Rem sleep brain waves

Stages of Sleep – Introduction to Psychology & Neuroscience

By the end of this section, you will be able to:

Differentiate between REM and non-REM sleep
Describe the differences between the three stages of non-REM sleep
Understand the role that REM and non-REM sleep play in learning and memory

Sleep is not a uniform state of being. Instead, sleep is composed of several different stages that can be differentiated from one another by the patterns of brain wave activity that occur during each stage. These changes in brain wave activity can be visualized using EEG and are distinguished from one another by both the frequency and amplitude of brain waves (Figure SC.7). Sleep can be divided into two different general phases: REM sleep and non-REM (NREM) sleep. Rapid eye movement (REM) sleep is characterized by darting movements of the eyes under closed eyelids. Brain waves during REM sleep appear very similar to brain waves during wakefulness. In contrast, non-REM (NREM) sleep is subdivided into three stages distinguished from each other and from wakefulness by characteristic patterns of brain waves. The first three stages of sleep are NREM sleep, while the fourth and final stage of sleep is REM sleep. In this section, we will discuss each of these stages of sleep and their associated patterns of brain wave activity.

Figure SC.7 Brainwave activity changes dramatically across the different stages of sleep. (credit “sleeping”: modification of work by Ryan Vaarsi)

NREM Stages of Sleep

The first stage of NREM sleep is known as stage 1 sleep. Stage 1 sleep is a transitional phase that occurs between wakefulness and sleep, the period during which we drift off to sleep. During this time, there is a slowdown in both the rates of respiration and heartbeat. In addition, stage 1 sleep involves a marked decrease in both overall muscle tension and core body temperature.

In terms of brain wave activity, stage 1 sleep is associated with both alpha and theta waves. The early portion of stage 1 sleep produces alpha waves, which are relatively low frequency (8–13Hz), high amplitude patterns of electrical activity (waves) that become synchronized (Figure SC.8). This pattern of brain wave activity resembles that of someone who is very relaxed, yet awake. As an individual continues through stage 1 sleep, there is an increase in theta wave activity. Theta waves are even lower frequency (4–7 Hz), higher amplitude brain waves than alpha waves. It is relatively easy to wake someone from stage 1 sleep; in fact, people often report that they have not been asleep if they are awoken during stage 1 sleep.

Figure SC.8 Brainwave activity changes dramatically across the different stages of sleep.

As we move into stage 2 sleep, the body goes into a state of deep relaxation. Theta waves still dominate the activity of the brain, but they are interrupted by brief bursts of activity known as sleep spindles (Figure SC. 9). A sleep spindle is a rapid burst of higher frequency brain waves that may be important for learning and memory (Fogel & Smith, 2011; Poe, Walsh, & Bjorness, 2010). In addition, the appearance of K-complexes is often associated with stage 2 sleep. A K-complex is a very high amplitude pattern of brain activity that may in some cases occur in response to environmental stimuli. Thus, K-complexes might serve as a bridge to higher levels of arousal in response to what is going on in our environments (Halász, 1993; Steriade & Amzica, 1998).

Figure SC.9 Stage 2 sleep is characterized by the appearance of both sleep spindles and K-complexes.

Stage 3 is often referred to as deep sleep or slow-wave sleep because this stage is characterized by low frequency (less than 3 Hz), high amplitude delta waves (Figure SC.10). During this time, an individual’s heart rate and respiration slow dramatically. It is much more difficult to awaken someone from sleep during stage 3 than during earlier stages. Interestingly, individuals who have increased levels of alpha brain wave activity (more often associated with wakefulness and transition into stage 1 sleep) during stage 3 often report that they do not feel refreshed upon waking, regardless of how long they slept (Stone, Taylor, McCrae, Kalsekar, & Lichstein, 2008). It is worth noting that sometimes you may see slow-wave sleep divided into two stages, rather than just one. Previously, researchers distinguished between these two stages as being characterized by increased delta waves. However, it is now accepted as a single stage, Stage 3, known as slow-wave sleep.

Figure SC.10 (a) Delta waves, which are low frequency and high amplitude, characterize (b) slow-wave stage 3 sleep.

