Why Do We Sleep?

Given that our hunter-gatherer ancestors potentially risked their lives every night by going to sleep, it’s safe to say that shuteye has a highly important function. The rejuvenation we feel after a good snooze indicates that sleep has a role to play in our long-term wellbeing.

Anyone who has gone without sleep – even for a short period of time – will know what an emotional experience it can be. Our working memory is likely to be slowed, and we’re more likely to get stressed. For more information, why not check out our article on insomnia.

Sleep definitely appears to impact upon our mental and physical well-being, but how exactly does it do this? Scientists are still unsure exactly why we need to sleep. However, current theories suggest that we need to sleep in order to:

• help the body repair itself
• consolidate information we need
• remove information we do not need

What happens to the body during sleep?

You might be aware of the major phases of sleep. These are called rapid eye movement (REM) sleep, and non-REM sleep. Both are essential to the sleep cycle, but have different impacts on the body.

During REM sleep, electrical activity in the brain is much the same as when a person is awake. However, during non-REM sleep, slow brainwaves come to the fore. Studies have found that these serve to increase proteins in the brain, a lack of which can cause mental fatigue and impairment. In the long run, a lack of such proteins is thought to contribute towards dementia.

It’s also been found that the body releases growth hormone during non-REM sleep. A lack of growth hormone in the body can impact on cognitive function, including our energy levels and memory. Physically, it can help us repair damaged cells, regulate our metabolism and – for younger people – help us grow!

So it appears that sleep gives the body a chance to repair itself, and dispose of any ‘waste’ gathered that day. This would explain why we often wake having forgotten yesterday’s worries, or at least with them firmly in perspective. It’s the makeup of this ‘waste’ that scientists are still trying to discern.

Current research

During our waking hours, cells in our brain connect with other cells when we experience something. This could be as simple as meeting a new person to a work process we need to remember. Extend this to every trivial experience – such as brushing our hair or discussing the weather with a stranger – and our brains are connecting with other cells thousands of times per day.

Scientists have studied brain cell connectivity in sleeping rats. Research has found that some of the cells connecting during the day become strengthened when they slept, whereas other connections are disconnected. From this, it would seem that the brain is strengthening important links, and removing links they do not need. This is a process called ‘plasticity’, and is thought to be mirrored in humans and all living organisms.

The future

Research is ongoing as to what all this means specifically. Plasticity may be a definite cleansing/strengthening process, but how the brain does this, how it picks and chooses what to keep and what to discard, still remain theoretical. It’s clear that the brain takes on a huge amount of activity at a time we once thought it simply ‘switched off’. But much of the rest remains speculative.

For now, we can rest assured that sleep is doing us the power of good every time we drop off. And sleep is one issue that will continue to fascinate scientists – and us – long into the future.