Dual Core 1, or DC1, is a schedule which logically follows Segmented sleep, and it is the first Dual Core schedule, with the reduction of some sleep from the second core of Segmented and the addition of one daytime nap to compensate for the reduced amount of REM in the second core. This allows for some sleep reduction on the schedule, and polyphasic sleepers will now officially be able to learn to nap, as Segmented sleep does not have any naps.
DC1 is also considered an ideal polyphasic schedule to attempt, given his total sleep, which ranges from ~5.3-6.3h and is very friendly for beginners.
DC1's mechanisms largely carry on from the original Segmented sleep. Each core sleep is located around each respective sleep peak to further consolidate the overall sleep structure. The first core may remain around the same length or some slight reduction compared to the first core of Segmented sleep, to preserve the amount of SWS, while the second core is reduced in length so that REM can be alleviated in the nap. There have been some changes in DC1's scheduling proposals over the years, and now the standard variant is recommended to have a core sleep of 3h20m and 1h40m respectively. The cycle length does not follow the common 90m rules mostly because of the effects of sleep peaks, which may lengthen the cycles of the dominant sleep stage in the peak (e.g, longer REM cycle around REM peak and longer SWS cycle around SWS peak). DC1 in its original design was intended to have a total of at least 5h for both core sleeps, which is a reasonable upgrade from the sleep total of Segmented, while not being overly taxing to adapt to when a daytime nap is introduced.
The nap also serves to bridge the long daytime wake gap which has increased because of the reduced total sleep from both cores combined. It is also placed in the circadian nadir around noon and early afternoon, which can give a familiar sense of daytime napping on E1 and Siesta. Alertness dips often occur around these hours, so DC1's nap takes advantage of the natural energy dips to facilitate napping. However, the nap on DC1 does not always guarantee a high percentage of REM sleep. For some attempters, it only contains NREM2, or very small amount of REM, especially if the nap is placed somewhat late in the afternoon (after ~3 PM). Despite all that, the nap can sustain alertness for a long time until the first core (~7-8h) , because it is generally easier to stay awake in the day than during the night (~4-5h between 2 cores).
DC1 is often compared to E2, because both of them are the first schedules in their respective schedule series (Dual Core & Everyman). They have a similar amount of total sleep and the same number of sleep blocks (3) per day. The only difference is that E2's first nap is now a core in DC1, and that DC1's first core is recommended to start earlier than E2 core.
There are 2 methods to adapt to DC1. The mainstream method is often cold turkey, a straight transition from monophasic sleep. Another method is to first adapt to Segmented sleep and then transition to DC1. Each method has pros and cons.
This method mostly benefits naturally Segmented sleepers, who are accustomed to waking up at night or even involuntarily doing Segmented sleep without their own awareness. Non-natural Segmented sleepers can also jump into DC1 cold turkey if there is not enough time to pull off a gradual adaptation, but the adaptation process is considered much more strenuous, except the extended variants. Since ~3h20m-3h30m core duration does not cover all SWS from the beginning (it usually takes 3 uninterrupted cycles, or at least ~4.5h core to do so), repartitioning of SWS and REM sleep into each core sleep is required. Assuming an average amount of SWS requirement (~90-120m), the repartitioning process may be more or less intense. High SWS requirements (at least ~150m) will likely require the extension of the first core (~4.5h instead) to cover all the SWS needs. Regardless of the disadvantage, several cold turkey adaptations to DC1 and its extended versions have reported success.
This adaptation is likely slower than cold turkey, but the transition is designed to be less stressful from an adapted Segmented to a new DC1. However, there is no guaranteed success for DC1, and this method actually has seen lower success rate than the cold turkey method. This is largely due to the amount of time it would take to achieve good results on 2 successive adaptations.
However, for sleepers who have been adapted to Segmented and remain on it for a long time, the transition to DC1 at this point puts them on equal grounds with natural Segmented sleepers who are about to start a DC1 adaptation.
