Hi I'm Michael Corayer and this is Psych Exam Review. In this video we're gonna look at the
different stages of sleep. So you might think that you're either awake or just asleep but
within your sleep there's actually different stages that you move through. So these were
first identified in the 1950s by researchers including Nathaniel Kleitman, Eugene Aserinsky,
and William DeMent. And the way that these researchers identified these different stages
of sleep was by looking at EEG recordings of people who were sleeping. So you might recall
from the video on brain scanning techniques that the EEG or electroencephalogram is a device that
has electrodes which attach to the scalp and these electrodes can detect electrical activity of the
brain underneath and then this brain activity is graphed. This gives us these brain waves alright,
these waves of electrical activity. Now when you're awake the waves look something like
this. Now you can do an image search and find actual EEG recordings to look at I've just
drawn this by hand here but what we see is these sort of rapid low amplitude waves. Now
within the waking state there are different waves that we see. There's alpha waves which
are associated with sort of relaxed meditative states. If you're feeling maybe a little drowsy,
and then there's beta waves which are associated with states of vigilance. So if you're threatened
by something you have that fight-or-flight response you'll probably see beta waves. But in
general we see this sort of low amplitude rapid activity of the brain in the waking state. Now
when you fall asleep things start to change. When you first fall asleep you move into what's called
stage 1 asleep and in stage 1 sleep your brain activity isn't that different but it's a little
different right? So we see something sort of like this and these are called theta waves and they're
a little bit slower than the waking state and they're a little bit more irregular. All right
so what is stage one sleep like? Well you've probably experienced it if you've been asleep
for just a few minutes and you suddenly wake up, you sort of have a feeling that you were asleep,
maybe you had some imagery but you weren't really dreaming right ? You had maybe some thoughts that
were occurring you might have even experienced what's called a "hypnic jerk" and this is a sudden
muscle contraction that occurs. It's not entirely clear why this happens and it might even wake you
up but if you stay asleep you move from stage one after a few minutes into stage two. So in
stage 2 sleep we continue these same waves we had in stage 1 and these are called theta waves. So
theta waves continue in stage 2 but there's some characteristics that identify stage 2 from stage
1. So if you were looking at an EEG you could tell if somebody was in stage 2 because you'd see
these sudden bursts of activity and you'd also see sudden high amplitude spikes. These bursts
are called "sleep spindles" and these spikes are called "K complexes" and these are characteristic
of stage 2 sleep. So we have theta waves with the addition of sleep spindles and K complexes and one
theory of these sleep spindles and K complexes is they might have something to do with brain
activity that's designed to keep you asleep. When you first enter stage 2 you'll stay there
for about fifteen to twenty minutes but you'll return to this stage repeatedly throughout the
night and so over the course of an entire night you'll spend about 50% of your total sleep time
in stage two. Ok, after stage two we move to, you might guess, stage three. This is where the brain
activity really starts looking quite different from the waking state, you know? So in stage one
and two we have these theta waves but starting in stage 3 we have these higher amplitude,
slower waves. We have things that look something like this right? And these are called delta waves.
This stage of sleep is called slow-wave sleep because of these delta waves and this is the
most different from the waking state. It's the highest amplitude and the slowest waves that
you'll have and this explains why it's so hard to wake up from stage 3 sleep. If you've ever
been awakened while you are in this state you've probably experienced what's called "sleep inertia"
and this is this groggy feeling of like it takes you a few minutes to kind of get your bearings and
figure out what's going on. The reason for this is because your brain activity is so different;
these delta waves are very different from your waking activity and so it takes a little bit of
time to sort of get your brain back to its waking state. Whereas if you wake up from stage one,
you know, if you fall asleep for just a minute or two and then you wake up you know you can
sort of jump right back to what you were doing but when you're in stage 3 it takes a while. Now you
may see in some other texts reference to stage 4 sleep. There used to be a stage 4 but in 2007 it
was consolidated into stage 3. It was also Delta waves also this slow wave sleep and it was decided
that they they weren't really differentiated enough. So now they're considered the same stage
it's all stage 3. Okay, so the three of these stages together are all called "non-REM sleep".
So all three of these here would be non REM sleep and that might be an indication that the next
stage that we're getting to is going to be REM sleep. So what does this stand for? REM stands for
"Rapid Eye Movement". That's because in this stage of sleep your eyes start moving around, whereas in
the other stages, non-rapid eye movement sleep, you don't see this eye movement. Okay, so now
we have this interesting stage of REM sleep. So far things have probably made sense in what you
might imagine about stages of sleep; the longer you've been asleep the sort of slower things get,
your brain activity changes to become slower and it's sort of a deepening of sleep throughout this
process. That probably makes sense to you but then we get to REM and things are a little weird,
and this is why REM is also called "paradoxical sleep". So why is REM sleep paradoxical? Well,
the first reason is that your brain activity looks a lot more like the waking state. You go
from these slower waves that you had in stage 3 and then suddenly you start seeing this increase
in brain activity and you get activity that looks very similar to the waking state. So we have an
increase in brain activity, it becomes more rapid. The other things that we see are an increase in
your heart rate and your blood pressure and your breathing also increases, and you even
show signs of sexual arousal. So we have this sort of increase in all of this activation here
and then we also have paralysis of the body so we have a decrease in body movement. You move around
during the other stages of sleep; you can sort of toss and turn and move around in your bed but in
REM you stop moving. Your body becomes paralyzed except your eyes start moving and you have this
increase in your heart rate and your breathing and also the sexual arousal. So what's going on here?
Well, what's happening during REM, this is when you have vivid dreaming. If you wake people up
from other stages of sleep they might report some imagery or some thoughts but it's not
very coherent, whereas you wake people up from REM sleep and this is when they report vivid dreams,
stories that have some narratives to them and they have some objective; they were trying to escape
from something that was chasing them, right? This is where we have the intense forms of dreaming.