REM Sleep

As mentioned earlier, REM sleep is marked by rapid movements of the eyes. The brain waves associated with this stage of sleep are very similar to those observed when a person is awake, as shown in Figure SC.11, and this is the period of sleep in which dreaming occurs. It is also associated with paralysis of muscle systems in the body with the exception of those that make circulation and respiration possible. Therefore, no movement of voluntary muscles occurs during REM sleep in a normal individual; REM sleep is often referred to as paradoxical sleep because of this combination of high brain activity and lack of muscle tone. Like NREM sleep, REM has been implicated in various aspects of learning and memory (Wagner, Gais, & Born, 2001; Siegel, 2001).

Figure SC.11 (a) A period of rapid eye movement is marked by the short red line segment. The brain waves associated with REM sleep, outlined in the red box in (a), look very similar to those seen (b) during wakefulness.

If people are deprived of REM sleep and then allowed to sleep without disturbance, they will spend more time in REM sleep in what would appear to be an effort to recoup the lost time in REM. This is known as the REM rebound, and it suggests that REM sleep is also homeostatically regulated. Aside from the role that REM sleep may play in processes related to learning and memory, REM sleep may also be involved in emotional processing and regulation. In such instances, REM rebound may actually represent an adaptive response to stress in nondepressed individuals by suppressing the emotional salience of aversive events that occurred in wakefulness (Suchecki, Tiba, & Machado, 2012). Sleep deprivation in general is associated with a number of negative consequences (Brown, 2012).

The hypnogram below (Figure SC.12) shows a person’s passage through the stages of sleep.

Figure SC.12 A hypnogram is a diagram of the stages of sleep as they occur during a period of sleep. This hypnogram illustrates how an individual moves through the various stages of sleep.

View this video about the various stages of sleep to learn more.

Dreams

Dreams and their associated meanings vary across different cultures and periods of time. By the late 19th century, German psychiatrist Sigmund Freud had become convinced that dreams represented an opportunity to gain access to the unconscious. By analyzing dreams, Freud thought people could increase self-awareness and gain valuable insight to help them deal with the problems they faced in their lives. Freud made distinctions between the manifest content and the latent content of dreams. Manifest content is the actual content, or storyline, of a dream. Latent content, on the other hand, refers to the hidden meaning of a dream. For instance, if a woman dreams about being chased by a snake, Freud might have argued that this represents the woman’s fear of sexual intimacy, with the snake serving as a symbol of a man’s penis.

Freud was not the only theorist to focus on the content of dreams. The 20th century Swiss psychiatrist Carl Jung believed that dreams allowed us to tap into the collective unconscious. The collective unconscious, as described by Jung, is a theoretical repository of information he believed to be shared by everyone. According to Jung, certain symbols in dreams reflected universal archetypes with meanings that are similar for all people regardless of culture or location.

The sleep and dreaming researcher Rosalind Cartwright, however, believes that dreams simply reflect life events that are important to the dreamer. Unlike Freud and Jung, Cartwright’s ideas about dreaming have found empirical support. For example, she and her colleagues published a study in which women going through divorce were asked several times over a five month period to report the degree to which their former spouses were on their minds. These same women were awakened during REM sleep in order to provide a detailed account of their dream content. There was a significant positive correlation between the degree to which women thought about their former spouses during waking hours and the number of times their former spouses appeared as characters in their dreams (Cartwright, Agargun, Kirkby, & Friedman, 2006). Recent research (Horikawa, Tamaki, Miyawaki, & Kamitani, 2013) has uncovered new techniques by which researchers may effectively detect and classify the visual images that occur during dreaming by using fMRI for neural measurement of brain activity patterns, opening the way for additional research in this area.

Alan Hobson, a neuroscientist, is credited for developing activation-synthesis theory of dreaming. Early versions of this theory proposed that dreams were not the meaning-filled representations of angst proposed by Freud and others, but were rather the result of our brain attempting to make sense of (“synthesize”) the neural activity (“activation”) that was happening during REM sleep. Recent adaptations (e.g., Hobson, 2002) continue to update the theory based on accumulating evidence. For example, Hobson (2009) suggests that dreaming may represent a state of protoconsciousness. In other words, dreaming involves constructing a virtual reality in our heads that we might use to help us during wakefulness. Among a variety of neurobiological evidence, John Hobson cites research on lucid dreams as an opportunity to better understand dreaming in general. Lucid dreams are dreams in which certain aspects of wakefulness are maintained during a dream state. In a lucid dream, a person becomes aware of the fact that they are dreaming, and as such, they can control the dream’s content (LaBerge, 1990).