Currently, there have been a few DC1 variants that have been successful, although success rate is still assessed as "Your Mileage May Vary". These alternate variants serve different purposes of different polyphasic adapters and have a varying success rate as reported.
Less common core duration combination
In this variant, both core sleeps still give a total of 5h, however, there is a slight difference from the currently used version. This variant was the first one proposed by Polyphasic Society. The first core sleep is as long as the equivalent first core on Segmented sleep, based on the idea that the extra 30m sleep starting from the 3h mark gives some more REM sleep (even though this most definitely does not apply to every individual). This core length is also applied in E3 a lot of times. However, the sleep peaks that are utilized in DC1 possibly give a different effect on cycle lengths, so a 3.5h core may not yield the same kind of result as a 3.5h core starting out of SWS peak would.
This variant would be a strong evolution step after adapting to Segmented with the first core being 3.5h, because the transition and learning of 3.5h core habits has been formed. This variant has little success throughout the years, because it is reliant on a gradual adaptation from Segmented, which lengthens the adaptation time it takes to adapt to this variant.
It is well-established that 2.5h core is very uncommon and difficult to tame, because for an average person it induces mid-cycle (SWS/REM) wakes right at the start of adaptation. This in return increases oversleeping chance, especially in the first core. Waking up from SWS has mostly been the most challenging awakening, while waking up from REM is usually more manageable (even though both can be just as disgusting during Stage 3 adaptation). This variant, however, would suit individuals with lower SWS needs and higher REM sleep, as the morning sleep is lengthened. Some may also prefer a longer morning sleep to be more productive at early morning hours, especially if they have been used to the night hours between the cores. Success rate up to date remains low, because attempting a 2.5h core from the get-go is discouraged except in the case of experienced sleepers or those with EEG tracking and sufficient understanding of their sleep architecture.
On DC1, a lot of sleep compression may occur, which in return can result in 4 sleep cycles (2 from each core), each of which lasts for ~75 minutes. Theoretically this should only occur for individuals with a large amount of sleep reduction from their monophasic baseline. However, this possibility needs more EEG data to confirm, after the adaptation process is completed.
This variant has seen at least 1 success over time, relying on the buffer extra sleep that lines up with the 90m multiple rule (to ease scheduling) and a longer second core to account for a higher REM need. The higher total sleep also increases the chance for flexing either cores to greater effects. However, it still remains largely unpopular to date. Attempting this variant is not discouraged, but the 2.5h second core is expected to be uncomfortable especially during stage 3.
Slightly shortened core durations
There have been a couple attempts at this variant, however, success rate remains humble. The primary reason is the relatively low total sleep, almost looking like Triphasic sleep. Repartitioning of sleep stages will be a lot more intense than on the standard version. The immediate benefit from picking this variant would be a lot of extra wake time it provides, while requiring only 3 sleeps per day, with long wake gap between each sleep for various activities. Beginners should not attempt this variant, and it would be better for individuals with lower sleep requirements (e.g, 7h monophasic, or average 8h monophasic but lower REM requirement). It is also unknown how flexible after adaptation the variant would be, since there are no records of its flexibility, and the successful cases did not continue to maintain the schedule or attempt to make it flexible after a couple months on it.
The origin of these variants was derived from Triphasic sleep, whose total sleep is also 4.5h. The goal of both variants is to have a longer sleep around SWS peak to further support SWS, while decreasing the would-be daytime core of Triphasic to a 30m nap. Over time, both of them have been acknowledged to be DC1-modified rather than Triphasic-modified, because there are 2 cores and 1 nap. Each of these variants with odd-cycle length has only reported 1 adaptation success. The rare adaptations only make sense because of the sleep lengths and require a lot more efforts to make them work. Though mostly not a good idea, the first variant (2.5-1.5) may be attempted over the second variant, and for short term (a couple months), it can give a lot of extra wake hours as burst time to complete a lot of commitments.
