Nrem Sleep: Better Or Worse Than Rem?

Sleep is a complex and mysterious process that humans spend about a third of their lives doing. It is generally split into two types: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. NREM sleep is further divided into four stages, each with unique characteristics such as brain wave patterns, eye movements, and muscle tone. NREM sleep is a time when the brain is quieter and slower, while REM sleep is when the brain is more active and dreaming is more likely to occur.

The function of the alternation between these two types of sleep is not yet fully understood. However, it is known that NREM sleep is important for physical repairs and the consolidation of declarative memories, while REM sleep is important for the processing and storage of emotions and emotional memories, as well as learning. The quality and duration of each sleep stage can be affected by various factors, including age, depression, medications, and circadian rhythm disorders.

NREM sleep is restorative and accounts for around 80% of total sleep time

The first stage of NREM sleep is a transitional period between wakefulness and sleep. During this stage, the brain slows down, and the heartbeat, eye movements, and breathing slow with it. This stage lasts for around five to ten minutes, and the brain is still relatively active.

The second stage of NREM sleep is deeper sleep, during which the body temperature drops further, and eye movements stop. The brain also begins to produce bursts of rapid, rhythmic brain wave activity, known as sleep spindles, which are thought to be important for memory consolidation.

The third and fourth stages of NREM sleep are the deepest stages of sleep, during which the body is completely relaxed, and the brain produces slow brain waves known as delta waves. This is the stage when the body starts its physical repairs, and the brain consolidates declarative memories. NREM sleep is important for growth and repair, as growth hormones are released, which enable the body to grow and repair bones, muscles, tissues, and organs. It is also during this stage that the immune system is restored.

NREM sleep is longer in infants and young children, who need more of this restorative sleep for their development. As people age, they tend to spend less time in NREM sleep, particularly the deeper stages 3 and 4. Older adults may experience disrupted NREM sleep due to factors such as decreased melatonin levels and the advanced circadian rhythm that comes with age.

Overall, NREM sleep is essential for restoring and repairing the body and brain, and it plays a crucial role in maintaining overall health and well-being.

NREM sleep is divided into four stages, each with unique characteristics

Stage 1 NREM Sleep:

• This is the lightest stage of NREM sleep and usually lasts only a few minutes, making up about 2-5% of total sleep time.
• During this stage, the brain transitions from wakefulness to sleep, with a slowdown in brain waves, heartbeat, eye movements, and breathing.
• Muscle movements also diminish, but muscle twitches called hypnic jerks may occur.
• It is easy to wake someone during Stage 1 sleep.

Stage 2 NREM Sleep:

• Stage 2 is a deeper sleep, but still relatively light compared to the later stages.
• Brain waves slow down further, and there are noticeable pauses between short bursts of electrical activity.
• These bursts are believed to be the brain organizing and processing memories and information from the day.
• Stage 2 accounts for about 45% of total sleep time and gets longer with each successive cycle.
• Body temperature also starts to drop during this stage.

Stage 3 NREM Sleep:

• Stage 3 is a deep sleep, with slow and strong brain waves.
• The body takes advantage of this stage to repair injuries and boost the immune system.
• Growth hormones are released, enabling the repair and growth of bones, muscles, tissues, and organs.
• This stage makes up about 25% of total sleep time in adults, but the percentage decreases with age.

Stage 4 NREM Sleep:

• Stage 4 is the deepest stage of NREM sleep, with increased amounts of high-voltage, slow-wave brain activity.
• The arousal threshold is highest during this stage, making it the most difficult to wake someone.
• It lasts approximately 20-40 minutes in the first sleep cycle and makes up about 10-15% of total sleep.

Together, Stages 3 and 4 are often referred to as slow-wave sleep (SWS) and are crucial for physical restoration and recovery.

REM sleep is when the brain is most active and dreaming occurs

Sleep is divided into two types: non-REM (NREM) and REM (rapid eye movement) sleep. While NREM sleep is when the brain is quieter and slower, REM sleep is when the brain is more active and we are more inclined to dream.

REM sleep is named after the rapid eye movement that occurs during this phase. The brain is very active during REM sleep, using more oxygen than when we are awake. During REM sleep, the brain forms new connections by processing the day's thoughts and assimilating this information into our existing knowledge. This is how we can come up with new ideas after a good night's sleep.

REM sleep is also when we file our memories. Each night, our brain replays the events of the day, removing distracting background noise and saving only the important information in our long-term memory. It also reviews our long-term memory, rearranging information and removing anything unnecessary. This regular tidying ensures our brains do not become cluttered with old, irrelevant information.

The last phase of REM sleep is in the morning and is the longest, meaning most of our dreaming occurs early in the morning.

While NREM sleep is the more relaxing and restorative phase, accounting for around 80% of our sleep time, REM sleep is far more active. During REM sleep, our brain activity is similar to when we are awake, but our body is still relaxed. There is rapid movement under the eyelids, our heart rate increases, our breathing becomes more erratic, and our body temperature increases.