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Stages of Sleep | Introduction to Psychology

Learning Objectives

Differentiate between REM and non-REM sleep
Describe the stages of sleep

Sleep is not a uniform state of being. Instead, sleep is composed of several different stages that can be differentiated from one another by the patterns of brain wave activity that occur during each stage. These changes in brain wave activity can be visualized using EEG and are distinguished from one another by both the frequency and amplitude of brain waves. Sleep can be divided into two different general phases: REM sleep and non-REM (NREM) sleep. Rapid eye movement (REM) sleep is characterized by darting movements of the eyes under closed eyelids. Brain waves during REM sleep appear very similar to brain waves during wakefulness. In contrast, non-REM (NREM) sleep is subdivided into three stages distinguished from each other and from wakefulness by characteristic patterns of brain waves. The first three stages of sleep are NREM sleep, while the fourth and final stage of sleep is REM sleep. In this section, we will discuss each of these stages of sleep and their associated patterns of brain wave activity.

[Note that psychologists originally identified four stages of non-REM sleep, but these were revised in 2008, resulting in just three distinct phases of NREM sleep. You will see that stage 3 of NREM sleep is sometimes presented as both stage 3 and stage 4 in various texts.]

NREM Stages of Sleep

In terms of brain wave activity, stage 1 sleep is associated with both alpha and theta waves. The early portion of stage 1 sleep produces alpha waves, which are relatively low frequency (8–13Hz), high amplitude patterns of electrical activity (waves) that become synchronized. This pattern of brain wave activity resembles that of someone who is very relaxed, yet awake. As an individual continues through stage 1 sleep, there is an increase in theta wave activity. Theta waves are even lower frequency (4–7 Hz), higher amplitude brain waves than alpha waves. It is relatively easy to wake someone from stage 1 sleep; in fact, people often report that they have not been asleep if they are awoken during stage 1 sleep.

Figure 1. Brainwave activity changes dramatically across the different stages of sleep.

As we move into stage 2 sleep, the body goes into a state of deep relaxation. Theta waves still dominate the activity of the brain, but they are interrupted by brief bursts of activity known as sleep spindles (Figure 3). A sleep spindle is a rapid burst of higher frequency brain waves that may be important for learning and memory (Fogel & Smith, 2011; Poe, Walsh, & Bjorness, 2010). In addition, the appearance of K-complexes is often associated with stage 2 sleep. A K-complex is a very high amplitude pattern of brain activity that may in some cases occur in response to environmental stimuli. Thus, K-complexes might serve as a bridge to higher levels of arousal in response to what is going on in our environments (Halász, 1993; Steriade & Amzica, 1998).

Figure 3. Stage 2 sleep is characterized by the appearance of both sleep spindles and K-complexes.

Stage 3 of sleep is often referred to as deep sleep or slow-wave sleep because these stages are characterized by low frequency (less than 3 Hz), high amplitude delta waves (Figure 4). During this time, an individual’s heart rate and respiration slow dramatically. It is much more difficult to awaken someone from sleep during stage 3 than during earlier stages. Interestingly, individuals who have increased levels of alpha brain wave activity (more often associated with wakefulness and transition into stage 1 sleep) during stage 3 often report that they do not feel refreshed upon waking, regardless of how long they slept (Stone, Taylor, McCrae, Kalsekar, & Lichstein, 2008).

Figure 4. Delta waves, which are low frequency and high amplitude, characterize slow-wave stage 3 sleep.

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REM Sleep

As mentioned earlier, REM sleep is marked by rapid movements of the eyes. The brain waves associated with this stage of sleep are very similar to those observed when a person is awake, as shown in Figure 5, and this is the period of sleep in which dreaming occurs. It is also associated with paralysis of muscle systems in the body with the exception of those that make circulation and respiration possible. Therefore, no movement of voluntary muscles occurs during REM sleep in a normal individual; REM sleep is often referred to as paradoxical sleep because of this combination of high brain activity and lack of muscle tone. Like NREM sleep, REM has been implicated in various aspects of learning and memory (Wagner, Gais, & Born, 2001), although there is disagreement within the scientific community about how important both NREM and REM sleep are for normal learning and memory (Siegel, 2001).

