When you wake up in the morning, it might feel like your brain just switched on at the ring of an alarm, although you still might feel groggy for a while. But the actual process the brain goes through to wake up is a gradual, coordinated event. So exactly how does it happen?

First, let's define what it means to be awake. "Being awake means the brain is in a state that supports awareness, movement and thinking," Rachel Rowe, a professor of integrative physiology at the University of Colorado Boulder, told Live Science in an email. "Unlike sleep, where brain waves are slow and synchronized, wakefulness is marked by faster, more flexible activity that lets us respond to the world around us."

There isn't a single moment when the brain flips from asleep to awake, however, said Aurélie Stephan, a sleep researcher at the University of Lausanne in Switzerland. Research has shown that the subcortical regions of the brain — a group of neural formations located below the cerebral cortex — are responsible for waking us up. The reticular activating system (RAS) first acts like the "starter switch," Rowe explained, sending signals to activate the thalamus, a structure that relays sensory information to other parts of the brain, and then the cerebral cortex, the wrinkled outer layer of the brain.

In a 2025 study, Stephan and her colleagues also found that the brain executes a signature pattern of activity upon waking. When the study participants woke up from non-REM sleep, which comprises different stages of sleep ranging from light to deep sleep — their brain activity first showed a short burst in slower, sleep-like waves, followed by faster waves linked to wakefulness.

When they woke up from REM sleep — a sleep stage characterized by vivid dreams and rapid eye movements — their brain waves went straight to faster activity. Overall, regardless of which stage of sleep participants were in, their brain activity appeared to start from the front and central regions of the brain and move to the back of the brain as they woke up, the researchers found.