5 Sleep Stages Psychology

[Miriam]

Duringwakefulness, certain neurons fire in our brains, making us aroused and alert. However, during sleep, these neural circuits are inhibited, our muscles are completely relaxed, and our body becomes completely inactive (Schwartz & Roth, 2008).

Though research reveals that it is much more complicated, the levels of consciousness can be thought of in three components: conscious, preconscious, and unconscious, as originally defined by Sigmund Freud.

A sleeping person, for example, is in a state of unconsciousness; so is an individual in a coma or someone who has fainted. The difference, however, is that a sleeping person can be aroused if the stimulus is strong enough (for example, shaking the person, shining a bright light, or making a loud noise).

But how do our bodies know when to go back and forth between sleep and wakefulness? Luckily, we all have an internal clock telling us when to do so. The circadian rhythm, our 24-hour clock, operates as our sleep/wake cycle.

During non-REM sleep, electrical activity in the brain slows, growth hormone secretion occurs, and there is a decrease in muscle activity, heart rate, respiration, and oxygen consumption (Purves et al., 2001).

This stage is heavily regulated by the brainstem (McCarley et al., 1995), which is the region of the brain that connects the cerebrum with the spinal cord. It consists of the midbrain, medulla oblongata, and pons.

During REM sleep, brain activity increases, voluntary muscles are inhibited, and rapid eye movements and dreams occur (McCarley et al., 1995). The next section will go into more detail on REM sleep as well as the characteristics of the specific stages of non-REM sleep.

In 1957, William Dement, along with Nathaniel Kleitman, came out with another revolutionary paper that discussed the specific sleep stages that together form the internal cycle that occurs every night we sleep (Dement & Kleitman, 1957).

In the beginning of stage 1, the brain produces high-amplitude alpha waves and begins to produce theta waves as the stage progresses (Abeln et al., 2014). Put simply; brainwaves are electrical pulses in the brain that change according to what we are doing or how we are feeling (Abhang et al., 2016).

Alpha waves are the highest frequency (thus, the fastest) of the three brain waves that characterize sleep, explaining why, when we have just fallen asleep and are not yet in a state of deep sleep, we can be easily awoken.

Stage 2 (N2) is still a period of light sleep, marked by similar characteristics as in N1, such as a continued slowing of both the heartbeat and breathing and the muscles relaxing even further than in N1 (Lockett, 2020).

Formerly known as stages 3 and 4, stage 3 (N3) is the final stage of non-REM sleep. During N3, your heartbeat and breathing slow to their lowest levels, and your muscles are so relaxed that it may be hard to awaken you (Lockett, 2020).

Sleepwalking, or somnambulism, occurs when sleeping and waking are combined, and the individual wanders around in a dazed and uncoordinated state (Kales et al., 1980). Night terrors are partial waking from sleep during which behaviors such as screaming, kicking, and panic occur (Kales et al., 1980).

EEG is an electrophysiological monitoring method to record the electrical activity of the brain, and this technology is commonly used in sleep studies to measure brainwave activity (Niedermeyer & da Silva, 2004).

At birth, humans spend about one-third of a 24-hour day in REM sleep. As we mature, the percentage of REM sleep declines rapidly so that by approximately age 10, the adult percentage of REM sleep is reached roughly 20-25% of total sleep time (McCarley et al., 1995).

However, REM rebound, or the increase of REM sleep above normal levels, can occur after a period of sleep deprivation (Verma et al., 2001). That is, there is an increase in REM sleep after a night of little REM sleep.

Evidence of dreams occurring during REM sleep is illustrated by studies in which subjects who are awakened from REM sleep recall elaborate, vivid, emotional dreams, as opposed to subjects awakened during non-REM sleep who report fewer, less vivid dreams (Purves et al., 2001).

Humans may be unique in a lot of ways, but the fact that we sleep is not one of them. As discussed, sleep is important for recovery, memory storage, and growth, so it makes perfect sense that other animals need sleep, too.

Fish and amphibians reduce their state of awareness but do not ever become unconscious (Siegel, 2008). Insects, on the other hand, do not appear to sleep (and have never been shown to enter REM sleep), although they may experience periods of inactivity (McCarley et al., 1995).

Although research on reptile sleep cycles is not completely conclusive, a 2016 study on the brain of a lizard, the Australian dragon, revealed that slow wave and REM sleep patterns oscillated continuously with a period of roughly 80 seconds each (Shein-Idelson et al., 2016).

It is possible that reptiles dream since past studies reveal they also exhibit some form of REM sleep (Libourel et al., 2018; Shein-Idelson et al., 2016), but researchers are still uncertain as to whether this is completely true.

And while it is difficult to discern whether animals do dream, it is even more challenging to understand the specific content of these dreams. It becomes clear that further research is necessary for this field.

An individual sleep cycle typically lasts around ninety minutes to two hours, during which the brain cycles from slow-wave sleep to REM sleep. However, the sleep cycle is not as simple as cycling through the stages sequentially.

In adults, REM sleep increases as the night progress and is the longest in the last one-third of the time spent asleep. N2 begins to account for the majority of non-REM sleep, and N3 can even disappear altogether (Altevogt & Colten, 2006).

On an average night, adults typically need to complete at least four or five sleep cycles per night, or 7 to 9 total hours of sleep (Hirshkowitz et al., 2015). However, there is a large degree of variability from person to person and from night to night (Carskadon & Rechtschaffen, 2011).

Babies, for example, have shorter sleep cycles, lasting only about 50 minutes for the first nine months of life, and it is typical for newborns to sleep anywhere from 14 to 18 hours a day (Hirshkowitz et al., 2015).

And when it is time to go to sleep for the night, make sure you are giving yourself a minimum of 7 hours of sleep. The bottom line is that sleep is important, and you should make sure to get enough sleep every day!

After attending the University of Washington, Dement went on to the University of Chicago School of Medicine, where the only person studying sleep was faculty member Nathaniel Kleitman (Stanford, 2008).

A typical sleep cycle lasts about 90 to 110 minutes, consisting of different stages: non-REM sleep stages 1, 2, 3, and the REM (Rapid Eye Movement) stage. Most adults experience 4 to 6 of these cycles per night.

A REM (Rapid Eye Movement) cycle, in which most dreaming occurs, varies in length throughout the night. The first REM cycle is typically short, about 10 minutes, and occurs 90 minutes after falling asleep. Subsequent REM cycles lengthen, with the final one lasting up to an hour.

As a sleeper progresses from stage 1 sleep to REM (Rapid Eye Movement) sleep, brain waves undergo distinct changes. In stage 1 sleep, brain waves slow down with irregular patterns known as theta waves.

In contrast, during REM sleep, brain waves become faster and more similar to the waves observed during wakefulness. This is when vivid dreaming occurs, and the brain shows increased activity and resembles the alert state. These transitions between sleep stages reflect different aspects of sleep and the corresponding brain activity.

It is 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.

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