How Much Sleep Do Teenagers Really Need ... and Why?

The first is called long-term potentiation. This is when the brain grows more synapses, and actually increases its communication and connectivity.

The other flavor is long-term depression. This is when the brain actually reduces and cuts back on synaptic connections, and talks less.

Interestingly, when we're awake, just living our lives (like right now), our brain almost exclusively performs long-term potentiation. It's persistently growing new networks; talking to itself.

Now, this is actually a problem. Imagine if all the brain did was continue to grow and expand …

Eventually you'd run out of space, and your brain would explode or collapse on itself.

So, how do we combat this issue?

Enter sleep. During sleep, the brain primarily performs long-term depression.

This means that while you're asleep, the brain resets itself; it pulls back all these new synapses to equalize/balance itself, and effectively return to normal so that you can start the next day fresh.

But here, we have a second problem: if the brain eliminates all of these synapses while we sleep, how do we ever remember anything?

In other words, if the brain just keeps re-setting itself, how can memory possibly function?

We need some sort of mechanism to keep key memories and ideas online … and that mechanism is sleep spindles -- which is what this paper is about.

This paper takes a look at how the brain holds on to key memories while you're sleeping.

So, while you're asleep, your brain is just kind of cycling through this really slow, repetitive pattern … and that's the mark of long-term depression.

It’s rigorously pulling all these synapses back -- but, every once in a while, your hippocampus fires up ...

So, a quick aside -- there's an area in your brain, right in the middle, called the hippocampus, which we call your gateway to memory. If you want to remember anything, that information must pass through your hippocampus.

So, every once in a while, while you’re asleep, your gateway to memory just starts firing up. It starts sending out these really sharp waves, and it more-or-less looks like it's awake.

And, what we think is happening is that, during these times, the hippocampus is replaying memories from that day; it’s re-running key bits of information that you learned previously.

Just like a VCR (if you’re old enough to remember what that is), your sleeping brain repeatedly hits rewind-play-rewind-play … and it keeps replaying these key memories over and over again.

Now, every time this occurs, distinct waves ripple out to the edge of your brain, and you get these little things called sleep spindles, whereby little spots on the edges of your brain start to look like they're awake.

So, even while the majority of the brain is resting, we occasionally get small areas of sleep spindles that resemble wakefulness …

And, what we think is happening is that these sleep spindles are protecting the synapses in these spots of the brain from being pulled back during sleep (during long term depression) so that you can hold onto these specific memories.

So, in reality, these little sleep spindles that are locking down our memories -- this is our memory mechanism!

If you don't sleep, you don't make new memories … so making sure our students recognize that sleep is the key to memory formation is critical.

The more we can get students to start taking control over their sleep and taking care to get enough sleep every night, the more we can move forward and help make learning stick.

Now, there's one more thing with this paper that I want to share … so, when you sleep, you go through what are called sleep cycles.

These are approximately 90-minute windows of sleep stage progressions. You can assume that during a normal eight-hour night of sleep, you’ll experience around five of these 90-minute sleep cycles.

During each sleep cycle, you move through multiple sleep stages: stage one is kind of a light sleep; stage two is where you start to get deeper; and stage three this is the deepest sleep … and, after a period of deep sleep, you cycle back through the lighter stages until you’re out.

Now, this is important, because sleep spindles only actively lock down our memories during stage two sleep. But interestingly, you don't spend the same amount of time in each sleep stage during each cycle.

During your first two cycles each night, you spend most of the 90-minutes in deep stage three, as your brain vigorously ‘washes itself out’ through long-term depression, and resets itself so you can survive the next day.

It's not really until cycles three, four or five that you really spend a lot of time in stage two sleep … which means that sleep spindles (your memory consolidation mechanism) are heavily weighted to later sleep.

Now, why would this matter?

Because something very interesting happens with sleep patterns during adolescence.

So, every human being has what is called a circadian rhythm -- which is an approximately 24-hour rotation during which we naturally cycle through being awake and asleep.

For the majority people, we start to get tired around 8:00 pm, we fall asleep by 10:00 pm, we go through multiple cycles of deep sleep by 1:00 or 2:00 am, and we are awake again by 6:00 am.

However, this is not the normal routine for a teenager. During adolescence, our circadian rhythms naturally shift forward about 2 to 3 hours …

Which means that teenagers don't even start to get tired till 10:00 or 11:00 pm, and they don’t finish going through their deep sleep cycles until 4:00 or 5:00 am. Yet most teenagers still have to wake up around 6:00 or 7:00 am (at least on school days).

So, let’s put the pieces together.

If most of our memory formation/consolidation does not occur until later sleep cycles, and most teenagers don't spend much time in these cycles, there are obvious issues that arise.

If you and I get a solid 8-hours of sleep (covering about 5 full sleep cycles), we experience around 3 ½ hours of dense memory consolidation ...

But if a teenager only makes it through three sleep cycles during a typical night because aren’t going to bed until late yet still waking up early -- sure their brain will do a lot of rigorous cleaning, and they should feel fine the next day -- but they're only getting about 1 ½ hours (or less) of robust memory consolidation.

So, during adolescence, because the sleep cycle naturally shifts forward, if we continue to wake teenagers up at an early time, we can expect their memories to suffer.

And I'm sure many of you recognize this pattern, since it's not uncommon for the learning and academic performance of teenage students to noticeably deteriorate.

So, what does this mean for us as teachers and educators?

Well unfortunately, this is a complex and multi-layered issue, and there are no hard and fast answers … it's just something we have to remain cognizant of.

However, for all the people advocating for later start times for school -- say by pushing it back by 90 minutes -- hopefully you’re starting to see where their argument is coming from.

What they're basically implying is that if we can get teens even just one more sleep cycle, we can effectively double the time they spend in stage two sleep every night -- which will almost certainly strengthen their memory and boost their academic performance.

Unfortunately, the counter-argument is that schools aren’t populated only by teenagers. There are younger kids who don't have this problem, as well as adults who have lives to lead beyond the classroom.

So, we have a real point of contention here ... and perhaps one of the best things we can do as teachers and parents is simply help teenagers recognize that this is an issue, and teach them about their unique sleep patterns/circadian rhythms.

And here's where things like routine become very important.

If we can help teenagers shut down digital technology by a certain time, and ideally get them in bed with lights-off by 10:00 or 11:00 pm, sure they might not be naturally tired …

But, repeat that routine consistently, night after night, and eventually teenagers can start to move their circadian rhythm backward in time -- which will help them get more (and better) sleep, and support their learning and performance.

Thank you all so much for watching. I hope you're well, and I hope you took a lot of value from this video.

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