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The Science Of Sleep

A scientific guide on how sleep works in simplistic language.

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Studying sleep

Sleep science

Sleep science is an extremely complex topic which involves a multitude of differentiators.

The trouble scientists often have is that they can only examine one variable at a time, measuring reactions to other changing variables.

This makes it difficult to understand the exact mechanical procedure that we go through when we sleep (or get sleepy) but there are a few things that scientists are confident about.

The last thing I want to do is misinform you, so I will explain the processes that scientists are fairly certain about and that I, myself, understand.

It’s important for me to point out that I am a student of life, I am not a sleep scientist and we, as a species, still have a lot to learn in this department; however, I am relatively adept at transforming seemingly complex explanations, provided by scientists, into easily understandable ideas. That is exactly what I will be doing here…

For a short overview of the details discussed below, please read the article entitled The Science Of Sleep Summarised.

The circadian rhythm or “sleep cycle”

The hypothalamus

The hypothalamus is a peanut-sized region, deep in the centre of the brain.

It contains a cluster of thousands of cells that control sleep by receiving information from the eyes regarding light exposure.

This cluster of cells is called the suprachiasmatic nucleus or ‘SCN.’

Light exposure is the trigger for the body’s behavioural rhythm – our ‘body clock’ or ‘circadian rhythm’…

Circadian rhythm

A circadian rhythm is any biological process in living things (including plants, fungi and bacteria) that cycles roughly around a 24 hour period (in line with the Earth’s rotation).

The wake-sleep cycle is part of our circadian rhythm.

Circa comes from Latin, meaning “around” or “approximately”

Diēm, comes from Latin, meaning “day”

Scientists believe that we have evolved with such rhythms because, being able to anticipate environmental cycles, allows us to adjust our internal physiology to suit external conditions.

Just a few examples include adjusting our eating habits, digestion and body temperature to survive in differing seasons.

Just think, what do you prefer to eat in the summer? A nice cool, crisp salad or a bulging, hot pot of stew? Having less appetite in hot weather isn’t an accident – your body just doesn’t require as many calories as it does in the winter to keep you warm.

According to Debra Sheats – the director of Nutrition and Dietetics at St. Catherine University – “we burn 10 percent fewer calories in the hot weather because we don’t have to work as hard to stay close to 98.6.”

For those of you who don’t know, 98.6 degrees Fahrenheit (37 Celsius) is considered normal body temperature.

The brainstem

The brainstem is found at the base of the brain and is attached to the spinal cord.

Its job is to control the flow of messages between the brain and the rest of the body; as well as controlling basic bodily functions such as breathing, swallowing, heart rate, blood pressure, consciousness, etc.

It is also key in controlling whether you’re awake or sleepy.

When the brainstem receives messages from the hypothalamus that it is time to sleep, the brain stem passes those messages on to the rest of the body – “Muscles! It’s time to relax!”

The pineal gland

The pea-sized, pinecone-shaped pineal gland is a hormone producing gland (endocrine gland) that is situated in the centre of the brain, between the two hemispheres.

It receives signals from the SCN (see hypothalamus above) when darkness becomes prevalent, leading to an increased production of the hormone melatonin which is released into the blood…


Melatonin is a serotonin-derived hormone which modulates sleep and wakefulness.

It is involved in the synchronisation of circadian rhythms (described above) and seasonal sleep cycles.

Once melatonin levels in the blood increase, you start to become less alert and sleep becomes more inviting.

According to modern research, melatonin in the blood is barely detectable during the daytime.

Pineal gland


The basal forebrain

The basal forebrain, as the name suggests, is located in the base of the front of the brain.

It plays an important role in the production of acetylcholine which is known to promote wakefulness.

Receptors in the basal forebrain also react to the presence of adenosine (a sleep promoting chemical – explained below), inhibiting the release of acetylcholine and therefore inducing slow wave sleep


As explained above, adenosine is the chemical which suppresses arousal by combining with specific receptors in the brain, resulting in sleepiness and reducing the release of acetylcholine in the basal forebrain (above).

As you might guess, suppressing arousal encourages sleep.

Adenosine is prevalent in the body’s energy sources: adenosine triphosphate (ATP), adenosine diphosphate (ADP) and adenosine monophosphate (AMP).

In simple terms – these are chemical compounds that are broken down by your body to release energy.

Adenosine naturally accumulates in the blood stream when energy sources such as ATP break down (ATP being the primary energy source in most cells).

Logically, adenosine levels in the blood rise when most energy is being used – during waking periods.

As ATP reserves (stored as glycogen in the brain) start to deplete, adenosine levels rise, telling the brain and body (there are also adenosine receptors in the heart and kidneys) that it needs to rest.

This triggers a reduction in mental activity, organ activity and urine production leading to “non-REM,” or “deep sleep,” allowing the body to replenish and rebuild glycogen stores. In simple terms – the body refuels.

The enzyme responsible for continuously metabolising (breaking down) adenosine is adenosine deaminase.

Because the adenosine deaminase continuously metabolises adenosine during sleep, adenosine levels continuously reduce, ultimately leading to waking.

Recent studies seem to suggest that he rate of this metabolism and differences in adenosine levels between individuals, impacts upon the intensity, duration and quality of sleep.


Caffeine is explained in our article Effects Of Caffeine.

In short, caffeine is a competitor of adenosine.

It competes for the same receptors in the brain and body but does not induce the sleep promoting feelings that adenosine does.

The more caffeine you consume, the more receptors get occupied.

