Researchers found that a single night of total sleep deprivation and several days of chronic sleep restriction produce distinct patterns of brain reorganisation, rather than a single uniform “sleep-deprived state”.

Adequate sleep is essential for maintaining cognitive abilities, including learning, emotional stability and mental health, and is also crucial for regulating biochemical, metabolic and immunological processes.

Although the brain remains active during sleep, the study shows that different forms of sleep loss significantly alter its functional architecture.

The research was conducted by an international team from the University of Warsaw, the Jagiellonian University, the Nencki Institute of Experimental Biology of the Polish Academy of Sciences, the Université Grenoble Alpes, the National Institute for Research in Digital Science and Technology, and the University Hospital in Toulouse.

The study used functional magnetic resonance imaging (fMRI) to analyse brain function in 28 healthy participants under three conditions: after normal, restorative sleep; after one night of total sleep deprivation (approximately 26 hours without sleep); and after five nights of chronic sleep restriction (approximately five hours per night).

Each condition represented a different type of physiological stress — acute and intense versus chronic and cumulative. The study was longitudinal, meaning the same participants were scanned in all three states, allowing researchers to observe individual changes in brain function.

To capture subtle changes in brain activity, researchers modelled the brain as a complex network and applied graph theory and machine learning techniques. This approach enabled analysis of both local disruptions and the global organisation of brain connectivity.

In a rested state, the brain’s functional network is highly organised and contains so-called hubs — regions that act as central nodes integrating information from different parts of the brain. These hubs function like large airport transfer points, enabling rapid and efficient information flow across the system.

The study found that both forms of sleep deprivation lead to reorganisation of brain network topology, but in distinct and systematically different ways.

‘Until now, sleep deprivation has often been compared to a depleted battery: the less we sleep, the more tired and +discharged+ we become. It seemed, therefore, that a sleepless night and several days of sleep deprivation were the same phenomenon, just with different intensity. Our research, however, shows something completely different. These are two distinct states that affect the brain in different ways’, said Patrycja Ściślewska from the University of Warsaw.

A single night of total sleep deprivation triggered rapid changes primarily affecting the brain’s resting-state network — a system involved in self-reflection, mind-wandering and emotional processing. In this condition, key hubs lost their dominant coordinating role, reducing their ability to integrate information flow, while other regions increased connectivity and partially compensated for this loss of function.

‘What we observed appears to be a compensatory mechanism - some brain regions lose connections, while others gain them. It seems, therefore, that the brain is trying to +remedy the situation+ by reorganizing its structure’, Ściślewska said.

In contrast, chronic sleep restriction led to slower, more diffuse and widespread reorganisation across multiple brain systems. These changes were less abrupt but affected a broader range of regions, including those responsible for emotional regulation, decision-making and behavioural control.

The cerebellum, a structure primarily associated with movement coordination and behavioural automation, was also found to play a greater role under chronic sleep restriction.

‘Our study suggests that under conditions of chronic sleep deprivation, the cerebellum's importance in the brain network increases, which may indicate a greater importance of behavioural automation. This seems consistent with our intuition: after several nights of poor sleep, we often feel like we're operating on autopilot’, said Aleksandra Domagalik-Pittner, PhD, head of the Magnetic Resonance Imaging Laboratory at the Jagiellonian University Brain Research Centre.

Unlike acute deprivation, where changes appear rapid and targeted, chronic sleep restriction does not lead to a sudden breakdown but to gradual adaptation — though at the cost of reduced efficiency and stability. Researchers compared this to a computer that slows down but continues operating.

In both conditions, the central disruption involves the brain’s network topology — the balance between specialised processing and integrated communication. In a healthy brain, different regions perform specialised functions while remaining efficiently connected. Sleep deprivation disrupts this balance, making the network more random and less efficient in information transfer.

To confirm these distinctions, researchers used machine learning methods to classify brain states based on connectivity patterns. The algorithms successfully distinguished between total sleep deprivation and chronic sleep restriction, confirming that these are separate neurobiological states rather than different degrees of the same condition.

The study also found individual variation in susceptibility. Participants with stronger circadian rhythms were more resistant to sleep loss, while so-called “night owls” showed greater differences between acute and chronic sleep deprivation.

Researchers added that recovery patterns also differ: a single sleepless night can typically be mitigated with one or two nights of recovery sleep, whereas chronic sleep restriction may require many days of stable and sustained rest.

They also noted that while acute sleep deprivation produces immediate awareness of impairment, chronic sleep loss can lead to psychological adaptation in which individuals underestimate their own reduced performance.

PAP - Science in Poland, Ewelina Krajczyńska-Wujec (PAP)

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