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Episode
107

Sleep

First published on
November 17, 2020
How Stuff Works
-
17
minutes
Sleep
The Human Body
Natural world

Humans will spend from a quarter to a third of our lives sleeping.

But what actually happens when we sleep? Why do we need to sleep? How does it work?

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Transcript

[00:00:00] Hello, hello hello, and welcome to English Learning for Curious Minds, by Leonardo English. 

[00:00:12] The show where you can listen to fascinating stories, and learn weird and wonderful things about the world at the same time as improving your English.

[00:00:22] I'm Alastair Budge and today we are going to be talking about How We Sleep.

[00:00:29] Sleep is something that everyone in the world does, every single day, or at least we should do it every single day. 

[00:00:37] Indeed, we will all spend anywhere from a quarter to a third of our entire lives asleep.

[00:00:45] Yet there is still quite a lot of mystery about what actually happens when we sleep, and why we sleep.

[00:00:53] So, that is what we’re going to be talking about today, I hope it’ll be an interesting one.

[00:00:59] Sleep is an activity that has mystified people throughout the course of human history. 

[00:01:08] Not just every human, but also every animal, needs to sleep, at least once every 24 hours.

[00:01:16] Humans normally sleep in one go, all at once, while other animals, dogs for example, tend to sleep in shorter periods, multiple times a day.

[00:01:28] We are hardwired to do this, we need to sleep, there’s no way of getting around the fact that after a certain period of time, no matter how much coffee you might have drunk or other stimulants that you might have consumed, your body is going to need to sleep.

[00:01:46] But why do we need to do this? 

[00:01:49] What biological reason is there that causes us to need to sleep?

[00:01:55] In fact, the answer to this question has eluded scientists for centuries. 

[00:02:01] We still don’t know exactly what function sleep plays, we don’t know exactly why we sleep.

[00:02:09] We do know that there must be a very good reason for it.

[00:02:13] Firstly, from an evolutionary point of view, sleeping is when an animal is most vulnerable to attacks, if you’re asleep you have a limited ability to defend yourself or even realise that a predator is creeping up on you. 

[00:02:31] So if there weren’t a very good reason to do it, animals wouldn’t have developed the biological requirement to sleep.

[00:02:40] Secondly, we know that we normally feel a lot better after we sleep. We feel refreshed, re-energised, and ready for the day. 

[00:02:50] So something good must be happening.

[00:02:53] Conversely, if you haven’t had enough sleep you feel tired, grumpy, unable to think clearly, and just generally, not very well.

[00:03:04] So if not sleeping is bad, and sleeping makes you feel better and refreshed, then it clearly plays an important role in our general wellbeing, even if we don’t know exactly what role that is.

[00:03:19] Before the 1950s, people used to think that the function of sleep was just for you to be completely still, completely passive, with your brain almost on standby, not doing anything. 

[00:03:35] While people didn’t know why this was important, they thought that a period of switching off was important, because of course everyone knows that you feel better after sleeping.

[00:03:49] As scientists started to do more research into why we sleep, it became clear that the brain is far from switched off, there is actually a lot of activity that is going on while we sleep, even though it may not look like it. 

[00:04:06] If you see someone asleep, it certainly doesn’t seem like there’s a lot going on - their eyes are closed, they aren’t moving, their heartbeat and breathing is slow.

[00:04:17] But beneath the surface, there’s a lot of activity happening.

[00:04:22] While we don’t know exactly what function sleep plays, it’s now believed that the brain is engaging in a number of different activities that are crucial for our quality of life. 

[00:04:34] While it’s hard to say exactly what sleep is doing just by analysing people sleeping, it’s easier to study the consequence of people not getting enough sleep and hypothesise, well, sleep must be doing something that stops people developing these problems.

[00:04:54] And as I’m sure you know, not getting enough sleep is linked to all manner of different negative health consequences, from heart problems to a risk of obesity, from a weakened immune system to depression and anxiety.

[00:05:10] It’s clear that we need to sleep to avoid these kinds of health conditions, but scientists still don’t know exactly why.

[00:05:20] What we do have some idea about though, is what happens to our bodies when we sleep, and the different stages of sleep.

[00:05:30] To an outside observer, it might seem like you just close your eyes and wake up several hours later, refreshed and re-energised.

[00:05:40] But our sleep is divided into two different categories of sleep, what’s called Rapid Eye Movement, or REM, sleep and non-REM sleep, and you can split this further to give four distinct stages of sleep, which are repeated throughout a normal night.

