In his novel The Wise Man's Fear, Patrick Rothfuss says that "you never really appreciate sleep until you wake up". He makes a good point here, as we often don't want to sleep even though we know that we'll be bad tempered, tired and miserable over the next day as a consequence. This is mainly because we have better, more interesting things to do so spending 8 - 10 hours asleep* seems like a pointless waste of our valuable time. However, as we all know, sleep is essential and shouldn't really be cut back on unless it's completely unavoidable. For example, sleep allows the levels of neurotransmitters in our brains to recover after a hard day's activity, allows us to repair damaged tissue and is even an essential factor for effective weight loss!
|In order to fall asleep your core body temperature must drop. Sadly, this means that the traditional British tradition of taking a 'nightcap' of a spirit before bed actually makes it harder to fall asleep as alcohol raises the core body temperature.|
As you would expect for such an obviously important biological process then, sleep has been extensively researched for decades. Much of this research has been fairly mundane, revealing fairly obvious facts like our sleep cycle runs as a circadian rhythm (one that repeats itself every 24 hours) and that lack of sleep has negative effects, such as reducing our mental and motor functions; our ability to cope with new and unexpected situations/events; and (usually), causes us to put on weight. Other areas of research however have been much more interesting and have yielded more titillating results.
Research into the sleep cycle itself is one such area, and has found that humans have 5 different stages of sleep. These stages fall into two major categories: Non-Rapid Eye Movement (NREM) sleep, which is sometimes called 'quiet sleep' and Rapid Eye Movement (REM), which is also called 'active' or 'paradoxical sleep'. NREM sleep consists of 4 of the 5 stages of sleep, which are designated as Stage 1, Stage 2, Stage 3 and Stage 4 respectively. REM sleep, which is arguably the most important state, only forms our final and deepest stage. Our bodies cycle through these stages over the period that we are asleep, with each stage being significantly 'deeper' than the one before it. Obviously then, we are much more awake in the earlier stages than in the latter, which is mainly due to differences in the brainwave patterns used by our brains. The earlier stages produce short, fast brainwaves called beta waves, which eventually progress into slower alpha waves. During these early stages, when you're not quite asleep, many people experience intense sensations called hypnagogic hallucinations. These are perfectly normal, and common examples include the sudden sensation of falling and hearing someone calling your name. Many people also experience sudden starts in the early stages, where they wake up with a twitch for no apparent reason. These starts are called myoclonic jerks and are not a cause for concern in most cases.
It is worth noting however that the body does not progress through these stages sequentially and upon falling into sleep, the body enters Stage 1. After this it progresses through to Stage 2, Stage 3 and Stage 4, which makes sense really. However, before entering REM, the body reverts back into Stage 3 and then Stage 2. It is only after reaching Stage 2 for its second time that the brain jumps directly into REM sleep. After the body has finished with REM sleep it returns back to Stage 2, which forms one complete cycle and typically takes 90 minutes. Our bodies typically undergo 4 or 5 of these cycles every night (consecutively) and spend more time in REM and less time in NREM sleep with each cycle. Thus, the body spends only a short amount of time in REM at the beginning of the night, but by the end, can be in it for up to an hour at a time.
|The invention of the electroencephalograph in 1924 allowed scientists to see a person's brainwaves in real-time. Thus, it allowed them to study sleep as they never could have before and led to the discovery of the 5 stages of sleep.|
Although this sleep cycle seems overly elaborate and pointless (as we're only asleep), it is actually very clever and each stage has its own characteristics and biological functions. Stage 1 for example, can be considered as our gateway into and out of sleep and typically lasts for only 5 - 10 minutes. Stage 1 is characterised by high amplitude theta waves in the brain, which are a very slow type of brainwave and, if a person is woken during this stage, they probably won't even realise they were asleep because their brainwaves are very similar to those displayed when they are awake.
Stage 2 last for up to 20 minutes and can be compared to a 'track changer' on a rail-road system and directs our brainwave patterns back into Stage 1 (so that we wake up), further in NREM sleep or deep into REM. Therefore Stage 2 effectively controls the sleep cycle and is characterised by the appearance of rapid, rhythmic bursts of brain activity called sleep spindles. It is in this stage that our core body temperature and heart rate begins to drop, which lowers our metabolism and energy consumption to allow our breathing to slow.
Stage 3 is a transitional period between light and deep sleeps and is marked the the appearance of delta waves, which effectively prepares our minds for low-intensity dreaming. Stage 4 follows on shortly after the appearance of delta waves, and is the first stage in which we dream. Stage 4 typically lasts for about 20 minutes and is the most likely stage for bed-wetting and sleepwalking to occur in.
Most of our dreaming occurs in REM, which, as mentioned before, is our final and deepest stage of sleep. This also explains why we rarely remember of dreams in REM even though it is here that they are at their most vivid - our brainwaves are so completely different to the patterns our brains use when we are awake, that they are almost completely incompatible with each other! Think of the difference between video cassettes and DVDs, which both show the same media despite doing in completely different ways...
Bizarrely our bodies actually become more active in REM sleep than in NREM, which is why it is sometimes called 'paradoxical sleep'. This can be seen just by looking at someone in REM as their eyes flick around in their sockets very rapidly, which gives the stage its name. To prevent people thrashing around in their beds and acting out their dreams our bodies employ a clever trick: they secrete a chemical that paralyses all of our voluntary, skeletal muscle so that we are unable to move!
An addition to understanding what goes on when we sleep, much research has also begun to unravel why we need to sleep in the first place, finding it to be essential for our long-term health. There are three main theories of why we sleep that do not have antagonistic values with each other, so may all be correct to varying degrees. The first, and probably most accepted theory, is called the 'Repair and Restoration Hypothesis'. This theory suggests that our bodies use sleep to heal and repair any damaged tissues and restore all of the physiological processes that allow our bodies and minds to function efficiently. Studies into this theory have found that people spend more time sleeping after periods of strenuous mental or physical activity, which would be expected really if our bodies were indeed healing during sleep. Research has found that the body greatly increases the rate of cell division and protein synthesis during NREM sleep, which is essential for growth (in a child) and for repairing physical trauma. Evidence also suggests that the high brain activity seen in REM sleep allows the body to replenish and 'restock' its levels and reserves of neurotransmitters so that the brain can function more easily and efficiently the next day.
The second major theory of sleep suggests that it is a mechanism for the brain to make sense of and store all of the information and events that it has been exposed to throughout the day into the brain's long-term memory. This is called the 'Information Consolidation Theory of Sleep' and research has provided much evidence that supports it.
The third and final of the major theories is called the 'Evolutionary (or Adaptive) Theory of Sleep' and suggests that sleep is used as a mechanism for conserving energy (due to decreased physical activity) during periods in which it would be dangerous for that animal to be active in, such as at night in humans due to our relatively poor ability to navigate our environment in the dark. The main support for this theory comes from the fact that animals with few or no natural predators, such as lions, sleep for much longer periods of time than those with many predators, such as mice, which only sleep for a few hours a day.
So, it is obvious that sleep is an essential and a very important process for our health. It allows us to conserve energy, repair damaged tissue, helps us to form long-lasting memories and helps to us prepare for the days to come. Skipping sleep in favour of other, more interesting activities, really isn't a good idea and you should ensure that you are getting the amount of sleep that your individual body requires each night. All of the sleep-deprivation studies to my knowledge associate a lack of sleep with direct, negative side-effects that can easily be avoided.
* on average, depending on your age.