Understanding Sleep Stages and Effects of Sleep Deprivation

the topic of this lecture will be the stages of sleep so what we're going to talk about will

be the stages of sleep and how we cycle through sleep during the course of a typical night

so on average sleeping falling asleep takes about 25 minutes on average but it depends on a number of factors um some

people tend to fall asleep much more quickly than other people do also uh people there's only a lot of variability

within people over over time as well some nights I'm able to go to sleep pretty quickly when I turn off my

bedside light some nights it takes me quite a while so within the same individual there are also uh there's a

considerable considerable amount of variability on average it seems like it takes people

usually about 25 minutes or so so let's go through the the stages of sleep and it'll be important for you to

know a couple of things one will be how the stages progress and then also what each stage is going to be characterized

by so let's start with stage one sleep stage one sleep is kind of a brief

transitional stage of sleep it only lasts for a short time about one to seven minutes again depending on number

of factors What's Happening Here is that our brainwave activity is captured by things like eegs right the amount of

electrical activity in the typical activity is beginning to change so lower frequency sorts of waves the amplitude's

starting to be a little bit higher as we're kind of drifting off into sleep initially

one of the things that is not uncommon during stage one sleep is to experience something referred to as hypnic jerks

these are going to be a little muscular contractions so for example for some individuals it's not uncommon for them

as they're kind of drifting off and first kind of going into stage one sleep for their arms or legs to kind of jerk

and and for them to actually wake themselves up in some cases right now one of the things that many of us have

probably experienced is as you're starting to fall asleep having a sensation of falling right and kind of

waking yourself up with this kind of startle where it feels like you're getting ready to fall out of bed or fall

off the couch or wherever you are when in fact everything's perfectly fine um that's going to be related to this

idea of hypnic jerks and it has to do with the way in which the body is relaxing

um and sometimes the little kind of hiccups if you will that happen in in stage one sleep causing things like

muscular contractions that that might actually kind of startle us awake now for many of us hypnic jerks are

something that we experience and frequently um every once in a while I'll experience

this whereas I'm starting to fall asleep like my leg will jerk and kind of wake me up in that case it's usually fairly

easy for me to go back to sleep afterward but for some individuals um this is a recurring problem that

really interferes with their ability to sleep for example there's something called restless leg syndrome which we'll

talk about later that's going to be related to this and it's a similar sort of idea where there are these muscular

contractions as people are starting to go to sleep that prevent them from kind of getting deeper into sleep and so

we'll return to this sort of idea later stage two sleep spindles high frequency spikes and activity makes the EG

activity so sleep is getting a little bit deeper right again we're getting higher amplitude in terms of the EEG

we're also getting lower frequency but with stage two sleep there are going to be these little kind of punctuations of

high frequency spikes so even though things in general are slowing down there are times where there's kind of these

bursts of activity right so this is why we're talking about this being kind of mixed EEG activity because it's a

general slowing with these kind of punctuations of high uh high frequency uh low amplitude sorts of activities and

this can last for about 10 to 25 minutes or so stage three and four sleep is going to

be slow wave sleep each of these lasts for about 30 minutes and as as you think back and when we talked about the EEG

patterns from a previous lecture we talked about those being very high amplitude very low frequency periods of

sleep so electrical activity is really slowing down during stage three and stage four sleep we typically refer to

this as being deep stage sleep the final stage of sleep that we'll want to talk about is REM sleep right REM

sleep rapid eye movement sleep this is actually going to be kind of a return to stage one sleep right so sometimes

people will get confused about well how many stages of sleep are there well it depends on how you're thinking about REM

sleep so the typical progression is we'll talk about soon is when people first go to

sleep they hit stage one then after a little while they move to stage two then stage three stage four

which is the deepest stage of sleep and then they start to move back up then they go from stage four to stage three

to stage two and where you would expect them to hit stage one they hit REM sleep right so rapid eye movement sleep

the EEG activities we saw from a previous lecture is going to be relatively similar to when people are

actually awake right so the amplitude of the waves are typically fairly small the frequency is high so it looks like these

people from EEG activity it's not terribly different from when people are awake

there's going to be a lot of vivid dreaming that takes place um some at first it may be a relatively

short period of the dreaming then can be a little bit longer one of the other things that we experienced during REM