[00:06:01] The first stage of non-REM sleep is when you go from being awake to being asleep. 

[00:06:08] This normally isn’t an immediate process, you feel yourself fall towards sleep, and you drift off

[00:06:17] What’s happening to your body is that your brain is beginning to slow down, your muscles are starting to relax, and your eyes stop moving.

[00:06:28] This part normally lasts less than 5 minutes. This isn’t that it takes everyone only 5 minutes from when they start trying to go to sleep to falling asleep, for lots of people it takes a lot longer, but this period of actually falling asleep typically takes around 5 minutes.

[00:06:50] The second stage of non-REM sleep is the period of light sleep before you start to sleep deeply. 

[00:06:58] By this time your heartbeat and your breathing have slowed, your muscles have relaxed even more, and your eyes have completely stopped moving. 

[00:07:09] This stage normally lasts about an hour, and is the longest of the four stages of sleep.

[00:07:17] Then it’s on to stage 3, we’re still in the non-REM type here, and this is when everything slows to its slowest during the night. 

[00:07:28] It’s thought to be the part when you are most deeply asleep, it’s hardest to wake you, and if you are woken up during this part you won’t feel particularly refreshed.

[00:07:40] This stage only lasts for around 20 minutes in general.

[00:07:45] The final stage of sleep, stage 4, is REM sleep, rapid eye movement sleep.

[00:07:52] If you’ve been adding up the numbers now, this normally happens around 90 minutes after you fall asleep.

[00:08:00] Even though your eyes are still closed and you’re still very much asleep, your brain activity starts increasing again, and your eyes move around quickly, hence the name, Rapid Eye Movement.

[00:08:13] Your breathing becomes faster and less regular, and your muscles start to tighten, to be almost paralysed, unable to move.

[00:08:23] It’s during this phase of sleep that we dream. 

[00:08:27] Now, dreaming is too large a subject to cram into this one episode, so I think we’ll need to do another episode just on dreaming, but here’s an overview of some of the theories about why we dream, and what happens when we dream. 

[00:08:46] If sleep is still mysterious to us, dreaming is even more so. 

[00:08:52] There’s no obvious biological reason why we dream, and it's a magical experience that all humans share.

[00:09:01] The current theories about why we dream are mainly based around the fact that it helps us process our emotions. 

[00:09:11] Throughout history people have tried to interpret their dreams, and while most people now don’t believe that our dreams show us what’s going to happen in the future, they are a way of processing what has happened during the day, and often reflect emotions that we felt during that day.

[00:09:32] It’s thought that dreams happen because the brain creates random electrical activity, and the analytical part of our brain, the part that processes and interprets information, tries to process what’s going on. 

[00:09:51] We don't normally have any control over how our brains interpret this activity, which is why you can’t control what you want to dream about, it just happens.

[00:10:03] In a normal night’s sleep of between 7 and 9 hours we normally spend around 2 hours dreaming, but the most intense periods of the dream might only take a few minutes, with the most vivid and longest dreams normally taking place at the very end of our sleep, which is why we often wake up in the morning from a dream and it seems very real.

[00:10:30] Indeed, unless you wake up immediately after a dream, it’s normally forgotten. 

[00:10:37] 95% of dreams are believed to be forgotten, and there are some people who say that they never remember any dreams.

[00:10:47] So, dreams are complicated, both evolutionarily speaking why we dream, if indeed there is an evolutionary reason, and what actually happens when we dream.

[00:10:59] One thing you might be left wondering though is how do we know when we need to go to sleep?

[00:11:06] This is actually something that we do know, unlike why we sleep or why we dream.

[00:11:12] Our bodies regulate our sleep in two ways.

[00:11:15] Firstly, something called homeostasis

[00:11:18] It’s a technical term, but it’s essentially an internal timer on how long we’ve been awake for. 

[00:11:26] As you know, the longer you’ve been awake, the more you need to go to sleep. 

[00:11:30] Our bodies need a certain amount of sleep, depending on factors like our age, and homeostasis is what makes us feel tired if we haven’t slept enough, and eventually what sends our bodies to sleep if we are seriously sleep deprived.

[00:11:47] The other factor that regulates our sleep is the circadian alerting system, your body’s daily biological clock. 

[00:11:57] Our bodies are naturally programmed to be awake when it’s light outside, and we fall asleep more naturally when it’s dark outside. 

