Article: A Fresh Take on Sleep Patterns
For much of human history, uninterrupted eight-hour sleep was an anomaly rather than the standard. Instead, people were accustomed to dividing their nights into two distinct segments, widely referred to as "first sleep" and "second sleep." These sleeps were marked by several hours each, bridged by a period of wakefulness lasting an hour or more. Historical accounts from all corners of the globe—Europe, Africa, Asia, among others—illustrate how people would retire shortly after nightfall, awaken around midnight, and then return to sleep until dawn.
This split sleeping pattern likely altered how nights were experienced, with the tranquility of the midnight interval giving the long winters a defined midpoint, thus making evenings feel more palatable. During these intervals, people engaged in various activities like stirring the fire or checking on livestock; others took time for meditation or reflecting on dreams. Documentation from pre-industrial eras reveals that these quiet hours were often utilized for reading, writing, or engaging in low-key social interactions with family or neighbors. Couples frequently used this time for intimate connections.
The prevalence of a segmented night is echoed in literature from antiquity, including works by Greek poet Homer and Roman poet Virgil, which reference "the hour which terminates the first sleep."
How the 'Second Sleep' Was Lost
The erosion of the second sleep occurred over the last two hundred years, spurred by fundamental societal transformations. The emergence of artificial lighting played a key role. Beginning in the 1700s and progressing through the 1800s, the advent of oil lamps then gas and eventually electric light began transforming nighttime into viable personal time. Instead of sleeping shortly after sunset, people began staying awake longer in lamplight.
Exposure to bright lights at night impacted our internal biological clocks, diminishing our tendency to awaken after a few hours of sleep. Ordinary "room" lighting before sleep suppresses and postpones melatonin production, prompting later sleep onset. The Industrial Revolution not only reshaped occupational landscapes but also our sleep habits, promoting a singular sleep period through factory schedules. By the early 20th century, the norm shifted towards eight continuous hours of sleep, phasing out the two-sleep cycle.
Studies mimicking extended winter nights by eliminating evening light and clocks showed lab participants often reverting to two sleeps with a serene interval between. Similarly, a 2017 study of a non-electrified Madagascan farming community revealed predominant biphasic sleep, with a rise at midnight.
Long, Dark Winters
Light not only orchestrates our internal clocks but also influences our perception of time. When these cues are absent or reduced, as in winter or under artificial illumination, our sense of time can blur. In winter, the subsequent later and dimmer morning light complicates circadian alignment, as morning light is critical in synchronizing biological rhythms by providing more blue light, which efficiently stimulates cortisol production and melatonin suppression.
Experiments in time-isolated labs and caves show how people, when deprived of natural light and chronological markers, or even in total darkness, easily lose track of days, a phenomenon echoing the transient sense of time felt in polar winters without distinct sunrises or sunsets.
Populations in high-latitude regions or those with established routines often fare better adapting to fluctuating polar light cycles than transient visitors, although this can vary. Communities adhering to shared daily routines tend to adapt more efficiently. A 1993 study found Icelanders and their Canadian descendants exhibited unusually low rates of winter seasonal affective disorder (SAD), suggesting genetic factors might aid adaptation to prolonged Arctic winters.
Research from Keele University’s Environmental Temporal Cognition Lab, which I direct, underscores the profound link between light, emotion, and temporal perception. Using 360-degree virtual reality, we aligned UK and Swedish landscapes for light and time settings. Participants felt the two-minute intervals stretched longer in evening or dim scenes versus brighter ones, especially those reporting low mood.
A New Perspective on Insomnia
Sleep experts note that sporadic awakenings are common, often aligning with sleep stage transitions, notably near REM sleep associated with vivid dreaming. The key is in our response to these awakenings.
The perception of time is flexible; anxiety, boredom, or diminished light can expand our sense of time, whereas engagement and tranquility contract it. Awakening at 3am without occupying oneself can make time seem sluggish, drawing attention to its slow passage. Cognitive behavioral therapy for insomnia (CBT-I) suggests leaving bed if wakefulness persists after 20 minutes, engaging in a dim-lit quiet activity, then attempting sleep once drowsy. Sleep specialists advocate ignoring clocks and relinquishing time awareness when sleep eludes. Embracing wakefulness calmly, along with insights into our temporal perception, may pave the surest route back to slumber.
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