Sleep Cycles Explained: Understanding Core Sleep

Struggling to get a whole night of recommended sleep is an experience many of us, unfortunately, can relate to. Instead of trying to get their sleep all in one block, numerous have attempted staggering their sleep into periods of rest throughout the evening and sometimes throughout the day. 

 

Core sleep is essential for anyone exploring or implementing biphasic or polyphasic sleep, the terms for staggering your sleep into two or more blocks. 

 

In this article, we'll explain core sleep, its science, and what else you need to know before implementing a multi-phased sleep pattern into your life. 

 

Understanding Sleep Cycles and the Various Types of Sleep Patterns

Sleep is a complex subject. It may often be regarded as one long block of slumber. But ask any of the millions of Americans experiencing sleep issues each year, and you'll find out that isn't the case.   

 

Even those with perfectly functioning sleep do not rest in one large block overnight. That's because our rest is divided into four to six sleep cycles each night. Lasting roughly 70 10 120 minutes, each sleep cycle is made up of four sleep phases [1] containing either rapid eye movement (REM) or non-REM (NREM):

1. Stage 1, NREM sleep or N1: 1-7 minutes of light sleep      
2. Stage 2, NREM sleep or N2: 10-25 minutes of light sleep     
3. Stage 3, NREM sleep or N3: 20-40 minutes of deep sleep     
4. Stage 4, REM sleep: 10-60 minutes of vivid dreaming

 

N3 and N4 are particularly important to getting healthy rest. This is made possible by the deep sleep achieved during this 30-60 minute window. During this period, the mind can rejuvenate the body, mind, and other core functions [2].

 

Not everyone sleeps the same, whether by choice or otherwise. As such, sleep patterns are categorized into three groupings: 

• Monophasic [3]: The most common type of sleep, involving a single, multi-hour block of rest, typically at night 
• Biphasic [4]: A twice-daily sleep pattern, where rest is divided into two periods overnight, or once at night with a shorter nap in the morning or afternoon.
• Polyphasic [5]: Several sleep phases over a day, comprised of general and core sleep. With many schedule structures, polyphasic sleep cycles intend to achieve less than eight hours of sleep per night using a variety of sleep periods and cycles. 

 

What is a Core Sleep?

A core sleep is the longest period a person rests during a 24-hour day.

Core sleep windows vary depending on a person's rest cycle. Monophasic core sleep encompasses the entire single sleep period, usually seven to nine hours. With biphasic and many polyphasic sleep cycles, one period contains the most sleep in a given day. This period is called core sleep. 

 

Biphasic and polyphasic core sleep can be more challenging to determine. With biphasic sleep, the core sleep is typically easy to identify, with one prolonged rest period and a shorter nap. The only exception would be if someone splits the two sleep periods equally, eliminating either being the core sleep. 

 

In some cases, polyphasic sleep is also divided equally, often into four to six periods. In other cases, one prolonged sleep is supplemented by several shorter naps, totaling just a few hours of rest each day.

 

Examples of polyphasic sleep cycles and their core sleep include [6] [7]:

1. Uberman Sleep Schedule: Six 20-minute naps evenly spaced during the day, totaling two hours of sleep throughout the day. Core sleep on this schedule should be challenging or impossible to determine, with each cycle ideally lasting the same amount of time. 
2. Dymaxion Sleep Schedule: Four 30-minute naps every six hours, totaling two hours of sleep throughout the day. Core sleep on this schedule should be challenging or impossible to determine, with each cycle ideally lasting the same amount of time. 
3. Everyman Sleep Schedule: Three hours of nightly core sleep supplemented by three 20-minute naps daily, totaling four hours of sleep throughout the day. 
4. Triphasic Sleep Schedule: Three short sleep periods happen after dusk, before dawn, and in the afternoon, creating four to five hours of sleep per day. The core sleep varies by the individual's preference and ability to sleep. 

 

Benefits and Risks

Core sleep is essential to gaining the deep sleep needed in the N3 and REM stages. Core and general sleep stages often allow for ample opportunities to achieve deep sleep when using monophasic or biphasic sleep schedules. The challenge becomes more difficult with polyphasic sleepers. 

 

Depending on the polyphasic sleep pattern, achieving critical deep and REM sleep can be difficult during general or core sleep periods. Many polyphasic schedules are geared toward two to four hours of daily sleep, making many likely wonder how much deep and REM sleep is needed to maintain their health and core functions. These short windows also leave little time to establish a core when most cycles last 30 to 60 minutes. 

 

Polyphasic sleep supporters hold onto the assertion that their sleep method works. Some of their main reasons for using polyphasic sleep includes: 

• Increased productivity: Self-reports have found numerous polyphasic sleepers claiming to experience improved productivity, claiming they get more done with less time spent resting. 
• Lucid dreaming: Lucid dreams occur when the person is aware that they are dreaming while asleep. It is believed that since frequently waking up during the night can increase chances of lucid dreaming [8], then a polyphasic sleep cycle should help improve those odds.     
• Improved cognitive function: Sleep helps people refresh and rejuvenate their body's many functions, including memory and learning. Polyphasic sleepers believe several naps during the day should help do the same at the same or better rate than monophasic sleep. While possible, research suggests that sleep periods under 30 minutes do not produce these rejuvenation-like outcomes [9]. 
• Aligns with work or essential life schedule: Whether healthy or not, some professions and life schedules demand people dedicate themselves for prolonged periods. In that case, polyphasic sleep may help. 