While no less difficult than the likes of Triphasic, these variants' advantage lies in the short daytime nap, which is more convenient to schedule than Triphasic, and less chance to be interrupted during adaptation. If an adaptation is possible, the long-term prospect is also more promising than Triphasic. The nap may be somewhat flexible after adaptation; unfortunately, the flexibility potential was never demonstrated by either successful attempters.
Long morning wake gap
The idea was originally posited by Polyphasic Society, where the heavy concentration of both cores at night resembles E1 or some sort of Biphasic schedule. The wake gap between 2 cores decreases to 4h, while there is an 8h wake gap between the second core and the nap. The promised utility from this setup is that it has a better chance to work from morning to afternoon hours without the possibility to have a nap around noon or during work. However, this has been very difficult, and has essentially zero successful adaptation because of the long morning gap. Individuals with lower sleep requirement can take advantage of this variant, because they usually can stay awake longer with a more distant sleep distribution, than an average person would.
This is a common ground in scheduling with E2 as well, with the morning gap between both naps usually no longer than ~6h to ensure no excessive tiredness during the whole wake gap to be adaptable. The afternoon wake gap on DC1 and E2 (from the last nap of the day to the core) is usually tolerable even if they appear to be longer than the recommended length. Since it is deemed easier to stay awake during the day, up to 9h wake is viable for the afternoon gap (for average individuals).
It is uncertain what the advantages of this scheduling would be compared to the traditional setup, where the second core is placed at hours that are virtually safe from any real life interruptions. However, some individuals do claim that a short nap around sunrise hours would give more chance for vivid dream recall than a core sleep, probably because of a higher percentage of REM sleep in a nap than in a core, and the period of REM that ends before awakening is likely shorter on a nap than on a core. Only one person has reportedly succeeded at adapting to this variant. The daytime core looks like that on Siesta, but it is questionable how it can be managed long-term, while a daytime nap is a lot more convenient to schedule.
Both of these variants over the years have reported a lot of success (although more for the 4.5-1.5 core distribution). They are very beginner-friendly and offer a reasonable amount of sleep reduction (~90m of sleep cut from an 8h monophasic baseline). Those with a higher monophasic baseline (~9h) are also recommended to pick either variant. The choice between either variants comes down to REM and SWS requirements. A higher REM requirement would favor the 3-3 core combination, while a person with high SWS needs or exercise a lot for muscle growth can pick the 4.5-1.5 variant. Both variants also have an advantage that the regular version oftentimes does not, is the ability to have a somewhat later first core sleep, to start around ~11 PM rather than 9 or 10 PM on the default version.
Another benefit that either variant can afford is the ability to have a long morning wake gap, up to ~8h before the nap is taken because of a higher total sleep. Wakefulness sustaining is expected to be a lot easier than on a regular DC1 variant. This could allow one to stay awake through work, and then have a nap after work (~4-5 PM). There are also a lot of flexibility potential after the adaptation to this variant. One can choose to proceed to DC2, or simply learn to make the extended version flexible to adapt to DUCAMAYL.
The non-reducing version is only a very niche option for people who do not want to reduce their total sleep time because of personal reasons. Because DC1 is heavily built on the Segmented sleep habits, naturally Segmented (non-reducing) individuals can learn to add a daytime nap around the hours they are drowsy enough. This would effectively create a non-reducing DC1 variant. Since there is no sleep reduction, it is possible to somewhat flex each sleep block with small increments during adaptation, rather than having to stick to strict sleep times everyday. Despite this, non-reducing DC1's true adaptation success is very rare, and mostly rely on the naturally Segmented tendency coupled with the circadian nadir around noon-afternoon to take the nap accordingly. It may also be redundant to a lot of people, because non-reducing Segmented already provides all the necessary sleep in the cores, and does not require taking any daytime naps.
However, a slight benefit from doing this variant is to start to learn to have effective daytime naps to further transition to other reducing schedules/variants, because Segmented sleep does not teach napping skills. Even so, with the overall much lower sleep pressure on a non-reducing schedule, it may still be a tough task to fall asleep in the nap.