[00:12:07] There are, of course, lots of things that can alter this - from stimulants like caffeine and cigarettes to being exposed to light in the night time, there are lots of things that can disrupt our body’s natural rhythms, but we are hardwired, we are biologically programmed, to feel tired at certain times of the day, and having a sleep pattern that’s radically different to this, for example working night shifts, can be very difficult to adjust to.

[00:12:41] We’re going to end this episode with an idea about sleep that I became really interested in when I was a student, and it’s the concept of polyphasic sleep, of sleeping multiple times during the day, for short periods.

[00:12:58] As I said at the start of the episode, humans generally sleep all in one go. Other animals, such as dogs, sleep in smaller batches throughout the day.

[00:13:10] But what would happen if we slept in small batches, like dogs do?

[00:13:16] Indeed, this isn’t just a theory, it’s not just a ‘what if’ situation.

[00:13:21] It’s called polyphasic sleep.

[00:13:24] There are some famous people from history who were reportedly polyphasic sleepers, and the people who do it today claim that it’s an incredibly liberating life change, and it has a devoted following.

[00:13:40] The idea is that you can sleep for short periods of time throughout the day, meaning you end up sleeping a lot less than you would do if you slept just once during the night.

[00:13:51] To give you a working example, one idea of polyphasic sleep is to sleep once every 4 hours, but only for 20 minutes at a time. 

[00:14:02] This means that you end up sleeping for just 120 minutes, 2 hours, during every 24 hour period, which obviously means that you have a lot more time to do other things.

[00:14:16] Proponents of polyphasic sleep point at people such as Napoleon, Leonardo Da Vinci, and Nikolas Tesla, who were all supposed polyphasic sleepers. 

[00:14:28] The theory goes that if you get into the rhythm of sleeping polyphasically you can go to sleep immediately, and wake up feeling refreshed 20 minutes later, then have another 4 hours of being awake, then sleep again, wake up feeling refreshed, and this just goes on forever, in perpetuity.

[00:14:49] Although it’s quite an interesting concept, especially for those of us who think that there are never enough hours in the day, most serious sleep scientists are pretty wary of this, and there haven’t been any long term studies on the health effects of living and sleeping in this way. 

[00:15:09] Indeed, if you end up having 6 more waking hours every day but you drop dead 20 years earlier, I wonder how many people would still be interested in becoming polyphasic sleepers.

[00:15:25] OK then, that is it for this little look at How We Sleep.

[00:15:30] I hope it’s been an interesting one, that it’s shone a little light onto this crucial part of being a human, although it’s clear that there is a lot that we still don’t know.

[00:15:42] As always, I would love to know what you thought of this episode.

[00:15:46] Do you remember your dreams? 

[00:15:47] Have you ever dreamt in English, or in a foreign language? Have you tried polyphasic sleep?

[00:15:54] I’d love to know. The place to go for all of that is our community forum, which is at community.leonardoenglish.com

[00:16:02] You’ve been listening to English Learning for Curious Minds, by Leonardo English.

[00:16:07] I’m Alastair Budge, you stay safe, and I’ll catch you in the next episode. 

[END OF PODCAST]


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[00:00:00] Hello, hello hello, and welcome to English Learning for Curious Minds, by Leonardo English. 

[00:00:12] The show where you can listen to fascinating stories, and learn weird and wonderful things about the world at the same time as improving your English.

[00:00:22] I'm Alastair Budge and today we are going to be talking about How We Sleep.

[00:00:29] Sleep is something that everyone in the world does, every single day, or at least we should do it every single day. 

[00:00:37] Indeed, we will all spend anywhere from a quarter to a third of our entire lives asleep.

[00:00:45] Yet there is still quite a lot of mystery about what actually happens when we sleep, and why we sleep.

[00:00:53] So, that is what we’re going to be talking about today, I hope it’ll be an interesting one.

[00:00:59] Sleep is an activity that has mystified people throughout the course of human history. 

[00:01:08] Not just every human, but also every animal, needs to sleep, at least once every 24 hours.

[00:01:16] Humans normally sleep in one go, all at once, while other animals, dogs for example, tend to sleep in shorter periods, multiple times a day.

[00:01:28] We are hardwired to do this, we need to sleep, there’s no way of getting around the fact that after a certain period of time, no matter how much coffee you might have drunk or other stimulants that you might have consumed, your body is going to need to sleep.

[00:01:46] But why do we need to do this? 

