Modern medicine scientifically explains how the instability of the 'spirit' described in the Donguibogam manifests as the phenomenon of 'digital insomnia'. The primary culprit behind sleepless nights is the blue light emitted from digital devices such as smartphones and tablets. This blue light stimulates specialized photoreceptors in the retina of our eyes called melanopsin. This melanopsin detects the presence of light and sends signals to the suprachiasmatic nucleus (SCN) in the brain, and the SCN regulates the circadian rhythm, which serves as our body's biological clock.
The problem is that blue light shares a similar wavelength range with daytime sunlight. Our brain perceives blue light as a signal indicating that it is still daytime and time to be awake. Looking at a smartphone screen at night causes the brain to mistakenly assume it is morning. When this happens, the secretion of melatonin, the hormone that induces sleep, is suppressed or delayed. Melatonin naturally increases in secretion at night to encourage sleepiness and guide us into deep rest, but blue light disrupts that timing.
Furthermore, smartphone use is not solely a matter of blue light. The constant flood of information and stimuli from digital devices, such as social media, games, and news, continuously activates our brain. Smartphone use particularly stimulates dopamine secretion associated with the brain's reward system, delivering momentary pleasure and satisfaction, but this simultaneously triggers brain arousal and leads to cognitive hyperarousal. This operates on a principle similar to being unable to sleep after watching an engaging movie late at night. Lying in bed, wondering about the next episode of a webtoon or waiting for a friend's reply, keeps our brain away from sleep.
This cognitive hyperarousal increases the heart rate and raises body temperature, creating physical conditions ill-suited for rest. Additionally, smartphone use can disrupt the balance between REM sleep and non-REM sleep, degrading sleep quality. In particular, as slow-wave sleep, which represents deep sleep, decreases, we wake up the next morning feeling unrefreshed and fatigued despite having slept. Eventually, this can lead to various issues such as impaired concentration, memory impairment, and emotional volatility. Just as the Donguibogam emphasized stabilizing the 'spirit', modern medicine demonstrates that rest and stability for the brain are the very core of healthy sleep.