Similar to Segmented sleep, DC1 offers a variety of scheduling options in its arsenal. A lot of variants have been tried and succeeded over time, although the bulk of the success is from the extended versions. Either way, DC1 demonstrates that one can enjoy the night gap between the cores, keep up the Segmented habit, and further cement the schedule with a daytime nap for another chance at rejuvenation. Because of the ability to take advantage of the sleep peaks and the circadian nadir around noon, DC1 (extended) is considered a well-rounded schedule. The second core sleep is also great for a lot of REM sleep and can sustain alertness well into the afternoon, setting the foundation for very efficient morning productivity. With the option to delay the first core to later evening hours without a lot of compromise, the extended version also spares more room for social time in the evening as total sleep is high enough to rake in quality SWS with strong dark period management. However, like a typical Dual Core schedule, the first core sleep often starts at earlier hours than Everyman sleep to make use of the SWS peak, so an Everyman schedule (e.g, E2, E3-extended) still has more vantage points in terms of evening social time.
Because of the characteristically different features of both core sleeps, it can be beneficial to study before the first core, and then revise the learned materials during the night gap. SWS, which is prevalent in the first core, is responsible for storage of declarative/explicit memory, e.g, recall of explicit factual information. A history, or a biology test, X happened on date Y. A in the body does which thing B. On the other hand, REM is responsible for storage of procedural memory, i.e. remembering how to do certain things by following a procedure. Examples include how to walk, how to ride a bike, how to play a specific piano piece. In addition, REM is also responsible for emotionally related memory consolidation, and for spatial memory consolidation (together with light sleep), (e.g, which way to walk to a friend's house). If one is trying to remember procedures by repetition, napping is a good way to boost that, and the nap on DC1 can fulfill such purpose. If they are trying to remember chunks of information, they won't get any gain there until the core sleep and it is best to study such materials before the core. Note that this does not only apply to DC1 - Segmented and other schedules with Dual Core features can also benefit from the experiment. The sole nap's function on DC1 also applies to the nap(s) any other schedules that are within the adaptability range and have been proven to be stable long term.
DC1, however, is generally harder than its counterpart E2, which is reflected on the much lower amount of success (barring extended versions), and the borderline with inflexibility after adaptation. So far there are not many adapted DC1 (5.3h sleep) sleepers that can flex the core sleeps by a lot. It would require lower sleep requirements overall, or experienced sleepers to be able to manage a flexible DC1. While it is possible to achieve this, the second core may have to remain stationary, and the first core may not be any more flexible than 1h range (earlier/later than the originally scheduled time). The nap on DC1 may be flexible, but it is uncertain how flexible it can be. Regardless, more data is required to determine how flexible DC1 can be, compared to E2, whose second nap is highly flexible in a lot of adapted people.
Having only 1 daytime nap, DC1 is suitable for a lot of regular jobs that allow 1 nap to be taken during lunch/noon break. Thus, its long-term potential is also very shining. The small nap also gives it a great advantage over any schedules that require a daytime core (e.g, Siesta, Triphasic) which is more difficult to schedule. However, while the extended variants are more resilient, the default variant is less likely so. It will be crucial to pay attention to any nighttime activities that force the first core to be delayed into the night, which also causes a shift in the entire schedule. While it is possible to recover from such incidents once in a while after adapted, DC1 poses an overall more difficult adaptation than Segmented, and its lowered total sleep means that it becomes necessary to consider various factors that could affect the adaptation, such as: current level of exercise, health status, long-term sustenance and mental health. The longer night gap between the cores may also not be suitable for everyone, because staying awake for many hours at night everyday can be boring and eventually overwhelming.
All in all, DC1 remains a solid schedule to attempt, as it is one of the most balanced schedules with moderate difficulty. Being adapted to DC1 is no banal achievement, while the extra time, benefits of the night gap, the maneuvering of both sleep peaks, a unique experience from both core sleeps (one core is very deep, potentially near a blackout yet peaceful and calm, while the other one is often explosive with wild dreams) promise a blistering adaptation experience.