[00:01:49] What biological reason is there that causes us to need to sleep?

[00:01:55] In fact, the answer to this question has eluded scientists for centuries. 

[00:02:01] We still don’t know exactly what function sleep plays, we don’t know exactly why we sleep.

[00:02:09] We do know that there must be a very good reason for it.

[00:02:13] Firstly, from an evolutionary point of view, sleeping is when an animal is most vulnerable to attacks, if you’re asleep you have a limited ability to defend yourself or even realise that a predator is creeping up on you. 

[00:02:31] So if there weren’t a very good reason to do it, animals wouldn’t have developed the biological requirement to sleep.

[00:02:40] Secondly, we know that we normally feel a lot better after we sleep. We feel refreshed, re-energised, and ready for the day. 

[00:02:50] So something good must be happening.

[00:02:53] Conversely, if you haven’t had enough sleep you feel tired, grumpy, unable to think clearly, and just generally, not very well.

[00:03:04] So if not sleeping is bad, and sleeping makes you feel better and refreshed, then it clearly plays an important role in our general wellbeing, even if we don’t know exactly what role that is.

[00:03:19] Before the 1950s, people used to think that the function of sleep was just for you to be completely still, completely passive, with your brain almost on standby, not doing anything. 

[00:03:35] While people didn’t know why this was important, they thought that a period of switching off was important, because of course everyone knows that you feel better after sleeping.

[00:03:49] As scientists started to do more research into why we sleep, it became clear that the brain is far from switched off, there is actually a lot of activity that is going on while we sleep, even though it may not look like it. 

[00:04:06] If you see someone asleep, it certainly doesn’t seem like there’s a lot going on - their eyes are closed, they aren’t moving, their heartbeat and breathing is slow.

[00:04:17] But beneath the surface, there’s a lot of activity happening.

[00:04:22] While we don’t know exactly what function sleep plays, it’s now believed that the brain is engaging in a number of different activities that are crucial for our quality of life. 

[00:04:34] While it’s hard to say exactly what sleep is doing just by analysing people sleeping, it’s easier to study the consequence of people not getting enough sleep and hypothesise, well, sleep must be doing something that stops people developing these problems.

[00:04:54] And as I’m sure you know, not getting enough sleep is linked to all manner of different negative health consequences, from heart problems to a risk of obesity, from a weakened immune system to depression and anxiety.

[00:05:10] It’s clear that we need to sleep to avoid these kinds of health conditions, but scientists still don’t know exactly why.

[00:05:20] What we do have some idea about though, is what happens to our bodies when we sleep, and the different stages of sleep.

[00:05:30] To an outside observer, it might seem like you just close your eyes and wake up several hours later, refreshed and re-energised.

[00:05:40] But our sleep is divided into two different categories of sleep, what’s called Rapid Eye Movement, or REM, sleep and non-REM sleep, and you can split this further to give four distinct stages of sleep, which are repeated throughout a normal night.

[00:06:01] The first stage of non-REM sleep is when you go from being awake to being asleep. 

[00:06:08] This normally isn’t an immediate process, you feel yourself fall towards sleep, and you drift off

[00:06:17] What’s happening to your body is that your brain is beginning to slow down, your muscles are starting to relax, and your eyes stop moving.

[00:06:28] This part normally lasts less than 5 minutes. This isn’t that it takes everyone only 5 minutes from when they start trying to go to sleep to falling asleep, for lots of people it takes a lot longer, but this period of actually falling asleep typically takes around 5 minutes.

[00:06:50] The second stage of non-REM sleep is the period of light sleep before you start to sleep deeply. 

[00:06:58] By this time your heartbeat and your breathing have slowed, your muscles have relaxed even more, and your eyes have completely stopped moving. 

[00:07:09] This stage normally lasts about an hour, and is the longest of the four stages of sleep.

[00:07:17] Then it’s on to stage 3, we’re still in the non-REM type here, and this is when everything slows to its slowest during the night. 

[00:07:28] It’s thought to be the part when you are most deeply asleep, it’s hardest to wake you, and if you are woken up during this part you won’t feel particularly refreshed.

[00:07:40] This stage only lasts for around 20 minutes in general.

[00:07:45] The final stage of sleep, stage 4, is REM sleep, rapid eye movement sleep.

[00:07:52] If you’ve been adding up the numbers now, this normally happens around 90 minutes after you fall asleep.

