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Here’s what actually happens in your brain if you get a good night’s sleep – and if you don’t

New research has discovered why sleep is so important to the brain: It not only flushes away the brain's waste products, sleep also consolidates your memory and protects you against the risk of Alzheimer's disease among other benefits. 

Here’s what actually happens in your brain if you get a good night’s sleep – and if you don’t

Are you getting at least seven hours of sleep each night? (Photo: iStock/People Images)

You’re aware that the average person needs at least seven hours of sleep per night, and you don’t need another reminder that you haven’t quite met the quota all this time, thank you very much. Besides, what’s the big deal? You might need a coffee or two in the morning to kickstart your day but, on the whole, you think you’re coping all right.

A new BBC documentary, How To Sleep Well With Michael Mosley, might just be the wake-up call you need. In the hour-long programme, presenter and chronic insomniac Michael Mosley spoke to sleep experts and put himself through tests to find out the true cost – not just sleepiness – of sleep deprivation.

For starters, you’re not simply lying in bed dreaming away each night. Sleep, as it turns out, is your brain’s way to flush out the very waste associated with Alzheimer’s disease, regulate your emotions as well as consolidate the previous day’s memories.

To do all that – and more – your brain needs time to cycle through the four stages of sleep each night, according to Dr Rachel Sharman, a postdoctoral assistant with the Sleep and Circadian Neuroscience Institute at University of Oxford:

  • Stage 1: Your brain waves start to slow down from the short and fast waves when you’re awake. Physically, your eyes are rolling and your head is nodding if you’re still upright at this point.
  • Stage 2: The brain waves look similar to Stage 1 but they also show little peaks of activity. Your brain is now prepping itself for learning and processing the day’s memories for the later stages of sleep.
  • Stage 3: Slow brain waves are produced and this is when deep sleep occurs. This is a crucial stage for physiological repair, memory and boosting the immune system’s ability to fight infections.
  • Stage 4: Your brain waves return to shorter and faster patterns, similar to the ones when you’re awake. This is when rapid eye movement (REM) sleep occurs. Your body is paralysed but your eyes move rapidly as you dream. This is also when vivid dreams occur and is a stage important for emotional regulation.
Your brain needs time to cycle through the four stages of sleep each night. (Art: iStock/nambitomo)

“In a typical eight-hour sleep, the four stages are repeated several times in what are known as sleep cycles,” said Dr Sharman. In fact, you could go through four to six sleep cycles per night, according to the Sleep Foundation. And not all sleep cycles have the same length; on average, they last about 90 minutes each.

Seeing what your body does at each stage of sleep gives you a better idea why “it’s just not enough to get enough sleep but also enough of the individual stages of sleep”, said Dr Sharman. And the research backs this up: When you’re not sleeping enough, you’re exposing yourself to higher risks of cardiovascular disease, metabolic dysfunction and even cancer.

Here’s a closer look at some of the research featured in the show that discusses how sufficient sleep doesn’t only keep you from nodding off at a meeting but also live longer and healthier:


“We need deep sleep to detoxify the brain. It’s our brain’s laundry system,” said Dr Sharman. “You want about 20 per cent of your lights-off to lights-on in deep sleep.”

Just what sort of toxins are being washed away? “Things like amyloids,” said Laura Lewis, an assistant professor of biomedical engineering at Boston University. “Amyloids are proteins that have been implicated in Alzheimer’s disease. So, for someone who doesn’t sleep well, you don’t get this waste clearance.”

Deep sleep is your brain’s laundry system. (Photo: iStock/SilviaJansen)

And the medium, which the brain uses to detoxify itself, is the very liquid that it is suspended in: The cerebral spinal fluid. Her team discovered this when the MRI scans they studied showed that the waves of the cerebral spinal fluid appeared in step with the slow brain waves generated during sleep.

“Waste products produced in the brain tissue can get moved into this liquid and get flushed and cleared from the brain,” said Asst Prof Lewis.


In the documentary, Mosley spent almost 30 minutes trying to find his way to the middle of a maze. But after a night’s sleep, he was able to accomplish the job in just over six minutes. Sounds like a tip you could use to navigate Orchard MRT station but how does it work?

University of California’s Professor Gina Poe, whose research on how sleep serves memory consolidation and restructuring, explained that it boils down to what’s happening in the brain during specific parts of the sleep cycle.

We need sleep to connect things that we cannot see when we’re awake. (Photo: iStock/RyanKing999)

“We need sleep to connect things that we cannot see when we’re awake,” said Prof Poe. For instance, the various directions you make to navigate a maze don’t occur simultaneously “and because of that, it’s hard for us to put all of that together”.

But thanks to the brief period during the transition from deep sleep to REM sleep, when the hippocampus (it has a major role in learning and memory) writes your temporary memories into long-term memory storage, “you can dredge up memories from yesterday that you might not even be aware of at the time”, she said.

“And it’s only during REM sleep that we can selectively disengage pieces of memory. It’s a time when you can write new memories in as well as erase pieces of memory that you need to erase. And we can wire together the proper synaptic pattern that is associated with solving the problem,” said Prof Poe.


When Mosley’s blood samples were examined, University of Surrey’s Professor Simon Archer was able to see which genes were switched on or off in the blood – and from there, determine which sample was taken before or after a self-imposed sleepless night.

That’s not a good sign because this shows that sleep deprivation causes some genes to be switched on and revved up when normally they wouldn’t be, said Prof Archer. Take, for instance, your immune system. “When your immune system is in overdrive when it shouldn’t be, that’s not a good thing. It’s bad because you haven’t got pathogens to respond to,” he said.

It is not good when your immune system is in overdrive when you haven’t got pathogens to respond to. (Art: iStock/BlackJack3D)

It is also worrying when the lack of sleep causes the mitochondria, the “engine” part of your cells that produces energy, to dysfunction. This “downregulation” in mitochondria is similar to the mitochondria dysfunction associated with Alzheimer’s, said Prof Archer. “The problem comes when people are frequently missing sleep and accumulating those negative effects, and how that associates with health problems,” he said.

And it’s not just Alzheimer’s. The lack of sleep affects almost every system in the body, said Prof Archer. For example, trying to function after sleep deprivation is akin to having a blood alcohol level of two to three pints of beer, said Dr Sharman. “You wouldn’t drink and drive. So, what about drowsy driving?”


There are two hormones you need to be familiar with: Leptin and ghrelin. “Leptin is produced by the fat cells in the body. When you get more fat stores in the body, leptin levels go up and they tell the brain that fat stores are sufficient,” said Dr Wendy Hall, a nutrition scientist at King’s College London.

On average, those who don't sleep enough consume 385 more calories a day. (Photo: iStock/vadimguzhva)

However, those who are sleep deprived tend to “have lower levels of leptin”, said Dr Hall, which means their bodies aren’t getting the signal that the fat reserves are sufficient when they are.

Ghrelin, on the other hand, is a hormone that regulates hunger and its levels go up when you haven’t eaten for a while, she said. “There is some evidence that ghrelin levels are higher in people who are short sleepers, so they’re getting a constant hunger signal.”

Just how much more do we eat after a bad night’s sleep? “On average, people consume 385 more calories a day,” said Dr Hall. “It’s about 20 per cent of the average woman’s energy requirements. It’s a considerable amount that will lead to weight gain.”

How To Sleep Well with Michael Mosley airs on Starhub and Singtel on May 3.

Source: CNA/bk