Figure 5. A period of rapid eye movement is marked by the short red line segment. The brain waves associated with REM sleep, outlined in the red box, look very similar to those seen during wakefulness.

Figure 6. This hypnogram illustrates how an individual moves through the various stages of sleep. Deeper NREM sleep occurs early on in the night, while the duration of REM sleep increases as the night progresses.

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Think It Over

Researchers believe that one important function of sleep is to facilitate learning and memory. How does knowing this help you in your college studies? What changes could you make to your study and sleep habits to maximize your mastery of the material covered in class?

Glossary

alpha wave: type of relatively low frequency, relatively high amplitude brain wave that becomes synchronized; characteristic of the beginning of stage 1 sleep

delta wave: type of low frequency, high amplitude brain wave characteristic of stage 3 sleep

K-complex: very high amplitude pattern of brain activity associated with stage 2 sleep that may occur in response to environmental stimuli

non-REM (NREM): period of sleep outside periods of rapid eye movement (REM) sleep

rapid eye movement (REM) sleep: period of sleep characterized by brain waves very similar to those during wakefulness and by darting movements of the eyes under closed eyelids

sleep spindle: rapid burst of high frequency brain waves during stage 2 sleep that may be important for learning and memory

stage 1 sleep: first stage of sleep; transitional phase that occurs between wakefulness and sleep; the period during which a person drifts off to sleep

stage 2 sleep: second stage of sleep; the body goes into deep relaxation; characterized by the appearance of sleep spindles

stage 3 sleep: third stage of sleep; deep sleep characterized by low frequency, high amplitude delta waves

theta wave: type of low frequency, low amplitude brain wave characteristic of the end of stage 1 sleep

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Sleep stages and the benefits of deep sleep

Sleep accounts for between one quarter and one third of a person's lifespan. A good night's sleep is just as important as regular exercise and a healthy diet. When you don't get quality sleep, your body suffers serious physiological consequences.

Sleep plays a role in the functioning of the endocrine and immune systems. During sleep, most body systems are in an anabolic state, helping to restore the immune, nervous, skeletal and muscle systems. nine0003

In this article, we will describe the stages of sleep and the benefits of deep sleep.

Stages of sleep

When you sleep, your brain cycles through the four stages of sleep. Stages 1 to 3 is what is considered non-rapid eye movement (NREM) sleep, also known as restful sleep. Stage 4 is rapid eye movement (REM) sleep, also known as active sleep or REM sleep.

NREM sleep occurs first and consists of three stages: N1, N2 and N3, the last of which is also called delta sleep or non-REM sleep. nine0003

REM sleep, also known as REM sleep, accounts for a minority of total sleep time. This is the main reason for dreams (or nightmares) and is associated with desynchronized and fast brain waves and eye movements.

The NREM/REM sleep cycle takes an average of 90 minutes and is repeated 4 to 6 times during a good night's sleep. The sleep cycle usually proceeds in the following order: first N1, then N2, then N3, then N2, and finally the REM phase. nine0003

REM sleep occurs when a person returns to stage 2 or 1 after deep sleep. Deep sleep (stage N3) is greater at the beginning of the night, while REM sleep increases in two cycles just before natural awakening.

Let's look at the 4 stages of sleep:

Stage 1

The first stage of the sleep cycle is the transition between wakefulness and sleep. During stage 1 sleep:
- Your brain slows down,
- Your heartbeat, your eye movements and your breathing slow down along with it.
- Your body relaxes and your muscles may twitch.
This short sleep period lasts five to ten minutes. At this time, the brain is still quite active and produces high-amplitude theta waves, which are slow brain waves originating primarily in the frontal lobes of the brain.
Stage 2

