When you wake up in the morning, your alarm may go off and your brain feels like it’s turned on, but you may still feel groggy for a while. But the actual process of waking up the brain is a gradual, coordinated event. So how exactly does that happen?
First, let’s define what it means to be awake. “Being awake means the brain is in a state that supports consciousness, movement, and thinking,” Rachel Rowe, a professor of integrative physiology at the University of Colorado Boulder, told Live Science via email. “Unlike sleep, where brain waves are slow and synchronized, wakefulness is characterized by faster, more flexible activity, allowing us to react to the world around us.”
But Aurélie Stephan, a sleep researcher at the University of Lausanne in Switzerland, says there is never a single moment when the brain switches from sleep to wakefulness. Research has shown that the subcortical region of the brain (a group of neuroplastics located below the cerebral cortex) is involved in our wakefulness. Dr. Lowe explains that the reticular activating system (RAS) acts like a “starter switch,” first sending signals to activate the thalamus, the structure that transmits sensory information to other parts of the brain, and then the cerebral cortex, the wrinkled outer layer of the brain.
you may like
In a 2025 study, Stephan and colleagues also discovered that the brain carries out a characteristic pattern of activity when we wake up. When study participants woke up from non-REM sleep, which consists of various stages of sleep from light to deep sleep, their brain activity first showed short bursts of slower sleep-like waves, followed by faster waves associated with wakefulness.
When they woke up from REM sleep, a stage of sleep characterized by vivid dreams and rapid eye movements, their brain waves immediately shifted to faster activity. Overall, the researchers found that regardless of what stage of sleep the participants were in, their brain activity seemed to start in the front and center of the brain and move to the back of the brain when they woke up.
Why do I feel tired in the morning?
Even when we wake up, it still takes some time for our brains to reach full cognitive capacity. This period, called sleep inertia, can last 15 to 30 minutes or even an hour, Stefan says. Researchers don’t know why we feel groggy in the morning, but the time we wake up may play an important role in our mood. Turning off your alarm clock may also help.
“Your brain [naturally] Mr. Stefan will send a signal at a reasonable moment to end the sleep. We explained that many areas, taking into account internal and external signals, talk to each other about when to enter different stages of sleep and, ultimately, when to wake up spontaneously.
Our arousal system listens to these internal and external inputs, creating a cycle of increased alertness approximately every 50 seconds. Our arousal levels fluctuate within 50 seconds, growing and declining over and over again.
“During the buildup phase…it’s hard to wake up,” Stefan said. But when that cycle weakens, “our sleep becomes more fragile and we wake up more easily,” she says. “So basically in those 50 seconds, there are periods of sustained sleep and periods of vulnerable sleep.”
That’s why Stefan advises his friends to always wake up at the same time and not use an alarm.
“Your brain waits for the right 50-second moment, so when you wake up you’ll feel less sleepy,” she says. “When you have an alarm clock, it becomes random in a way. You can end up waking up at the worst moment ever and then develop strong sleep inertia.”
Still, much of what we know about awakening remains a mystery. Scientists still don’t understand why the same amount of sleep can make you feel refreshed one day but not the next. Some research suggests that your diet and length of sleep can influence your morning wakefulness, or how your brain switches from wakefulness to sleep.
“What causes our brains to wake up spontaneously really remains an open question,” Stefan says.
Sleep Quiz: How much do you know about sleep and dreams?
Source link
