Hello. My name is Theresa Lee and I'm a professor of psychology and neuroscience, and I'm here today to talk to you about the relationship between circadian rhythms and sleep, and in particular, how those relationships change across the lifespan and help us to understand why people sleep differently at different ages. So to begin with, I want to talk about what is your sleep pattern? Why is sleep so very important? We'll then talk about the relationship specifically between the daily rhythms and the things that change across the day and sleep, how sleep changes, and then why in particular adolescents have so much trouble with their sleep. So the very first thing I want you to do is just to read through this list of 15 questions. It's a survey, and answer in your own head true or false for each of these questions and keep a count of the number that you say are true. Now, I don't need to read these to you, so I'm just going to stop here for a minute and let you read these. Okay, so, did you answer yes to more than five of these questions? If you did, then you should not be driving today. It is a sign that you are sleep deprived. If you've answered yes to three or more, then you need to get a better night's sleep in the coming night but you're probably not endangering anyone. In fact, if you went into a sleep research clinic and they were to put you in a sleep center to measure your sleep and get an idea of whether you've had a sleep disruption, if you scored five or more on this kind of questions, they wouldn't let you drive home. They'd insist that you call someone to drive you home or they'd put you in a cab. What I want to talk about today is how do we end up in a position where we need something to wake us up every day? That we can't stay awake while we're listening to a lecture. That we fall asleep when we sit down to watch television. That this is a very typical pattern for many adults in America? A few more questions, and this really gets at the circadian aspect. That first set of questions really just gets you to think about, do I get enough sleep, but the circadian part, that is what time of day you sleep really matters as well. So, typically, how many hours a night do you sleep? Are you sleeping six hours, eight hours, four hours? What is your typical night? And you might think about this during the week versus the weekend because people often differ as I'll show you in a few minutes. Do you go to bed at a regular time most nights, and do you get up at a regular time most mornings? I just want to keep those ideas in mind. What's your typical pattern is and how much sleep you get, and when we go through this lecture, we'll come back to a point where you'll stop and ask yourself, "Am I doing all the things I need to do to have a healthy sleep pattern?" So first of all, lots of people try to tell us that we don't know why people sleep, that sleep isn't really necessary. I've had colleagues over the years who studied eating behavior or drinking behavior, and we know that those are critical, you'll die if you don't eat or drink but is sleep really necessary? You can find any number of media statements that say, no, sleep isn't really all that important or that used to. I'm here to tell you, yes, sleep is absolutely critical. You need to sleep just as much as you need to eat and drink and maintain an appropriate body temperature. If you go without eating or drinking for an extended period or if you're overly hot or overly cold, we know that that can lead to death. Well, not sleeping for an extended period also leads to death. But quite with these other basic drives and needs, the drive to sleep takes a while before... not sleeping takes a while to cause you serious harm. But very quickly, with only a night or two of not, of insufficient sleep or nights of no sleep at all, you begin to see deficits in your ability to function. Interestingly, the reason we need to sleep is at least in part for the same reasons we need to do these other three things, and that is to maintain an appropriate metabolic state. Sleep is clearly an important part of doing that. So what are the functions of sleep? I'm going to show you several theories that have been developed and just tell you a little bit about some of the kinds of data that support every one of them. One, to start with what I'll just say is that sleep has many functions. Now, the first one that lots of people have pointed out is that it is clearly adaptive, based on the idea that all forms of animals show sleep. In fact, all vertebrates sleep, that is, from fishes to primates. We sleep, but it's not just vertebrates. Insects go through rest and active phases and during the rest phases their metabolism is reduced and a variety of changes happen in their nervous systems, much like what we see in humans or other vertebrate animals. Cells even go through different metabolic functions and doing different things at different times of the day. So, sleep is adaptive, we believe, just because we have so much evidence that all living multi-cellular organisms do it. Plants rest and don't rest. Animals go through rest and activity and so on. We've often thought that sleep might be important for restoration and repair, and we think of that because of the fact that when we wake up we feel better. We also tend to sleep more when we're ill, so it appears to be important for helping us get over illness. It's clear that the brain undergoes changes in response to sleep. That when we're awake for an extended period of time, there are chemical changes in the brain which lead us to have the sense of sleepiness and the drive to actually get some sleep, and that during sleep those changes are undone. And it takes a certain amount of sleep to make that happen. Now in this lecture, I'm mostly going to talk about this from the perspective of humans because that's what you're interested in, but I have to tell you that it's true for other organisms as well. Even organisms that sleep much less than us, they need to sleep to undergo these kinds of physiological changes that seem to occur only during sleep and help repair and restore our brains and bodies. Is sleep important for adjusting metabolic needs? Well, this is really a very simple question because the answer is yes. When you're in the rest phase, a whole variety of organs and bodily functions go down, your body temperature goes down, and the brain undergoes a change to function in a different way than it normally does. Now, in this lecture, I'm not going to talk about those things because I know that other lecturers in this series have