sleep is paralysis right so what happens is while we're sleeping our body basically experiences a

paralytic state which prevents us from acting on the dream content at least for the vast majority of us now this is

important because if you think about it when you're having a dream so let's say for example you have a dream of a of a

tiger chasing you through a forest or something of that sort right if you're having that sort of dream what you want

is for your body to be locked down so you can't actually act in accordance with the dream right so in your dream

when there's a tiger chasing you through the jungle you don't want your body to LEAP out of bed and begin running across

the bedroom right that would be very dangerous for you and so what most of us experience is something called brim

paralysis where even during a particularly Vivid and frightening dream right we may toss a little bit right we

might kind of jerk around a little bit but for the most part most of us are not acting in accordance with the content of

our Dream right and that's really important and extremely helpful for our safety

so let's take a look at this overview of the typical sleep cycle so they're going to be a few different pieces of

information in this figure so first of all we've got time up here we've got uh wakefulness of what people are

experiencing here so let's say this person's awake they go to bed around a little before 11 o'clock or so so they

go to bed around 11 they fall asleep and so now we can see the person is moving in stage one sleep here

after a few minutes they move into stage two sleep here we can see the EEG indicating stage two sleep then stage

three sleep for a bit then stage four sleep after they've been in stage four for a

while they go back up to stage three then up to stage two and now where you would expect them to hit stage one they

hit REM sleep right so Rim is going to be rapid eye movement sleep it's referred to as rapid eye movement sleep

because our eyes dart back and forth during REM sleep you can see this because the structure

of the human eye we have a cornea on the front of the eye that sticks out just a little bit so if you have your eyes

closed like while you're sleeping if you move your eyes back and forth the cornea pushes out on your eyelid just a little

bit so you can kind of see the eye darting back and forth if you have a pet dog or pet cat right you can do the same

thing if you watch them while they sleep you can see their eyes starting to dart back and forth and you can see that

under the eyelid as the cornea pushes out a little bit on the eyelid so after we go through a period of REM

sleep we then go back to stage two then stage three stage four three two Rim notice that the rim period

here tends to be a bit longer when we get to it the second time after being in rim for a while we go to stage two stage

three now notice as the night progresses people may not necessarily make it all

the way back to stage four right so after a couple of sleep cycles the person may go from REM to stage two

to stage three and not actually make it all the way back down to stage four rather they're in stage three for a

while then they go back up to stage two they experience rim for a while back down to stage two and now as the night

is getting uh is turning into morning maybe they don't even make it to stage three now they just go from round to

stage two they're in stage two for a bit back to brim back to stage two then the person's alarm goes off and they wake up

right a couple of other pieces of information I want to point out about about this figure one it shows kind of

changes in sleep position which are not uncommon right a lot of us tend to move a little bit during the course of the

night right you may turn from one side to another maybe you sleep for a little while on your back maybe you turn over

on your stomach right so there are various sorts of positions we might find ourselves in you might kind of throw the

cover off for a few minutes pull it back on when you get a little cold right those sorts of movements are not

uncommon it also isn't uncommon for us to wake up periodically throughout the night so for example during a normal

night it wouldn't be terribly unusual for someone to wake up three or four times maybe those waking periods are

very very brief so that the next morning you don't even remember waking up right that's not unusual

typically in order for us to remember a waking episode during the night we usually have to be awake for at least a

couple of minutes or so uh also this figure shows uh the likelihood and kind of vividness and

intensity of dreams during different periods you can see that when people first start to drift off it's possible

you may experience some dreams that are fairly Vivid usually our dreams are going to be most Vivid and intense

during brim episodes but we can experience dreams during any stage of sleeping it's just that they're more

likely to be Vivid and concentrated around our Rim periods right as we can see here also we can see uh here it

shows the sort of eye movements we're likely to experience so you can experience some eye movements during any

stage of sleep but they're typically most concentrated around Rim episodes right as we can see from this figure

also notice that during the course of a typical night right you might have something like four different sleep

cycles four or five depending on a variety of factors but this person would have likely had some sort of dream

content at least during these four Rim episodes now it's possible if they slept all the way through the night that they

may not remember any of their dreams at all or if they do remember one of their dreams that may be the sort of dreams

that were taking place during this Rim episode that were that was closest to waking right but it's difficult to it's

difficult to tell there are changes in sleep patterns over time in a previous lecture we talked

about recommended amounts of sleep this is going to refer to what people actually get during certain stages of

life so when children are really really young just a couple weeks old they're sleeping

in the ballpark around 16 hours a day notice that a good chunk of that sleep time is spent in REM sleep right about

