Sleep

Sleep is the most obvious case where the state of our consciousness is altered, yet it remains very poorly understood. In the first place, nobody is really sure why we need it? Experiments done on rats and sleep deprived people led scientists to believe that sleep was important for memory formation. Yet elephants who are famous for their memories are very short sleepers. As far as we know, there is no single overarching reason for sleep. There are a host of housekeeping functions which are done at the time of sleep.

One would think that a sleeping elephant would be a common sight in the wild, but it is surprisingly rare. It turns out that for some reason bigger animals tend to need lesser sleep. A sloth would sleep for 12 to 14 hours a day. A human being is “supposed” to need 8 hours of sleep a day but an elephant in the wild only sleeps about 2 hours. When migrating with its herd to escape poaching or predation, elephants can go for many days without sleep. Even in zoos, free from the threat of lion or human attack, they don’t usually sleep for more than 4 hours a day.

Sleeping_asian_elephant.jpg

Sleeping Asian Elephant

I am not sure if any academic has studied this properly, but elephants have been used for physical labour in south and south east Asia for millennia. It would be interesting to compare whether those numbers change for elephants following a human defined work day.

Sleep patterns have changed over the course of human civilization. The 8 hours sleep in a single block we consider a norm is a modern compression. This is termed “monophasic sleep”. In the east and in the pre-industrialised world, “polyphasic” sleep which consisted of several naps spaced throughout the day was common.

In Japan from the 1600s to the early modern period, samurai were woken in the middle of the night to study as part of their training. This was considered a harsh measure to toughen them up.

In the Rennaisance, doctors classified people as choleric (extroverts) and phlegmatic (introverts). Choleric people were considered to need only 5 to 7 hours of sleep while introverts were supposed to need up to 9 to 10 hours. Again, this was not necessarily taken in a monophasic block.

A common pattern during the Renaissance was about that the period around dusk was used by people to unwind and relax. They would then sleep for about four hours. Then they would wake up sometime between 12 to 2, for about half an hour to an hour. This was called the watching hour where they would typically at home. They would then sleep again for another 4 hours till morning. There would then be another 2 hour cycle as they warmed up for the day. In all, the cycle could last up to 12 hours a day.

The standardization of the monophasic sleep pattern common worldwide today happened with the industrial revolution. Thomas Edison invented the light bulb and cheap artificial lighting meant factories could be run at all hours and people could be made to work at all hours. Shift work started.

But night shift workers have been studied and been found susceptible to immune and metabolic disorders leading to increased number of infections. These problems arise when people repeatedly act in opposition to their body clock or circadian rhythm. The body regulates the circadian rhythm, based on the light it sees from outside.

There are photosensitive ganglion cells in the eye which measure the overall brightness of the surroundings and calibrate the body clock. These cells are different from those that are linked to the visual cortex. Hence their effect is sometimes even seen in the blind.

Not just the amount of light, but also the frequency plays an important role. Many neighborhoods that adopted LED lighting early now have sleep deprivation problems. Early LEDs emitted a light that was predominantly blue. This is now known to drastically impact the body clocks of both people and animals. The problems of sleep loss are not confined to the residents but also the local wildlife. Newer LED lights are softer with greater components of yellow light and cause less harm.

ledLighting

LED street lighting

A study in Britain concluded that the British get an average of 6.5 hrs of sleep a day. A study at the University of Surrey asked volunteers to increase their sleep by just 1 hour a day to 7.5 hours. Blood samples were taken from the volunteers as well as from a control group.

The results showed changes in the behaviour of 500 genes. When the volunteers reverted to a 6.5 hour sleep time from a 7.5 hour time, the researchers found an increase in the activity of genes associated with inflammation, immune response, stress response, diabetes and cancer risk. The reverse happened when the volunteers added an hour of sleep.

So we don’t know exactly what sleep is for or why it evolved, but its important to get the right amount of it.

 

References

http://www.bbc.co.uk/programmes/b04wmx7k

http://www.bbc.co.uk/programmes/p04tz7pg

http://spectrum.ieee.org/green-tech/conservation/led-streetlights-are-giving-neighborhoods-the-blues

http://www.bbc.com/news/magazine-24444634

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