We Finally Know How The Brain Wakes Up – And Why It Sometimes Sucks So Much

If all that sounds familiar, then a new study from researchers in Switzerland might explain why. It turns out that how we go from asleep to awake is more complex than we thought – and that how, and more importantly when we wake up can have a big effect on how we feel immediately after.

How we sleep

We’ve known for a long time – at least as long as the band REM has been around – that sleep happens in cycles. There’s stage I sleep, where, counterintuitively perhaps, you’re kind of still awake – this is the bit where you may feel yourself “falling asleep”, perhaps experiencing some hypnic jerks on the way. Eventually, that shifts to stage II sleep, or “light sleep”, from which you can be roused fairly easily; this then moves into stage III, the deepest level of sleep, from which it is hardest of all to wake up. 

We oscillate through these stages throughout the night, punctuating each fall and rise with a burst of REM sleep and, more often than you might think, a little period of wakefulness. 

Now, throughout this cycle, our brains are going through some pretty incredible changes. Our brain waves, normally a steady alpha oscillation when you’re chilled out, shift into a theta pattern – a rhythm often associated with memory formation and navigation – which are interrupted sporadically by sudden, short bursts of neural activity known as “sleep spindles”. Eventually, in deep sleep, our brain waves slow down so much that they become delta waves, with frequencies as low as 0.5 Hz.

We know all of this thanks to EEG – that is, electroencephalography. But what we haven’t known so far is how we wake up from this cycle. Could that same technique be used to answer this new question?

The Swiss team thought it was worth a shot. “Conventional electroencephalography […] is the standard technique to record sleep in a naturalistic setting and across clinical disorders,” they point out in their new paper – but “regional EEG changes at the precise moment of the transition from sleep to wakefulness have not been investigated in detail.”

That’s despite some pretty compelling reasons to take a look. Documenting what happens in the brain as it wakes up is “of major interest,” the authors write – “not only to better understand how the regional reestablishment of wakefulness affects cognition and behavior, but also because many sleep disorders, including insomnia and parasomnias, are characterized by incomplete, excessive, or abnormally timed arousals.” 

“Better understanding the spatial dynamics underlying these arousals may thus improve their detection and help identify the underlying neural substrates,” they suggest.

Out of the darkness

You might expect that waking up is the same as falling asleep, just in reverse. That’s not the case, it turns out: “really waking up is this ordered wave of activation that moves from the front to the back of the brain,” Rachel Rowe, a neuroscientist at the University of Colorado Boulder who was not involved in the study, told Nature News last week.

That’s the conclusion the team drew from their analysis of more than 1,000 awakenings – both spontaneous and as a result of an alarm – experienced by 20 study participants each wearing 256 EEG sensors on their scalps. To be clear, that’s a lot of sensors: “in its usual setup, [an EEG] uses only a few electrodes,” the paper notes.

Across all that input, you’d expect some amount of randomness – but “the surprise is how consistent [this pattern] was across every awakening,” Francesca Siclari, a researcher at the Netherlands Institute for Neuroscience and senior author of the study, told Nature. The march from sleep to wakefulness begins, it seems, in the front, in regions associated with executive function and decision-making; alertness then spreads backwards through the brain, eventually ending up at a region in the back associated with vision. 

“This progression likely reflects how signals from subcortical arousal centres (deeper in the brain) reach the cortex,” explained Aurélie Stephan, a postdoctoral researcher at the University of Lausanne and first author of the study, “with shorter paths to frontal areas and longer ones toward regions further back.”

At least, that’s normally the case. “The brain responds differently to arousing signals depending on the stage it’s in,” continued Stephan, in a statement on the research.

So, that front-to-back wave of waking up? Technically, that’s only true when we wake up from REM sleep – that’s the sleep associated with vivid dreams, when brain activity is most similar to when we’re awake. Apparently, it’s also a state we need to be jolted out of: when we wake out of REM sleep, “the cortex immediately responds with the fast, wake-like, activity,” Stephan explained.

Waking from non-REM sleep, in contrast, is more of a gradual process – and it has an extra step, with alertness starting slowly in a central “hub” in the brain. It’s only after that that the standard front-to-back pattern starts up.

The reason for that is fundamental to how non-REM sleep works, Stephan explained. “In non-REM sleep, neurons that connect arousal centres to the cortex alternate between states of activity and silence – a dynamic known as ‘bistability’,” she said. “As a result of this bistability, any arousing stimulus first triggers a slow wave, before transitioning to faster activity.” 

“In contrast, REM sleep does not have this bistable pattern”.

Hit the snooze

So, with the waking process now understood in greater detail than ever, can we finally wave goodbye to those horrible groggy mornings, dragging yourself out of bed only to fall back asleep while you brush your teeth? Well… maybe, actually – because as it turns out, there is a noticeable pattern as to how awake you feel based on how and when you wake up.

“We found a new aspect in which slow waves can present very distinct and opposite behaviors,” Stephan said. “Some slow waves are actually acting like arousal elements – they are part of the ‘wake up!’ signal. The more these waves occur just before awakening, the more alert you tend to feel upon awakening.”

Meanwhile, she explained, “the other slow waves – whether they are present before waking up or persisting after – are the reason we sometimes feel so sleepy in the first moments of the day.”

It’s only an early step – but the team hope that their results may be used in future research into various sleep disorders. With further investigation, they can see their findings helping to predict sleepiness in those with sleep apnea, or to control sleep-related seizures. “If we understand the process more, we can also better identify signs of hyperarousal in sleep disorders,” Stephan said.

Overall, “this study provides a new perspective looking at the brain’s journey from sleep to wakefulness,” she added, “offering a window into one of the most fundamental transitions in human consciousness.”

The study is published in the journal Current Biology.