When you need to be at your best, a good night’s sleep should be at the top of your priorities.
There are certainly times in our lives when it is not easy to get all the sleep we need e.g. becoming a parent, long distance travel or experiencing illness. Although when you have the choice and you need to perform, a good quality night’s sleep, should be your priority no. 1.
In this article we will explore the why and what of sleep, then look at the impact that a lack of sleep has on us.
In Part 2 of this series, we will cover tips on getting a better night’s sleep when it is most needed.
WHY do we sleep?
Restore and build:
Sleep is the most effective way to restore our brain and body’s health, including factors such as: brain development, muscle growth; cell and tissue repair; enhanced digestion; the release of hormones such as growth hormone.
Sleep also benefits and rejuvenates our cardiovascular system by significantly lowering heart rate and blood pressure.
Learn and memorise
It is during sleep that our brains take input from the waking day (stored in our short-term memory) and process it into long-term memory. This applies to both factual input (e.g. the name of the person you met) and to procedural input (how you do something, e.g. how to better manage email or how to use a new piece of software). There are three steps to forming new memories.
- Acquisition is the introduction of new input to the brain which happens while we are awake
- Consolidation, which occurs as we sleep is the process making the memory stable. Please see the sleep stages below for more information on how this occurs.
- Recall is the ability to access the stored information (memory) consciously or unconsciously
Impact on daily functioning
If we simplify the functioning of the brain using the Rider and Elephant metaphor (see this article for more on this metaphor), the Rider who handles most of our executive functions at work (solving problems, making decisions, controlling our impulses, communicating, planning/strategy) is one of the most energy hungry parts of our brain and tires easily.
The Rider has a limited, common resource for making decisions, planning and exerting self-control. For example, using effort on self-control will limit the resources we have left for solving problems. Quality sleep increases our Rider’s resources and capacity to implement our executive functions.
Getting a good night’s sleep is the most effective way of increasing our brain’s ability to use its executive functions: solving problems, making decisions, controlling our impulses, communicating and creating plans/strategies.
WHAT regulates our sleep?
It is considered that most of us ideally require 7-8 hours of sleep, which provides 16-17 hours of optimised brain function.
We have two governing systems that regulate sleep and wakefulness: The circadian rhythm and a kind of sleep pressure (sleep drive) system, which is based on a neurotransmitter called Adenosine.
We explore each of the processes in more depth below.
Image 1 – The Circadian Rhythm and the hormones Melatonin (rest and recovery hormone) and Cortisol (activating/alertness hormone, also know as one of the stress hormones).
The Circadian Biological Clock regulates our 24-hour sleep-wake cycle. It is controlled by a group of cells in a part of our brain called the hypothalamus. This group of cells is called the Suprachiasmatic Nucleus (SCN).
The SCN synchronises physiological factors such as, melatonin secretion via the pineal gland (promoting sleep), cortisol secretion via the adrenal glands (promoting alertness – wake drive) and body temperature.
The circadian clock knows what time it is due to our exposure to light. Light travels from the optic nerve of the eye, to the SCN, indicating to the clock that it is daytime and time to be alert. When it is dark, sleep is promoted.
For example, the reason why electronic screens (think Phone, TV, PC) negatively impact sleep is because the blue light that they emit, trick the SCN and reduce the amount of melatonin produced (the rest and recovery hormone that promotes sleep).
Adenosine build up process
Image 2 source: An Introduction to Sleep By Christine Laymon.
In Image 2, we see Process-C, which is the circadian rhythm’s rise and fall of cortisol (the wake drive hormone) shown as the red line. The adenosine build up, Process-S (sleep drive) is shown as the blue line. The higher the sleep drive (adenosine levels – blue line), the lower the wake drive (cortisol – red line) and vice-versa.
While we are awake, neurons in the brain produce adenosine, a by-product of the cells’ activities. The build-up of adenosine in the brain is thought to be one factor that leads to us feeling drowsy.
The longer you are awake the higher the sleep pressure becomes (higher the drive to sleep) and the more drowsy we become.
