Sleepscore's Accuracy In Differentiating Light And Rem Sleep

Sleep is a complex and mysterious body process that is essential for our health and well-being. The quality and quantity of sleep we get can have a significant impact on our physical and mental health. To understand our sleep patterns and improve our sleep hygiene, many people turn to sleep-tracking technologies, such as SleepScore. But how accurate are these tools in distinguishing between the different stages of sleep, specifically Stage One and REM sleep?

REM sleep and dreaming

Sleep is divided into four stages, three of which are non-rapid eye movement (NREM) sleep, also known as quiet sleep. The fourth is rapid eye movement (REM) sleep, also known as active sleep. During REM sleep, the eyes move rapidly, the body experiences atonia (a temporary paralysis of the muscles), breathing becomes irregular, the heart rate rises, and brain activity increases. Dreams typically happen during REM sleep.

REM sleep is believed to be essential to cognitive functions like memory, learning, and creativity. It is also 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.

Each sleep stage has a unique function and role in maintaining the brain's overall cognitive performance. Some stages are also associated with physical repairs that keep you healthy and get you ready for the next day.

REM sleep plays a role in memory consolidation, emotional processing, brain development, and dreaming. Most adults need about two hours of REM sleep each night.

During the REM stage, the eyes move rapidly, the body is relaxed and immobilized, the breathing is faster and irregular, and the heart rate rises. The brain's activity most closely resembles its activity during waking hours.

The REM stage of sleep usually begins about 60 to 90 minutes after falling asleep. As part of a full night's sleep, you cycle through four stages of sleep multiple times: three stages of NREM sleep followed by one stage of REM sleep. Each cycle through all the sleep stages takes 90 to 120 minutes to complete. With each new cycle, you spend increasing amounts of time in REM sleep, with most of your REM sleep taking place in the second half of the night.

REM sleep is one of the most fascinating stages of sleep, partly because it's so different from other stages. In non-REM sleep, the eyes don't move, brain waves are much slower, and there is partial muscle tone.

Dreams mostly happen during REM sleep. In the REM stage, you may experience temporary paralysis to prevent you from acting out your dreams. On average, people spend about two hours dreaming every night.

Dreams can occur during any stage of sleep, but the vivid dreams that you remember tend to happen during REM sleep. A 2020 study found that dream recall was more prevalent after REM sleep. Participants were also more likely to report not having a dream or having a "white dream" (remembering the feeling of dreaming but not the content) after NREM sleep.

NREM sleep stages

Non-rapid eye movement (NREM) sleep, also known as quiet sleep, is divided into three stages.

The first stage of the sleep cycle is a transition period between wakefulness and sleep. During this stage, the brain slows down, and the heartbeat, eye movements, and breathing slow with it. The body relaxes, and muscles may twitch. This stage lasts for around five to ten minutes.

During the second stage, you become less aware of your surroundings. Your body temperature drops, eye movements stop, and your breathing and heart rate become more regular. The brain also begins to produce bursts of rapid, rhythmic brain wave activity, known as sleep spindles, which are thought to be a feature of memory consolidation. This stage lasts for about 20 minutes per cycle, and people spend about half of their total sleep time in this stage.

The third stage is the deep sleep stage, during which it is harder to wake the sleeper. In this stage, the muscles are completely relaxed, blood pressure drops, and breathing slows. The brain consolidates declarative memories, and the body starts its physical repairs. This stage is critical to restorative sleep, allowing for bodily recovery, growth, and a boost to the immune system.

The amount of time spent in each stage of the sleep cycle can change from night to night and over your lifetime. For example, babies spend a lot of time in the REM stage—up to 50% of their sleep—while adults spend only about 20%.

