Friday, June 4, 2010
Chapter 1: Introduction to Sleep
@ 2:08 AM
[Sleep is] the golden chain that ties health and our bodies together.
Thomas Dekker (1572-1623)
Why do we sleep? What exactly is happening when we are asleep? What is quality sleep? This chapter provides an introduction to the basic mechanics of sleep. The following chapter, Chapter 2: Hijacking Sleep, discusses about how we can harness the power of sleep to help us in learning.
Our minds exhibit certain brain waves all the time. These waves are produced by neurons activities in our brain and can be measured by electrodes attached to the scalp. This process is known as electroencephalography (EEG). The EEG reading can be used to determine the current state of mind of the subject. Below is an example of how an EEG reading looks like.
Diagram 1.1 EEG graph
You do not have to understand diagram. To put it simply, when we are alert and processing much information, our brainwave are more intense and when we are drowsy and switching off, our brainwave are less intense. When we are asleep, our brainwave patterns can be classified into 5 different stages by convention. Our brains transit from one stage to another frequently throughout our entire sleep cycle.
Below is a graph showing the state of sleep a typical person is in (in 8 hours of night's sleep). It may different from person to person.
Diagram 1.2 Typical sleep cycle pattern
This graph give us an idea of which stage of sleep are we at, given elapsed time into our sleep. By comparing the level of sleep we are in at a given time and the characteristic of the different stages of sleep, we can then understand the activities going on in our body and mind at the given time.
Below is a brief description of the characteristic of each of the stages of our sleep.
Stage 1: Drowsiness
Remember the feeling when you are switching off (and dreaming of your lala land) during lectures? This is the state of your mind you exhibit when we drift off into an altered state. At this stage, our brain exhibit slightly lower brainwaves called alpha brainwaves. We are awake at this stage but we exhibit several characteristics of sleep such as relaxed muscles, slow movement of eyes under the eyelids, and lower body temperatures, heart rate, and respiration rate. This stage would usually last 5 - 10 minutes before we enter a deeper stage of sleep.
Stage 2: Light Sleep
This stage is largely similar to that of stage 1, we are still easily woken up at this stage; subjects woken up at this stage may still claim that they were still awake. Here, our brains experience sudden bursts of brain activities and our brains exhibit K-Complexes brainwave patterns. This stage is characterised by further dip in body temperature and heart rate, however, eyes movement under eyelids cease.
Stage 3-4: Deep Sleep
At stage 3-4, our brainwaves reach their lowest frequency, exhibiting brainwaves alternating between the delta and theta brainwave patterns. At this stage, subjects are difficult to be awakened, and they may feel slightly disoriented up to several minutes should they be awakened. Here, the body restores energy and repairs itself. Blood flow to the brain is minimal while it is redirected to muscles, restoring physical energy and repairing damages. Research also shows that our body immune system also increases during deep sleep. This stage is characterised by the lowest point of body temperature, heart rate, blood pressure, and respiration.
Stage 5: Rapid Eye Movement (REM)
Dreams occur during REM and we have 3-5 REM cycles every night on average, lasting of 1.5 to 2 hours in a night’s sleep. During REM, our brains exhibit similar brainwave pattern of that in our waking state, thus there is no one specific brainwave pattern of one in REM sleep. The functions of REM sleep will be discussed in further details later.
From the graph, we can see that the first half of the sleep cycle is effectively deep sleep, suggesting that the body is repairing itself. The second half of the cycle is mostly REM sleep and the importance of this segment of the sleep cycle will be discussed in greater details in Chapter 2: Hijacking Sleep.
Thomas Dekker (1572-1623)
Why do we sleep? What exactly is happening when we are asleep? What is quality sleep? This chapter provides an introduction to the basic mechanics of sleep. The following chapter, Chapter 2: Hijacking Sleep, discusses about how we can harness the power of sleep to help us in learning.
Our minds exhibit certain brain waves all the time. These waves are produced by neurons activities in our brain and can be measured by electrodes attached to the scalp. This process is known as electroencephalography (EEG). The EEG reading can be used to determine the current state of mind of the subject. Below is an example of how an EEG reading looks like.
Diagram 1.1 EEG graph
You do not have to understand diagram. To put it simply, when we are alert and processing much information, our brainwave are more intense and when we are drowsy and switching off, our brainwave are less intense. When we are asleep, our brainwave patterns can be classified into 5 different stages by convention. Our brains transit from one stage to another frequently throughout our entire sleep cycle.
Below is a graph showing the state of sleep a typical person is in (in 8 hours of night's sleep). It may different from person to person.
Diagram 1.2 Typical sleep cycle pattern
This graph give us an idea of which stage of sleep are we at, given elapsed time into our sleep. By comparing the level of sleep we are in at a given time and the characteristic of the different stages of sleep, we can then understand the activities going on in our body and mind at the given time.
Below is a brief description of the characteristic of each of the stages of our sleep.
Stage 1: Drowsiness
Remember the feeling when you are switching off (and dreaming of your lala land) during lectures? This is the state of your mind you exhibit when we drift off into an altered state. At this stage, our brain exhibit slightly lower brainwaves called alpha brainwaves. We are awake at this stage but we exhibit several characteristics of sleep such as relaxed muscles, slow movement of eyes under the eyelids, and lower body temperatures, heart rate, and respiration rate. This stage would usually last 5 - 10 minutes before we enter a deeper stage of sleep.
Stage 2: Light Sleep
This stage is largely similar to that of stage 1, we are still easily woken up at this stage; subjects woken up at this stage may still claim that they were still awake. Here, our brains experience sudden bursts of brain activities and our brains exhibit K-Complexes brainwave patterns. This stage is characterised by further dip in body temperature and heart rate, however, eyes movement under eyelids cease.
Stage 3-4: Deep Sleep
At stage 3-4, our brainwaves reach their lowest frequency, exhibiting brainwaves alternating between the delta and theta brainwave patterns. At this stage, subjects are difficult to be awakened, and they may feel slightly disoriented up to several minutes should they be awakened. Here, the body restores energy and repairs itself. Blood flow to the brain is minimal while it is redirected to muscles, restoring physical energy and repairing damages. Research also shows that our body immune system also increases during deep sleep. This stage is characterised by the lowest point of body temperature, heart rate, blood pressure, and respiration.
Stage 5: Rapid Eye Movement (REM)
Dreams occur during REM and we have 3-5 REM cycles every night on average, lasting of 1.5 to 2 hours in a night’s sleep. During REM, our brains exhibit similar brainwave pattern of that in our waking state, thus there is no one specific brainwave pattern of one in REM sleep. The functions of REM sleep will be discussed in further details later.
From the graph, we can see that the first half of the sleep cycle is effectively deep sleep, suggesting that the body is repairing itself. The second half of the cycle is mostly REM sleep and the importance of this segment of the sleep cycle will be discussed in greater details in Chapter 2: Hijacking Sleep.