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What would happen to our sleeping pattern if we had no indication if it was day or night? Would we still have a regular schedule? A French adventurer and scientist, Michel Siffre, sought to find out. We will be looking at one of his studies here. Before that, let's define some terms related to sleep and set the background of the study.
We have a regular sleep/wake pattern on a 24-hour day due to biological rhythms – internal biological clocks in our body that govern different bodily functions/cycles. There are different biological rhythms, and one of these is the circadian rhythm.
The circadian rhythm lasts for 24 hours. A well-known circadian rhythm is a sleep-wake cycle. This cycle is our pattern of sleeping and wakefulness during a 24-hour day. Everyone's sleep-wake cycle is different, and different things can affect the sleep-wake cycle, such as external cues. These external cues are called exogenous zeitgebers, and the most notable one affecting the sleep-wake cycle is daylight.
Biological rhythms
Internal biological clocks in our body that govern different bodily functions/cycles
Circadian rhythm
A biological rhythm that lasts for 24 hours.
An example of a circadian rhythm is the sleep-wake cycle.
An example of an exogenous zeitgeber that influences the sleep-wake cycle is daylight.
The sleep-wake cycle is a classic example of circadian rhythms, freepik.com/pch.vector
The aims of the study were:
On 14 February 1972, Siffre went into Midnight Cave, Texas, USA and stayed there for six months. He stayed in a tent with a bed, table, and chair.
He took a supply of frozen food and 780 gallons of water into the cave.
When Siffre woke up and thought it was daytime, he phoned the research team above ground, and they switched on the lights in the cave.
He conducted daily experiments, taking his blood pressure, memory, and physical tests. When he felt tired, he thought it was then nighttime; he would phone the research team again, informing them he thought it was night and they would turn the lights off, and Siffre would go to sleep.
After some time in the cave, Siffre became depressed and despondent at his lack of freedom. He was also excruciatingly lonely, he wanted to trap a mouse so he would have some companionship, but in the process of trapping it, he accidentally killed the mouse. In his own words, 'Desolation overwhelms me.'
In addition, his record player broke, and his books got ruined due to dampness. His condition was so dire that Siffre thought of suicide. His short-term memory, mental health, and eyesight all got worse.
Here is an account of his experience in the cave:
Overcome with lethargy and bitterness, I sit on a rock and stare at my campsite in the bowels of Midnight Cave, near Del Rio, Texas. Behind me lie a hundred days of solitude; ahead loom two and a half more lonely months. But I - a wildly displaced Frenchman - know none of this, for I am living "beyond time," divorced from calendars and clocks, and from sun and moon, to help determine, among other things, the natural rhythms of human life.—Siffre (1975)
For the first 35 days, Siffre had a sleep-wake cycle of 26 hours.
On day 37, he stayed up for a few more hours and then slept long. This pattern of being awake and then asleep for a long time occurred periodically for the next month.
Then on day 63, he returned to a cycle of 26 hours. Nine weeks later, his sleep-wake cycle became more varied and random again for 20 days.
Sometimes it was 48 hours as the people in previous studies. When his sleep-wake cycle varied, the cycle could be from 18–52 hours. On day 150, he returned to a 26-hour cycle that lasted until the experiment's end.
Michel Siffre spent six months in a cave without daylight to study the natural sleep-wake cycle, freepik.com/upklyak
Siffre thought that astronauts would be able to manage their biological rhythm without any exogenous zeitgebers; however, they would need companionship as the isolation would not be manageable. Siffre concluded that time is not something humans could work with and understand without any external environmental cues.
Let's look at the strengths and weaknesses of Siffre's (1975) study.
The study produced a lot of quantitative and qualitative data.
The study was done over a long time, six months, which allowed Siffre to investigate his sleep-wake cycle and show how irregular it became.
When Siffre woke up, strong lights were put on, and when he went to sleep, they were turned off. The lights could have acted as an external cue, which affects the study's internal validity.
Siffre was the only participant in the study, so it is hard to generalise his findings, such as how he did to astronauts.
Siffre lived in a cave alone for six months to investigate the sleep-wake cycle and what it would be like without any external environmental cues. In the cave, when Siffre woke up and thought it was daytime, he phoned the research team above ground, who switched on the lights in the cave. He conducted daily experiments, taking his blood pressure, memory, and physical tests. When he felt tired and thought it was nighttime, he would phone the research team again, they would turn the lights off, and Siffre would go to sleep.
Siffre conducted three experiments in total where he lived in a cave to investigate the sleep-wake cycle.
In Siffre (1975), he lived in a cave alone for six months. He was very lonely and became depressed, and his short-term memory, mental health and eyesight all got worse.
Although his sleep-wake cycle was irregular, it was manageable. In Siffre (1975), sometimes it was at a regular 26-hour cycle. When it varied, it could be anything between 18 and 52 hours. However, he thought time was not something humans could work with and understand without any external environmental cues.
Siffre proved that our internal body clock can still be managed without external environmental cues.
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