[00:08:00] Even though your eyes are still closed and you’re still very much asleep, your brain activity starts increasing again, and your eyes move around quickly, hence the name, Rapid Eye Movement.

[00:08:13] Your breathing becomes faster and less regular, and your muscles start to tighten, to be almost paralysed, unable to move.

[00:08:23] It’s during this phase of sleep that we dream. 

[00:08:27] Now, dreaming is too large a subject to cram into this one episode, so I think we’ll need to do another episode just on dreaming, but here’s an overview of some of the theories about why we dream, and what happens when we dream. 

[00:08:46] If sleep is still mysterious to us, dreaming is even more so. 

[00:08:52] There’s no obvious biological reason why we dream, and it's a magical experience that all humans share.

[00:09:01] The current theories about why we dream are mainly based around the fact that it helps us process our emotions. 

[00:09:11] Throughout history people have tried to interpret their dreams, and while most people now don’t believe that our dreams show us what’s going to happen in the future, they are a way of processing what has happened during the day, and often reflect emotions that we felt during that day.

[00:09:32] It’s thought that dreams happen because the brain creates random electrical activity, and the analytical part of our brain, the part that processes and interprets information, tries to process what’s going on. 

[00:09:51] We don't normally have any control over how our brains interpret this activity, which is why you can’t control what you want to dream about, it just happens.

[00:10:03] In a normal night’s sleep of between 7 and 9 hours we normally spend around 2 hours dreaming, but the most intense periods of the dream might only take a few minutes, with the most vivid and longest dreams normally taking place at the very end of our sleep, which is why we often wake up in the morning from a dream and it seems very real.

[00:10:30] Indeed, unless you wake up immediately after a dream, it’s normally forgotten. 

[00:10:37] 95% of dreams are believed to be forgotten, and there are some people who say that they never remember any dreams.

[00:10:47] So, dreams are complicated, both evolutionarily speaking why we dream, if indeed there is an evolutionary reason, and what actually happens when we dream.

[00:10:59] One thing you might be left wondering though is how do we know when we need to go to sleep?

[00:11:06] This is actually something that we do know, unlike why we sleep or why we dream.

[00:11:12] Our bodies regulate our sleep in two ways.

[00:11:15] Firstly, something called homeostasis

[00:11:18] It’s a technical term, but it’s essentially an internal timer on how long we’ve been awake for. 

[00:11:26] As you know, the longer you’ve been awake, the more you need to go to sleep. 

[00:11:30] Our bodies need a certain amount of sleep, depending on factors like our age, and homeostasis is what makes us feel tired if we haven’t slept enough, and eventually what sends our bodies to sleep if we are seriously sleep deprived.

[00:11:47] The other factor that regulates our sleep is the circadian alerting system, your body’s daily biological clock. 

[00:11:57] Our bodies are naturally programmed to be awake when it’s light outside, and we fall asleep more naturally when it’s dark outside. 

[00:12:07] There are, of course, lots of things that can alter this - from stimulants like caffeine and cigarettes to being exposed to light in the night time, there are lots of things that can disrupt our body’s natural rhythms, but we are hardwired, we are biologically programmed, to feel tired at certain times of the day, and having a sleep pattern that’s radically different to this, for example working night shifts, can be very difficult to adjust to.

[00:12:41] We’re going to end this episode with an idea about sleep that I became really interested in when I was a student, and it’s the concept of polyphasic sleep, of sleeping multiple times during the day, for short periods.

[00:12:58] As I said at the start of the episode, humans generally sleep all in one go. Other animals, such as dogs, sleep in smaller batches throughout the day.

[00:13:10] But what would happen if we slept in small batches, like dogs do?

[00:13:16] Indeed, this isn’t just a theory, it’s not just a ‘what if’ situation.

[00:13:21] It’s called polyphasic sleep.

[00:13:24] There are some famous people from history who were reportedly polyphasic sleepers, and the people who do it today claim that it’s an incredibly liberating life change, and it has a devoted following.

[00:13:40] The idea is that you can sleep for short periods of time throughout the day, meaning you end up sleeping a lot less than you would do if you slept just once during the night.

[00:13:51] To give you a working example, one idea of polyphasic sleep is to sleep once every 4 hours, but only for 20 minutes at a time. 

[00:14:02] This means that you end up sleeping for just 120 minutes, 2 hours, during every 24 hour period, which obviously means that you have a lot more time to do other things.

