Lateralized rhythmic acoustic stimulation during daytime NREM sleep enhances slow waves

Slow wave sleep (SWS) is characterized by the predominance of delta waves and slow oscillations, reflecting the synchronized activity of large cortical neuronal populations. Amongst other functions, SWS plays a crucial role in the restorative capacity of sleep. Rhythmic acoustic stimulation (RAS) during SWS has been shown a cost-effective method to enhance slow wave activity. Slow wave activity can be expressed in a region-specific manner as a function of previous waking activity. However, it is unclear whether slow waves can be enhanced in a region-specific manner using RAS. We investigated the effects of unilaterally presented rhythmic acoustic sound patterns on sleep electroencephalographic (EEG) oscillations. Thirty-five participants received during SWS 12-second long rhythmic bursts of pink noise (at a rate of 1 Hz) that alternated with non-stimulated, silent periods, unilaterally delivered into one of the ears of the participants. As expected, RAS enhanced delta power, especially in its low-frequency components between 0.75 and 2.25 Hz. However, increased slow oscillatory activity was apparent in both hemispheres regardless of the side of the stimulation. The most robust increases in slow oscillatory activity appeared during the first 3-4 seconds of the stimulation period. Furthermore, a short-lasting increase in theta and sigma power was evidenced immediately after the first pulse of the stimulation sequences. Our findings indicate that lateralized RAS has a strong potential to globally enhance slow waves during daytime naps. The lack of localized effects suggests that slow waves are triggered by the ascending reticular system and not directly by specific auditory pathways

Contributions of sleep, auditory cueing and electrical brain stimulation to the consolidation of emotional memory

This doctoral thesis aimed at better understanding the contribution of sleep, Targeted Memory Reactivation and transcranial Direct Current Stimulation (tDCS) on the consolidation of neutral and emotional memories. In the first part of this work, we found that REM-enriched naps and more specifically rapid eye movement density is associated with the consolidation of sad stories, suggesting a possible implication of Ponto-Geniculo-Occipital (PGO) waves in the consolidation of sad information. In addition, we observed an increase in emotional reactivity during re-exposure to the sad story following a REM-enriched nap. We postulate that REM sleep favored the consolidation of the emotionalsalience of the sad memories, leading to exacerbated emotional reactivity during re-exposure. We also investigated the impact of TMR during NREM sleep on the consolidation of neutral and negative word pairs leanred with a specific sound. We found an equal benefit of the TMR procedure on neutral and emotional material, suggesting that emotion does not modulate the selective enhancing effect of TMR during NREM sleep. In an additional study, we tested the impact of verbatim presentation of the pairs of words during NREM sleep and did not find the memory benefits of TMR. We ascribed the absence of TMR memory benefit to the detrimental effect of the auditory presntation of the second word which impaired the memory reactivation processes initiated by the presentation of the first word. Together, theseresults indicate the crucial role of a sensitive plastic time window necessary for the successful processes of memory reactivation during sleep. Finally, we evaluated how the combination of tDCS and TMR procedure during a wakeful rest consolidation interval benefits memory consolidation. We found that TMR alone led to selective memory benefits for cued word pairs. When the TMR procedure was combined with either right-anodal or left anodal tDCS, we observed a significant improved global learning, suggesting that tDCS does not potentiate but overshadows the TMRprocedure. Altogether, these studies offer new perspectives in the field of memory consolidation. More specifically, the application of an alternating current during post-learning sleep concomitantly to a TMR procedure might favor the specific brain oscillations involved in successful memory reactivation, and might enhance the associated memory gains.Doctorat en Sciences psychologiques et de l'éducationinfo:eu-repo/semantics/nonPublishe

Memory reactivation during resting wakefulness enhances retrieval of neutral and emotional verbal material

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Neutral and emotional memories equally benefit from resting wakefulness memory reactivation

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Within-sleep auditory cueing rescues verbal neutral declarative learning from forgetting

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Does sleep protect declarative memory against emotional interference?

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Sleep and the decontextualisation of emotional memories

The role of sleep for memory consolidation is now well documented, but less is known about the role of sleep for the processing of memories associated with an emotional context. In a series of three studies, we investigated whether sleep, and especially Rapid Eye Movement (REM) sleep, promotes unbinding between neutral memories and their emotional envelope, as suggested by van der Helm & Walker (2009). In a first study (Deliens & al. 2012), participants were induced in a sad or happy mood, being instructed to imagine themselves in a sad or happy situation while listening to congruent emotional musical excerpts. After this mood induction phase, they learned a series of neutral word pairs, had a regular sleep night or were deprived of sleep, and then had 2 regular nights of sleep. At day four, participants had to recall half of the word pairs after induction of the same mood context than at learning, and the other half of word pairs after induction of the opposite mood context. Our results disclosed a mood-dependent memory [MDM] effect (i.e. higher performance in same than different mood context) after sleep deprivation but not after regular sleep, suggesting a protective role of sleep against emotional interference. These results were in line with the Sleep to Forget and Sleep to Remember (SFSR) proposal (Van der Helm & Walker 2009) that emotional memories are reactivated during REM sleep, leading to the reprocessing of emotional experiences and unbinding the affective tone initially associated with the memories. In a second study (Deliens & al. 2013a), we tested the specific hypothesis that REM sleep subtends the demodulation process. The learning procedure was similar to the first study, unless participants benefitted after learning from 3 hours of early sleep (NREM sleep dominant) vs. 3 hours of late sleep (REM sleep dominant). Results revealed a MDM effect in both NREM and REM sleep conditions, failing to support the proposal of a specific role for REM sleep in the demodulation of the emotional context of memories. Finally, we tested the hypothesis that several sleep NREM/REM cycles are actually needed to unbind memories from their emotional context (Deliens & Peigneux 2013b). Again, results revealed a MDM effect both after a full night of sleep or a day awake, suggesting that the demodulation process needs several nights to achieve.info:eu-repo/semantics/nonPublishe

Rôle du sommeil dans la résistance à l’interférence émotionnelle rétroactive

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Prefrontal Transcranial Direct Current Stimulation Globally Improves Learning but Does Not Selectively Potentiate the Benefits of Targeted Memory Reactivation on Awake Memory Consolidation.

Targeted memory reactivation (TMR) and transcranial direct current stimulation (tDCS) can enhance memory consolidation. It is currently unknown whether TMR reinforced by simultaneous tDCS has superior efficacy. In this study, we investigated the complementary effect of TMR and bilateral tDCS on the consolidation of emotionally neutral and negative declarative memories. Participants learned neutral and negative word pairs. Each word pair was presented with an emotionally compatible sound. Following learning, participants spent a 20 min retention interval awake under four possible conditions: (1) TMR alone (i.e. replay of 50% of the associated sounds), (2) TMR combined with anodal stimulation of the left DLPFC, (3) TMR combined with anodal stimulation of the right DLPFC and (4) TMR with sham tDCS. Results evidenced selective memory enhancement for the replayed stimuli in the TMR-only and TMR-sham conditions, which confirms a specific effect of TMR on memory. However, memory was enhanced at higher levels for all learned items (irrespective of TMR) in the TMR-anodal right and TMR-anodal left tDCS conditions, suggesting that the beneficial effects of tDCS overshadow the specific effects of TMR. Emotionally negative memories were not modulated by tDCS hemispheric polarity. We conclude that electrical stimulation of the DLPFC during the post-learning period globally benefits memory consolidation but does not potentiate the specific benefits of TMR.info:eu-repo/semantics/publishe

Sleep develops resistance to emotional interference in memory consolidation

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