Stages of Sleep – Consciousness (PSY)

00:01 When we’re not alert, we’re tired and we’re going to sleep.

00:06 And so, sleep is really important in terms of managing our level of A, consciousness and our cognitive ability.

00:12 We know that if you aren’t getting good sleep and if you aren’t getting the appropriate amount of sleep, this is going to really impact your cognitive ability and your ability to function.

00:20 So, stages of sleep are clearly distinguished and studied using a sleep test or a polysomnogram.

00:26 So, again, this is something that’s near and dear to my heart because I’ve spent a lot of time working in a sleep disorder clinic and we work with patients and we have them come in and they come for sleep studies, where they spend the night and we connect.

00:39 We connect them with a whole bunch of electrodes.

00:41 And on this figure, you can see some of the places that you’d place the electrodes so you’d have your EEG, which measures brain activity or brain waves, then you have the EOG or electrooculogram.

00:51 This measures eye movements.

00:53 And then we also have the EMG, which measures muscle tension in your face.

00:58 So what we’ll do is hook these people up and it allows us to understand a lot of different things.

01:04 It allows us to understand what stage of sleep we’re in, and we’re going to go through those in just a moment.

01:08 And it’s going to allow us to understand the amount of brain activity that’s happening.

01:14 So a PSG or a polysomnogram is a multimodal technique used to measure physiological processes during sleep.

01:20 So I just highlighted a couple of the different modes of information and one was the EEG, which is electrical activity, EMG is skeletal muscle movements, and then we have EOG, which is eye movements.

01:32 So multimodal refers to different modes or types of information, and we use that to measure physiological activity during sleep.

01:42 So, a PSG or polysomnographic test research has shown the presence of four stages of sleep in humans.

01:49 So we know that there are four stages of sleep and something called REM.

01:52 So non-REM sleep is stages one through three or also known as N1, N2, N3.

02:00 And then there’s REM, which is the Rapid Eye Movement stage.

02:03 So, you might be looking flipping through some old textbooks or even online and you’ll sometimes find that they have stages one through for plus REM.

02:10 So, the more current version of the sleep phases is one through three and REM.

02:16 Now, REM is defined is Rapid Eye Movement stage and as the name implies, during this stage of sleep, your eyes move around a lot and extremely active.

02:26 It’s kind of freaky if you’ve never seen it before but really, really interesting.

02:29 So the next time, you know, your roommates were asleep or your girlfriend or boyfriend or parents, sneak in and take a look and watch them.

02:37 And if they’re in the REM stage, and this is the stage where we do a lot of our dreaming, you’ll notice that their eyes are closed, but their eyeballs underneath their eyelids are moving around frantically.

02:47 And it’s because they’re actually -- it’s quite activated and their brain is very active in that stage.

02:53 So we’ll take a look at each stage and then you’ll see what I mean.

02:55 So stage one (N1) is light sleep.

02:58 You’re feeling sleepy, drowsy but you’re not actually in a deep sleep.

03:02 So this is right when you literally lay down and, you know, you have your, you know, Mickey Mouse pajamas on and you’re all comfortable and you’re lying there and you’re just starting to get in that relaxed, I’m starting to feel sleepy, getting the heavy eyelids stage.

03:18 So it’s a transition between sleep and wakefulness.

03:22 The muscles are active, the eyes roll slowly, but the eyes could still be open.

03:26 Now, if we’re looking at brain activity, we notice alpha waves and this is a specific frequency of eight to thirteen hertz when you’re awake, to theta waves, which is three to seven hertz.

03:36 So this represents a small portion of your sleep, so only 5% to 10% because you’re just starting to get to sleep.

03:41 So in terms of the MCAT, you should be very familiar with the different stages of sleep and my advice would be you should be also familiar with the types of brain wave activity that you see in that stage of sleep.

03:51 So looking at it in terms of the EEG, these little squiggly lines represent the type of brain wave activity that you’re seeing.

04:00 So what do you notice here? So, stage one theta waves look like they’re getting smaller and you can see the smaller level of activity.

04:08 Now, if we get to stage two (N2), we continue to become less responsive.

04:12 And this represents a larger chunk of your sleep so, almost half of your sleep.

04:17 And what’s happening here is you’re seeing two characteristic features that let us know that you are entering stage two.

04:24 So remember, stage one is the heavy eyelids.

04:26 Stage two is that you are now can be considered sleep because you’re no longer eyes are open and you start to see these two characteristic features, the K-complex and sleep spindles.

04:37 The K-complex is that dramatic peak and valley and it has a duration of about half a second and it’s quite large and slow.

04:43 So your brain wave activity is little scribbles and all of a sudden you’ll have this rise and fall and that lasts, you know, a couple of seconds -- sorry, half a second, and then you have the sleep spindle, which are bursts of activity and around the frequency of 12 to 14 hertz.

04:58 So these are key characteristics for a stage two sleeper.

05:03 Very little eye movement at this point and very moderate EMG activity.

05:06 So EMG refers to the muscle tension in your face.

05:09 So if you’re asleep and you’re in this stage, you’re going to notice that your eyes are not moving, so you’re not in REM, and you’re going to have this kind of droopy -- droopy face. Not a lot of muscle activity happening.

