A history of sleep. What can we learn?
Since the beginning of time, humans have been interested in sleep. Trying to make sense of the different experiences people have during sleep, and theorising about why we sleep. The old testament contains a lot of references to sleep, ancient Egyptians wrote about sleep, and the Greeks worshipped the god of sleep, Hypnos.
Normal human sleep
From the earliest human records and writings until the beginning of Industrialisation in the mid 18th century, sleep in humans was consistently described as a period of deeper sleep in the first part of the night, followed by a period of awakening, then light sleep or dozing until dawn. It wasn’t until industrialisation, that an expectation of sleep occurring within an eight hour window began to evolve. In the mid 19th century with increasing industrialisation and gas and electrical lighting, waking activity encroached further in to the night, with sleep relegated to occurring in a single period of up to 8 hours.
This pattern was further entrenched with labour movements and enshrinement of the 8 hour workday in a range of societies. Robert Owen formulated the goal of the eight-hour day and coined the slogan: “Eight hours’ labour, Eight hours’ recreation, Eight hours’ rest” in 1817. Australia led the way with this, with workers fighting for the 8 hour work day from the 1850s and having it introduced across a range of trades over the subsequent years.
With societal expectation of sleep occurring in a single period not exceeding 8 hours, it is often thought that this represents normal human sleep. Some people, who are ‘good’ sleepers, can conform easily to this pattern. In fact most of us have had periods in our live when we sleep very well, such as in primary school, adolescence or early adult life, which reinforces this belief that we should all be able to sleep continuously throughout the night.
However, history shows us that normal sleep for humans is 3-4 hours of deeper sleep at the start of the night, then waking, taking some time to get back to sleep and dozing until dawn.
Explanations of sleep related phenomena
In the same way that expectations about sleep and what is considered normal have evolved through the ages, the explanation of things that happen during sleep has also evolved in keeping with broader societies beliefs at the time.
Until the early 20th century, nerve cells were thought to turn off and not produce any electrical signals or activity during sleep. Therefore, to explain dreams, other causes needed to be found. Prior to Sigmund Freud’s theories on dreaming summarised in his book ‘The Interpretation of Dreams’ published in German in 1900, most explanations of dreams had a religious or spiritual basis. Writing of dreams as visitations from God are throughout the Old Testament, but also present in a range of other religions. In the Inquisition in Germany between 1480-1520s, sleep paralysis, which can be associated with visual hallucinations, was felt to be evidence that those that experienced them were witches. People who admitted to experiencing these phemomena were burst at the stake by Inquisitors. Around 150 years later in Puritan New England, similar experiences were called ‘Old Hag’ and also felt to demonstrate evidence of witchcraft.
In the late 19th century, Sigmund Freud began to espouse conflict theory to explain the phenomena of dreams and the content of dreams. Freud’s theory was that as nerve cells didn’t contain any energy during sleep, for dreaming to occur, conflict had to be present to generate energy for dreaming. Conflict between id and ego, or between expressed and true beliefs and desires.
In the late 1930s and early 1940s the first brain recordings during sleep were measured. For the first time, this showed that nerve cells during sleep were just as active as they were during wakefulness and more active that during non-REM sleep. As society in the 20th century looked more to scientific explanations for a range of things, it was felt that dreaming represented nothing more that a random re-organisation of memories. As such, the content of dreams was of no significance. This explanation outlines what actually happens during the brain during dreams, but it doesn’t completely answer the question of why we dream.
What can we learn from history?
Important understandings from the history of sleep that we can take on board are:
- Humans sleep best in sync with the day/night cycle
- Sleep in one continuous block is not how humans sleep in a natural environment
- Some humans can sleep for 8 hours in one block, but many can’t adapt to that pattern
- Unusual experiences during sleep are common, and just reflect different phases of sleep and transitions between full wake and full sleep, rather than having any religious or spiritual connotations.
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