People spend approximately 50% of their total sleep time during NREM Phase 2, which lasts about 20 minutes per cycle. During stage 2 sleep:
- You become less aware of your surroundings,
- Your body temperature drops,
- Your eye movements stop, and
- Your breathing and heart rate become more regular.
The brain also begins to produce bursts of fast, rhythmic brain wave activity known as sleep spindles. At this stage, memory consolidation occurs. The brain collects, processes and filters new memories received from the previous day. The body then slows down in preparation for stage 3 NREM sleep and REM sleep, which are the stages of deep sleep. nine0003
Stage 3

Deep, slow brain waves known as delta waves begin to appear during phase 3 of non-REM sleep. This stage of sleep is also called delta sleep. This is a period of deep sleep, when any noise or activity in the environment may not wake the sleeping person. Getting enough NREM sleep in Stage 3 allows you to feel rested the next day. During phase 3 non-REM sleep:
- Your muscles are completely relaxed,
- Your blood pressure drops, your breathing slows down, and you fall into the deepest sleep.
During this stage of deep sleep, your body begins physical recovery. Meanwhile, your brain integrates declarative memories such as personal experiences and other things you've learned.
Stage 4

REM sleep begins approximately 90 minutes after falling asleep. Currently:
- Your brain is on fire,
- Your body is relaxed and immobile,
- Your breathing is fast and uneven,
- Your eyes are moving fast, and
- You begin to daydream.
During REM sleep, your brain activity most closely resembles that of your waking hours. However, your body is temporarily paralyzed. This is good, as it prevents you from realizing your dreams.

As in stage 3, memory consolidation also occurs during REM sleep. However, REM sleep is thought to be when emotions and emotional memories are processed and stored. Your brain also uses this time to solidify information, making it an important learning step. nine0003

Benefits of deep sleep

Brain glucose metabolism increases during deep sleep, supporting short and long term memory and general learning. Deep sleep also occurs when the pituitary gland releases important hormones such as human growth hormone, which leads to growth and development of the body. Other benefits of deep sleep include:

energy recovery,
cell regeneration,
increased blood flow to muscles,
stimulate growth and repair of tissues and bones, and
strengthen the immune system.

The study of the phase of long sleep confirms the holographic theory of consciousness

Consciousness cannot be localized in certain parts of the brain: it is a product of the dynamic integration of neurons, European neuropsychologists who study the phase of long sleep have established. The new data confirm the integrative hypothesis of consciousness, which goes back to the works of Alexander Luria and Lev Vygotsky. nine0003

Deep sleep, when consciousness “disappears”, and wakefulness, when it “returns”, are two modes of brain functioning, by comparing which one can approach the solution of one of the most important tasks of neuropsychology — to understand the processes responsible for the formation of consciousness.

Thus, the connection between dreams and REM sleep (which, as it turned out, accounts for the largest number of dreams that we remember), discovered in the early 50s of the last century in one of the laboratories of the University of Chicago, became one of the favorite objects of study by neuropsychologists (especially European ones), since it paradoxically combines the characteristics of deep sleep, when the brain functions as a “black box” with the input/output channels turned off, and the EEG activity characteristic of the waking brain. nine0003

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Meanwhile, the REM phase is not fully "unconscious": in this phase, a person can not only be aware of himself, but even control his behavior in the dream world. And recent experiments with MRI scans of the brains of hypnonauts, conducted in Germany, and even allowed to decode some elements of dreams, confirmed reality lucid dreams, no matter how paradoxical it may sound.

But what happens to the brain in the phase of slow-wave sleep (SMS), more precisely, in its second stage, when consciousness turns off, as well as in the third and fourth (deepest) stages of this phase?

PMS research is carried out by a team of diversified specialists from the cyclotron laboratory of the University of Liege (Belgium), the National Institute for Health and Medical Research at the Pierre and Marie Curie University (Paris) and the Institute of Geriatrics in Montreal (Canada), whose article "Hierarchical clustering of human brain activity in non-REM sleep" publishes Proceedings of the National Academy of Sciences .

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The authors of the article immediately point out the “fundamental difficulty in defining the boundaries of their research” in a situation where there is no elementary consensus on what exactly should be understood by the phenomenon of “consciousness”, not to mention how this phenomenon arises and is maintained when we are awake. Meanwhile, no definitions cancel the fact that in the phase of slow sleep, consciousness, whatever we understand by it, is either strongly suppressed or absent - in complete contrast to wakefulness. nine0003

It is possible that by comparing these two modes, one can come closer to understanding how exactly consciousness is formed, to understand how neuroactivity in the phase of non-REM sleep differs from the mode of wakefulness.

