Periodic Reporting for period 2 - TweakDreams (Tweaking dreams: non-invasive modulation of the level and content of mental activity during sleep)
Reporting period: 2022-11-01 to 2024-04-30
Sleep and wakefulness have traditionally been regarded as two mutually exclusive states characterized by differences in consciousness and responsiveness to the environment. However, the last two decades of research have demonstrated that sleep is actually a locally regulated phenomenon and that cortical islands of sleep- and wake-like activity can often coexist across distinct brain areas. Intriguingly, this mosaic of activity is also directly related to the presence and content of mental activity during sleep. In line with this, many sleep disorders, including insomnia and arousal disorders, are associated with significant local alterations in the balance between wake- and sleep-like activity. In spite of these considerations, the classical view of sleep as a uniform global state is still dominant in both basic and clinical research. Moreover, it remains unclear whether the occurrence of local wake-like activity is related to specific physiological functions of sleep.
The TweakDreams project aims to achieve a deep understanding of the mechanisms that regulate sleep at a local level. At the core of the proposal is the idea that particular sensory-stimulation protocols may allow us to directly modulate sleep intensity in a local, region-specific manner. Such approaches could be used to non-invasively perturbate regional sleep-related brain activity, thus allowing us to investigate the causal consequences on sleep mentation, subjective sleep depth, and sleep-related functions, including learning and memory. Of note, the same approaches could also find application in counteracting alterations of local sleep regulation in pathological conditions.
Knowledge gathered within the project could yield potential breakthroughs in numerous key applications of clinical, social, and economic interest, including the treatment of sleep disorders and prevention of sleepiness-related accidents.
The TweakDreams project aims to achieve a deep understanding of the mechanisms that regulate sleep at a local level. At the core of the proposal is the idea that particular sensory-stimulation protocols may allow us to directly modulate sleep intensity in a local, region-specific manner. Such approaches could be used to non-invasively perturbate regional sleep-related brain activity, thus allowing us to investigate the causal consequences on sleep mentation, subjective sleep depth, and sleep-related functions, including learning and memory. Of note, the same approaches could also find application in counteracting alterations of local sleep regulation in pathological conditions.
Knowledge gathered within the project could yield potential breakthroughs in numerous key applications of clinical, social, and economic interest, including the treatment of sleep disorders and prevention of sleepiness-related accidents.
During the first 30 months of the project, we set up a new sleep laboratory and started data collection for two experiments aimed at exploring the effects of sensory stimuli applied before or during sleep on brain and mental activity. The sleep laboratory has been equipped with a high-density EEG system and tools for EEG electrode digitization, the collection of verbal and behavioral responses from participants, and the presentation of a wide range of sensory stimuli during both wakefulness and sleep. Moreover, the team developed several tools for data processing and analysis that will be shared with the scientific community upon publication of the project’s results.
Although our project relies on group comparisons that will be computed at final sample sizes, we opted to conduct initial analyses to confirm the consistency of our data with previously published results. In particular, we analyzed data collected from adult volunteers who underwent four overnight high-density EEG recordings in combination with a serial awakening protocol. We specifically analyzed data collected from awakenings from NREM-N2 sleep and not preceded by any systematic sensory stimulations. In line with the previous literature, volunteers reported that they were dreaming just before they woke up in about 40% of the awakenings, whereas they reported that they had the impression of having dreamt but were not able to recall the content (so-called “white dreams”) in 30% of the cases. No subjective experiences were reported in the remaining 30% of the awakenings. Further assessments showed that the majority of white dreams were associated with the impression of having had simple, non-salient dreams, rather than rich and significant experiences, suggesting that these dreams may have just failed to leave a trace in memory because of their scarce relevance. We also made an unexpected observation regarding the cases in which participants reported no conscious experiences upon awakening. In particular, we found that in about 40% of these instances, volunteers actually had the impression of being conscious during sleep, but their subjective experience lacked any specific content. Finally, we observed that subjective sleep depth was lowest in cases of ‘consciousness without content’ and highest either during vivid immersive dreams or when the volunteers reported a complete disappearance of consciousness. These findings have been presented during international scientific conferences and will represent an important reference for our further analyses and experiments within the project.
Although our project relies on group comparisons that will be computed at final sample sizes, we opted to conduct initial analyses to confirm the consistency of our data with previously published results. In particular, we analyzed data collected from adult volunteers who underwent four overnight high-density EEG recordings in combination with a serial awakening protocol. We specifically analyzed data collected from awakenings from NREM-N2 sleep and not preceded by any systematic sensory stimulations. In line with the previous literature, volunteers reported that they were dreaming just before they woke up in about 40% of the awakenings, whereas they reported that they had the impression of having dreamt but were not able to recall the content (so-called “white dreams”) in 30% of the cases. No subjective experiences were reported in the remaining 30% of the awakenings. Further assessments showed that the majority of white dreams were associated with the impression of having had simple, non-salient dreams, rather than rich and significant experiences, suggesting that these dreams may have just failed to leave a trace in memory because of their scarce relevance. We also made an unexpected observation regarding the cases in which participants reported no conscious experiences upon awakening. In particular, we found that in about 40% of these instances, volunteers actually had the impression of being conscious during sleep, but their subjective experience lacked any specific content. Finally, we observed that subjective sleep depth was lowest in cases of ‘consciousness without content’ and highest either during vivid immersive dreams or when the volunteers reported a complete disappearance of consciousness. These findings have been presented during international scientific conferences and will represent an important reference for our further analyses and experiments within the project.
While preliminary, the contributions described above not only confirm previous findings but also extend them significantly. Indeed, our results highlight the complexity and variability of conscious processes during NREM sleep and demonstrate that, contrary to long-held views, consciousness is likely to entirely vanish only during a small portion of our sleep. Further analyses will allow us to verify our observations and investigate whether subjective experiences may be effectively modulated and controlled through sensory stimulation protocols. In particular, by the end of the project, we will be able to determine whether particular sensory stimulations could be used to modulate i) the level of consciousness during sleep or the encoding of experiences into memory, ii) the content of dream experiences, iii) subjective sleep depth and quality. Moreover, we will use collected data to develop and validate a set of tools and guidelines concerning the acquisition, processing, and analysis of sleep- and dream-related data. These tools will be openly shared with the scientific community.