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The Sleeping Brain

Updated: Sep 19, 2022

Sleep is very complex. We have been investigating sleep for decades but we still aren't sure what all the functions of sleep are. In this blog post I discuss

  • What happens when we sleep

  • The activity in our brains when we sleep

  • Mental health and sleep

  • Implications of sleep deprivation (loss of sleep)

What Happens When We Sleep?

Sleep Stages

Sleep is categorised into 2 stages, Rapid Eye Movement (REM) and Non-rapid Eye Movement (NREM).

REM Sleep

REM sleep is the sleep stage associated with greater dreaming. Your brain is highly active when in REM sleep. Your brain is just as active in REM sleep as it is in when you are awake, if not more so.

When in REM sleep your brain stem switches off so that you lose all control of your muscles in the body (Atonia). This is a protective mechanism.

Your brain puts your body in a state of Atonia so that you do not act out your dreams, which I think we would agree, is a great thing especially when I think about my dreams lately...

NREM Sleep

Non-rapid eye movement sleep is the sleep stage where your brain can switch off and relax. NREM sleep is split into three progressive stages: 1, 2 and 3 (not very creative).

To make it easy to understand, these stages can be considered as 'lighter sleep, light sleep and deep sleep'. These stages all differ with heart rate and breathing.

In lighter sleep, your heart rate and breathing is the fastest where as in the deeper sleep they are the slowest. Some dreaming does occur in NREM, just not so much as in REM sleep.

The Brain When We Sleep


When we wake up in the morning we start to produce a hormone called Adenosine. Adenosine builds up throughout the day. The catch here is that the more Adenosine builds up, the sleepier we feel.

When we sleep, the build up of Adenosine decreases and we start fresh the next day. We cant stop the hormone Adenosine, we shouldn't want to because sleep is incredibly important.

However, caffeine acts as a block for Adenosine transmission. Specifically, caffeine blocks the Adenosine receptors. We still produce Adenosine but it just builds up in the synapse, waiting to be received by the receptors.

This is why we get caffeine crashes. When the effects of caffeine start to wear off around 7-10 hours after caffeine intake (the Adenosine receptors become free again), the built up of Adenosine floods the receptors. Making us feel very, very tired.

Brain Development

Sleep has a massive impact on our brain development. Peirano and Algarin (2007) looked into brain chemistry and sleep. They concluded that both NREM and REM sleep are very important for normal synaptic development and brain maturation. They also concluded that sleep is crucial for normal neuronal development.

Do you wake up in the night? Waking up in the night disrupts your sleep cycle and can have negative effects on the brain. Branger et al (2016) found that the frequency of waking up in the night was associated with a decrease in grey matter volume (a major component of the central nervous system).

Branger also found that less sleep reported by participants was related to an increase in anxiety and depression.

Mental Health

Branger was not the only one to find this. Annu Rev (2014) conducted a review of studies into mental health and sleep. The review found that nearly all anxiety or mood disorders are comorbid with sleep difficulties.

Regarding emotion, Annu Rev found that when in REM sleep, there is a lot more activity in the emotion-related areas of the brain.

Parcell et al (2006) looked into sleep changes after a traumatic brain injury. Parcell et al found that the more that their sleep had changed post-injury, the more individuals felt anxious and depressed.

Loss of Sleep

Parcell et al (2006) concluded from their study that around 80% of participants suffering from a traumatic brain injury reported a difference in their sleep after their injury.

Specifically, the participants spent a lot longer trying to get to sleep. They also reported more awakenings in the night, which (if you read above) is associated with a decrease in grey matter volume.

Another interesting finding in loss of sleep is that a loss of sleep is associated with an increase in experience of pain (Krause et al, 2019). I find this very interesting. It also may also explain some of my clients symptoms as they have terrible sleep! More research needs to be done in this area though.

Annu Rev (2014) also concluded from their review that restricting sleep to 5 hours a night (a little sleep loss) is associated with an increase in emotional disturbance. I am sure you know someone who doesn't get a lot of sleep and is quite emotional!


Sleep is vital to you and your brain. REM and NREM sleep both play very important roles in the development and maintenance of your brain. To disrespect sleep is to disrespect your brain.

If you do wake up frequently in the night, maybe you need to consider your quality of sleep? Do you go to bed with blue light in your face? Do you wind down before bed? Do you do enough in the day?

When I was travelling I was struggling to sleep. I wasn't sure why. Since coming back I have been a lot more active and awake in the day which makes me think that my troubles sleeping whilst travelling was down to my activity levels.

There are lots of things to consider when getting a good night sleep. Only some of them are noted here. One thing is clear though, if you are struggling with sleep, talk to someone and find out why. Sleep is vital to you and your brain.



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