[00:14:16] Proponents of polyphasic sleep point at people such as Napoleon, Leonardo Da Vinci, and Nikolas Tesla, who were all supposed polyphasic sleepers. 

[00:14:28] The theory goes that if you get into the rhythm of sleeping polyphasically you can go to sleep immediately, and wake up feeling refreshed 20 minutes later, then have another 4 hours of being awake, then sleep again, wake up feeling refreshed, and this just goes on forever, in perpetuity.

[00:14:49] Although it’s quite an interesting concept, especially for those of us who think that there are never enough hours in the day, most serious sleep scientists are pretty wary of this, and there haven’t been any long term studies on the health effects of living and sleeping in this way. 

[00:15:09] Indeed, if you end up having 6 more waking hours every day but you drop dead 20 years earlier, I wonder how many people would still be interested in becoming polyphasic sleepers.

[00:15:25] OK then, that is it for this little look at How We Sleep.

[00:15:30] I hope it’s been an interesting one, that it’s shone a little light onto this crucial part of being a human, although it’s clear that there is a lot that we still don’t know.

[00:15:42] As always, I would love to know what you thought of this episode.

[00:15:46] Do you remember your dreams? 

[00:15:47] Have you ever dreamt in English, or in a foreign language? Have you tried polyphasic sleep?

[00:15:54] I’d love to know. The place to go for all of that is our community forum, which is at community.leonardoenglish.com

[00:16:02] You’ve been listening to English Learning for Curious Minds, by Leonardo English.

[00:16:07] I’m Alastair Budge, you stay safe, and I’ll catch you in the next episode. 

[END OF PODCAST]


[00:00:00] Hello, hello hello, and welcome to English Learning for Curious Minds, by Leonardo English. 

[00:00:12] The show where you can listen to fascinating stories, and learn weird and wonderful things about the world at the same time as improving your English.

[00:00:22] I'm Alastair Budge and today we are going to be talking about How We Sleep.

[00:00:29] Sleep is something that everyone in the world does, every single day, or at least we should do it every single day. 

[00:00:37] Indeed, we will all spend anywhere from a quarter to a third of our entire lives asleep.

[00:00:45] Yet there is still quite a lot of mystery about what actually happens when we sleep, and why we sleep.

[00:00:53] So, that is what we’re going to be talking about today, I hope it’ll be an interesting one.

[00:00:59] Sleep is an activity that has mystified people throughout the course of human history. 

[00:01:08] Not just every human, but also every animal, needs to sleep, at least once every 24 hours.

[00:01:16] Humans normally sleep in one go, all at once, while other animals, dogs for example, tend to sleep in shorter periods, multiple times a day.

[00:01:28] We are hardwired to do this, we need to sleep, there’s no way of getting around the fact that after a certain period of time, no matter how much coffee you might have drunk or other stimulants that you might have consumed, your body is going to need to sleep.

[00:01:46] But why do we need to do this? 

[00:01:49] What biological reason is there that causes us to need to sleep?

[00:01:55] In fact, the answer to this question has eluded scientists for centuries. 

[00:02:01] We still don’t know exactly what function sleep plays, we don’t know exactly why we sleep.

[00:02:09] We do know that there must be a very good reason for it.

[00:02:13] Firstly, from an evolutionary point of view, sleeping is when an animal is most vulnerable to attacks, if you’re asleep you have a limited ability to defend yourself or even realise that a predator is creeping up on you. 

[00:02:31] So if there weren’t a very good reason to do it, animals wouldn’t have developed the biological requirement to sleep.

[00:02:40] Secondly, we know that we normally feel a lot better after we sleep. We feel refreshed, re-energised, and ready for the day. 

[00:02:50] So something good must be happening.

[00:02:53] Conversely, if you haven’t had enough sleep you feel tired, grumpy, unable to think clearly, and just generally, not very well.

[00:03:04] So if not sleeping is bad, and sleeping makes you feel better and refreshed, then it clearly plays an important role in our general wellbeing, even if we don’t know exactly what role that is.

[00:03:19] Before the 1950s, people used to think that the function of sleep was just for you to be completely still, completely passive, with your brain almost on standby, not doing anything. 

[00:03:35] While people didn’t know why this was important, they thought that a period of switching off was important, because of course everyone knows that you feel better after sleeping.

[00:03:49] As scientists started to do more research into why we sleep, it became clear that the brain is far from switched off, there is actually a lot of activity that is going on while we sleep, even though it may not look like it. 

