We sleep for one third of our lives - yet, sleep remains a scientfic mystery. But now, for the first time, MIB researchers and colleagues have identified the whole-brain activity underlying the stages of human sleep.

05.03.2019 | Hella Kastbjerg

The current understanding of sleep hinges inseparably on our ability to categorise, and derive patterns from, brain activity. This started in the 1930s when it became possible for the first time to record scalp potentials during sleep using electroencephalography (EEG). This led to the first attempts at describing sleep as a consequence of different brain states. The current consensus reduces human sleep to four stages of rapid-eye movement (REM) and non-REM configurations of brain activity, based on measurements in a few EEG electrodes of frequency- and amplitude patterns, many of which were already described in the original studies of the 1930s. In spite of great advances in modern techniques for recording brain activity, tradition has kept our view of brain activity during sleep unnecessarily narrow.

Now, thanks to the efforts of a large international team, researchers have used modern functional magnetic resonance imaging (fMRI) recordings to discover more about the complex choreography of sleep and the whole-brain activity underlying the conventional stages of human sleep, according to a study published Monday 4th of March 2019 in the open-access journal Nature Communications, led by Dr Angus Stevner, Dr Diego Vidaurre, Prof Peter Vuust, Prof Eus Van Someren and Prof Morten Kringelbach from the University of Oxford (UK), Center for Music in the Brain, Aarhus University (Denmark), University of Pompeu Fabra, Barcelona (Spain) and Netherlands Institute for Neuroscience (Amsterdam, the Netherlands).

Whereas the definitions of the traditional sleep stages routinely rely on expert human observers inspecting traces of EEG and identifying patterns of amplitude and frequency, the team used a completely data-driven analysis of fMRI data to reveal recurring states of unique configurations of interactions between brain regions and transitions between these, not unlike the choreographies used to describe music and dance. When comparing these data-driven fMRI states with the conventional EEG sleep stages, the findings show how a higher-resolution picture of brain activity portrays human sleep as vastly more complex than what traditional accounts have suggested. Rather than being reduced to a matter of overall changes in EEG frequencies, the team shows how the difference between wakefulness and sleep is reflected in large-scale reorganization of brain networks. The boundary between wakefulness and sleep, the loss of awareness that we experience every night, has challenged the conventional sleep staging for decades, and the data-driven results confirm that the current definitions are inconsistent. A result that could change the way we understand sleep and not at least the way we approach disorders of sleep, such as insomnia.

Dr Angus Stevner, the lead author of the study says: “Sleep and the associated changes in consciousness is not just a topic of scientific puzzlement, they represent a vital need for healthy functioning. Today we lack a consistent understanding of what happens in the brain when sleep suffers, in conditions such as insomnia but also in psychiatry where sleep disruption is ubiquitously present. It is our hope that a more complete and data-driven representation of whole-brain network changes during sleep can assist in the development of better models of the role of sleep in such disorders”.

Prof Morten Kringelbach, senior author, adds “The findings show the complex choreography of brain activity during normal sleep. In addition to breaking new grounds in our understanding of sleep, we have also taken the unorthodox step of finding new ways to listen to the findings. We have worked closely together with composer Milton Mermikidis to use our findings to produce beautiful musical compositions: ‘Sound asleep’, the music of your brain falling asleep and waking up”.

For more information please contact Dr Angus Stevner: angus.stevner@clin.au.dk

Notes
* The paper “Discovery of key whole-brain transitions and dynamics during human wakefulness and non-REM sleep” is published in the high-impact journal Nature Communications and is freely available on the journal website:

https://www.nature.com/articles/s41467-019-08934-3.