It looks like the chosen method has borne fruit:

the results of the study turned out to be quite paradoxical, and the neurophysiological "machinery" that accompanies the switching on and off of consciousness is more understandable.

According to the authors, the purpose of the study was to test the hypothesis of neuropsychologist Giulio Tononi about consciousness as the adaptive ability of the brain to dynamically integrate information flows. With the help of a new method that allows you to measure the exchange of signals between groups of neurons based on EEG and functional MRI data, brain activity was studied in 13 people who were in a state of slow sleep and wakefulness. nine0003

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In contrast to the local-functional approach, which connects certain and/or specifically switched structures of the brain with consciousness, Tononi's integrative model presents consciousness as a permanent dynamic process of neuron binding, instantly, within fractions of a second, changing neurophysiological localization (the “dynamic core” hypothesis) ). nine0003

Tononi's hypothesis is consistent with the observations of the neuropsychologist Alexander Luria (1902–1977), a student of the eminent Russian psychologist Lev Vygotsky (1896–1934), whose work greatly influenced the development of Western neuropsychology, and explains, for example, why the brain may persist in severe traumatic lesions. memory and higher mental functions. In this sense, consciousness can be compared to a hologram that does not disappear even if pieces are cut off from a photographic film on which a two-dimensional interference pattern, encoding a three-dimensional image, is imprinted. nine0003

Because of this similarity, the integrative hypothesis of consciousness is sometimes called the holographic hypothesis.

EEG and fMRI methods each have their own advantages and disadvantages in brain imaging.

EEG can track the electrical activity of the brain with millisecond resolution, but does a poor job of localizing this activity. Functional MRI, on the contrary, localizes the processes taking place in the tissues with pinpoint precision, but does so too slowly to present them in dynamics. Combining both methods using a special mathematical model, the authors of the article managed to trace how connections in the neural network of the brain are reconfigured during the slow phase of sleep - of course, not at the level of individual neurons (modern technology does not yet allow this), but at the level of groups of neurons (clusters). ), and compare the data with the picture obtained by the same method during the waking period. nine0003

The results were unexpected.

It turned out, for example, that during the phase of non-REM sleep, the exchange of information between neurons increases significantly, and does not fall. At the same time, the routing of the exchange looks different compared to the period when a person does not sleep: during FMS, the exchange of signals increases between small clusters of neurons grouped in one part of the brain, while communication with clusters located in other parts of the brain , falls. In other words, during FMS, large hierarchically organized neural networks with long connections between nodes connecting different parts of the brain are divided into smaller and independent modules grouped according to a “territorial” feature. nine0003

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Such a modular topology with a predominance of short links makes data integration difficult, which confirms the integrative hypothesis of consciousness, which “turns off” during FMS. In particular, she explains why dreams in the long phase are remembered much worse than in the REM phase, when consciousness is “on” (more precisely, even to say “collected”), as well as the phenomenon of sleepwalking, another specific manifestation of the long phase (after regaining consciousness , lunatics do not remember that in a dream they performed quasi-meaningful actions). nine0003

The disintegration of the neural network during the transition to sleep is a series of phase transitions between different configurations of neural connections, accompanied by the evolution of the brain wave landscape with the gradual displacement of fast rhythms by slower ones. These transitions correspond to the four stages of FMS - from the stage with a predominance of alpha and theta rhythms, to the fourth, deepest stage of non-REM sleep with a predominance of high-amplitude waves with a frequency of 2 Hz (delta waves).

Paradoxically, if by brain activity we mean the volume of information circulating between its subunits, then in the slowest delta stage the brain continues to be active, and even, as calculations have shown, more informationally active than during wakefulness, due to the reconfiguration of the neural network - increasing the number of short links between smaller nodes. During FMS, data exchange continues in these local "mini-networks" of the brain, so that the total amount of information processed does not decrease at a lower level of activity (delta rhythm). nine0003

In turn, another phase state of the brain — a “supernetwork” — corresponds to a different topology of the neural network and a different rhythmic pattern with a predominance of high-frequency waves, when the brain begins to process signals coming from outside.

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