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Continuous sleep is a modern habit, not an evolutionary constant, which helps explain why many of us still wake up at 3 a.m. and wonder if something is wrong. It can be comforting to know that this is a deeply human experience.
For much of human history, sleeping eight hours straight was not the norm. Instead, people used to sleep in two periods per night, often referred to as “first I am” and “second I am”.
Each of these periods lasted several hoursseparated by a waking phase of one or more hours in the middle of the night, explains the professor of Cognitive Psychology at Keele University Darren Rhodes no .
Historical records from Europe, Africa, Asia, and elsewhere describe how, after dark, families went to bed early, woke up around midnight for a while, and then returned to sleep until dawn.
Breaking the night in two phases probably changed the perception of time. The interval of silence gave the night a clear midpointmaking the long winter nights less continuous and more manageable.
The midnight break it wasn’t dead time; it was time livedwhich shaped the way the night was experienced. Some people got up to do household chores, like stoking the fire or checking on the animals. Others remained in bed to pray or reflect on the dreams they had just had.
Letters and diaries from pre-industrial times mention people using these quiet hours to readwriting or even discreetly socializing with family or neighbors. Many couples took advantage of this midnight vigil for moments of intimacy.
The literature, from the Greek poet Homer to the Roman Virgilcontains references to the “time when the first sleep ends”, indicating how common the night was in two periods.
How we lost our “second sleep”
The disappearance of the second sleep occurred over the last two centuries due to profound social changes.
Artificial lighting is one of the main causes. In the 18th and 19th centuries, first oil lamps, then gas lighting, and finally electricity began to turn the night into useful time to be awake. Instead of going to bed shortly after sunset, people began to stay up later, under the light of lamps.
Biologically, bright light at night also changed our internal clock (the circadian rhythm) and made the body less likely to wake up after a few hours of sleep. Timing of light exposure is crucial. “Normal” bedroom light before bed suppresses and delays melatonin, delaying the onset of sleep.
A Industrial Revolution transformed not only the way people worked, but also how they slept. Factory schedules encouraged a continuous block of rest. At the beginning of the 20th century, the idea of eight uninterrupted hours replaced the secular rhythm of two periods of sleep.
In multi-week sleep studies that simulate long winter nights in darkness and eliminate clocks or nightlights, participants often end up adopt two sleep periods with a calm interval of vigil.
A 2017 study in a Madagascar farming community without electricity concluded that people still slept mostly in two periodsgetting up around midnight.
Long dark winters
Light regulates our internal clock and influences the perception of the passage of time. When these signs disappearlike in winter or under artificial lighting, we lose track of time.
In winter, the later and weaker morning light hinders circadian synchronization. Morning light is particularly important for regulating the circadian rhythm, as it contains a greater amount of blue light, which is the most effective at stimulating cortisol production and suppressing melatonin.
In temporal isolation laboratories and cave studiespeople lived for weeks without natural light or clocks, or even in constant darkness. Many participants in these studies they miscounted the days that passeddemonstrating how time changes easily without light signals.
Similar distortions occur during the polar winterwhere the absence of sunrise and sunset can give the feeling that time is suspended. People native to high latitudesor long-term residents with stable routines, are better able to cope with polar light cycles than temporary visitors, although this varies by population and context.
Adaptation is better when the community shares a regular daily schedule. A 1993 study on Icelandic populations and their descendants emigrated to Canada revealed unusually low disturbance rates seasonal affective disorder (SAD) during the winter, suggesting that genetics may help these populations cope with the long Arctic winter.
Studies from the Environmental Temporal Cognition Lab at Keele University, of which Rhodes is director, show the strength of link between light, mood and perception of time.
In 360-degree virtual reality, researchers from Keele’s Cognition Lab compared scenarios from the United Kingdom and Sweden in terms of environment, light intensity and time of day.
Participants saw six videos of around two minutes and evaluated two-minute intervals like longer ones in night scenes or low light than in daytime or bright scenes. The effect was stronger in participants who reported low mood.
A new perspective on insomnia
Sleep clinicians note that brief awakenings are normaloften occurring during phase transitions, including near REM sleep, associated with vivid dreams. What matters is how we react.
The brain’s perception of duration is elastic: anxiety, boredom or low light tend to lengthen time, while involvement and calm compress it.
Without the time between getting up to do something or talk, waking up at 3 am makes time seem slower. In this context, attention focuses on time, and the minutes that pass can seem endless.
Cognitive behavioral therapy for insomnia (CBT-I) recommends that peopleand get up after about 20 minutes of being awakecarry out a quiet activity in dim light, such as reading, and return to bed when you feel sleepy.
Sleep experts also suggest cover the clock and stop measuring time when there is difficulty sleeping. Accepting wakefulness calmly, combined with understanding how our mind perceives time, can be the most effective way to get back to rest.
