By Emaan Adeel for National Geographic
Using a tablet at night may feel like rest, but exposure to light and ongoing stimulation can keep the brain in astate of alertness, even as the body winds down.
For many people, rest no longer marks the end of the day—it interrupts it. Work slows, notifications quiet, and the body finally stops moving. Yet sleep arrives lightly, if at all, and morning brings the same dull fatigue as the night before.
In sleep laboratories, researchers are seeing a pattern: reduced time spent in slow-wave sleep—the stage most closely linked to cellular repair and metabolic recovery—despite normal total sleep duration. Eight hours in bed no longer guarantees that the body has fully reset.
It’s tempting to frame this as a personal failure: too much screen time, an inability to unplug. But sleep scientists say the problem runs deeper. “You may end your day,” says Orfeu Buxton, a sleep researcher at Pennsylvania State University, “but your brain hasn’t received the hormonal and neural signals that it’s safe to let go—cortisol declining, parasympathetic pathways activating, and the circadian clock shifting fully into night mode.”
In "Dopamine Nation", Stanford psychiatrist Anna Lembke writes that constant digital stimulation pushes the brain’s reward system toward craving, leaving it restless even after the screen goes dark. Emerging research supports that shift. A 2025 study in Frontiers in Psychiatry
found that higher levels of smartphone dependence were strongly associated with poorer sleep quality and greater psychological distress—even among people who deliberately carved out time to rest.
The problem isn’t simply that screens push bedtime later. It’s that even when we protect eight hours and the lights go out on schedule, the physiology of restoration may fail to engage.
To understand why that signal is breaking down, researchers are now looking beyond bedtime and into the biology of how the body recognizes that it’s safe to let go. The stress system is designed to remain active in the presence of unfinished demands. Recovery occurs only after the brain disengages its monitoring systems. When that disengagement doesn’t happen, the body may be inactive, but physiological recovery remains incomplete.
In laboratory settings, that incomplete recovery is measurable. Nighttime cortisol declines more slowly, heart rate variability stays suppressed—signaling reduced parasympathetic activity.
Even neuroimaging studies show sustained activation in the brain’s salience network, the circuitry responsible for
detecting threat and unresolved demands, even in the absence of immediate stimuli.
Modern digital life makes that neurological shift harder to achieve. “When we’re caught in the digital vortex, we’re in a constant state of reactivity,” says Lembke, prolonging vigilance even after work has stopped.
Buxton describes this state as “human fracking.” The digital economy, he says, is built to extract attention through high-pressure engagement that is both addictive and exhausting — our vigilance becoming the resource being mined. The consequence is not just later bedtimes, but disruption of what researchers now call “sleep health”—timing, regularity, and depth, not merely hours logged.
Artificial light at night does more than delay circadian rhythms. It also activates non-circadian alerting pathways in the brain, increasing cortisol and temporarily masking sleepiness. A person may feel alert enough to keep scrolling even as homeostatic sleep pressure builds beneath the surface. When notifications, feeds, and unresolved demands repeatedly pull attention back into circulation, the nervous system receives no unambiguous signal that the threat-scanning phase has ended.
Read the entire article in National Geographic here.