Rem Sleep: Is Brief Enough For Health?

Sleep is divided into four stages: light sleep, deep sleep, REM sleep, and wakefulness. REM sleep, or rapid-eye movement sleep, is the crucial last phase of each sleep cycle, during which our eyes move rapidly, our brainwaves speed up, our temperature fluctuates, and our muscles are immobilised. While there is no official consensus on how much REM sleep is needed, it is estimated that for healthy adults, 20-25% of their total sleep time should be REM sleep. This amounts to roughly 90 minutes for every 7-8 hours of sleep.

REM sleep is one of four stages of sleep

Sleep is divided into two types: rapid-eye movement (REM) sleep and non-rapid eye movement (NREM) sleep. NREM sleep is further divided into three stages, while REM sleep is the fourth and final stage of the sleep cycle.

REM sleep is characterised by rapid eye movements in different directions, and brain activity similar to that during wakefulness. Dreaming typically occurs during REM sleep. The first REM cycle is the shortest, lasting about 10 minutes, with each subsequent cycle getting longer, and the final one lasting up to an hour.

During the three stages of NREM sleep, the body and brain are less active than in REM sleep. In the first stage of NREM sleep, a person is easily awakened, and this phase usually lasts only a few minutes. The second stage is a deeper sleep, where heart rate and breathing slow down and body temperature drops. The third stage is the deep sleep stage, which is harder to wake someone from. In this stage, the body repairs injuries and boosts the immune system.

The sleep cycle typically lasts between 90 and 120 minutes, and most people go through four or five cycles per night. The cycle begins with the first stage of NREM sleep, followed by the second and third stages, and then REM sleep. After the first REM cycle, the process starts over again, returning to the first or second stage of NREM sleep.

It is the mentally restorative stage

REM sleep is the "mentally restorative" stage of sleep, during which the brain converts short-term memories made during the day into long-term ones. It is also associated with memory consolidation, emotional regulation, and learning.

During REM sleep, the eyes move rapidly behind closed eyelids, brainwaves speed up, temperature fluctuates, and muscle activity is suppressed. It is one of the sleep stages in which we dream. Since REM mimics wakefulness in certain ways, some scientists refer to it as "active sleep".

The first stage of REM sleep typically starts about 60 to 90 minutes after falling asleep and lasts for only about 10 minutes. As the night progresses, we phase in and out of REM cycles, and the time spent in each cycle gets longer. The last stage of REM can last up to an hour, so most of our REM sleep happens in the latter half of our sleep.

The amount of time spent in REM sleep varies depending on age, with babies typically spending more time in this stage than older adults. On average, healthy adults should aim for 20-25% of their total sleep time to be in the REM stage, which equates to about 90 minutes for every 7-8 hours of sleep.

If you are not getting enough REM sleep, you may experience problems with concentration and memory, low mood, low sex drive, lack of energy, and weakened immune function.

While getting enough REM sleep is crucial, it is also important to ensure you are getting sufficient overall sleep. The quality of sleep is a complex and multifaceted aspect of health, and a healthy sleep pattern requires adequate amounts of both REM and non-REM sleep stages.

It is important for memory consolidation

REM sleep is important for memory consolidation. It is the fourth and final stage of sleep, characterised by relaxed muscles, quick eye movement, irregular breathing, an elevated heart rate, and increased brain activity. Memory consolidation is the process by which the brain transforms new knowledge into long-term memories.

During REM sleep, the brain processes new learnings and motor skills from the day, committing some to memory, maintaining others, and deciding which ones to delete. REM sleep is also when the brain replays neuronal activity seen during prior learning episodes, which may be evidence for memory consolidation. However, this replay of neuronal events could also be involved in genetically programmed neuronal development or the extinction of memory traces.

Animal studies have shown that REM sleep may be important for memory consolidation. For example, post-training REM sleep deprivation during "REM sleep windows" has been shown to interfere with spatial reference memory in maze learning. Furthermore, hippocampal ensemble discharges reflecting awake experience have been reproduced in a temporal order during subsequent REM sleep. However, neuronal firings recapitulating those evoked by prior tasks have also been detected during slow-wave sleep, suggesting that REM and slow-wave sleep may play complementary roles in memory consolidation.

Human studies have also shown that REM sleep is important for memory consolidation. For example, a study found that participants who napped between learning sessions learned just as easily in the evening as they did at noon, whereas the group that didn't nap experienced a significant decrease in learning ability. Another study tested the effect of REM sleep on the ability to solve anagram puzzles, which require strong creative thinking and problem-solving skills. The researchers found that when participants were woken up during REM sleep, they could solve 15 to 35% more puzzles than when they were woken up during non-REM sleep.

Overall, while the specific role of REM sleep in memory consolidation is still being elucidated, it is clear that sleep is important for memory consolidation and that a lack of sleep impairs cognition and memory.

The amount of REM sleep needed changes with age

Sleep is divided into four stages: light sleep, deep sleep, REM sleep, and wake sleep. REM sleep, or rapid eye movement sleep, is the "mentally restorative" stage of sleep during which the brain converts short-term memories into long-term ones. It is also when most vivid dreams occur.

The amount of REM sleep needed does change with age. For newborn babies, REM sleep can be 50% of their total sleep time, but this percentage drops significantly early on and continues to decrease gradually as we get older. For healthy adults, spending 20-25% of your time asleep in the REM stage is a good goal. That's about 90 minutes for every 7-8 hours of sleep.

Older people tend to have a harder time falling asleep and wake up more often during the night and earlier in the morning. They also spend more time in the earlier, lighter stages of sleep and less time in the later, deeper stages. This may be due to changes in the body's internal clock, which is located in a part of the brain called the hypothalamus. The internal clock controls 24-hour daily cycles, or circadian rhythms, which influence when people get hungry, when the body releases certain hormones, and when a person feels sleepy or alert. As people age, deterioration in the function of the internal clock can disrupt these circadian rhythms, directly influencing when they feel tired and alert.

Additionally, older adults may experience less exposure to daylight, which is one of the most powerful cues for maintaining circadian rhythms. Changes in hormone production, such as decreased melatonin secretion, may also play a role in disrupted sleep in older adults.

A lack of REM sleep can have negative health consequences

A lack of REM sleep can have a range of negative health consequences, including:

• Fatigue
• Irritability
• Mood changes
• Memory issues
• Problems with cognition and problem-solving
• Cardiovascular issues
• Increased risk of Type 2 diabetes
• Increased risk of cancer, stroke, and neurodegenerative diseases like Alzheimer's
• Obesity
• Metabolic disorders
• Sleep apnea
• Depression

Frequently asked questions