At the Frontiers of Sleep: When the Brain Never Quite Switches Off

Existing classifications fall short of a complex phenomenon

The researchers explained that the classification of sleep used since the 1960s – light sleep, deep sleep and REM sleep – is no longer sufficient to capture the full complexity of our states of consciousness. Their approach explores the transitional states between wakefulness and sleep, sometimes extremely fleeting, during which the boundaries between the two begin to blur.

Using electroencephalographic measurements, analyses of mental content and behavioural experiments, the team is seeking to redefine sleep itself: not as a single state, but as a mosaic of brain, mental and physiological activity.

Exploring the tipping point

To investigate the boundary between wakefulness and sleep, the DreamTeam drew inspiration from a technique used by Salvador Dalí and Thomas Edison: falling asleep while holding an object, being awakened when it drops, and immediately recording the images or ideas that came to mind.

In the laboratory, this approach has shown that a very brief period in the first stage of sleep triples the likelihood of solving a problem creatively. Just one minute on the threshold of sleep is enough to stimulate the mechanisms involved in creativity. This finding provides scientific support for an intuition often described by artists and inventors: new associations may emerge precisely within this hybrid state, neither fully awake nor entirely asleep.

Between wakefulness and sleep

In other experiments, Delphine Oudiette and her team have shown that falling asleep does not entail a complete disconnection from the outside world. By playing sounds to sleeping participants and recording subtle facial movements, the researchers observed that some were still able to respond to instructions, confirming that the brain can retain a window of wakefulness during light or REM sleep.

Conversely, Thomas Andrillon studies the emergence of brain waves characteristic of deep sleep in people who are awake. This phenomenon, known as “local sleep”, reflects a temporary disengagement of certain areas of the brain. It could help explain lapses in attention, drowsiness at the wheel, or certain neurodevelopmental disorders such as ADHD, in which sleep-like waves appear more frequently during wakefulness.

Practical implications for brain health

These discoveries open up significant therapeutic and preventive avenues:

– gaining a better understanding of insomnia and the subjective perception of sleep;

– developing tools to detect drowsiness and improve road safety;

– using markers of local sleep as potential early indicators of neurological disorders.

By revealing the continuity between wakefulness and sleep, the DreamTeam’s work is opening up an entire field of research into brain health: how the brain balances its internal states, and how attention, memory and creativity are reorganised across them.

Exploring this “inner continent” remains one of the keys to gaining a deeper understanding of the human brain and learning how to harness its full potential.