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 [link].
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 four stages distinguished from each other and from wakefulness by characteristic patterns of brain waves.
In this section, we will discuss each of these stages of sleep and their associated patterns of brain wave activity. Brainwave activity changes dramatically across the different 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 [link]. 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. 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 [link].
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. Stage 2 sleep is characterized by the appearance of both sleep spindles and K-complexes.
Stage 3 and stage 4 of sleep are often referred to as deep sleep or slow-wave sleep because these stages are characterized by low frequency up to 4 Hz , high amplitude delta waves [link]. It is much more difficult to awaken someone from sleep during stage 3 and stage 4 than during earlier stages. 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 [link] , 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.
At very slow levels, theta brain wave activity is a very relaxed state, representing the twilight zone between waking and sleep. Alpha brainwaves Hz. They are associated with a state of relaxation and represent the brain shifting into an idling gear, waiting to respond when needed.
If we close our eyes and begin picturing something peaceful, there is an increase in alpha brainwaves. Beta brainwaves 13 — 38 Hz are small, faster brainwaves associated with a state of mental, intellectual activity and outwardly focused concentration. This is basically state of alertness. Gamma brainwaves 39 — 42 Hz are the fastest and most subtle brain waves.
Gamma rhythms modulate perception and consciousness. Each of us, however, always has some degree of each of these brainwave bands present in different parts of our brain. If we are becoming drowsy, there are more delta and slow theta brainwaves creeping in. Some even propose that binaural beats could help you sleep better. A study found that a certain type of binaural beat helped some people achieve a meditative state. More research is need to learn about how it could be adapted for relaxation and stress reduction in the future.
Your brain produces five kinds of brain waves, each of which operate at a different speed. Some are very fast, while others are much slower. Theta waves are slower than gamma, beta, and alpha waves, but faster than delta waves.
There is still a lot to learn about the electrical activity of the brain. What we know so far about theta waves is that they help us learn, and perhaps one day, we will know more about how we can use this knowledge to improve our ability to relax and learn more effectively.
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