Understanding Deep Sleep: Rem Vs. Non-Rem

Sleep is a complex and dynamic process that affects how we function in ways scientists are only beginning to understand. Sleep can be divided into two categories: REM (rapid eye movement) sleep and non-REM sleep. During REM sleep, the eyes move rapidly and the brain is active, similar to when we are awake. Dreams typically occur during this stage. Non-REM sleep, on the other hand, is deeper and is associated with slower breathing, a lower heart rate, and a drop in blood pressure and body temperature. This stage is crucial for physical repair and regeneration.

Non-REM sleep is deeper than REM sleep

Non-REM sleep is divided into three stages, known as N1, N2, and N3. N1 is a transitional period between wakefulness and sleep, lasting about 5-10 minutes. During this stage, the body begins to slow down, with heart and breathing rates decreasing, eye movements slowing, and muscles relaxing. A person can be easily awakened during N1 sleep and may not even realise they were asleep.

N2 is a period of light sleep, typically lasting 10-25 minutes. During this stage, eye movement stops, the heart rate continues to slow, brain waves become slower, and muscles relax further.

N3 sleep is the deepest stage of sleep, lasting 20-40 minutes. During this stage, the brain becomes less responsive to external stimuli, making it very difficult to wake the sleeper. N3 sleep is essential for tissue repair and regeneration, and it is also believed to be the stage during which the brain flushes out toxic waste.

While REM sleep is important for learning, memory, and emotional processing, Non-REM sleep is crucial for physical repair and regeneration. During Non-REM sleep, the body repairs and regenerates tissues, builds bone and muscle, and strengthens the immune system. Additionally, Non-REM sleep is associated with the brain restoring its supply of adenosine triphosphate (ATP), which is necessary for energy production.

The amount of time spent in each stage of sleep changes throughout a person's life, with the need for deep sleep decreasing as we age. Newborns spend up to 50% of their sleep in the REM stage, while adults only spend about 20-25%. The percentage of REM sleep remains relatively constant throughout adulthood, but it may drop in people aged 65 and older.

Non-REM sleep has three stages

The second stage of non-REM sleep is a period of light sleep, during which the body temperature drops and eye movements stop. The heart rate and breathing become more regular, and the body slows down in preparation for the third stage of non-REM sleep and REM sleep. 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 of non-REM sleep is the deep sleep stage. It is harder to wake someone during this stage, and if they are woken, they will likely feel disoriented for a few minutes. During this stage, the body starts its physical repairs, and the brain consolidates declarative memories. This stage of sleep may last up to 40 minutes.

After the third stage of non-REM sleep, the body usually returns to the second stage before entering the REM stage. The cycle then repeats, with each cycle lasting about 90 minutes.

REM sleep is initiated through acetylcholine secretion

The secretion of acetylcholine in the SubC activates neurons in the ventral medial medulla (VMM), which causes the release of GABA and glycine onto skeletal motoneurons. This, in turn, inhibits skeletal motoneurons, resulting in muscle paralysis and REM sleep.

The secretion of acetylcholine in the SubC is also influenced by other brain regions, such as the ventrolateral periaqueductal gray, dorsal paragigantocellular reticular nucleus, and the laterodorsal and pedunculopontine tegmentum in the brainstem. These regions contain GABAergic neurons, which are either REM-active or REM-inhibiting. The REM-active neurons are thought to silence wake-promoting neurons, while the REM-inhibiting neurons may prevent the activation of the REM-generating circuit.

The secretion of acetylcholine in the SubC is also modulated by the hypothalamus, which contains melanin-concentrating hormone (MCH) neurons that are REM-active. These MCH neurons project to wake-active serotonergic neurons and promote REM sleep.

Overall, the initiation of REM sleep through acetylcholine secretion involves a complex network of brain regions and neurotransmitter systems. The interaction between these systems is crucial for the regulation of REM sleep and its characteristics, such as muscle paralysis and cortical activation.

Non-REM sleep is important for memory consolidation

Memory consolidation is a process that researchers believe occurs during sleep, particularly during slow-wave sleep or deep sleep, which is part of the non-REM sleep cycle. During this process, encoded sequences are integrated by chemical connections into new and existing neuronal knowledge networks and filed for long-term storage in the neocortex.

Non-REM sleep may also provide the brain with time to make space for new memories by removing or reducing the strength of neural links tied to memories that are no longer useful. A process called pruning culls excess neuronal links during human development. Sleep may aid in this mental tidying-up process, scaling back increased neuronal activity from exposure to specific stimuli and maintaining homeostatic balance in the brain.

Additionally, non-REM sleep is associated with the brain restoring its supply of adenosine triphosphate (ATP). ATP is an energy-carrying molecule found in the cells of all living things. Overall, non-REM sleep is important for memory consolidation and plays a crucial role in the formation and storage of long-term memories.

Non-REM sleep is important for tissue repair and regeneration

Non-REM sleep is vital for tissue repair and regeneration. During the deeper stages of non-REM sleep, the body repairs and regenerates tissues, builds bone and muscle, and strengthens the immune system. This is because the body and brain become less active, allowing the body to heal injuries and repair issues that occurred while awake.

The first two stages of non-REM sleep involve changes in muscle and eye movement, respiratory rate, and body temperature. These changes are followed by two other stages in which a decrease in delta waves from the brain results in deep sleep. Growth hormone (GH), which is secreted after the delta stage of sleep, is responsible for growth in infancy and is crucial for continuous tissue restoration and repair of damage incurred during wakefulness.

Cell division and protein synthesis reach their highest levels during sleep and diminish throughout the day. The rate of healing of damaged tissues is greater during sleep. A lack of sleep is one of the crucial factors influencing the wound healing process.

The circadian rhythm, which is related to critical bodily changes such as hormone production, brain activity, heart and respiratory rates, body temperature, and tissue regeneration, also plays a role in tissue regeneration. The physiological changes during sleep, such as temperature, pH, CO2 level, and hormone production, contribute to stem cell homeostasis, creating an optimal microenvironment for stem cells to proliferate, migrate, and differentiate.

Additionally, studies suggest that slow-wave sleep, which occurs during the third stage of non-REM sleep, may aid in the process of the brain flushing out toxic waste.

Frequently asked questions