Eeg Sleep Architecture

[Debora Mccaffery]

Itis also critical to think about sleep quality and whether the time spent sleeping is actually restorative. Progressing smoothly multiple times through the sleep cycle, composed of four separate sleep stages, is a vital part of getting high-quality rest.

Sleep is not uniform. Instead, over the course of the night, your total sleep is made up of several rounds of the sleep cycle, which is composed of four individual stages. In a typical night, a person goes through four to six sleep cycles Trusted Source National Library of Medicine, Biotech InformationThe National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information.View Source . Not all sleep cycles are the same length, but on average they last about 90 minutes each.

There are four sleep stages, including one for rapid eye movement (REM) sleep and three that form non-REM (NREM) sleep. These stages are determined based on an analysis of brain activity during sleep, which shows distinct patterns that characterize each stage.

During N1 sleep, the body has not fully relaxed, though the body and brain activities start to slow with periods of brief movements. There are light changes in brain activity associated with falling asleep in this stage.

It is easy to wake someone up during this sleep stage, but if a person is not disturbed, they can move quickly into stage 2. As the night unfolds, an uninterrupted sleeper may not spend much more time in stage 1 as they move through further sleep cycles.

During stage 2, or N2, the body enters a more subdued state including a drop in temperature, relaxed muscles, and slowed breathing and heart rate. At the same time, brain waves show a new pattern and eye movement stops. On the whole, brain activity slows, but there are short bursts of activity Trusted Source National Library of Medicine, Biotech InformationThe National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information.View Source that actually help resist being woken up by external stimuli.

Stage 2 sleep can last for 10 to 25 minutes during the first sleep cycle, and each N2 stage can become longer during the night. Collectively, a person typically spends about half their sleep time in N2 sleep.

Stage 3 sleep is also known as N3 or deep sleep, and it is harder to wake someone up if they are in this phase. Muscle tone, pulse, and breathing rate decrease in N3 sleep as the body relaxes even further.

Experts believe that this stage is critical to restorative sleep, allowing for bodily recovery and growth. It may also bolster the immune system and other key bodily processes. Even though brain activity is reduced, there is evidence that deep sleep contributes to insightful thinking Trusted Source National Library of Medicine, Biotech InformationThe National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information.View Source , creativity Trusted Source National Library of Medicine, Biotech InformationThe National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information.View Source , and memory.

You spend the most time in deep sleep during the first half of the night. During the early sleep cycles, N3 stages commonly last for 20 to 40 minutes. As you continue sleeping, these stages get shorter, and more time gets spent in REM sleep instead.

During REM sleep, brain activity picks up, nearing levels seen when you are awake. At the same time, the body experiences atonia, which is a temporary paralysis of the muscles, with two exceptions: the eyes and the muscles that control breathing. Even though the eyes are closed, they can be seen moving quickly, which is how this stage gets its name.

REM sleep is believed to be essential to cognitive functions like memory Trusted Source UpToDateMore than 2 million healthcare providers around the world choose UpToDate to help make appropriate care decisions and drive better health outcomes. UpToDate delivers evidence-based clinical decision support that is clear, actionable, and rich with real-world insights.View Source , learning, and creativity Trusted Source National Library of Medicine, Biotech InformationThe National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information.View Source . REM sleep is known for the most vivid dreams, which is explained by the significant uptick in brain activity. Dreams can occur in any sleep stage, but they are less common and intense in the NREM periods.

Under normal circumstances, you do not enter a REM sleep stage until you have been asleep for about 90 minutes. As the night goes on, REM stages get longer, especially in the second half of the night. While the first REM stage may last only a few minutes, later stages can last for around an hour. In total, REM stages make up around 25% of sleep in adults.

