Slumber's Unexplored Landscape, Science News Online (9/25/99)
If sleeping patterns in traditional societies remain little known, those of prehistoric humans are a total mystery. Still, in settings that roughly mimic ancient nighttime conditions, sleep undergoes an intriguing shift, says psychiatrist Thomas A. Wehr of the National Institute of Mental Health (NIMH) in Bethesda, Md.
When prohibited from using artificial light from dusk until dawn, people who formerly slumbered in solid blocks of time begin to sleep in two periods separated by an hour or two of quiet rest and reflection.
Wehr and his coworkers asked 15 healthy adults to rest and sleep in darkness for 14 hours (6 p.m. to 8 a.m.) each night for several weeks. Volunteers slept for 11 hours each of the first few nights, apparently to catch up on their sleep. They then settled into a pattern of lying awake for a couple of hours before falling asleep for 3 to 5 hours in the evening. An hour or so of quiet wakefulness ensued, followed by about 4 more hours of sleep in the early morning.
Many mammals sleep in two major bouts during the night or day, Wehr says. Animals from rodents to giraffes and the experimental human sleepers secrete elevated amounts of the hormone prolactin when they rest quietly, even if they are not asleep. Prolactin may promote a state of calmness that accompanies sleep, the NIMH scientist suggests.
Participants in Wehr's study usually awoke out of REM sleep to end their first slumber session. During REM sleep, the brain becomes about as active as it is when wide awake. One function of this sleep phase may be to set the stage for waking up, Wehr holds.
If prehistoric people slept in two nightly periods, then regularly awakening out of REM sleep may have allowed them to reflect on and remember their dreams in a semiconscious state that's generally unavailable to modern sleepers. Sleep compressed into a single stint may thus encourage modern humans to lose touch with dreams, myths, and fantasies, Wehr argues.
These results, first reported in 1993, also raise the possibility that people who wake up once or twice each night don't necessarily suffer from insomnia. "A natural human sleep pattern may reassert itself in an unwelcome world and get labeled as a disorder," Wehr says.
The two-phase sleep pattern observed by Wehr corresponds remarkably closely to the way in which most Western Europeans slept between 500 and 200 years ago, according to historian A. Roger Ekirch of Virginia Polytechnic Institute and State University in Blacksburg. While doing research for a book on nighttime behaviors during that era, Ekirch came across several hundred references to what he identifies as "segmented sleep."
From country farms and villages to city apartments, early modern Europeans usually sank each evening into what they called a "first sleep," which lasted for several hours. Shortly after midnight, they awoke and spent 1 or 2 hours in a "watching period." A "second," or "morning," sleep followed.
The watching period presented many opportunities, Ekirch notes. People coming out of their first sleep often stayed in bed to pray, converse with a bedfellow, contemplate the day's events or the meaning of a dream, or simply let their minds wander in a semiconscious state of contentment that was prized at the time.
A 16th-century physician wrote that many laborers dozed off exhausted at the start of each night. Sexual intercourse with their wives typically occurred in the watching period, after a recuperative first sleep.
These days, Western societies treat sleep more as an unavoidable stretch of downtime than as a prelude to sex or a time for inner reflection. Only intensive investigations across cultures and classes will illuminate the lushness of sleep's landscape, Worthman predicts.
Adds Wehr, "We're going to have to reconceptualize what it means to sleep normally."
If sleeping patterns in traditional societies remain little known, those of prehistoric humans are a total mystery. Still, in settings that roughly mimic ancient nighttime conditions, sleep undergoes an intriguing shift, says psychiatrist Thomas A. Wehr of the National Institute of Mental Health (NIMH) in Bethesda, Md.
When prohibited from using artificial light from dusk until dawn, people who formerly slumbered in solid blocks of time begin to sleep in two periods separated by an hour or two of quiet rest and reflection.
Wehr and his coworkers asked 15 healthy adults to rest and sleep in darkness for 14 hours (6 p.m. to 8 a.m.) each night for several weeks. Volunteers slept for 11 hours each of the first few nights, apparently to catch up on their sleep. They then settled into a pattern of lying awake for a couple of hours before falling asleep for 3 to 5 hours in the evening. An hour or so of quiet wakefulness ensued, followed by about 4 more hours of sleep in the early morning.
Many mammals sleep in two major bouts during the night or day, Wehr says. Animals from rodents to giraffes and the experimental human sleepers secrete elevated amounts of the hormone prolactin when they rest quietly, even if they are not asleep. Prolactin may promote a state of calmness that accompanies sleep, the NIMH scientist suggests.
Participants in Wehr's study usually awoke out of REM sleep to end their first slumber session. During REM sleep, the brain becomes about as active as it is when wide awake. One function of this sleep phase may be to set the stage for waking up, Wehr holds.
If prehistoric people slept in two nightly periods, then regularly awakening out of REM sleep may have allowed them to reflect on and remember their dreams in a semiconscious state that's generally unavailable to modern sleepers. Sleep compressed into a single stint may thus encourage modern humans to lose touch with dreams, myths, and fantasies, Wehr argues.
These results, first reported in 1993, also raise the possibility that people who wake up once or twice each night don't necessarily suffer from insomnia. "A natural human sleep pattern may reassert itself in an unwelcome world and get labeled as a disorder," Wehr says.
The two-phase sleep pattern observed by Wehr corresponds remarkably closely to the way in which most Western Europeans slept between 500 and 200 years ago, according to historian A. Roger Ekirch of Virginia Polytechnic Institute and State University in Blacksburg. While doing research for a book on nighttime behaviors during that era, Ekirch came across several hundred references to what he identifies as "segmented sleep."
From country farms and villages to city apartments, early modern Europeans usually sank each evening into what they called a "first sleep," which lasted for several hours. Shortly after midnight, they awoke and spent 1 or 2 hours in a "watching period." A "second," or "morning," sleep followed.
The watching period presented many opportunities, Ekirch notes. People coming out of their first sleep often stayed in bed to pray, converse with a bedfellow, contemplate the day's events or the meaning of a dream, or simply let their minds wander in a semiconscious state of contentment that was prized at the time.
A 16th-century physician wrote that many laborers dozed off exhausted at the start of each night. Sexual intercourse with their wives typically occurred in the watching period, after a recuperative first sleep.
These days, Western societies treat sleep more as an unavoidable stretch of downtime than as a prelude to sex or a time for inner reflection. Only intensive investigations across cultures and classes will illuminate the lushness of sleep's landscape, Worthman predicts.
Adds Wehr, "We're going to have to reconceptualize what it means to sleep normally."
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