Now this makes sense with the body paralysis because when we have these vivid dreams we don't
want to act them out. So this is why we have this body paralysis. Let's say you're dreaming
that you're running from a predator, you don't want those messages to actually get to your leg
muscles and have you start running because you'll run out of bed and right into the wall and that
would probably be a bad idea. So this explains why we have this body paralysis, it keeps us from
acting out our dreams. Now an interesting side note here is, maybe you've had this experience,
where you dream that you're running, you're running from a predator or something,
and it feels weird right? It's like I can't really run, it feels like I'm running in slow motion or
like through molasses or something. This is really common, a lot of people report experiencing this
when they have you know running in a dream. So one theory of this is that what's happening is that
the paralysis occurs because the messages from the brain get blocked at the spinal cord so they
don't make it to your legs and have you actually start running. But normally when you're running,
if you're actually running in real life, you know, you're sending messages to your legs
to move and you're also getting feedback from those muscles telling your brain how things are
going. When you're dreaming, however, you don't get the messages, they don't get there and you
don't get any feedback from your leg muscles telling your brain how it's going. As a result
you have this sort of weird sensation. That's one possible explanation for this this common
occurrence that people report with this sort of slow running when they're dreaming. Okay,
so this is the REM state and now I'd like to look at sort of the course of the night, the sort of
passage from these different stages throughout the course of the night. So if you search for
stages of sleep online you'll certainly see charts like this. You may have it in your textbook and
you'll see something like this, we have sort of the waking state here and then we have you sort
of go down to stage one and you spend a few minutes there then you go down to stage two
spend a little longer there and then you go down to stage three down here spend some time there and
then you sort of come back up to stage two for a little bit and then you go up to here. Oh, whoops
and then you have this same thing here
and then down again.
Okay so you have some chart looking something like this and this is your sleep over the course of the
entire night. And actually this, another sort of side note here is when you think about these
early researchers doing these EEG recordings right, we sort of can simplify everything down
into one little chart here and say okay here's the different stages. But when they were doing
these recordings I mean they're using this EEG for eight hours at a time recording somebody sleeping
and so over the course of a night the amount of paper that they would use for one person sleeping
to record all that brain activity would be about a half a mile long. So you can imagine the
researchers having to go through and look at these brainwaves and make sense of things and figure out
the patterns that are occurring. It wasn't, you know, we have these sort of simplified graphs
that make it look like oh yeah you just look at it's easy to see stage one stage two. But when
they were doing this in you know they had half a mile of paper to look through for each person,
you know? Just one night of sleep to try to figure out what the patterns were. But anyway,
back to this graph here. So we have this sort of deepening of sleep that's what this is meant
to represent as we move down here. We're sort of deeper and deeper asleep. Stage 1 2 3 then we come
back up to 2 for a minute then we go to these top parts and this is what's a little bit confusing
about these graphs and so I wanted to make sure this is clear. This is not actually you know awake
and it's not stage 1 and usually hopefully this is sort of labeled on these charts that this is meant
to represent REM sleep here. Ok it's not actually, you know, like between awake and stage 1 and you
don't pass through it on your first time entering the sleep state but that's meant to indicate that
it's more similar to the waking state than the slow-wave sleep here. Ok, so a couple things to
notice about this chart. The first is that you have multiple REM sessions throughout the night
and you go back and forth between these different stages of sleep. You cycle through them over and
over. The first thing to notice, ok, so this is about an hour and a half here, this first
cycle from first falling asleep until the end of your first REM cycle takes about an hour to an
hour and a half. And as you go through the night you'll notice that the REM periods get longer. So
your first REM cycle this first part of REM might be 15 or 20 minutes. By the end of the night if
you've been sleeping for seven or eight hours you may have 45 minutes to an hour of interrupted REM
sleep. So we see REM increasing over the course of the night and you'll notice that the slow-wave
sleep does the opposite; it decreases. You have a longer slow-wave portion of sleep when you first
are sleeping in this stage three sleep. And as the night progresses this slow-wave sleep gets
shorter and shorter until eventually you stop going to slow-wave sleep. Sort of like you've
had enough of it and you no longer need to go to that state. Ok, this also explains if you've
experienced that sleep inertia right? When you wake up from slow-wave sleep and you really groggy
and out of it. If you're sleeping long enough, if you're sleeping for seven or eight hours a night,
that won't happen anymore because you won't be going into slow-wave sleep anymore. You'll either
be waking up from stage two or from REM and so it'll be easier to wake up feeling refreshed if
you've actually slept for seven or eight hours. This also explains when you try to set your alarm
and wake up early for something you sleep for like five hours or something that's not enough you have
a higher likelihood of waking up from stage three sleep and this is the sort of situation where
you're going to wake up, turn your alarm clock off and immediately fall back to sleep and you
won't even remember that you've done it. So then you, you know, wake up an hour later and realize
you missed your morning class and you don't even remember turning off the alarm. That's why that
happens it's because you probably were woken up during this slow-wave sleep and you're really out
of it and you know didn't get out of bed and give enough time for yourself to really wake up for
that sleep inertia to go away. Whereas when you wake up from REM you can sort of suddenly be wide
awake and you've probably had that experience if you've had a dream and you suddenly wake
up from the dream and you're like immediately alert, like "oh that was a dream and now I feel
wide awake" right? And that's happening because REM is more similar to that waking state. Ok,
so hopefully this made some sense of these different stages of sleep and sort of the order
that you move through them throughout the course of the night. I hope you found this helpful,
if so, please like the video and subscribe to the channel for more. Thanks for watching!