talked to you about the relationship between EEG changes and pharmacological changes in the brain that go on during sleep compared to during wakefulness, but many of those changes are related to changes in metabolism for the whole body as well. The last one that I always find fun is that sleep also helps us avoid bad things in the environment. This really relates in some ways back to the adaptive responses. If you don't need to be out running around in the world finding things to eat and drink, well then you don't have to worry about somebody, a predator, coming along and eating you or dislodging you from your home environment. So for most organisms, a particularly good reason to sleep is just to be quiet, save energy, and stay out of the way of bad things that can happen. There are a number of immediate effects that happen if you are sleepy and fatigued that demonstrate the impact of this on brain function. First of all, we have impaired reaction times. So for example, the ability to quickly move your foot from the gas pedal to the brake and stop because you see something move in front of you on the street is slowed when you are fatigued and feeling sleepy. It's slowed in part because you may not visually recognize what you've seen as quickly as you normally would. The visual system is actually firing more slowly and the recognition and attention that has to happen in the brain so that you can then make the reaction is slowed, and judgment is also often altered. So again with that example of something running across the road in front of you. Imagine that you don't correctly judge the distance between you and the object or the speed at which you're going and how fast you're approaching. So all of these things can lead to an increased likelihood of doing, not reacting appropriately particularly in an unexpected situation. We have problems with information processing and short-term memory. For students, this is really quite evident. If you're staying up very late, night after night, studying, for example during exam periods, you get into that exam and you know that you've read about topic X and you can't retrieve it. Your short-term memory, that memory for the things that you've most recently been working on and thinking about, you're not able to retrieve as quickly. Part of the reason for that is that memories are consolidated during sleep. So, if you've been studying and you didn't get some sleep, you actually didn't take advantage of a mechanism that helps store memories in a more permanent way in your brain. But it's also because with the fatigue, you're having a hard time processing that memory. Information processing refers to the ability to really deal with more complex problems. So you're taking that math test, you've practiced this kind of calculus problem a dozen times, and you know you need to work through it in a particular way but you're just not coming up with it because you're sleepy and fatigued. So I tell students very frequently, the best thing you can do before a test is get a good night's sleep because you will think better, you'll be able to retrieve what you know and work with it more effectively. We find that people who are sleep deprived and feeling fatigued have decreased ability to perform tasks, they have reduced vigilance and motivation. There are a variety of studies that have been done to examine this, but my favorite ones are those that have been done by the military because often people have to spend hours on a task that is very, very boring and you're looking for example, for something unusual to happen. So for example, the Navy was very involved in this because people sit in front of a radar screen and you've seen these in movies and TV if you haven't seen them in real life. You see a wand, for example, seeming to go across the screen, and as the radar is moving across space, when an object appears, it will appear on the screen as a blip. You can watch for hours and never see a blip. So if you're not vigilant, if you're not attending to that screen, you're not going to see something. But let's imagine that you're sleeping and you're vigilant, you're watching, you're watching, but your vision isn't as good. You don't notice the blip on the screen and your judgment is off. You judge that it's not actually a ship or you think it's just an accident and therefore you don't perform the appropriate task. Motivation comes into this, and that motivation is important for you to want to remain vigilant. Vigilance is hard to maintain for very long at a time. Our mind wanders, we tend to look around, and so it takes a good deal of self-awareness and motivation to remain vigilant to task and then to perform appropriately. The ability to do these things comes into play when we think about what truck drivers are doing when they drive through the night. They're tired, they need to remain motivated, to be vigilant about what's happening around them so that they can perform the task appropriately of driving their trucks. Same with ships and so forth. We've known for a good time that when people are sleepy and fatigued, they get moody. You're more likely to snap at your friends, to take what they say as meaning something different than they intended, that it's a negative response. People tend to become aggressive. And when we look at what goes on with teenagers and how their sleep is decreased during adolescence because of a change in the circadian timing of sleep, it's not too surprising that the sleep deprivation leads to moodiness and aggressive behaviors. Now, as we go through, if you have several nights where you're getting for example, less than six hours of sleep at night, our brain begins to try to find the time to sleep and you don't necessarily know that that's going on. It's not unusual for people to have what we describe as microsleeps. These are very brief, two to three seconds sleep episodes where the EEG shifts from an awake state to a light sleep state. People frequently don't know they're having these sleep episodes. They just know that you're sitting in a classroom and you've missed a couple of minutes of a lecture and you don't know how you did that because you're sitting there and you think you're paying attention. Or you're driving down the street and there's suddenly something in front of you and you didn't see it come. It can very well be that for two or three seconds, your mind has actually gone to sleep. Now, fatigue, this kind of level of fatigue interacts with alcohol in a very bad way. We know that if, from studies where we have people perform vigilance and reaction time