Throughout the night, we cycle between NREM and REM sleep. The first cycle normally takes about 90 to 120 minutes, and we go through four or five cycles per night.

Sleep cycles and stages were discovered using electroencephalographic (EEG) recordings

The sleep cycles and stages were discovered using electroencephalographic (EEG) recordings, which trace the electrical patterns of brain activity. The first overnight sleep recordings were performed by Loomis and colleagues, who faced the challenging task of describing typical sleep patterns in normal individuals. Several groups improvised this and, in turn, gave rise to the beginnings of sleep staging. However, it was only 17 years later, in 1953, that Aserinsky and Kleitman recognized rapid eye movement (REM) sleep, leading to the birth of modern methods of sleep staging.

EEG is a non-invasive and painless tool used to detect brain activity. It measures the general activity of the cortex by recording small (~10 uV) fluctuations in voltage. This technique does not measure electrical activity in a single neuron but instead measures the electrical activity of thousands of neurons to generate a large enough signal to detect. An EEG reading shows differences in both amplitude and frequency over time. An increase in amplitude indicates a higher degree of synchronous activity in cortical neurons, while the frequency of an EEG indicates how often neural synchrony occurs.

EEG patterns during sleep differ from those of a person who is awake. Usually, the awake EEG is dominated by high-frequency waves that increase with attention and mental activity. During sleep, the brain undergoes a very stereotyped pattern of activity changes. At times, neurons in the cortex exhibit synchronised patterns of firing, and at other times, cortical activity looks very similar to an awake brain.

Each night, a person's brain typically goes through two different phases: REM sleep and non-REM (NREM) sleep. NREM sleep is further divided into three stages: NREM1, NREM2, and NREM3.

NREM1 is the earliest stage of sleep and is also described as relaxed wakefulness, drowsiness, or light sleep. During this stage, the brain mostly exhibits alpha waves, and a person's muscles are still somewhat active. Their eyelids may open and close, and they may still respond to questions. As a person gets deeper into NREM1 sleep, more waves with lower and lower frequencies start to emerge. NREM1 transitions into NREM2, which is characterised mostly by theta waves.

NREM3, also called deep sleep, is when a person's physiological activity drops to its lowest point: heart rate, respiration, blood pressure, and metabolism all reach their minimum. In this stage, many cortical neurons fire in synchrony with one another, and the subsequent change in potentials cause large-amplitude deflections in the EEG, called delta waves.

The EEG trace of a person in REM sleep is quite the opposite of what is seen in deep sleep. Instead of large-amplitude events at a low frequency, the REM brain has a lot of low-amplitude events at a high frequency. Because of this asynchronous firing activity, REM sleep is sometimes also called paradoxical sleep.

To illustrate the stages of sleep that a person experiences each night, a hypnogram can be used. These charts plot time on the x-axis and stage of sleep on the y-axis. For an average night's rest, neural activity will fluctuate through the four phases relatively predictably. When a person first falls asleep, they will move from NREM1 down through NREM2 and then NREM3 before coming back out of deep sleep progressively back to NREM1. After NREM1, they may enter REM sleep before transitioning back through the stages to NREM3 again. This cycle of activity repeats roughly every one and a half hours.

Sleep quality and time spent in each sleep stage can be altered by depression, ageing, medications, and circadian rhythm disorders

Sleep is a complex and mysterious process that occupies about a third of our lives. The quality of sleep and the time spent in each sleep stage can be influenced by various factors, including depression, ageing, medications, and circadian rhythm disorders.

Depression and sleep problems often go hand in hand. People with insomnia are at a tenfold higher risk of developing depression, and among those with depression, 75% struggle with falling or staying asleep. Depression is associated with a reduction in restorative slow-wave sleep, which can weaken emotional resilience and increase vulnerability to depression in the future.

Ageing also impacts sleep quality and duration. Older adults commonly experience changes in their sleep architecture, spending more time in the lighter sleep stages and less time in the deeper stages. This shift can contribute to more frequent awakenings during the night and more fragmented sleep. Additionally, the body's internal clock, or the suprachiasmatic nucleus (SCN), deteriorates with age, disrupting circadian rhythms and affecting when people feel tired and alert. Hormonal changes, such as decreased melatonin production, can further disrupt sleep in older adults.

Medications can also influence sleep. Certain drugs, such as antidepressants, can have a sedating effect, while others may disrupt sleep. It is important to be aware of the potential side effects of medications on sleep quality and duration.

Circadian rhythm disorders are conditions that disrupt the body's natural sleep-wake cycle. These disorders can be caused by various factors, including brain damage, vision impairments, travel across time zones, and shift work. They can lead to insomnia, daytime sleepiness, and difficulty falling or staying asleep.

In summary, sleep quality and time spent in each sleep stage are dynamic and susceptible to alterations by factors such as depression, ageing, medications, and circadian rhythm disorders. Understanding these influences can help address sleep disturbances and improve overall sleep health.

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