The importance of getting enough total sleep time is becoming common knowledge. We really cannot separate the amount of sleep we get from the quality of our sleep. In general, sleep stages can be categorized into two: REM (rapid eye movement) and non~REM. non-REM includes light sleep (stage 1 and 2) and deep sleep (stage 3). In this article I deep dive into REM sleep (stage 4), one of the most important and fascinating stages of sleep.
Sleep happens in cycles of approximately 90 minutes. The first cycle is usually shorter and the subsequent cycles are longer. In every cycle, we usually go through the different stages of sleep sequentially ending with REM sleep. During the course of the night, the ratio of non-REM to REM changes. The cycles in the second half of our sleep are dominated by REM sleep whereas the first half is dominated by non-REM sleep.
Before entering REM sleep, The brainstem sends signals that inhibit the innervation of our muscles leading to complete paralysis of voluntary movement except for two muscle groups: the muscles controlling the movement of the eyes (extraocular muscles) and the inner ear muscles. This produces the characteristic rapid movement of the eyes which give this stage of sleep its name.
Although being a late stage of sleep, during REM sleep, our brains are far from being inactive. Once we enter REM sleep, there is an eruption of activity in the cerebral cortex. This activity is similar to that seen in wakeful states. This is why REM sleep is sometimes called paradoxical sleep. It is also the reason why paralysis of the muscles during this stage is crucial, to prevent us from ‘acting out’ our dreams. Most dreams at night occur during this stage (however, dreams are not only restricted to REM sleep).
REM sleep is also tied to hormone regulation. When we enter REM sleep, a surge in testosterone is seen while growth hormone released during sleep reaches a low.
Memory processing is thought to be a major component of REM sleep. Increased activity is seen in the hippocampus which is the region of the brain associated with memory formation. REM sleep also strengthens and maintains neuronal synapses associated with learning new skills and consolidating information. Individuals deprived of REM sleep show deficits in working memory and the ability to learn.
REM sleep seems to have a major role in regulating emotions. This condition of simultaneously processing emotions while inhibiting the body’s physical response to intense emotions such as fear and anxiety has been hypothesized to allow our brains to process emotions we experience during wakefulness in a safe and controlled manner. Parts of the limbic system in the brain which are responsible for the processing of emotions such as the Amygdala have been shown to be specifically affected in subjects with impaired REM sleep. This is also characteristically seen in many mental disorders.
Studies have shown that lower REM sleep is associated with increased all-cause mortality.
There are two main measurements when it comes to REM sleep:
The gold standard for sleep tracking is a lab test called polysomnography (PSG). Wearable devices such as Oura ring, Whoop band and others are becoming more and more accurate at measuring sleep stages. When compared to PSG, Whoop 3.0 has been shown to be more accurate than Oura. I wrote more about the accuracy of sleep wearables here.
REM latency is a measure of how long after getting into bed it takes a person to reach the first REM sleep stage. This includes the time it takes to actually fall asleep (sleep onset latency).
When you wake up from REM sleep, you are more likely to remember the dreams you were having. A subjective way of estimating if you are getting enough REM sleep is that if you wake up feeling refreshed, and remember your dreams, you are more likely to be getting enough REM sleep.
In healthy adults, REM sleep constitutes 20-25% of total sleep time. This equates to approximately 90 minutes if you sleep for 8 hours in total. REM sleep increases as the night progresses. It may last only 1 to 5 minutes in the first cycle and is the longest in the last one third of the night. REM sleep has been seen to naturally decrease with age, however, maintaining a higher REM sleep percentage as we age is likely associated with healthier aging.
A good goal for REM latency in healthy adults is under 100 minutes. It’s important to take into consideration that the longer it takes a person to fall asleep, the longer REM latency would be.
Anything that impacts our total sleep time such as insomnia and obstructive sleep apnea can lead to insufficient REM sleep even if the percentage of REM remains above 20%. Because REM sleep increases towards the end of the night, waking up ‘too early’ before getting the full amount of sleep you need can specifically impact REM sleep.
Increased number of awakenings during the night for various reasons can prevent us from reaching REM sleep enough. Similarly, if it takes us too long to fall asleep (measured by sleep onset latency) this will delay us from reaching REM sleep (measured by REM latency).
Alcohol is a REM blocker. While alcohol leads to quicker loss of consciousness, this does not equate to high quality sleep. Alcohol causes fragmentation of sleep and is associated with cutting our sleep short before getting the final cycles of sleep where REM plays a major role.
THC, the active component in Marijuana has a similar effect. Other substances that can block REM sleep include opioid pain medications, benzodiazepines and some antidepressants.
After checking for sleep disorders and other conditions that can impact sleep quality, adopting basic sleep hygiene such as:
There are more interventions that can help with specific problems causing REM sleep deficiency. One can consult a sleep specialist or consider working with our team of experts as Span who will help you find what works best for you.
https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC6986372/
https://pubmed.ncbi.nlm.nih.gov/22447623/
https://pubmed.ncbi.nlm.nih.gov/28092659/
https://pubmed.ncbi.nlm.nih.gov/27174984/
https://pubmed.ncbi.nlm.nih.gov/28515433/
https://pubmed.ncbi.nlm.nih.gov/28515433/
https://pubmed.ncbi.nlm.nih.gov/31303489/
