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Remembering painful or traumatic events can be deeply oppressive, especially when they impair cognitive function and mental health. Researchers have developed a technique to weaken negative memories by reactivating positive memories during non-REM sleep, the phase of sleep essential for memory consolidation. It involves reprogramming a list of words with no particular meaning so that they elicit more pleasant (rather than unpleasant) memories. Ultimately, this non-invasive approach could contribute to the treatment of mental disorders linked to traumatic memories.
Remembering painful or traumatic events can be deeply overwhelming, especially when they impair cognitive function and mental health. They can be associated with various mental disorders, such as depression, anxiety, post-traumatic stress disorder (PTSD) or even bipolar disorder.
Scientists have been searching for many years for methods to help manage these memories and their impacts on mental health. However, controlling aversive memories poses a significant challenge due to the intense emotions associated with them and their strong consolidation in memory, unlike other types of memories.
Previous studies have suggested that it may be possible to alleviate them using sleep-based approaches, as sleep influences both memory and emotional processing. Recent experiments have shown that activating positive memories during wakefulness can alleviate negative emotions and depressive symptoms in humans and animal models.
Furthermore, studies suggest that memories of daily experiences are spontaneously reactivated during sleep, which contributes to their consolidation. Memory consolidation could be selectively controlled by manipulating associated sensory signals during non-REM (non-REM or NREM) sleep – a procedure called “targeted memory reactivation” (TMR). Although TMR is generally used to consolidate memories, it could also be used to weaken them.
The research team, from the University of Hong Kong, proposes a new strategy that would weaken negative memories by interfering with positive memories — reactivating the latter during subsequent NREM sleep. “
We hypothesized that older aversive memories might be weakened by reactivating corresponding positive memories during NREM sleep », Explain the researchers in their study, published in the journal
PNAS.
Positive memories more likely to be remembered
The researchers designed a multi-day experimental protocol to explore their hypothesis. On the first day, 37 participants assimilated aversive memories and then benefited from a night’s sleep to consolidate them. To do this, they were asked to associate random words with no particular meaning with a list of images known to be negative (48 pairs), such as injuries or dangerous animals for example. Memory exercises were carried out before the night of sleep to consolidate memories.
Experimental procedure: On day 1, participants learned 48 unique pseudoword-picture pairs with only aversive pictures. On day 2, 24 of the same pseudowords were associated with positive images, introducing interfering memories. L1 and L2 denote the learning task with aversive or positive images, respectively. © Tao Xia et al.
-On the second day, participants assimilated positive memories by trying to associate half of the previously selected words with positive images (beautiful landscapes, smiling children, etc.), thus creating interference. During the ensuing night’s sleep, an audio recording of words spoken aloud was played during NREM sleep. “ During subsequent NREM sleep, we replayed memory cues associated with both aversive and positive images to weaken older aversive memories and affective responses. [qui y sont liées] », Explain the researchers.
The volunteers’ brain activity was monitored using electroencephalography. The research team assessed both memory and affective responses related to positive and negative memories. To perform this assessment, the researchers focused in particular on theta (4 to 8 Hz) and beta (16 to 30 Hz) brain activities. The former is associated with emotional processing and reactivation of emotional memory during sleep, while the latter is linked to memory interference during sleep and forgetting upon waking.
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Theta band activity increased in response to audio memory cues and was significantly higher when these cues were positive. By giving volunteers questionnaires to assess their memory, researchers also found that positive memories were more likely to be remembered than negative ones.
TMR weakened previously acquired aversive memories and strengthened positive interfering memories in the interference condition. (A) TMR signals in the interference condition reduced recall accuracy of aversive memories,
(B) but not in the no-interference condition.
(C and D)
TMR induced more positive memory intrusions in the interference condition
(C) but not in the no-interference condition
(D). In all panels, purple boxes indicate aversive dependent measures and green boxes represent positive dependent measures. © Tao Xia et al.
« We found that this procedure weakened the recall of unpleasant memories and also increased involuntary intrusions of positive memories.
“, they say. “ A non-invasive sleep-based intervention can thus modify aversive recall and affective responses “, they added.
However, it is important to note that this is a tightly controlled laboratory experiment. The results may not apply to actual experiments. The team also specifies that seeing aversive images in a laboratory environment does not have the same impact as experiencing a traumatic experience in real life. Nevertheless, these results would already constitute an interesting avenue to support therapeutic strategies for the treatment of mental disorders linked to traumatic memories.
