Researchers still aren’t certain about the reasons we occasionally feel sluggish after waking, but whether you arise spontaneously or with the assistance of an alarm clock possibly influences this. (Image credit: Tara Moore via Getty Images)
Upon waking in the morning, it could appear as though your brain only powered up at the sound of an alarm; nonetheless, you may continue to feel weary for a time. The genuine procedure of the brain awakening is a steady, planned occurrence. Precisely how does this occur?
To begin, let’s describe what being awake signifies. “Being awake indicates that the brain is in a condition that enables consciousness, movement, and thought,” Rachel Rowe, a professor of integrative physiology at the University of Colorado Boulder, conveyed to Live Science via email. “In contrast to sleep, where brainwaves are relaxed and aligned, alertness is defined by quicker, more versatile activity that permits us to react to our surroundings.”
However, Aurélie Stephan, a sleep expert at the University of Lausanne in Switzerland, stated that there is no particular instant when the brain switches from asleep to awake. Studies have revealed that the subcortical brain regions — a series of neural formations situated beneath the cerebral cortex — are accountable for waking us. The reticular activating system (RAS) works initially as the “ignition switch,” Rowe clarified, dispatching signals to trigger the thalamus, a structure that conveys sensory data to other sections of the brain, and then the cerebral cortex, the brain’s outer layer.
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Stephan and her team also discovered in a 2025 study that the brain performs a distinct action sequence as it wakes. When participants in the study awoke from non-REM sleep, which comprises a variety of sleep phases ranging from shallow to profound sleep — their brain activity initially displayed a brief surge of slower, sleep-related waves, succeeded by quicker waves associated with wakefulness.
Their brain waves transitioned instantly to quicker activity when they arose from REM sleep — a stage of sleep defined by vibrant dreams and quick eye movements. The researchers discovered that, irrespective of the sleep stage the participants were experiencing, their brain activity appeared to initiate in the front and central brain areas and travel to the back of the brain as they awoke.
Why we feel so groggy in the morning
Even after we are awake, our brains require time to attain their maximum cognitive capability. Stephan stated that this time, referred to as sleep inertia, can persist anywhere from 15 to 30 minutes, or even an hour at times. Researchers are unclear as to why this early-morning sluggishness occurs, although the time at which we awaken can significantly impact how we feel. Avoiding using an alarm clock may be beneficial.
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Stephan clarified that “when your brain wakes up [naturally], it will transmit a signal at a moment that is reasonable” to end your sleep. She stated that numerous brain areas are considering internal and external signals and are engaging in discussions with one another to determine when to transition to different sleep stages and, ultimately, when to wake you up naturally.
Our arousal mechanism observes these internal and external inputs and creates cycles wherein we are more attentive around every 50 seconds. Within those 50-second periods, our level of alertness varies, rising and falling continuously.
Stephan stated, “During the buildup phase … it becomes more challenging to awaken.” But as the cycle diminishes, she continued, “our sleep is more vulnerable, and it becomes simpler to wake up.” “So, basically, within this 50-second period, we undergo a time of sleep stability and a time of sleep fragility.”
That’s why Stephan suggests that her friends consistently get up at the same hour without the aid of an alarm.
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She stated, “Your brain will await the appropriate 50-second interval, and upon waking, you will feel less drowsy.” “Having an alarm clock introduces randomness. It could rouse you at the absolute worst time, resulting in profound sleep inertia.”
Still, much of what we understand about waking up is still not known. Scientists are still uncertain why the equivalent duration of sleep feels refreshing on some days and not on others. According to some research, dietary habits and amount of sleep can impact morning alertness, or how the brain transitions from being awake to being asleep.
Stephan stated, “What motivates our brain to wake up spontaneously is still an unanswered question.”
Sleep quiz: How much do you know about sleep and dreams?TOPICSLife’s Little Mysteries
Sara HashemiLive Science Contributor
Sara Hashemi serves as a journalist and fact-checker, specializing in environmental justice, climate issues, and the interplay between science and society. Her work has been featured in various publications, including Sierra, Smithsonian Magazine, Maisonneuve, and others. She earned a master’s degree in science journalism from NYU.
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