 

The above claims are mostly or entirely anecdotal at this time. Most clinical analysis suggests that little to no evidence has been found to support the claims that polyphasic sleep produces beneficial results, either as a core or general sleep. On the contrary, some analysis has highlighted potential concerns of polyphasic sleep:

• Chronic sleep deprivation: Prolonged periods of little to no sleep can negatively impact bodily functions such as [10]: 
• Heart and circulatory systems   
• Metabolic systems      
• Immune system    
• Nervous system    
• Various brain functions     
• Mental health
• Circadian rhythm disruption: Disrupted circadian rhythms can lead to increased feelings of fatigue and higher risks of contracting colds or other illnesses.
• Slowed reaction times: Another side effect of a disrupted circadian rhythm is delayed reactions. Slowed reactions are detrimental to anyone, from the classroom to the office. The worries grow more significant with anyone who's underslept and tasked with operating vehicles or other heavy machinery [11]. 

 

Adapting to Polyphasic Sleep and Finding Core Sleep 

Remember that most clinical research does not suggest switching to a polyphasic cycle, or at least one that aims for fewer hours of sleep than recommended. Still, those looking to adapt to a sleep schedule using a polyphasic approach may want to follow a path similar to one laid out by other proponents [12]:

1. Step 1: A period where the transition may feel simple, as sleep comes easy. However, glimpses into the post-adoption phase may reveal the sleep struggles ahead.
2. Step 2: Full immersion into polyphasic sleep, including increased tiredness, difficulty waking up, and sudden waves of fatigue throughout the day. 
3. Step 3: The stage where many fail to convert, where sleep debt reaches its height. However, reports of improved dream recall and overall sleep efficiency are standard. 
4. Step 4: Adaptation nears completion, signified by easier wake-ups, improved alertness, and increased lucid or vivid dreaming. In adverse outcomes, a person can undersleep and fall back into Stage 3.

 

While some sleep cycles claim to have a faster adaptation period, often spanning 5-10 days, some polyphasic proponents caution this option may lead to many not sticking with the sleep plan over time. 

 

Core Sleep Challenges and Considerations

Monophasic and biphasic sleep allows us to reach deep sleep regularly and get our recommended rest. These two traditional methods have their challenges and considerations. While these sleepers no doubt experience issues with minimal or light sleep, the concern is much more focused on polyphasic sleepers and their low total sleep times, particularly over a prolonged period. 

 

Additionally, maintaining an entire polyphasic sleep schedule, much less its core sleep is challenging. With under and oversleeping an issue, polyphasic sleepers walk a fine line between achieving what they often consider a deeper sleep and regressing into an early stage of adaptation. In any case, the effects on their circadian rhythm are no doubt immense. 

 

Consider your health and daily needs before embarking on a polyphasic sleep cycle. Can you maintain this sleep schedule? Evaluate your family, work, and other life commitments to see if shorter and modified sleep cycles could help or harm you. 

 

Don't forget to assess your health and any possible benefits or side effects of shorter sleep each night. Consult with a medical professional whenever possible. 

 

How Much Sleep Do I Need? 

The concept of core sleep clusters is intriguing and only grows in complexity as we stagger our sleep patterns. While biphasic and polyphasic sleep offer possible benefits, we must approach them with caution and awareness for our health.

 

Understanding core sleep clusters is essential to multi-stage sleeping, almost as important as knowing how much deep and REM sleep you need daily. By understanding these approaches, we can further understand the differences between REM, light, and deep sleep and how they impact our bodies. 

 

Polyphasic sleep will continue to be debated for some time. If you want to try one of these cycles, consider your health and speak with a trusted medical professional beforehand. Gather all the information and best prepare yourself. With the gathered information, you can determine if it's the proper method for you and where your ideal core sleep cluster may exist. 

 

Citations

1. Stages of Sleep: What Happens in a Sleep Cycle https://www.sleepfoundation.org/stages-of-sleep 
2. Aging of core and optional sleep https://pubmed.ncbi.nlm.nih.gov/1637928/#:~:text=Core%20sleep%20is%20the%20essential,(NREM%203-4). 
3. What Is Monophasic Sleep & Why Is It the Most Common Sleep Cycle? https://www.dreams.co.uk/sleep-matters-club/monophasic-sleep 
4. Biphasic Sleep: What It Is And How It Works https://www.sleepfoundation.org/how-sleep-works/biphasic-sleep 
5. Polyphasic Sleep Schedule https://www.sleepfoundation.org/how-sleep-works/polyphasic-sleep 
6. Polyphasic Sleep Schedule https://www.sleepfoundation.org/how-sleep-works/polyphasic-sleep 
7. What Is Polyphasic Sleep, and Is It Safe? https://www.healthline.com/health/polyphasic-sleep 
8. Sleep fragmentation and lucid dreaming https://pubmed.ncbi.nlm.nih.gov/32768920/ 
9. Comparing the Effects of Sleep and Rest on Memory Consolidation https://pubmed.ncbi.nlm.nih.gov/32099493/ 
10. Sleep Deprivation https://my.clevelandclinic.org/health/diseases/23970-sleep-deprivation 
11. Polyphasic Sleep Schedule https://www.sleepfoundation.org/how-sleep-works/polyphasic-sleep 
12. Adaptation Stages & Success https://www.polyphasic.net/adaptation/