[00:04:06] If you see someone asleep, it certainly doesn’t seem like there’s a lot going on - their eyes are closed, they aren’t moving, their heartbeat and breathing is slow.

[00:04:17] But beneath the surface, there’s a lot of activity happening.

[00:04:22] While we don’t know exactly what function sleep plays, it’s now believed that the brain is engaging in a number of different activities that are crucial for our quality of life. 

[00:04:34] While it’s hard to say exactly what sleep is doing just by analysing people sleeping, it’s easier to study the consequence of people not getting enough sleep and hypothesise, well, sleep must be doing something that stops people developing these problems.

[00:04:54] And as I’m sure you know, not getting enough sleep is linked to all manner of different negative health consequences, from heart problems to a risk of obesity, from a weakened immune system to depression and anxiety.

[00:05:10] It’s clear that we need to sleep to avoid these kinds of health conditions, but scientists still don’t know exactly why.

[00:05:20] What we do have some idea about though, is what happens to our bodies when we sleep, and the different stages of sleep.

[00:05:30] To an outside observer, it might seem like you just close your eyes and wake up several hours later, refreshed and re-energised.

[00:05:40] But our sleep is divided into two different categories of sleep, what’s called Rapid Eye Movement, or REM, sleep and non-REM sleep, and you can split this further to give four distinct stages of sleep, which are repeated throughout a normal night.

[00:06:01] The first stage of non-REM sleep is when you go from being awake to being asleep. 

[00:06:08] This normally isn’t an immediate process, you feel yourself fall towards sleep, and you drift off

[00:06:17] What’s happening to your body is that your brain is beginning to slow down, your muscles are starting to relax, and your eyes stop moving.

[00:06:28] This part normally lasts less than 5 minutes. This isn’t that it takes everyone only 5 minutes from when they start trying to go to sleep to falling asleep, for lots of people it takes a lot longer, but this period of actually falling asleep typically takes around 5 minutes.

[00:06:50] The second stage of non-REM sleep is the period of light sleep before you start to sleep deeply. 

[00:06:58] By this time your heartbeat and your breathing have slowed, your muscles have relaxed even more, and your eyes have completely stopped moving. 

[00:07:09] This stage normally lasts about an hour, and is the longest of the four stages of sleep.

[00:07:17] Then it’s on to stage 3, we’re still in the non-REM type here, and this is when everything slows to its slowest during the night. 

[00:07:28] It’s thought to be the part when you are most deeply asleep, it’s hardest to wake you, and if you are woken up during this part you won’t feel particularly refreshed.

[00:07:40] This stage only lasts for around 20 minutes in general.

[00:07:45] The final stage of sleep, stage 4, is REM sleep, rapid eye movement sleep.

[00:07:52] If you’ve been adding up the numbers now, this normally happens around 90 minutes after you fall asleep.

[00:08:00] Even though your eyes are still closed and you’re still very much asleep, your brain activity starts increasing again, and your eyes move around quickly, hence the name, Rapid Eye Movement.

[00:08:13] Your breathing becomes faster and less regular, and your muscles start to tighten, to be almost paralysed, unable to move.

[00:08:23] It’s during this phase of sleep that we dream. 

[00:08:27] Now, dreaming is too large a subject to cram into this one episode, so I think we’ll need to do another episode just on dreaming, but here’s an overview of some of the theories about why we dream, and what happens when we dream. 

[00:08:46] If sleep is still mysterious to us, dreaming is even more so. 

[00:08:52] There’s no obvious biological reason why we dream, and it's a magical experience that all humans share.

[00:09:01] The current theories about why we dream are mainly based around the fact that it helps us process our emotions. 

[00:09:11] Throughout history people have tried to interpret their dreams, and while most people now don’t believe that our dreams show us what’s going to happen in the future, they are a way of processing what has happened during the day, and often reflect emotions that we felt during that day.

[00:09:32] It’s thought that dreams happen because the brain creates random electrical activity, and the analytical part of our brain, the part that processes and interprets information, tries to process what’s going on. 

[00:09:51] We don't normally have any control over how our brains interpret this activity, which is why you can’t control what you want to dream about, it just happens.

[00:10:03] In a normal night’s sleep of between 7 and 9 hours we normally spend around 2 hours dreaming, but the most intense periods of the dream might only take a few minutes, with the most vivid and longest dreams normally taking place at the very end of our sleep, which is why we often wake up in the morning from a dream and it seems very real.

