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Sleeping Brain-y

December 1, 2018

Question: What is the worst sound in the world?

Answer: Your alarm clock going off on a Monday morning.

 

There is nothing quite like the gut wrenching noise of your alarm dragging you from the depths of slumber. Whether you are an early bird or a night owl, we all need to get a good 6-10 hours sleep a night to feel somewhat human. But if you think about what sleep actually is, it is a bit weird... Our well-being revolves around us routinely lying down on a sprung mattress, bundled in cloth for over a third of our lifetime. Evolutionarily, sleep seems like a period of vulnerability; leaving us unconscious to our surroundings and at the mercy of the elements, predators and thieves. And if we didn’t need sleep, just imagine what productive things you could do with those extra 8 hours? However, the mechanism of sleep is conserved across almost all species; indicating it is vital to survival. During your periods of unconscious rest, your brain is actually pretty active; carrying out essential processes. So, while we check out for our 20 nods, what happens in our brains? And what keeps us coming back to our bed night after night for another stint of Zzz’s?

 

Smile and Wave, Boiz

Every night when you are tucked up, your brain experiences 2 sleep states: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. These states occur in a specific pattern and each sequence lasts around an hour and a half; meaning you have about 5 sleep cycles a night. Using an EEG, neural activity (described by wave-patterns) of these cycles can be monitored. During the day, your wave patterns appear as a mix of many desynchronised, small bursts of activity (beta (β) waves), representing your synapses firing to keep you alert, and slower synchronised waves (alpha (α) waves) which you experience when you are relaxed. During sleep, these wave patterns change massively, with different patterns describing different stages of your snoozing cycle.

 

The NREM sleep can be split into 4 stages to describe your ‘light’ and ‘deep’ sleep:

 

1. Stage 1 & 2: Light Sleep

Stage 1 is responsible for that feeling when you start to nod off in a dark, warm meeting room and lurch back to reality as head drops like a dead weight. In your brain, this is characterised by an increase in theta (θ) wave activity; a wave pattern slightly slower and more synchronised than your relaxed alpha waves. The theta waves of stage 1 continue but with a few extra features added in called sleep spindles (an increase in wave frequency) and k complexes (an increase in wave amplitude) every few minutes to differentiate stage 2. if you are disturbed during this period of drifting off, you will quite easily switch back to wide-awake mode.

 

2. Stage 3 & 4: Deep sleep

Your third and fourth stages of sleep represent your ‘deep’ sleep. These phases are characterised by haaaaage, slow wave patterns called delta (δ) waves. Stage 3 has less than 50% delta wave pattern and stage four has over 50%. These big slow waves are almost the opposite to your wakeful state, so when you are left feeling completely disorientated after someone or something (that bloody alarm clock) waking you, blame it on the delta waves. Delta waves are also the patterns responsible for sleep talking or walking (or sleep change-of-clothing like I do – waking up in a completely different outfit to what you went to bed in is always fun).

 

The final stage of sleep is REM sleep. This happens at the end of your 90-minute sleep cycle, which goes from stage 1 to 4 and back up to stage 2. REM sleep is characterised by involuntary rapid eye movements and loss of muscle tone, leaving the REM sleeper almost paralysed. During this phase, your brain activity is the most similar to the brain activity you experience when you are awake; consisting of desynchronised activity of short low-frequency spikes. The length of REM sleep increases with each cycle, meaning the last cycle before you get up is when your brain is most awake. REM sleep is also when you dream as your brain is in a similar state to when you are awake. This means it can produce life-like simulations, but that handy paralysis stops you from acting your crazy sleep scenarios.  

 

Why do brains need sleep?

 

1. Memory

The 8-hour unconscious period representing sleep is the perfect time for your brain to consolidate information learnt during the day and prep itself to get geared up to learn more tomorrow. Memory formation involves the strengthening of synapses and when people are sleep deprived, this ability is out the window. The brain region required for memory formation, called the hippocampus, is super sensitive to not getting sleep and it is thought that lack of sleep disrupts plasticity in this region. Neuronal plasticity allows the alteration of synaptic strength necessary for memory formation, which requires making new proteins (through gene transcription) and increasing the number of receptors at the synaptic, making their connections stronger. If your brain doesn’t have this period, plasticity cannot occur, and you are unable to both consolidate what you have learnt that day or make space for new information the next day. So, although those late-night revision sessions might seem like the best way to cram for your morning test, a good night’s sleep is needed for you to remember the last-minute bites of info.

 

2. Attention

Attention is the ability to focus on a specific task without any distractions. For your brain, the mechanism of attention requires two active process; selecting important information to focus on and blocking out non-important background noise. For example, when you are sat in a crowded bar chatting with your friend, you can ignore all the background chatter and tune in to just them telling you all about their horrendous week in work. Your brain works in a similar way, with neurons in attention circuits (thought to be in the frontal and parietal lobes) firing strongly to one another while other brain regions have their activity dampened. The inactive brain regions show alpha wave patterns, like those your brain experiences when relaxed, as these provide ‘silent’ periods of neuron firing and make the desynchronised beta-wave patterns in the active regions seem even louder. Sleep represents an extreme version of this dampening, with prolonged periods of slow wave patterns across the entire brain. This enables all the active circuits in attention to be cut off from each other. The mechanisms surrounding why this cut off occurs is not completely understood but if you are sleep-deprived, the difference between your active attention signalling and suppression of background noise is lessened, making it more difficult to focus on your mate’s latest office dilemma.

 

3. Waste Clearance

During the day, your brain accumulates waste products released from cells in the extracellular space and during your sleep, it is thought clearance processes kick in to get rid of any rubbish. This is similar to you turning up to the office in the morning to see the carpets hovered, surfaces cleaned and bins emptied; the cleaners of your brain work while you unconsciously snooze. This clearance system is called the glymphatic system as it coordinated by immune brain cells called glia. These increase the volume of extracellular space in you brain to ‘flush out’ the old fluid and replace it with a fresh batch. This clearance is mainly active during sleeping periods so if you are deprived of sleep, some waste products remain in the brain. Over time, this can be bad for brain health and has been linked to susceptibility in developing Alzheimer’s disease (although this is not fully proven!).

 

The role sleep plays in your health and cognitive function is obviously huge, and we are only just starting to scratch the surface explaining the mechanisms behind these processes. Sleep is also important for the health of other organs in your body and tissue repair, explaining why it is super important to retire to our slumbers every night.

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After learning a bit more about the importance of sleep, make sure you always try to get your 80 winks. And if anyone shouts at you for sleeping in, tell them your brain needs it. 

 

Main Sources used (in case you want to keep awnnn readin’)

https://www.sciencedirect.com/science/article/abs/pii/S0306452215003942

https://www.sciencedirect.com/science/article/pii/S0166223615002258

https://www.livescience.com/54284-sleep-deprivation-selective-attention.html

https://www.theguardian.com/science/neurophilosophy/2013/may/22/dreaming-of-animals-and-other-warning-signs-of-neurodegeneration

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