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Avoid a heavy dinner to improve sleep. Photo: iStockphoto
Avoid a heavy dinner to improve sleep. Photo: iStockphoto

The fascinating science of sleep and its role in human evolution

It enhances immunity as well as the cognitive abilities that may have aided our descent from apes

It was the Upanishads that introduced me to the kinds of sleep. The Mundaka and the Chandogya Upanishad talk of “four states of consciousness". The first was Awake, the second was Dream-Filled Sleep, the third was the much sought-after Deep Sleep, and there was a very mysterious fourth stage. Called Turiya, it is a stage which transcends sleep; in many texts, it was referred to as samadh (or samadhi), and is akin to the deepest form of meditation. Only achieved by the truly awakened, it was where the self or atman is realized.

Modern society, however, has given sleep a bad reputation. Busy as we are, we tend to pride ourselves on how less we sleep. Corporate executives see sleep as a waste of time, children would rather watch TV, teenagers prefer the transcendental wonders of their mobile phone. Vladimir Nabokov called sleep the “nightly betrayal of reason, humanity, genius", Arnold Schwarzenegger advised those who want eight hours of it to “sleep faster", and Margaret Thatcher prided herself in getting by with four hours. Some modern champions repudiate this notion—Roger Federer is said to sleep for more than 10 hours; so do Lebron James and Usain Bolt.

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I chanced upon sleep again through another life-changing read: Why We Sleep: The New Science of Sleep and Dreams by British scientist Matt Walker. It made me realize that sleep is a superpower, and it is the third and neglected of the triad of diet, exercise and sleep, which make us healthy and disease-free. In this virus-ridden world, it is perhaps the strongest weapon we have to build immunity, more formidable than vitamins and turmeric. It is an overlooked stress-buster, can delay dementia, and can manage our stress and obesity. While these facts were new to me, perhaps the most intriguing was that it is sleep that could have caused our evolutionary tree to branch off and separate us from our simian cousins.

Before we delve deeper, let us touch upon sleep itself. Human beings sleep in 90-minute cycles—each comprising light sleep REM, or Rapid Eye Movement, and non-REM or deep sleep.

Deep sleep, as the name suggests, is the blessed intense sleep that all animals need to rest the day’s exertions off. As Walker writes: “Deep sleep is a therapeutic state during which we cast off the emotional charge of our experiences, making them easier to bear." Lack of sleep can affect our cancer-fighting immune cells; one night of short sleep can reduce our immune cells by 70%. Adults aged 45 years or older who sleep less than six hours a night are twice more likely to have a heart attack or stroke in their lifetime, as compared with those sleeping seven or eight hours a night. During deep sleep, deposits of the toxic protein amyloid, which cause dementia and Alzheimer’s, are washed away from the brain.

“During deep sleep, your brain goes into this incredible synchronised pattern of rhythmic chanting," says Walker. “There’s a remarkable unity across the surface of the brain, like a deep, slow mantra, almost like a coma."

However amazing non-REM sleep is, it is REM sleep that made us human. It is sometimes called paradoxical sleep, because the brain and heart patterns are identical to those when you’re awake. This is when short-term memory stored in the hippocampus is transferred to long-term memory in other parts of the brain. Here the brain and heart are active, we dream vividly, and our eyeballs rapidly move around. REM sleep renders our limbs totally inert. This is so that we do not flail around as we dream. REM sleep builds our cognitive abilities, so 80% of all sleep in babies is REM. We sleep to forget, but we also sleep to remember.

On the other hand, only 9% of a monkey’s sleep is REM. Limb-inertness induced by REM would imply that they would not be able to grasp the branches of the trees they sleep on, and fall. They also need to sleep light, since they are unprotected from predators. Around 15 million years ago, great apes solved this by making platforms and sleeping securely on them. The proportion of their REM sleep rose, raising their cognitive ability and consolidating memories. Some apes then started sleeping on the ground, and later, on beds, creating more space for REM sleep and a higher cognitive and memory ability, and eventually evolving into humans. Thus, it is the second stage of Upanishadic sleep, the “sleep of dreams" that helped make us human. Could the mysterious and yet unstudied fourth stage of Turaya perhaps make us super-human, like our ancient rishis and devatas? Sleep is a super power.

Jaspreet Bindra is the author of ‘The Tech Whisperer’, and founder of Digital Matters

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