[00:10:30] Indeed, unless you wake up immediately after a dream, it’s normally forgotten. 

[00:10:37] 95% of dreams are believed to be forgotten, and there are some people who say that they never remember any dreams.

[00:10:47] So, dreams are complicated, both evolutionarily speaking why we dream, if indeed there is an evolutionary reason, and what actually happens when we dream.

[00:10:59] One thing you might be left wondering though is how do we know when we need to go to sleep?

[00:11:06] This is actually something that we do know, unlike why we sleep or why we dream.

[00:11:12] Our bodies regulate our sleep in two ways.

[00:11:15] Firstly, something called homeostasis

[00:11:18] It’s a technical term, but it’s essentially an internal timer on how long we’ve been awake for. 

[00:11:26] As you know, the longer you’ve been awake, the more you need to go to sleep. 

[00:11:30] Our bodies need a certain amount of sleep, depending on factors like our age, and homeostasis is what makes us feel tired if we haven’t slept enough, and eventually what sends our bodies to sleep if we are seriously sleep deprived.

[00:11:47] The other factor that regulates our sleep is the circadian alerting system, your body’s daily biological clock. 

[00:11:57] Our bodies are naturally programmed to be awake when it’s light outside, and we fall asleep more naturally when it’s dark outside. 

[00:12:07] There are, of course, lots of things that can alter this - from stimulants like caffeine and cigarettes to being exposed to light in the night time, there are lots of things that can disrupt our body’s natural rhythms, but we are hardwired, we are biologically programmed, to feel tired at certain times of the day, and having a sleep pattern that’s radically different to this, for example working night shifts, can be very difficult to adjust to.

[00:12:41] We’re going to end this episode with an idea about sleep that I became really interested in when I was a student, and it’s the concept of polyphasic sleep, of sleeping multiple times during the day, for short periods.

[00:12:58] As I said at the start of the episode, humans generally sleep all in one go. Other animals, such as dogs, sleep in smaller batches throughout the day.

[00:13:10] But what would happen if we slept in small batches, like dogs do?

[00:13:16] Indeed, this isn’t just a theory, it’s not just a ‘what if’ situation.

[00:13:21] It’s called polyphasic sleep.

[00:13:24] There are some famous people from history who were reportedly polyphasic sleepers, and the people who do it today claim that it’s an incredibly liberating life change, and it has a devoted following.

[00:13:40] The idea is that you can sleep for short periods of time throughout the day, meaning you end up sleeping a lot less than you would do if you slept just once during the night.

[00:13:51] To give you a working example, one idea of polyphasic sleep is to sleep once every 4 hours, but only for 20 minutes at a time. 

[00:14:02] This means that you end up sleeping for just 120 minutes, 2 hours, during every 24 hour period, which obviously means that you have a lot more time to do other things.

[00:14:16] Proponents of polyphasic sleep point at people such as Napoleon, Leonardo Da Vinci, and Nikolas Tesla, who were all supposed polyphasic sleepers. 

[00:14:28] The theory goes that if you get into the rhythm of sleeping polyphasically you can go to sleep immediately, and wake up feeling refreshed 20 minutes later, then have another 4 hours of being awake, then sleep again, wake up feeling refreshed, and this just goes on forever, in perpetuity.

[00:14:49] Although it’s quite an interesting concept, especially for those of us who think that there are never enough hours in the day, most serious sleep scientists are pretty wary of this, and there haven’t been any long term studies on the health effects of living and sleeping in this way. 

[00:15:09] Indeed, if you end up having 6 more waking hours every day but you drop dead 20 years earlier, I wonder how many people would still be interested in becoming polyphasic sleepers.

[00:15:25] OK then, that is it for this little look at How We Sleep.

[00:15:30] I hope it’s been an interesting one, that it’s shone a little light onto this crucial part of being a human, although it’s clear that there is a lot that we still don’t know.

[00:15:42] As always, I would love to know what you thought of this episode.

[00:15:46] Do you remember your dreams? 

[00:15:47] Have you ever dreamt in English, or in a foreign language? Have you tried polyphasic sleep?

[00:15:54] I’d love to know. The place to go for all of that is our community forum, which is at community.leonardoenglish.com

[00:16:02] You’ve been listening to English Learning for Curious Minds, by Leonardo English.

[00:16:07] I’m Alastair Budge, you stay safe, and I’ll catch you in the next episode. 

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