05:24 How does that look? So you can see here, we’re seeing the spindles, we’re seeing the K-complex, and the activity, again, is quite muted.

05:32 Now, if we’re looking at stage three, this is the deep sleep now.

05:35 You’re really in deep. At this point, you’re pretty much out.

05:39 This represents about a quarter of your night and you start to see the delta waves, which are high amplitude and low frequency.

05:45 So about a half to three hertz.

05:47 Previously divided, this is the stage that was at three and four.

05:49 They’ve now just scooped that all into stage three, very little eye movement at this point, moderate EMG activity, and this the most -- one of the most restful stages of sleep.

05:58 So if you’re balancing around one and two, one and two and you’re not getting a lot of stage three sleep, you will still wake up extremely tired because this is where the restful nature of sleep kicks in.

06:08 So in terms of activity, you can see the brain activity has changed dramatically versus stage one and stage two.

06:14 Okay? So things have really slowed down.

06:17 Now, probably the start of the show for at least for me is the REM stage and this is the dream state.

06:25 So this is characterized by the rapid eye movements, thus, the name.

06:28 And you start to see a change in your EEG activity and it actually resembles the beta waves seen in individuals who are awake.

06:35 So you’re actually asleep, in deep sleep, yet your brain is acting like it’s actually awake.

06:41 Okay? So it’s not a coincidence because dreams are happening, that’s a very active time in your brain, and so, that’s being reflected in this EEG activity.

06:50 The REM waves are sawtooth in shape and low intensity and have variable frequency.

06:55 We’ll take a look at the image in just a sec.

06:57 Almost no EMG activity, there’s complete paralysis in your face.

07:01 This is the time in your sleep cycle when you wake and you have all that drool action on your pillow.

07:05 When you wake up and your pillow is all soaking wet, that’s actually a good thing.

07:08 That means you’ve achieved REM -- REM sleep and you’ve got drool all over your face, your pillow, your pajamas.

07:14 That’s a good night.

07:15 Now, it’s termed paradoxical sleep because physiologically speaking you seem awake.

07:21 Your brain is quite active.

07:23 But, there’s absolutely no muscle movement.

07:25 And this is evolution and this is us being self-protective because imagine if you had a dream, and in this dream, you actually acted out your dream and you were moving around and running around.

07:38 So if in your dream you’re being chased by wild dogs and you’re running in your dream, you really wouldn’t want that in bed, where you’re moving around and you’re kicking and you’re running, right? So your brain and body has evolved and so that it says, “Well, once I enter the REM state, I’m actually going to create a complete paralysis and I will be completely done so I can’t move and I can’t act on my dreams.” So you’re completely out, but your brain is extremely active.

08:02 So, it’s a paradox; brain is awake, the rest of the body is completely kaput.

08:05 Okay? So if you take a look at the brain activity, you can notice that the REM sleep is very, very similar to what you would see in an active state compared to, say, stage three, where it’s very slow and it’s very, very high amplitude.

08:20 So individuals will pass through the different stages of sleep in sequence.

08:23 So they actually start in N1, move to N2 and then go on to N3, and then -- so in terms of if we’re looking at the sleep stage, then we’re looking at hours of sleep.

08:32 So as the night progresses, what do you notice? Two things you should notice; first, that you have multiple episodes of REM.

08:39 That’s the first thing.

08:40 And the second thing is what? Look at the duration of REM.

08:43 Is it getting shorter or longer? It’s getting longer.

08:47 So what happens is as your night goes on, your periods of REM increase so the length of your dreams increase, which is partly why when you wake up in the morning, you tend to remember the last couple of dreams you had and not the one that you had in the beginning of your night.

09:01 So a typical sleep cycle is considered roughly 90 minutes which explains why you might have these awakenings throughout the night, because you cycle through very, very light sleep, stage two, stage three where you’re in really deep, then you have your dream.

09:15 And when your dream is complete, you kind of get kicked back out and you go back to stage one and that is when you might wake up.

09:20 You might toss and turn a little bit, you might want to get a glass of water, because that’s the closest point you’ll be in the night to being awake, and that happens a couple of times a night.

09:29 So this cycling is repeated throughout the night, which is why you have your multiple dreams, which is why you move around a couple of times throughout the night.

09:35 So as the night progresses, time in non-REM decreases and episodes of REM increase.

09:40 So, it’s an inverse relationship.

09:42 Okay? So individuals, you might ask yourself this.

09:47 Do you remember your dreams? Do you remember the dream that you had last night? Hopefully, I was in your dreams, right? So if you aren’t remembering your dreams, that might be an indicator that you’re actually not achieving REM.

10:00 And not to alarm you, but that’s not necessarily a good thing.

10:03 You’re going to want to achieve REM.

10:07 But you can have, you know, periods of REM that are short or you might not achieve lots of episodes of REM and still have some REM, but these are things that are indicators of how rested you are.

10:18 And how do you feel when you wake up in the morning? Do you feel really rested? Or are you saying, “I still get my eight hours but I’m exhausted”? So there might be some things that are preventing you from getting into REM.