Posted on February 6th, 2016 by Pete Keohane

Seems obvious right? To get some rest. Well, to quote Ben Goldacre, it turns out “it a bit more complicated than that…”

Definitely maybe

Why we sleep is the subject of significant ongoing research around the globe. The huge variety of hypotheses proposed to explain, or part explain, the function of sleep reflect the gap in current understanding. Even some of the most eminent researchers within the field still admit freely to being more than a bit unclear. For example, when Professor William C. Dement (founder of Stanford University’s Sleep Research Centre and a leading authority on sleep), was asked what he knew about the reason people sleep, he apparently answered:

“As far as I know, the only reason we need to sleep that is really, really solid is because we get sleepy”!

It is clear though that sleep, in one form or another, is pretty essential. If not, you would expect to find animals that:

  • Don’t sleep
  • Don’t need extra sleep after staying awake longer than normal
  • Don’t suffer significant consequences as a result of lack of sleep

Apart from some ‘basal’ animals that have no, or an extremely simple brain (e.g. coral, sponges, jellyfish – species that separated from other animal groups at the very early stages of evolution), no animals have been found that satisfy any of these points.

Some of the theory around sleep function

Although it is hard to draw concrete ‘truths’, there are a few assumptions we can start to draw out of the research. Firstly, it’s likely that sleep evolved to accomplish a single, primitive function (such as regeneration) and as time passed it is thought that additional functions were ‘added in’ – hence the complexity! How, when and why these were added are still a matter of contention but here are some of the main research outcomes around the function of sleep….

Early stage development (and beyond)

Unsurprisingly, sleep has been shown to be important in the growth and development. For example:

  • Loads of REM sleep in little people is thought to allow them to practice using the power of their brain without getting them into physically risky situations.
  • Sleep deprivation in early life is linked to behavioural problems, permanent sleep disruption, decreased brain mass and an abnormal amount of brain cell death.
  • REM deprivation in little people is linked to developmental delays and difficulties.

It’s not all about energy conservation

Energy could be preserved and recuperating without completely shutting off the animal from their environment – which is, when you think about it, potentially a really dangerous thing to!!

Interestingly, when animals complete hibernation, apparently pretty much the first thing they do post-hibernation is sleep! This is because, although they are well rested, they are sleep deprived!! A more horrible example of this is in studies where researchers have kept rats up indefinitely. Even if the rats are allowed to rest, they start to develop skin lesions, lose weight, experience hypothermia, and, eventually, get sepsis which kills them.

So we have learnt at least two things.. People can be really horrible to rats and sleep must offer something beyond just energy saving / recuperation.

Physical restoration

This is one of the most researched areas, suggesting consistently that sleep is important in physical and mental restoration. Check out some of the significant findings:

  • Sleep helps the brain and nervous system to clean itself. The ‘glymphatic system’ (the bin lorry of the central nervous system) increases waste clearing efficiency by 60% during sleep.
  • Sleep helps the body clean itself. ‘Metabolic’ waste is cleared at a faster rate when asleep.
  • Sleep deprivation affects the immune system and helps fight illness. Sleep-deprived rats’ show a 20% decrease in white blood cell count (the ones that fight infection and disease).  Interestingly, some even think that mammals that sleep longer might do it to build their immune system, as species that sleep longer seem to have higher white blood cell counts.
  • Sleep affects healing and regeneration. Sleep deprivation in rats slows the wound healing in burns.


This theory suggests that keeping an animal in a safe(ish) place during the most dangerous period of the day (e.g. dark bit for us humans) might serve a protective function. Different animals adapt to different parts of the day to best suit their abilities.

This idea falls down a bit when you consider the complete disengagement of consciousness in sleep…. Although the brain does use a huge amount of energy. Another criticism of this idea is that sleep is not a passive by-product of staying safe. There is a consistent, instinctive drive for it.

Learning & memory processing

Just tried to keep ‘the bare bones’ here because there is SO.. MUCH.. RESEARCH!! Consistently sleep has been found to be helpful in learning as well as memory and emotional processing. Check it out:

  • Sleep allows the weakening (and destruction) of unnecessary brain connections, helping us remember the important things (and forget the irrelevant – although the opposite seems to happen to me!).
  • Working memory function (the bit that temporarily holds and manipulates information) reduces by about 40% in sleep deprived people.
  • REM sleep seems to improve procedural memory (long-term memory for learning tasks) by around 25%. Our body can also compensate, so after we have learnt a new task, we have more REM sleep to help us learn it.. Clever eh!
  • Conversely, declarative memory (long-term memory for learning facts) benefits from lighter sleep – so both are important!
  • Learning new tasks, skills or information is a complex (as it requires new connections to be made in the brain) and the evidence says information is better solidified and organised at night (where there are no other distractions!!).
  • REM sleep has also been found to be critical in the consolidation of emotional aspects of memories.

Sleep & creativity

Some people say a lack of sleep can make them feel more creative, although there is very little evidence to support this idea. In fact there is quite a lot of research to support the opposite:

  • Sleep has been shown to improve cognitive flexibility (ability to take on new information).
  • Sleep also allows people to see complex patterns or rules more easily.
  • Deprivation of sleep can impair people’s ability to create new or original information.

A little about Psychoanalysis

Sigmund Freud suggested that dreams are the symbolic representation of unmet desires from the unconscious. He thought that using dream interpretation would uncover these desires and therefore help people meet their own needs. Although supporters of psychodynamic therapies often still support this (or similar) ideas, there is little evidence to support it. 

What can sleep affect?

As you can imagine given some of the information and research shown above, sleep duration and quality effects a lot.. Pretty much everything we do and experience to a greater or lesser degree. Some pertinent examples of this are our:

  • Work
  • Relationships
  • Friendships
  • Physical growth
  • Cognitive abilities (thinking and remembering)
  • Emotional processing
  • Emotional regulation
  • Physical health
  • Mental health
  • Ability to cope with life stresses

We could go on but you get the picture, it’s pretty important! Plus we come back to focus properly on specific things that get in the way / promote sleep later on in the series.

What’s in the next blog?

In the next blog we’ll do a whistle stop tour of the some of the sleeping ‘diagnoses’ as well as some of the more common complaints about sleep. We’ll also think about how much sleep you’re ‘recommended’ to get..

After the next blog, we will move on to think about what can get in the way of sleep and what can promote a solid 40 winks.

References & further reading

American Psychological Association –

NHS Live Well –

(American) National Sleep Foundation –