50 percent of their time is spent in real as we start moving uh older and older

when the kids are down to about when kids are up to about three to five months of age their sleep is down to

about 14 hours a day by the time they're two to three years of age now they're down to about 12 hours a day we're now

down also to about 25 percent of drain of sleep being REM sleep with about 75 percent of sleep being non-rim sleep

by the time we get to our teenage years we're now down to a little over eight hours on average with about 20 percent

of time being dedicated to REM sleep by the time we're in 33 to 45 we're now down to about seven hours on average

with a little less than 20 percent REM sleep by the time people are 50 or older we're now down to a little over six

hours per day on average with again about 20 to 23 percent being in rim now it's important to note that even

though people for example once they hit around 50 or so are now getting just over six hours of sleep that doesn't

mean that's what they need right what they need is probably actually up here a little bit closer to eight it's just

that a lot of adults end up being mildly sleep deprived in a chronic sort of way I would fall into this category I've

mentioned before I have sleep issues and I'm usually getting maybe six hours maybe seven on a on a really good night

it's not uncommon for me to get more like four or five hours of sleep six is I'm usually pretty happy with six which

is is not great right I'm not saying that's what I need I'm saying that's what I typically get

um it isn't uncommon for me to I typically I try to go to bed fairly early because I often will wake up early

it's not uncommon for me to wake up at 4 or 4 30 and being unable to go back to sleep so I typically go to bed around 10

o'clock or so now which is much earlier than I used to go to sleep in order to try to get six six and a half hours of

sleep so as you can see from this slide this shows the cultural variation and how

long people tend to sleep and so if we look across all countries if we're thinking about adults what we see is

some cultural variation in how long people tend to sleep with some countries like for example Portugal having

relatively long average sleep periods whereas countries like Japan have relatively short average sleep periods

and many other countries kind of falling in between now notice that even though there's some

cultural variability it isn't the case that these things are completely and utterly flexible right the the shortest

amount of sleep and Japan is still over 420 minutes per night so it isn't the case that people in Japan are only

sleeping like three hours or something of that sort rather what we're seeing is that our underlying biology seems to

form a window of how much sleep we can simply live with and then culture within that window is kind of directing where a

culture happens to fault where people within a culture happen to fall so for example it seems like cultural

influences in Portugal are leading people on average to sleep a little bit longer people in Japan to sleep a little

bit shorter sleep deprivation has some really important consequences for our physical

and mental functioning so complete sleep deprivation refers to the idea of not getting any sleep right not falling

asleep at all for most of us three or four days is about the maximum amount of time that

people can can manage to go without sleeping at all the longest period that's been recorded

was by a young man named Randy Gardner who is a high school student who for a science fair project in the 1970s had

some of his classmates and family members keeping him awake around the clock and he was able to go supposedly

for about 11 days although I'm a bit skeptical about whether those 11 days are all real because typically when

people become really really sleep deprived they'll engage your water referred to as micro sleeps where

they'll kind of nod off for a brief moment or two even if they aren't sleeping for very long

my assumption is that Randy Gardner probably experienced a fair number of those micro sleeps as the days went by

now if we think about some of the consequences of sleep deprivation there are a number of negative consequences

some of these are cognitive in nature irritability tends to go up we tend to experience cognitive impairments memory

tends to be impaired our moral judgments aren't so great we have a lot of yawning behavior in some extreme cases we can

even experience hallucinations and symptoms that are similar to ADHD our immune system can be impaired with a

prolonged sleep deprivation risk of type 2 diabetes goes up our heart rate becomes more variable risk of heart

disease increases over time our reaction time and accuracy begin to decrease so we have more trouble doing things that

require a quick reactions like driving for example engaging in sports we start having more Tremors and aches there are

also issues like growth suppression depending on how old the person is risk of obesity goes up and decreased body

temperature can also be seen in people who are experiencing a lot of sleep deprivation