Sleep disorders

• Central disorders of hypersomnolence (e.g. narcolepsy)
• Circadian rhythm sleep-wake disorders (e.g. jet lag, shift work sleep disorder)
• Sleep-disordered breathing (e.g. sleep apnea)
• Sleep-related movement disorders (e.g. restless leg syndrome)
• Parasomnias (e.g. sleep starts, sleepwalking, nightmares, REM sleep behaviour disorder)
• Insomnia
• Trouble thinking or concentrating
• Mood issues, including irritability, depression or anxiety
• A weakened immune system
• Metabolism problems and an increased risk of Type 2 diabetes
• Fatigue or exhaustion

If left untreated, sleep deprivation can cause:

• Microsleeps, which are brief moments where the brain falls asleep and can be dangerous if they occur during activities that require concentration, like driving
• Hand tremors, due to the nervous system's inability to regulate muscle movements and tone
• Hallucinations, as sleep deprivation disrupts the brain's ability to process information
• Impulsive or reckless behaviour, due to impaired self-control and judgment

Long-term, sleep deprivation has been linked to:

• Cardiovascular disease
• Metabolic conditions like Type 2 diabetes
• Cognitive impairment

Sleep quality

A good night's sleep involves progressing smoothly through the various stages of the sleep cycle, which typically occurs four to six times per night. These stages include three non-rapid eye movement (NREM) stages and one rapid eye movement (REM) stage.

• Sleep duration: Aim for seven to nine hours of uninterrupted sleep each night. This duration provides your body with sufficient time to transition through the different sleep stages and obtain the necessary amount of deep sleep and REM sleep.
• Sleep environment: Create a conducive sleep environment by maintaining a comfortable temperature, minimising light and noise disruptions, and ensuring your mattress, pillows, and sheets are comfortable.
• Sleep hygiene: Improve your sleep hygiene by establishing a consistent sleep schedule, getting natural daylight exposure, avoiding alcohol and caffeine before bedtime, and reducing exposure to electronic screens close to bedtime.
• Sleep disorders: Address any underlying sleep disorders, such as sleep apnea or insomnia, which can interrupt your sleep cycles and prevent you from reaching the deeper stages of sleep.
• Age: The amount and quality of sleep you need can change with age. Newborns require the most sleep, and as people get older, they tend to spend less time in REM sleep and more time in NREM sleep.
• Recent sleep patterns: Irregular or insufficient sleep over an extended period can disrupt your sleep cycles and affect the duration of each stage.
• Alcohol consumption: Alcohol can alter your sleep architecture by decreasing REM sleep early in the night and causing a REM rebound with prolonged REM stages later.
• Stress and lifestyle: Managing stress through relaxation techniques and establishing a calming bedtime routine can improve sleep quality. Exposure to daylight, regular exercise, and avoiding heavy meals, caffeine, nicotine, and alcohol before bed can also enhance sleep quality.

By focusing on these factors and prioritising sleep quality, you can optimise your sleep and promote overall physical and mental well-being.

Sleep architecture

Each sleep stage has a unique function and role in maintaining your brain’s overall cognitive performance. Some stages are also associated with physical repairs that keep you healthy and get you ready for the next day.

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.

The first stage of the sleep cycle is a transition period between wakefulness and sleep. During this stage, your brain slows down, and your heartbeat, eye movements, and breathing slow with it. Your body relaxes, and your muscles may twitch. This brief period of sleep usually lasts for around five to ten minutes.

During the second stage of 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 rapid, rhythmic brain wave activity, known as sleep spindles, which are thought to be a feature of memory consolidation.

The third stage of sleep is deep sleep, during which your muscles are completely relaxed, your blood pressure drops, and your breathing slows. This is the stage when your body starts its physical repairs. Getting enough deep sleep will make you feel refreshed the next day.

The fourth stage is REM sleep, during which your brain activity picks up, nearing levels seen when you are awake. At the same time, the body experiences atonia, or temporary paralysis of the muscles, with the exceptions of the eyes and the muscles that control breathing. REM sleep is associated with dreaming and is believed to be essential for cognitive functions like memory, learning, and creativity.

Each cycle, which includes all four stages, lasts around 90 to 120 minutes, and people typically go through four to six sleep cycles per night.

Frequently asked questions