It's a fairly long standing thought that a good nights sleep is important for the functioning of our brains. We (and medical professionals) encourage our children to make sure they get a good nights rest so their performance in school will be tip top! [1] However many people suffer from sleep disorders and getting a good nights rest is not always possible. Still many more of us live very hectic lives, full of more responsibilities then there are hours in the day to take care of them. As a result getting that good nights sleep is not always seen as an option, or at least not as a good use of those hours, so we sleep less. We wake up, feel groggy and drink our morning coffee, shrugging off our lack of sleep. Sure we might be a little tired but were adults, were experienced, our brains are working just fine. Right? Just how important is sleep to our ability to learn anyway?

A group of scientists from Switzerland tackle this question in an article published May 22, 2017 in Nature: Communications titled "Deep sleep maintains learning efficiency of the human brain.", and I would bet just by taking a look at that title you can already guess what the answer to the question we have posed is. Nevertheless, lets take a moment and dive into this research. I'd bet we all have quite a bit to learn when it comes to how our brains work ( I know I certainly have A LOT to learn ).

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Deep sleep or Slow Wave Sleep (SWS) is thought to be really important for resetting our nerves. When our nerves are used they experience a strengthening of the electrical currents in their synapses (the gaps between neurons) the stronger these currents get, the less responsive the nerves are to new stimulus. [3 So when I say that deep sleep is thought to be important for resetting our nerves, what I mean is that it is important for reducing the strength of these electrical currents, making the nerves ready to respond to new stimulation.

But what if you weren't sleeping much? Being awake all of the time is probably going to result in these synapses not resetting and slowly over time building up to a strong current state. [4] This means that those neurons would not be responsive to new information, and in theory that should not work out well for when we are experiencing a new situation and wanting to learn from it.

Studying this in humans is a bit more difficult then you might first consider, as there hasn't been too good of a way to deprive sleep from just one portion of the brain while leaving the remainder of it (and the subject) sleeping normally (and deeply aka in Slow Wave Sleep).

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Background: Stages of Sleep

This section will briefly cover the 4 stages of sleep just to familiarize you with the terminology. If you aren't interested in this and only want to see the results of the study, feel free to skip down to the next major heading!

Stage 1: Non-REM sleep -1

This is the stage of sleep that occurs in between being fully awake and actually asleep. This is the stage that you are entering when you are in class and starting to nod off, or are in a really boring meeting and just cant keep your head up straight. During this stage your breathing becomes more regular and your heart rate slows down. [5], [6]

Stage 2: Non-REM sleep -2

In Stage 2 you are now fully asleep, the activity of your muscles is decreasing. The frequency and amplitude of your brain waves is decreasing. It is in this period that a brain activity pattern called "sleep spindles" occurs.

Source: Sleep Spindles

Sleep spindles are high frequency bursts of brain activity that last for only 1 or 2 seconds and occur due to interactions between neurons. [5], [6]

Stage 3: Non-REM sleep -3 (Slow Wave Sleep)

Sleep stage three is a moderately deep sleep stage where the frequency of sleep spindles decreases and the amplitudes of low frequency brain waves increases (as detected by EEG). These low frequency brain waves are know as delta brain waves (these are the slow-waves that give this stage its name). During this stage your bodies temperature, breathing rate, blood pressure, and heart rate are all at the very lowest of any stage. [5], [6]

Stage 4: REM-Sleep

Finally we have REM-sleep, or Rapid Eye Movement, sleep. It typically occurs in durations of around 90-120 minutes and makes up as much of 25% of your total sleep time. REM sleep makes up more and more of the total time of a sleep cycle (the progression through all of the stages) each cycle pass. Interestingly there is no explanation for the purpose of the rapid eye movements in this sleep stage, however the hypothesis is that they are related to the images your brain is showing in your dreams. [5] (which I did not know, so neat!). It is during this sleep stage that the patterns of your brain waves returns to a more similar state as when you are awake.

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Results

What Were The Authors Doing?

They hooked people up to EEG's and monitored for when they entered 'Slow Wave' sleep (discussed above). It had been hypothesized that this slow wave stage was responsible for the restoration of the neurons to a rested, non strong, state. The authors here wanted to demonstrate that these slow waves were actually responsible for this. So they hit 13 (7 men, 6 women) subjects with sound stimulation to selectively disturb just the motor cortex region of their brains (stopping the slow wave sleep in this portion but letting the remainder of the subjects brain and the subject remain asleep).

To judge their learning ability relating to the motor cortex they were given a finger tapping exercises, where they had to learn new tapping exercises every morning and night in sessions which book ended a week of sleeping. In one session the participants underwent the sound stimulation when they slept, and in the other session they did not:

Source: Figure 1

What Did They Find?

• Applying their sound stimulation changed the slow wave characteristics of the participants sleep in the motor cortex (it was doing what they intended, they were disrupting this type of sleep in the motor cortex)

Source: Figure 2

Above shows the relative amounts of slow wave activity for the test versus control experiment. Blue is lower activity, and red means more slow wave activity. The white dots represent the area where the motor cortex is, and as we can see the slow wave activity there is lower. Success!

• The people whos slow wave sleep in their motor cortex was distrupted performed significantly worse in the tapping tests.

Source: Figure 5

So what we are looking at in (b) is a plot of the inter-tap interval (aka the time in seconds between key presses "tapping" in their tapping assignment), remember that D1 was before the week of normal sleep or sleep disruption of the motor cortex and D2 is after. What we can see is that the inter-tap interval went way up for the participants who had their motor cortex disrupted, while those who did not got a little better at the test (they learned).

In (c) we are looking at the electrical potentials created by the brain and sent to the muscles during the test as measured by an EMG (electromyogram). Aka they were looking at nerve function! What we can see here is that the response after the experiment for those that had the sleep disrupted brains were worse than those who slept normally (compare Mor D2 orange line (sleep disrupted) to green line (not sleep disrupted). The "facilitation index" is a mechanism for determining the strength of the signal (and perhaps some of you traders are familiar with this as a means to determine the strength of a trend in the markets :D ).

Some Conclusions

• The authors showed that messing with the slow waves in the motor cortex during non REM sleep affected subjects performance in motor learning experiments. AKA they were worse in how they performed in the experiments.
• Messing with the slow waves however did not effect overall performance gains as a result of the experiments. What the people were struggling with was adapting to new parts of the patterns they were expected to tap. So while they still learned, they struggled to adapt to changes.
• They have created a new technique for the study of the biological function of sleep and have provided evidence linking Slow Waves during sleep to returning the nerves to their baseline function level.
• The authors findings indicate that deep sleep is important for maintaining the brains abilities to respond to and adapt to changes in our environments.

Answering Our Titles Question

Yes, deep sleep (a good nights sleep) appears quite important for our brains abilities to restore nerves to their baseline function levels, and allow us to learn and adapt to new situations or information.

Bad sleep would indeed make this more difficult.

Sources

1. http://www.cbsnews.com/news/new-sleep-guidelines-for-babies-kids-and-teens/
2. https://www.nature.com/articles/ncomms15405
3. http://www.cell.com/neuron/fulltext/S0896-6273(13)01186-0
4. http://www.cell.com/cell/fulltext/S0092-8674(08)01298-1
5. https://www.howsleepworks.com/types_nonrem.html
6. https://www.ncbi.nlm.nih.gov/books/NBK10996/

All Non Cited Images Are From Pixabay.com And Are Available Under Creative Commons Licenses

Any Gifs Are From Giphy.com and Are Also Available for Use Under Creative Commons Licences

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