in addition to complete deprivation we can also experience partial or partial deprivation or sleep restriction this is

when people don't get enough sleep so it's not they aren't getting any sleep at all but rather they're being

partially sleep deprived so 63 percent of adults report getting less than eight hours of sleep per night which isn't

great because it seems like most of us need about eight hours a night to do really really well 31 of folks report

getting less than seven hours of sleep a night which again isn't great if we need more along the ballpark of eight hours

now again as I've mentioned I would be somewhere here in probably the less than seven I'm more like maybe six six and a

half on on a on a good night so I should definitely be continuing to work on improving My Sleep Quality as well

when people are experiencing partial deprivation or sleep restriction their attention can be impaired their reaction

time can be impaired coordination isn't all that great decision making may be a bit off

um these sorts of partial deprivation or sleep restriction episodes have been associated with a number of different

accidents over time for example the Chernobyl disaster the nuclear meltdown at Chernobyl sleep restriction was seems

to be an issue among some of the the folks uh who were on duty when the nuclear meltdown started having problems

the Exxon Valdez crash which was a oil tanker that crashed it also some of there's some implications that uh that

sleep restriction among the uh among the crew may have had some issues with why some of the decision making was so poor

around the Exxon Valdez crash there can also be selective deprivation of REM sleep so if people are

selectively deprived of REM sleep what you can see is a rebound effect where if we're if we're denied of any particular

type of sleep our body tries to make up for that on subsequent nights so let me show you how this would work

so this is a data from uh from a num from a same person over multiple successive nights of a sleep deprivation

study this is a a rim a deprivation study where basically they go into a sleep lab there's a research assistant

who's there who stays up and monitors the person all night and basically what happens is they're hooked up to an EEG

and each time the person when they fall asleep when they get close to REM the the research assistant comes in and

wakes them up right so each of these red bars indicates an Awakening where the research assistant has to go in and wake

the person up so notice that on night one when they go in they're woken up a little after

midnight because they're getting they're hitting REM sleep a person is awakened for a few minutes they go back to sleep

they quickly get back to Rim the ra has to come back in and wake them up again so a little bit of time goes by they

have period of Awakenings where they're getting to REM sleep pretty quickly and so the the research assistant has come

in and wake them up you see another kind of about here a little before 2 30 in the morning

here's another period where there are some Rim episodes all happening between three and three Thirty between 3 30 and

4 a period time goes by where the person isn't hitting rims and there's kind of this little burst of activity and by the

time we're getting close to six o'clock in the morning the research assistant is coming in quite frequently to wake the

participant up because they're getting to REM sleep very very quickly now notice that during night one they were

awakened 31 times by the research assistant same person now you know gets up at 6 30

they go about their day they come in the next day uh the next night they go to bed they're quickly hitting brim

episodes in uh day two right so uh they're getting some Grim Awakenings uh just before one o'clock here's some

between 1 30 and 2 between 2 30 and 3 between 3 30 and 4 and so on so night two they're 51 awake and it's right

after being denied REM sleep during the first night their body basically is trying to bounce back and get a lot of

rim on night too right and things get even worse on night three when they now are awakened 64 times during night three

and this is a typical pattern if we're deprived any particular type of sleep our body is going to work really hard to

try to get back to that it's this rebound effect same thing happens if we're denied uh like stage four sleep

for example if we're woken up each time we get stage four basically our body will work really hard to get back to

stage four as quickly as it can what are the impacts of sleep deprivation we've talked about some of

them but this is a relatively famous study that points out an interesting issue about sleep deprivation here we

have an experimental group and a control group who are the experimental group was deprived to sleep for one night

the experimental and then the next morning that both both groups performed at Cog of the task it had to do with

critical thinking the issue here if you look at the bar graph is the experimental group performed much more

poorly than the control group even after only being deprived to sleep for one night right so not a lot of sleep

deprivation just one night of being kept away the experimental group performed

significantly worse than the control group on the critical thinking test but they said they had actually worked

harder in terms of their effort their concentration and thought they had performed better

right the reason why I wanted to point this out is that this is going to allude one of the one of the crucial issues

that we see is that when people experience sleep deprivation what typically happens is they don't even

recognize right what the impact is for their own behavior right they don't see it as being that big of a deal right

they don't see it as really impairing their abilities