Sleep and memory are closely linked: it is during the night that memories are recorded in the cortex. This phenomenon is called "consolidation." It is even possible to consolidate learning by reactivating, during certain phases of sleep, the memory of the day before.", says Francis Eustache, a neuroscience researcher at Inserm, for Science and Future.
Scientists from the University of California experimented with this last year. Stimulating certain brain areas while patients were sleeping improved their memory.
Based on this observation, Dutch researchers tried to improve patients' memory of a very specific memory: their therapy session. The goal? To consolidate the benefits of this session. Their results were published in the journal Current Biology.
Post-traumatic stress disorder affects memory
This new study involves 33 patients suffering from post-traumatic stress disorder. This psychiatric disorder can occur following a traumatic event that one has experienced or witnessed.
It can have multiple consequences: nightmares, increased vigilance, hyperactivity, mood problems, sleep problems, or even flashbacks. Indeed, trauma affects memories. The hippocampus, the brain area that allows memory to be formed, is overstimulated and no longer functions normally.
Memories crystallize and lose their context. We then observe traumatic resurgences, that is to say that memories are violently imposed on the person, who has the impression of reliving them. This is one of the symptoms of post-traumatic stress, " explains Pierre Gagnepain, researcher at Inserm, during an interview for Science and Future.
Read also“Faced with trauma, being more resilient can (also) be learned!”
Treating Post-Traumatic Stress Disorder
Currently, there are several treatments for this syndrome. On the one hand, psychotherapy by prolonged exposure which aims to reprogram the emotions associated with the traumatic memory. It involves a confrontation with stimuli evocative of the trauma but " up to 50% patients do not respond well to this treatment, " deplore researchers from the University of Amsterdam.
However, there is another solution, better tolerated by patients: EMDR (Eye Movement Desensitization and Reprocessing). During these sessions, " Therapists guide patients through their traumatic memories while using moving lights or clicking sounds to distract them, " they continue. EMDR consists of visualizing various memories by following with your eyes the hand of the therapist for example, who makes slow gestures in several directions.
Sometimes, it is not a question of following the therapist's movement with your eyes, but of tapping alternately on both knees, or of following auditory stimuli, such as clicking sounds. It is on the basis of EMDR sessions that the researchers at the University of Amsterdam worked. They then sought to consolidate its effects during the patients' sleep. "This idea is all the more relevant since there is a relationship, not yet fully elucidated, between the mechanisms at play in EMDR and in certain phases of sleep (notably paradoxical sleep) where rapid eye movements are observed," Francis Eustache is a passionate enthusiast.
Clicking to consolidate therapeutic benefits
First, all participants underwent an EMDR session during which a clicking sound was played. At night, when the patients fell asleep, the same signal was played to half of them. The researchers then recorded the brain wave activity of all the patients.
Result: Those who were re-exposed to the clicking noises showed larger and longer slow oscillations than the others. And precisely, these oscillations are known to be strongly linked to the consolidation of memory, " says Hein van Marle, first author of the study, for Science and Future, satisfied with these first results. The presentation of clicks therefore improved the physiology of sleep responsible for memory consolidation. » All this without causing any negative effects on patients' sleep.
In all participants, EMDR significantly improved symptoms of post-traumatic stress disorder. So far, the researchers have not noted a difference in symptom reduction between the two groups.
But they are starting new work this fall, to repeat this method over several consecutive days. Hein van Marle's team hopes that this work can inspire new research aimed at exploring the beneficial effects of this consolidation in other pathologies, such as phobias or anxiety disorders.
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