The three natural sleep processes — Transformative Insights

Introduction

Sleep is regulated by three physiological / biological processes. One of which regulates "sleep pressure" (feeling we need to sleep), one regulates our "sleep window" (when we sleep) and the final one (down)regulates our "level of activation" (so we actually fall asleep and physiologically restore during sleep).

Our ancestors’ lifestyle was largely regulated by the external environment which allowed these three natural sleep process to do their job and set them up for good sleep (both quantity and quality).

One of the downsides of our modern, 24/7 and high-tech way of living is that these natural processes are interrupted and as such good sleep has become elusive for many. Of course, this also illustrates the pathway to restoring sleep for most people - “simply” allow these natural processes to get back to doing their job.

This blog provides an overview of these three natural processes. The Practice to restore or enhance good sleep article covers the various strategies you can adopt to restore the functioning of the three processes.

Process 1: Sleep pressure

Sleep pressure, also called sleep drive, is regulated by a neurotransmitter in our brain called adenosine, which slows down the activity in our brain when it binds with receptors in our brain cells. On average we build up an hour of sleep pressure for every two hours of awake time up to reach high levels during the evening.

During daylight hours, your internal clock generally counteracts this sleep pressure by producing an alerting signal that keeps you awake. The longer you are awake, the stronger the sleep pressure becomes. Eventually the alerting signal decreases and the drive to sleep wins out. When it does, you fall asleep.

During the night the adenosine stored in your brain gradually diminishes and alerting hormones (such as cortisol) increase, reversing the process and as a result you feel alert and awake come morning.

Caffeine is very similar in its structure to and competes with adenosine. Because the brain cannot sense adenosine in the presence of caffeine, the brain cells maintain their level activity and we stay alert. Even if we do fall asleep after consuming caffeine, the patterns of sleep can be affected for some time. For example, caffeine generally decreases the quantity of slow-wave sleep and REM sleep (see the Sleep Stages article) and tends to increase the number of awakenings.

There is some research that suggests a high-fat low-carb (ketogenic) diet may increase adenosine and that substances that block the enzymes (ADA) that break down adenosine may also help. The most reliable and effective way to increase adenosine levels though, is through physical and mental activity.

Process 2: Sleep window

The sleep window (times between which we sleep) is determined by our natural circadian rhythm. The circadian rhythm is organised by our "masterclock" in conjunction with "clock cells" within every cell and tissue throughout our body. This master clock is a tiny region, called the suprachiasmatic nucleus (SCN), located deep in our brain in the hypothalamus.

The SCN is tiny but boosts a big punch through its connection with the clock cells. About 15% of the genes in our body are being turned on and off by the SCN, which illustrates the wide reach of our circadian rhythm and gives us a bit of an inkling of how important this system may be for us.

The SCN regulates your sleep and wake time by sending alerting signals of varying strengths to your mind and body throughout the 24-hour period. The signals synchronise our entire body to the external environment and as such regulates physical, mental, and behavioral changes making us function and behave in the right way at the right time.

An illustration of a typical circadian rhythm

The times in the illustration above display the general pattern of the circadian rhythm and for most people the natural sleep window is between 22:00 and 07:00. The exact times for you are influenced by daylight hours, your biological tendency to prefer staying up later or waking up earlier as well as lifestyle. Want to find out yours? Take this “Morningness Eveningness” questionnaire.

This is important as the circadian rhythm is biologically predetermined and we only derive optimal benefit from our sleep when it is inside our natural circadian rhythm. In other words, sleep outside of natural circadian rhythm (even if it is the same amount) is not going to be as good and is not going to have the same restorative effect!

Our circadian rhythm needs what we call “light anchoring” to stay in time as it responds primarily to light and darkness in our environment. We have specific cells in the back of our eyes (retinal ganglion cells) which detect light intensity and translates this light signal into a nerve signal that travels directly to the SCN.

Light is made up of the seven colours of the rainbow, each colour having a different impact on our bodies. During the day we need blue light to boost mood, alertness and reaction times but at night we want to avoid blue light. When the nerves signal to the SCN that there is reduced light intensity and a change in the colour, from bright blue light we get from the sun to dim orange light we used to get from for example fires, we experience what we call "dim-light melatonin onset". The hormone melatonin is produced in the pineal gland and "directs" 500 genes throughout our body to let them know it is dark outside and time to start "shutting" down.

For our ancestors the light and darkness times regulated their lives and they spend most of their daytime outdoors. The advancement of technology and changes in the way we live and work changed two crucial things. Firstly, we now spend about 90% of our time indoors and as such don't get exposed enough during the day to bright blue light from the sun. And secondly in the evening we turn on our artificial lights, TVs and devices that all emit the blue light we shouldn't be exposed to after sunset.

As a result, in the morning the cells in our eyes don’t get enough bright blue light from the sun so the signal to the SCN that it is daytime is not strong enough. And in the evening these same cells are not receiving the signal that darkness has set in so melatonin production is reduced and delayed. Our sensitivity to artificial light at night is much greater also when we don't get enough exposure to bright blue light in the morning, further compounding this negative effect of “abnormal” external environments.

Our brain then wakes up too late in the day and underperforms as it hasn't been stimulated enough into turning on and at night our brain is overactive with the obvious impacts on our sleep. This gives us a sense we have been running in first gear throughout the day (often with day-time sleepiness) and suddenly switch into fourth gear in the evening with our brain being more active than at any other time during the day.

Process 3: Level of activation

Last but not least we need a low level of physiological activation in order to fall asleep. Our physiological state is regulated by the autonomic nervous system (ANS) which is divided into two branches, the sympathetic branch (SNS) – also known as the fight & flight response, and the parasympathetic branch (PNS) – also known as the rest and digest and calm & connect response. Both of these branches are always active and by and large "fight" each other for control.

When the SNS branch is dominant we enter a state of activation, alertness and heightened energy to respond to challenges in our environment and to perform throughout the day. This is of course completely normal and functional during the day.

The SNS does not have its own “brake” however and therefore only has an accelerating effect on our physiology and indirectly on our psychology. It relies on the braking mechanism of the PNS to downregulate us.

If our SNS becomes too dominant (for example as a result of stress) and / or the PNS brake isn't working all that well, we experience insufficient capacity for down-regulating our systems, to unwind and relax enough in the evening. Staying physiologically activated during the evening and not allowing the parasympathetic branch to "take over" can significantly inhibit our ability to fall asleep and tends to reduce the restorative effect of our sleep.

The good and the bad news

There is simultaneously good and bad news in all of this. The bad news is that our modern way of living has a nasty side-effect of interrupting and dysregulating these natural processes. And when these natural processes stop working properly, no amount of will-power, medication and effort is going to bring us good sleep.

The really good news is that each of us has these natural processes build into our biology. We all therefore already have the capacity for really good sleep and all we need to do is allow these natural processes to do the job, they know so well how to do.

This is where adopting a good sleep practice enters the scene which is the topic of The Practices to restore or enhance sleep article.