What Is Sleep Architecture?

Sleep architecture is the basic pattern of normal sleep. You experience two main types of sleep—rapid eye movement (REM) and non-rapid eye movement (NREM). NREM sleep has three different stages, all of which feature different depths of sleep and can be identified by experts through brain-wave patterns, eye movements, and muscle tone.

Structure

Sleep architecture allows experts to produce a picture of what your sleep looks like over the course of a night, taking into account various depths of sleep as well as coming out of sleep. It can be represented by a graph called a hypnogram, which is created with the use of an electroencephalogram (EEG).

Typically, you should go through four or five different sleep cycles during a given night, and each of the different cycles lasts for between about 90 minutes and two hours. Some cycles will contain all three phases of NREM sleep and REM sleep, but not all of them contain each phase.

NREM Stage 1 Sleep

In NREM stage 1, you've just drifted off to sleep. You're not consciously aware of your surroundings but it's easy to jar you awake—and if you are awakened, you may not even realize you'd fallen asleep. This phase is characterized by:

• Relaxing muscles
• Body temperature beginning to drop
• Slow side-to-side eye movements
• Brain waves transition from rhythmic alpha waves to mixed-frequency theta waves

NREM stage 1 sleep generally lasts for just five to 10 minutes. You may return to it a few times overnight but not necessarily in each cycle. The amount of time you spend in NREM 1 increases with age, making it harder to fall asleep and stay asleep.

NREM Stage 2 Sleep

Once you're fully asleep, you enter NREM stage 2. It's more difficult to awaken you during this phase, but brain waves show that a certain amount of vigilance remains. For instance, if you make a loud noise or whisper someone's name during this phase, EEG shows the brain responding with a distinctive wave called a K-complex. This phase is characterized by:

• Lack of eye movement
• A continued drop in body temperature
• More regular breathing and heart rate
• Rapid bursts of brain activity (sleep spindles on EEG) believed to indicate the brain is organizing and storing memories

In your first cycle through all of the sleep phases, NREM 2 lasts between 10 minutes and 25 minutes. It gets longer with each cycle, and it's common to spend about half the night in this phase. It may alternate with REM sleep for much of the night, without NREM stage 3 in between.

NREM Stage 3 Sleep

Also called deep sleep or slow-wave sleep, NREM stage 3 sleep is when it's hardest to wake you up. This phase is believed to be essential for restorative sleep, which is when your body repairs itself and allows you to awaken feeling refreshed. NREM 3 also appears to be important for memory and creativity.

This phase is characterized by:

• Increased relaxation
• Decreased pulse and breathing rate
• Less blood flow to the brain
• Release of growth hormone (for tissue repair)
• Increased immune-system activation
• Slow brain waves called delta waves

You spend more time in this phase early in the night, when it may last for up to 40 minutes. Later on, this phase gets shorter as REM phases get longer, and it may not be part of the later cycles at all. Also, you don't progress directly from NREM 3 to REM. From NREM 3, it's typical to go back into NREM 2 and then REM.

REM Sleep

Rapid eye movement (REM) sleep is the deepest state of sleep and is when you dream. Just as NREM 3 is when the body is restored, experts believe REM sleep is when the brain is restored and prepared for the next day. This phase is characterized by:

• Muscle immobility
• Increased breathing rate, heart rate, and blood pressure (daytime levels)
• Increased body temperature
• Bursts of rapid eye movements
• Increased brain activity
• Theta and slow alpha brain waves

Consistent interruptions to REM sleep can lead to a host of potential issues, such as sleep paralysis and an inability to retain new information. 

You may enter REM sleep between three and five times per night, about every 90 minutes, alternating with NREM 2. These phases become longer and more frequent during the latter part of the night, eventually lasting up to around 30 minutes.

Influencing Factors

While it's simpler to talk about what's "typical" of sleep architecture, these patterns can vary greatly from one person to the next, and in the same person over time. Sleep architecture is influenced by a wide variety of factors, including:

• Age
• Sex
• The time of day you sleep
• How much time you allocate to sleep
• Use of caffeine, nicotine, alcohol, marijuana, and other drugs
• Sleep disorders

Associated Conditions

Some sleep disorders and other illnesses involve abnormal sleep architecture, while others can cause disruptions to sleep architecture. Some of these are:

• Insomnia: The probability of moving from NREM 2 to NREM 1 appears to be higher, leading to more frequent awakenings and lighter total sleep.
• Narcolepsy: REM sleep is reached much more quickly than usual, possibly depriving the body of important restorative phases.
• Sleep apnea: Pauses in breathing during sleep especially interrupt REM sleep, which disturbs the restorative processes occurring in the brain.
• Depression: Less time appears to be spent in NREM 3, and REM sleep may be reached earlier than is typical.
• Schizophrenia: Less time appears to be spent in NREM phases, especially NREM 3. REM sleep may be reached earlier than is typical, but this could be due to the high rates of depression in people with schizophrenia.

Regardless of the cause, disordered or disrupted sleep architecture can lead to sleep deprivation, which can leave you tired and sluggish during the day, decrease your energy, and possibly lead to cognitive dysfunction and other health problems.

Testing

If your healthcare provider suspects you have a sleep disorder or a problem with sleep architecture, they may order a sleep study (polysomnogram). This generally involves spending the night in a sleep lab with electrodes measuring your brain waves and other indicators of sleep stage and quality, such as muscle movement and respiration rate. The results will then be examined by a healthcare provider, usually a sleep specialist.

Before the sleep study, or if the study is inconclusive, your healthcare provider may ask you to keep a sleep log listing the hours you sleep and possibly evaluating your daytime sleepiness and other symptoms. You may also be sent for lab tests to check for other possible causes of your symptoms.

Treatment

Depending on your diagnosis or what your healthcare provider suspects is causing your symptoms, you may be treated for sleep-architecture problems in a variety of ways.

• Sleep hygiene improvement: The first step is often education in proper sleep hygiene, which includes establishing healthy bedtime routines such as going to bed at the same time every night. It improves sleep quality for many people.
• Lifestyle changes: Getting more exercise, cutting down on caffeine or other drugs that impair your sleep, and reducing stress may all improve your sleep. Changes like this may be aided by cognitive behavioral therapy (CBT).
• Phototherapy: Some sleep disorders respond well to exposure to therapeutic light that helps reset the body's natural rhythms.
• Medications: While they may not directly improve sleep architecture, sedatives may help you get to sleep faster and stay asleep longer. To combat daytime sleepiness in narcolepsy, stimulant drugs can help.
• Medical devices: A CPAP (continuous positive airway pressure) machine is the standard treatment for obstructive sleep apnea. Mouth appliances may also be used.

Frequently Asked Questions

Which stage of sleep is most important?

Stages of sleep are interdependent and hence all are important. NREM stage 3 appears to be a physiologic need. When a person reduces the amount of NREM stage 3 one night, there appears to be physiologic need to compensate the following night.

Can alcohol help you sleep?

A pre-bedtime drink can make it easier to fall asleep, but alcohol can lead to more awakenings during the night and reduce the quality of sleep. It disrupts REM sleep, which can lead to health and memory problems. Chronic, moderate to high alcohol consumption can also lead to insomnia.

A Word From Verywell

Sleep is essential for good health and quality of life. If your sleep quality is poor or has recently gotten worse, talk to your healthcare provider about why this may be so you can start down the road to diagnosis and treatment. You've got a lot of options for sleeping, feeling, and functioning better.