You can see this in Image 2, where the bigger the distance between Process-S and Process-C, the greater the sleep pressure will be (and hence greater the drive to sleep) and cortisol will be at its lowest. In Image 2, the sleep pressure/drive to sleep is at its highest at 11pm and cortisol is at its lowest.
While we sleep the pressure reduces and is completely removed after approx. 8 hours. A high sleep pressure does not necessarily mean it will be easy to fall asleep as this depends on the circadian rhythm – Process-C and what it is doing with our hormones.
Low sleep pressure (low sleep drive) corresponds to a circadian process that promotes wakefulness (cortisol and the wake drive is increasing) – see 7am in Image 2.
Phases of sleep
Image 3 source: http://www.centerforsoundsleep.com
- Stage 1 – Introduction to sleep. Light sleep, during which you are most easily woken (Non-REM or NREM).
- Stage 2 – Beginning of sleep. Light sleep, during which your brain waves start to slow and your eye movements stop (NREM).
- Stage 3 – Slow wave sleep. Deep sleep, during which very slow brain waves start to appear. Building up physical energy and restoration and taking recent experiences from a short-term memory to long-term (NREM).
- Stage 4 – Slow wave sleep. Deep sleep, during which very slow brain waves predominate. Building up physical energy and restoration and taking recent experiences from a short-term memory to long-term (NREM).
- Stage 5 – Dreaming state, known as REM sleep. Improves brain function and serves to integrate experiences (interconnecting new experiences with each other and past experiences into a larger model). During which there is temporary limb paralysis, rapid eye movement and rapid, shallow and erratic breathing. REM Sleep is key for innovative insights and problem solving (REM).
The REM stage gets longer throughout the night as you can see in image 3 above.
The impact of sleep deprivation
A regular lack of sleep has a significant impact on our health, response to stress and performance. Sleep deprivation results in a reduction of blood supply to the Rider and more activation of the Elephant’s threat response. This leaves us in a reactive, emergency state whilst having lowered executive functions. You can think of the Elephant as our emotional accelerator and the Rider as the emotional brake.
Tempted to skimp on sleep or pull that all-nighter? You would be much better off getting a good night’s rest as the Rider’s alertness and cognitive abilities will be significantly reduced, ending in inhibited memory, problem solving, decision making, language ability and self-control.
After being awake for more than 16 hours, the Rider experiences a dramatic deterioration. After being awake for 19-20 hours your mental capacity is so impaired that you are functioning the same as someone who is legally drunk.
Here are some further studies demonstrating the impact:
- Inability to learn and form new memories. For example, a 40% reduction in the ability to form new memories after 38 hours of sleep deprivation (especially positive memories).
- Increased aggression and fear. A lack of sleep (more specifically REM sleep) makes you more reactive and triggers the threat response, whilst dampening awareness of positive experiences.
- Promotes development of the metabolic syndrome and increased risk of heart disease, stroke and diabetes: Regularly getting less than six hours a night of sleep is linked to a 30 percent increased risk of high blood sugar and excess belly fat, as well as 56 percent higher odds of hypertension, compared to sleeping longer than 6 hours. Another study found that getting six hours of sleep or less was linked to a 200% increased risk of a fatal heart attack or stroke.
- Food choices: Sleep deprivation increases the desire for weight-gaining high calorie foods (sweet, salty and starchy).
- Brain damage and Alzheimer’s. Due to the build up of beta amyloid (a toxic protein). During sleep our brains are cleaned of the toxic waste like beta amyloid. The more this toxin builds up, the greater the risk of developing the disease.
- Lowered immune system. One night of four to five hours of sleep leads to a 70% reduction in anticancer fighting immune cells. Routinely sleeping less than six or seven hours more than doubles your risk of cancer (bowel, breast, prostate).
- Lowered testosterone in men. A study found that men sleeping five hours a night for just one week had a level of testosterone that was the same as someone 10 years their senior.
Part 2 of this series contains tips on how to optimise sleep. Enjoy!