Most of us have days when we wish there were a few more hours to get things done. The solution proposed seems relatively straightforward, cut sleep short and sleep more efficiently. Right?
It is suggested that one way to achieve this might be with polyphasic sleep. However, from a scientific point of view, polyphasic sleep has little merit.
Polyphasic sleep involves sleeping in multiple bouts across each 24 hour day and potentially doing away with consolidated sleep at night. A number of different patterns exist for polyphasic sleeping. These range from the fairly benign (sleeping predominantly at night with an afternoon nap) to the more extreme (sleeping in three 1.5 hour naps across a 24 hour period or 6-8 20-minute naps across a 24 hour day, for example).
Proponents claim that by sleeping in small frequent bouts, you will be to make your sleep more “efficient”, and that this efficiency comes from eliminating nonessential sleep stages, such as light sleep, and experiencing only the deepest (slow wave) sleep and REM sleep. In turn, you will be able to cram many more hours of wakefulness into a newly improved version of a day, which will naturally be filled with increased productivity, motivation and excitement. It’s a nice sales pitch, but not one that is supported by good science.
We need at least 7 hours sleep each day
Call me substantially biased but the adage that hours spent sleeping are a waste of time is now quite outdated. From large population studies, we have known for some time that short sleep leads to some fairly nasty health problems – heart disease, increased BMI, type 2 diabetes, stroke, decreased immune function to name a few. Recent experimental evidence now provides cellular pathways for how these health problems may occur. Sleep provides a unique opportunity for the body to carry out its sleep-only tasks. These include sleep-only functions in organ systems, hormone production, cleaning the brain of harmful waste products and memory consolidation. Sleep is an opportunity for the body’s many physiological processes to work in a dedicated mode, in tandem, in order to obtain optimal functioning. Without sleep, many of these processes simply do not occur. Sleep not only has dedicated functions but we need enough of it to stay and function well.
From a performance point of view, there is pretty robust evidence to suggest that getting less than 7 hours sleep leads to immediate deficits in neurobehavioral functioning. Short sleep is associated with decreased alertness, poor decision making, poor concentration and motivation, less creative thinking and poor problem solving. The shorter we cut our sleep, the greater these deficits will be. In fact, after cutting our sleep to 6 hours per night for 2 weeks, our functioning is similar to when we have been awake for 24 hours straight. The difference? We just don’t seem to recognise our own level of impairment very well when we are missing out on sleep. (Have you ever met anyone who swears they can get by on a small amount of sleep? They likely fall into this category. Their functioning, however, is unlikely to match their claims, despite their perceptions of it.)
Polyphasic sleep is natural
A common argument by proponents of polyphasic sleep is that sleeping in a consolidated chunk at night is not our natural way of sleeping. In this, there is some accuracy. As I mentioned in a previous post, our sleep used to be more aligned with the natural day/night cycle. In historical times and in the absence of electrical light, we used to sleep in two chunks, separated by a few hours of wakefulness in between, during which we would read, converse, have sex and so on. Experimental studies support these historical accounts well. In situations with long nocturnal periods of darkness, we tend to sleep for 3-4 hours, wake for 2-3 hours and then sleep for another 2-3 hours. Notably though, we still naturally sleep for approximately 8 hours in these situations.
Sleep doesn’t contain extraneous sleep stages
It is argued that by sleeping polyphasically, we can cut out non-essential sleep stages, claimed to be N1 and N2 (collectively, light sleep), and achieve “core sleep” containing only slow wave and REM sleep in each of our sleep periods. I described normal sleep structure in a previous post and outlined that healthy sleep is comprised of all sleep stages. It is tempting to think of sleep stages as static entities that can be cut in and out of sleep at will. However, any given sleep stage is simply a categorisation, a way for us to make sense of sleep. Sleep stages are simplistic labels given to dynamic and complex brain activity – in one instance, a particular area of the brain may be very active and in the next a different one, and both instances may be categorised as Stage 2 sleep . We cannot afford to do away with any sleep stage.
Aside from this categorisation, neuronal activity that occurs during particular sleep stages has unique functions. When it comes to light sleep, Stage 2 sleep appears to be particularly important for developing cognitive and motor skills. Some processing of declarative information, in particular semantic information, is unique to Stage 2 sleep. Stage 2 sleep likely increases capacity for future learning of some tasks. Furthermore, supporting the fact that not all sleep is equal, memory of some motor skills appear to be unique to Stage 2 sleep when it occurs in the latter half of the overnight sleep period.
‘Core sleep’ is not desirable
It is possible to enhance the proportion of slow wave sleep (SWS) in a few circumstances: being awake for long periods of time (by implication, missing out on sleep) and cutting sleep short. SWS can also be enhanced with regular, intense exercise.
Slow wave sleep is a good indicator of our present need for sleep and of the homeostatic process, which ensures our needs for sleep are met. When our need for sleep is high, so is the proportion of SWS. This need dissipates across the night, in line with the distribution of slow waves across the sleep period (here). A high proportion of SWS in every sleep period means that our needs are not being met. Our daytime functioning also reflects this fact. In a polyphasic sleep pattern, during each small period of wakefulness, we function as if we have not had enough sleep and/or are at the end of our waking day. (Could you imagine going through most days constantly functioning like you do at 10-11pm or later?)
‘Core sleep’ is not achievable if we are well rested
It is claimed that polyphasic sleep patterns align well with your circadian body clock, although this is not likely. Not least from a sleep structure perspective. The structure of our sleep is dependent on the interaction between the sleep systems and the circadian body clock. This is particularly relevant for the pattern of REM sleep, which is dependent on both the time that the individual has been asleep and the time of day. We enter REM most quickly, and our REM periods are the longest and most intense just after the core body temperature minimum (for most people about 3-4am).
Can we choose when to sleep?
The average well rested person cannot simply force themselves to sleep at any time during the day that suits. As with REM sleep, we have periods of increased and decreased sleepiness across the day. Our periods of increased sleepiness are probably well known to many of us. The middle of the night, and that afternoon period when you go hunting for coffee and a biscuit. Individuals who have a high propensity for sleep at every point during the day are simply not getting enough sleep. For a healthy sleeper, there are also periods during the day when it is very difficult to fall asleep. (Any shift worker will know these well.) For the average person, these occur late morning and early-mid evening. Being able to fall asleep easily during these times is a good sign you’re not getting enough sleep.
For most people, polyphasic sleep is not an option, particularly given the social implications (social isolation (most people are not awake at 2am) and inter-personal relationships) and work implications (the need for frequent naps at work). However, for those who do give it a go, there are frequent reports of needing to get through a pretty rough adaptation phase before settling into a napping rhythm. It would seem that these individuals go through a period of extreme sleep deprivation, followed by a period of blissful ignorance, where they no longer recognise their own level of impairment.