Sleep stages are important because they allow the brain and body to recuperate and develop. Failure to obtain enough of both deep sleep and REM sleep may explain some of the profound consequences of insufficient sleep on thinking Trusted Source National Library of Medicine, Biotech InformationThe National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information.View Source , emotions, and physical health. Sleepers who are frequently awoken during earlier stages, such as people with sleep apnea, may struggle to properly cycle into these deeper sleep stages. People with insomnia may not get enough total sleep to accumulate the needed time in each stage.

While there is a typical pattern for sleep stages, there can be substantial individual variation based on a number of factors Trusted Source National Library of Medicine, Biotech InformationThe National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information.View Source .

A key step is to focus on improving your sleep hygiene, which refers to your sleep environment and sleep-related habits. Achieving a more consistent sleep schedule, getting natural daylight exposure, avoiding alcohol before bedtime, and eliminating noise and light disruptions can help you get uninterrupted sleep and promote proper alignment of your circadian rhythm. Your mattress, pillows, and sheets can also contribute to how comfortable your sleep environment is.

If you find that you have excessive daytime sleepiness or otherwise suspect that you might have a sleep disorder like sleep apnea, it is important to talk with a doctor who can most appropriately guide your care. Addressing underlying issues may pave the way for more complete and restorative sleep cycles.

When you've learned a significant amount of new information, an EEG will show more sleep spindles than is typical. That's one reason medical professionals believe sleep spindles show that the brain is processing memories.

Sleep architecture refers to the basic structural organization of normal sleep. There are two types of sleep, non-rapid eye-movement (NREM) sleep and rapid eye-movement (REM) sleep. NREM sleep is divided into stages 1, 2, 3, and 4, representing a continuum of relative depth. Each has unique characteristics including variations in brain wave patterns, eye movements, and muscle tone. Sleep cycles and stages were uncovered with the use of electroencephalographic (EEG) recordings that trace the electrical patterns of brain activity (Loomis et al., 1937; Dement and Kleitman, 1957a).

Over the course of a period of sleep, NREM and REM sleep alternate cyclically (Figure 2-1). The function of alternations between these two types of sleep is not yet understood, but irregular cycling and/or absent sleep stages are associated with sleep disorders (Zepelin et al., 2005). For example, instead of entering sleep through NREM, as is typical, individuals with narcolepsy enter sleep directly into REM sleep (Carskadon and Rechtschaffen, 2005).

The four stages of NREM sleep are each associated with distinct brain activity and physiology. Figure 2-2 shows the EEG patterns characteristic of the four NREM stages. Other instruments are used to track characteristic changes in eye movement and muscle tone.

Stage 2 sleep lasts approximately 10 to 25 minutes in the initial cycle and lengthens with each successive cycle, eventually constituting between 45 to 55 percent of the total sleep episode. An individual in stage 2 sleep requires more intense stimuli than in stage 1 to awaken. Brain activity on an EEG shows relatively low-voltage, mixed-frequency activity characterized by the presence of sleep spindles and K-complexes (Figure 2-2). It is hypothesized that sleep spindles are important for memory consolidation. Individuals who learn a new task have a significantly higher density of sleep spindles than those in a control group (Gais et al., 2002).

Sleep stages 3 and 4 are collectively referred to as slow-wave sleep (SWS), most of which occurs during the first third of the night. Each has distinguishing characteristics. Stage 3 lasts only a few minutes and constitutes about 3 to 8 percent of sleep. The EEG shows increased high-voltage, slow-wave activity (Figure 2-2).

The last NREM stage is stage 4, which lasts approximately 20 to 40 minutes in the first cycle and makes up about 10 to 15 percent of sleep. The arousal threshold is highest for all NREM stages in stage 4. This stage is characterized by increased amounts of high-voltage, slow-wave activity on the EEG (Carskadon and Dement, 2005).

In addition to the physiological changes listed in Table 2-1, there are other body system changes that occur during sleep. Generally, these changes are well tolerated in healthy individuals, but they may compromise the sometimes fragile balance of individuals with vulnerable systems, such as those with cardiovascular diseases (Parker and Dunbar, 2005). Physiological changes also occur in the following systems:

3a8082e126