Whether you feel like you slept well is not just the amount of time you sleep. It also reflects how deeply and continuously you believe you slept. Scientists still don’t fully understand what happens in the brain to create this deep, refreshing feeling of rest.
A new study by researchers at the IMT Lucca School of Advanced Studies shows that PLOS Biologyindicating an unexpected factor. Dreams, especially vivid and immersive dreams, can make you feel deeper and more restorative, rather than actually disrupting your sleep.
Rethinking deep sleep and brain activity
For decades, deep sleep was thought to be a state in which brain waves are slow, there is minimal activity, there is little awareness, and the brain is essentially “switched off.” In this traditional view, deeper sleep means less brain activity. In contrast, dreaming is typically associated with rapid eye movement (REM) sleep, which is thought to be a sign of partial “wake-up” of the brain.
However, this creates a contradiction. Although REM sleep includes intense dreaming and brain activity similar to wakefulness, people often report that this stage still feels like deep sleep.
To investigate this discrepancy, the researchers analyzed 196 overnight recordings from 44 healthy adults. Participants slept in the lab while their brain activity was monitored using high-density electroencephalography (EEG). The data comes from a wide-ranging project funded by a European Research Council (ERC) start-up grant investigating how different types of sensory stimulation affect the experience of sleep.
Dreams and perceived sleep depth
Participants were woken up more than 1,000 times over four nights and asked to describe what they experienced just before they woke up. They also rated how deeply they felt they were sleeping and how sleepy they felt.
They found that people reported experiencing their deepest sleep not only when they had no conscious experience, but also after having vivid, immersive dreams. In contrast, light sleep was associated with minimal or fragmented experiences, such as a vague sense of presence without clear dream content. “In other words, not all mental activity during sleep feels the same. The quality of the experience, especially how immersive it is, seems to be important,” explains Giulio Bernardi, professor of neuroscience at the IMT School and lead author of the study. “This suggests that dreaming can change how sleepers interpret their brain activity. The more immersed you are in your dreams, the deeper your sleep feels.”
How dreams sustain deep sleep
Another surprising discovery was revealed during the night. Physiological signs of sleep pressure gradually decreased, but participants reported feeling their sleep deepen over time.
This deepening of awareness was roughly equivalent to an increase in dream immersion. The findings suggest that dream experiences may help maintain the feeling of deep sleep, even when the body’s biological sleep demands decrease. Immersive dreams also help maintain a sense of separation from the external environment while parts of the brain are active. This is a key feature of restorative sleep.
Dream as a “guardian of sleep”
“Understanding how dreams contribute to the sensation of deep sleep opens new perspectives on sleep health and mental well-being,” Bernardi says. “If dreams help maintain a sense of deep sleep, changes in dreaming may explain, in part, why some people find it difficult to sleep well even when standard objective sleep indices appear normal. Immersive dreaming may be more than just a byproduct of sleep. , which may help to moderate fluctuations in brain activity and maintain the subjective experience of deep sleep.” This idea reflects a long-standing assumption in sleep research, and even classical psychoanalysis, that dreams may act as “guardians of sleep.”
A new interdisciplinary approach to sleep research
The study was carried out as part of a broader collaboration between the IMT School, the Scuola Superiore Sant’Anna in Pisa, and the Gabriele Monasterio Foundation, in which a new sleep laboratory was established to integrate expertise in neuroscience and medicine.
The facility supports multidisciplinary approaches to studying sleep and the sleep-wake cycle, allowing researchers to better understand how brain activity interacts with bodily processes. These findings represent the early stages of that effort and provide a foundation for future research into how brain and body dynamics shape sleep, both in healthy people and in people with sleep disorders.
