Feeling like you had “a good night’s sleep” depends on more than just how long you slept. It also reflects how deeply and continuously you believe you slept. Scientists still do not fully understand what happens in the brain to create this sense of deep, refreshing rest.
A new study from researchers at the IMT School for Advanced Studies Lucca, published in PLOS Biology, points to an unexpected factor. Dreams, especially those that are vivid and immersive, may actually make sleep feel deeper and more restorative rather than interrupting it.
Rethinking Deep Sleep and Brain Activity
For decades, deep sleep was viewed as a state where the brain is essentially “switched off,” with slow brain waves, minimal activity, and little awareness. Under this traditional view, deeper sleep meant less brain activity. In contrast, dreaming has typically been linked to Rapid Eye Movement (REM) sleep and considered a sign of partial “awakenings” in the brain.
However, this creates a paradox. REM sleep involves intense dreaming and brain activity that resembles wakefulness, yet people often report that this stage still feels like deep sleep.
To explore this contradiction, researchers analyzed 196 overnight recordings from 44 healthy adults. Participants slept in a laboratory while their brain activity was monitored using high-density electroencephalography (EEG). The data came from a broader project funded by a European Research Council (ERC) Starting Grant examining how different types of sensory stimulation influence the experience of sleep.
Dreaming and Perceived Sleep Depth
Over four nights, participants were awakened more than 1,000 times and asked to describe what they were experiencing just before waking. They also rated how deeply they felt they had been sleeping and how sleepy they were.
The results showed that people reported the deepest sleep not only when they had no conscious experience, but also after vivid, immersive dreams. In contrast, shallow sleep was linked to 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, appears to be crucial” explains Giulio Bernardi, professor in neuroscience at the IMT School and senior author of the study. “This suggests that dreaming may reshape how brain activity is interpreted by the sleeper: the more immersive the dream, the deeper the sleep feels.”
How Dreams May Sustain Deep Sleep
Another surprising finding emerged across the night. Even though physiological signs of sleep pressure gradually decreased, participants reported that their sleep felt deeper as time went on.
This perceived deepening closely followed an increase in how immersive their dreams became. The findings suggest that dream experiences may help preserve the feeling of deep sleep even as the body’s biological need for sleep declines. Immersive dreams may also help maintain a sense of separation from the external environment, which is a key feature of restorative sleep, even while parts of the brain remain active.
Dreams as “Guardians of Sleep”
“Understanding how dreams contribute to the feeling of deep sleep opens new perspectives on sleep health and mental well-being,” says Bernardi. “If dreams help sustain the feeling of deep sleep, then alterations in dreaming could partly explain why some people feel they sleep poorly even when standard objective sleep indices appear normal. Rather than being merely a by-product of sleep, immersive dreams may help buffer fluctuations in brain activity and sustain the subjective experience of being deeply asleep.” This idea echoes a long-standing hypothesis in sleep research — and even in classical psychoanalysis — that dreams may act as “guardians of sleep.”
A New Multidisciplinary Approach to Sleep Research
The study was carried out as part of a broader collaboration between the IMT School, Scuola Superiore Sant’Anna in Pisa, and Fondazione Gabriele Monasterio, where a new sleep laboratory has been established to integrate neuroscientific and medical expertise.
This facility supports a multidisciplinary approach to studying sleep and the sleep-wake cycle, enabling researchers to better understand how brain activity interacts with bodily processes. These findings represent an early step in that effort and provide a foundation for future research into how brain-body dynamics shape sleep in both healthy individuals and those with sleep disorders.