This means that there are fewer available for adenosine, the sleep promoting compound, to bind to; thus, neural activity is NOT slowed by the effects of adenosine – sleeplessness is prolonged.

Stress, cortisol and the amygdala

Chronic, continuous stress from overworking and arguments at home impacts on the quality of your sleep because of the affect it has on your cortisol levels.

Stress initiates from the ‘Hypothalamus Pituitary Adrenal axis’ (HPA axis), a series of interactions between endocrine glands in the brain and kidney.

When your brain perceives a stressful situation, your HPA axis activates and releases a hormone called cortisol which primes your body for immediate action. This is your fight or flight response!

It’s logical to assume an increase in the fight or flight response is not going to help you to sleep!

Struggling to sleep

High levels of cortisol in the body for long periods of time has been shown to impact upon the activity level in the amygdala.

The amygdala is the part of the brain that processes your emotional experiences and is sometimes referred to as your ‘fear centre.’

When the amygdala becomes overactive, sleeping is difficult.

The bad news is that your cortisol levels and amygdala responsiveness increases when you are not getting sufficient sleep; creating a vicious insomnia-driven downward spiral!

Stress creates cortisol that affects your 24-hour body clock (circadian rhythm) and in turn your 24-hour body clock affects your cortisol levels!

Stress = cortisol = amygdala activity = lack of sleep = more stress = more cortisol = more amygdala activity = more sleeplessness.

Nitric oxide

Research carried out by Children’s Hospital Boston and the University of Helsinki, combined previous sleep observations to determine that nitric oxide production in the basal forebrain “is both necessary and sufficient to produce sleep.”

However, this conclusion was demonstrated in the brain cells of rats. It was proven that the release of adenosine (explained above) is stimulated by nitric oxide.

When the researchers studied mildly sleep-deprived rats (kept awake for an extra three hours), they found that nitric oxide production in the basal forebrain, but not in other parts of the brain, increased by 50% to 150%.

When compounds that inhibit nitric oxide production were injected into the basal forebrain of rats, adenosine levels did not increase and sleep was completely eradicated.

These results were also identical when researchers injected a compound that scavenges nitric oxide.

In simple terms, this compound mopped up nitric oxide and rendered it inactive.

When a nitric oxide “donor” (an agent that induces nitric oxide levels) was introduced to the basal forebrain of the rats during a normal sleep-wake cycle, adenosine levels increased and they fell into a deep slumber, much like recovery sleep that occurs after prolonged wakefulness.

It’s also interesting to note that blocking adenosine receptors with caffeine seemed to prevent this nitric-oxide-induced slumber.

Other science-based sleep matters

The thalamus

The thalamus situates at the top of the brain stem, near the hypothalamus, and is responsible for relaying information from the sensory receptors (eyes, ears, mouth, etc.) to the cerebral cortex (the wrinkly grey matter, covering the brain, which interprets and processes information) – resulting in thought and action.

Throughout most stages of sleep, the thalamus is subdued, allowing you to tune-out from your external environment; however, during REM sleep, the thalamus is active, sending sensations to the cerebral cortex that fill our dreams.

This causes the amygdala (the emotional part of the brain – explained above) to become increasingly active during REM sleep.


Gamma-Amino Butyric Acid (GABA) is an amino acid that acts as an “inhibiting” neurotransmitter in the central nervous system (CNS).

An “inhibiting” neurotransmitter blocks nerve pulses, reducing brain activity.

GABA is made inside brain cells from glutamate, which, surprisingly, has the opposite effect to GABA.

Glutamate is an excitatory neurotransmitter that encourages nerve impulses, resulting in higher brain activity.

As GABA hinders the transmission of nerve impulses from one neuron to another. It has a calming or quieting influence.

It is well established that activation of GABA receptors favours sleep; however, the benefits of taking GABA supplements to help you sleep have not been proven. Mainly because there is no proof that GABA supplements actually reach the brain (many cannot pass through the brain-blood barrier).

Exhaust (no pun intended) all of the techniques in our article How To Get A Good Night’s Sleep before even thinking about taking sleeping supplements!

The pituitary gland

The pea-sized pituitary gland, located in the base of the brain, is often referred to as the bodies’ “Master Gland” because of its involvement in regulating hormones.

Any disturbance of the pituitary gland can create a series of hormonal imbalances.

It is responsible for sending signals to the thyroid gland, adrenal glands, ovaries and testes, to produce thyroid hormone, cortisol, oestrogen, testosterone, and many more hormones.

Such hormones have dramatic effects on metabolism, blood pressure, sexuality, reproduction, and other vital body functions.

Pituitary gland

So how does it impact upon our sleep?

Well, pituitary gland-related sleep disorders often fall under two main categories:

  1. There’s too much hormone production (e.g. adrenaline), or
  2. The pituitary gland swells, physically squashing other structures within the brain. This has knock effects such as squashing the pineal gland (introduced above).

To reduce the effect of overproduction of hormones, like adrenaline, use techniques in our article: How To Get A Good Night’s Sleep, like completing sedentary tasks before bed (rather than stressful ones or intense exercise).

We all know what stress and cortisol do to our sleep! – If you don’t you need to re-read the passage above!

The science of sleep

The science behind sleep is far from simple!

There are so many nuances, making our bodies such extraordinary machines!

Above is just an overview of the science in simple terms.

There will be further breakthroughs as we progress as a species and there may well be things that turn out different to what we first thought, but understanding the science from a basic perspective will help us all to improve the quality of our sleep.

If you know of any interesting facts, opinions or studies that would add to the quality of this article, please use the comments box below!

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Pineal gland

The Science Of Sleep Summarised