen memories, this study focused on weakening aversive memories by reactivating competing positive memories.
Understanding the Basics of Memory
To truly appreciate the significance of this new research on weakening bad memories during sleep, it’s helpful to have a foundational understanding of how memory works. Memory isn’t a single, monolithic entity; instead, it’s a complex system involving various stages and brain regions working in concert.
Memory formation begins with encoding, transforming sensory information into a neural code the brain can store. This happens when we experience something – see a face, hear a sound, feel an emotion. These experiences trigger neural activity, creating temporary traces in the brain.
Next comes storage, which retains this encoded information over time. Memories aren’t simply filed away in one specific location. Instead, different aspects of a memory – visual details, emotional associations, contextual information – are distributed across various brain regions. For instance, the hippocampus, a seahorse-shaped structure deep in the brain, plays a crucial role in forming new episodic memories (memories of events). The amygdala is heavily involved in processing emotions associated with memories.
Finally, retrieval is accessing and bringing stored information back into conscious awareness. This can be triggered by cues, like seeing a familiar place or a particular song. The efficiency and accuracy of retrieval can be influenced by various factors, including the strength of the initial encoding, how often the memory has been accessed, and the presence of interfering information.
Multi-Day Memory Experiment
Researchers conducted their study with 37 participants over several days. On day one, participants learned associations between nonsense words and aversive images showing disturbing content, such as injuries or dangerous animals.
Participants returned for day two after an overnight sleep, allowing these negative associations to consolidate. During evening sessions, researchers introduced positive interfering memories by associating half of previously learned words with pleasant images like peaceful landscapes or smiling children. “For study, team used recognized databases of images classified as negative or positive – think human injuries or dangerous animals, compared with calm landscapes and smiling children.”
During participants’ second night of sleep, researchers unobtrusively played recordings of nonsense words during non-rapid eye movement (NREM) sleep. Scientists monitored brain activity using electroencephalography (EEG) throughout sleep sessions to track neural responses to memory cues.
Brain Activity Reveals Memory Processing
Researchers found that replaying memory cues during NREM sleep caused distinctive patterns in brain activity. Increased theta-band activity (4-8 Hz brain waves) linked to emotional memory processing was particularly interesting.
When participants heard cues for words associated with both negative and positive images, brain activity suggested stronger reactivation of positive memories. Using computational modeling, researchers found evidence showing memory cues facilitated evidence accumulation toward positive responses.
Morning testing revealed that participants had more difficulty recalling negative memories than positive images. Additionally, positive memories were more likely to intrude spontaneously when participants tried recalling aversive content.
From Lab to Real-World Applications
While findings show promise, researchers acknowledge limitations in translating laboratory results to real-world scenarios. Visual images shown briefly in controlled settings differ significantly from emotionally charged personal experiences that form traumatic memories. “Overall, our findings may offer new insights relevant for treatment of pathological or trauma-related remembering.”
Many variables influence memory processing during sleep, including types of memories involved, brain regions activated, and specific sleep phases. Future research must determine how memory editing might apply to different contexts and how long-lasting the effects might be.
Creating New Possibilities for Mental Health Treatment
Scientists have known for years that sleep involves brief memory replay, which contributes to consolidation. This groundbreaking study demonstrates that introducing competing positive information before sleep can weaken previously established negative memories.
Memory weakening during sleep may eventually offer new treatment approaches for conditions involving intrusive traumatic memories. By strengthening positive memories that compete with negative ones, therapists might help patients manage distressing recollections without requiring conscious effort.
Such approaches could potentially complement existing treatments like cognitive behavioral therapy or eye movement desensitization and reprocessing (EMDR) that address traumatic memories during wakefulness.
Scientific Method Behind Memory Modification
Researchers measured memory changes through several complementary techniques. During morning testing, participants completed cued recall tasks requiring them to describe images associated with each word verbally. Researchers also tracked involuntary memory intrusions, asking participants to report when competing memories spontaneously came to mind.
Affective responses were measured through rapid judgment tasks where participants quickly categorized words as positive or negative. Computational modeling revealed that cueing during sleep facilitated evidence accumulation toward favorable affect judgments.
When analyzing brain activity, researchers found that memory cues during sleep triggered increased power across delta, theta, sigma, and beta frequency bands in frontal and central brain areas. Further analysis revealed that the strength of theta activity during sleep predicted recall of positive memories following waking.
The Power of the Sleeping Brain
Sleep was viewed as a passive state of rest for the body for a long time. However, neuroscience has revealed that our brains are far from inactive while we sleep. Sleep is a dynamic and crucial period for various essential functions, including learning, physical restoration, and memory consolidation.
During sleep, the brain actively processes the information acquired during wakefulness, strengthening important memories and discarding less relevant ones. This process, known as memory consolidation, involves stabilizing and storing memory traces. Different stages of sleep play distinct roles in this process.
Slow-wave sleep (SWS), a deep stage of non-rapid eye movement (NREM) sleep, is vital for consolidating declarative memories – the memories of facts and events. During SWS, the hippocampus replays neural patterns associated with recent experiences, transferring these memories to the neocortex for more permanent storage.
Rapid eye movement (REM) sleep, characterized by vivid dreaming and increased brain activity that resembles wakefulness, is thought to play a crucial role in consolidating emotional memories and procedural memories (skills and habits). The intense neural activity and unique neurochemical environment of REM sleep facilitate the integration of emotional experiences into our memory network.
Looking Forward: Promise and Caution
Memory manipulation research raises possibilities for treating conditions like PTSD, phobias, and anxiety disorders. By weakening links between triggering stimuli and distressing emotional responses, sleep-based approaches might reduce suffering without requiring conscious confrontation with traumatic content.
Scientists emphasize the need for extensive research before clinical applications. Questions remain about how long memory modifications persist and which types of memories might respond best to such interventions.
For now, the study represents a meaningful scientific advancement in understanding how sleep processes can be harnessed to modify emotional memories. Research continues to explore how brain mechanisms during sleep influence what we remember and how we feel about those memories upon waking. As scientists deepen their understanding of memory consolidation during sleep, new possibilities emerge for addressing mental health conditions where troubling memories play central roles.
Source:
- Oyarzún, J. P., Morís, J., Luque, D., De Diego-Balaguer, R., & Fuentemilla, L. (2017). Targeted Memory Reactivation during Sleep Adaptively Promotes the Strengthening or Weakening of Overlapping Memories. Journal of Neuroscience, 37(32), 7748–7758. https://doi.org/10.1523/jneurosci.3537-16.2017