tasks like I was previously describing, that when you've been awake for 18 hours, your performance looks as though you have a 0.05% blood alcohol concentration. Now, a 0.05% is legal and indeed it's quite legal for you to be awake for 18 hours and working for 18 hours. But you should realize that you are slightly impaired. You're driving home at the end of a day, probably in the dark, you've been up all day, doing things in the evening, and you're sleepy, you're tired. And so, your ability to react to things that happen around you is a little bit slowed compared to the way you were earlier in the day. Now, if you're awake for 24 hours, you are now have the performance level of a 0.1% blood alcohol concentration. Quote, you're over the 'legal limit'. You are now impaired. If you were actually had alcohol in your system that I could measure and you got stopped for driving in some erratic way, the police officer would be able to take you away, say that you couldn't drive any longer. We have no way of measuring yet how fatigued you are, but you need to be aware that if you've been awake that long, that you are as impaired as someone who has drank more alcohol than is legally allowed. On four hours of sleep, so you've been awake for 20 hours, one beer can have the impact of a six-pack. And so it's not surprising that we now find that there's a strong relationship between fatigue and even small amounts of alcohol and an increase in accident rates. Now, accidents are interesting because most of them happen between midnight and 6:00 am, particularly for people under 25. Now, part of that is because they're more likely to be out between midnight and 6:00 in the morning, but we think about all the people who work a evening shift and get off at midnight and then go home or people who work at night shift and perhaps are out driving, taxi drivers, EMS workers, truck drivers, et cetera. So you're not necessarily under 25, and again, in the midafternoon when you're over 60. So in a couple of minutes I'm going to show you how circadian rhythms interact with fatigue and sleep, and it will become clear to you why it is that between 6:00 am, between midnight and 6:00 am, all of us can suffer and that in the midafternoon some people will also suffer. When there are accidents due to fatigue and insufficient sleep, most often the driver is alone and most often the individual is a male. These two things are driven very much by our culture. It is appropriate that if a group goes out for example, doing something together for fun on a Friday night for example, that the last person dropping everybody off will be a young man and therefore he will be the person last in the car. Alone matters, if there are three or four people, even if there's one other person in the car, even if you have a microsleep as the driver, someone else will see things likely that are happening in front of you and will call out, "Oh, look out for that deer " and you'll know to brake. So, having another person in the car helps avoid accidents but at the end of the evening somebody is the last man standing and it is usually a man. There are a couple of reasons for that. One is that the culture expects the male to be the person to put, get everyone home safely and we'll see in a few minutes that especially for young men, it is the case that their sleep is more delayed relative to everyone else, so they're likely to be more awake later, but that doesn't matter if you're sleep deprived. Well we have these kinds of accidents where someone falls asleep often because of a microsleep. The vehicle tends to, people who see it say that it drifted off the road. Suddenly the person's driving perfectly fine and then the car veers off in one direction or another, and often they hit a stationary object. There are also rear-end and head-on collisions where people have crossed the line where you have two lanes passing one another, or you come to a light and you don't notice that the light is there and you roll into the back of other individual. In each of these cases, there's typically no evidence of braking or any kind of evasive maneuvers. So, alone, often between midnight and 6:00 in the morning, you drift off and hit something stationary, and I can't tell you how many, I see every week in the newspaper somebody who has died because of exactly that accident or they run into someone head-on. Again, often because someone fell asleep. So, how do we decide that these accidents are due to falling asleep at the wheel? The person, if they are not seriously injured or dead, will tell you they don't remember what happened. They don't remember going off the road. They don't know why they went off the road or why they crossed the median. In today's world where we've become very aware of not driving while drinking and having someone drive for us, many of these accidents are the ones that do cause serious injuries and/or fatalities and, in fact, about half of all fatalities due to driving today are thought to be related to someone falling asleep at the wheel because they were fatigued. There are a variety of people who are particularly at risk and these include young people who again, we're going to talk about in a few minutes why they're particularly sleep deprived, but they are. They also tend to be people who work shifts. The newest guy on the job or the newest woman in the nursing shift often has the night shift. So you're more likely to be driving home at night and being quite tired. Commercial drivers do a lot of their driving between midnight and 6:00 in the morning. There are a variety of reasons that people have undiagnosed and untreated sleep disorders such as sleep apnea which keeps them in a fatigued state all of the time. Business travelers are often traveling and crossing time zones and then needing to rent a car and drive and be doing these kinds of things and then the elderly. Well, as we'll see the elderly tend, as we get to be quite elderly, to have fragmented and disrupted sleep at night, which leaves us fatigued and needing sleep during the day. Interestingly, in all of these cases, these individuals are likely to be suffering from a combination of sleep deprivation and a timing disruption in when they sleep. In every case, these people are not sleeping well or at all perhaps at the time of day when humans have been evolved to sleep, which is during the dark and during the night. Okay, so we're going to take a break now, having wrapped up sort of why we need to sleep and the importance of those functions and we'll come back and talk about the rhythmic aspect of sleep.
