Sleep – elusive, precious, restful sleep – is a topic close of many of our hearts. Such is the importance of this activity that sometimes people cling on to half-baked ideas about it with an unnatural fervour.
Consider a paper on sleep research published early this year, for instance, which garnered widespread media coverage. Thinking positively about how you slept may help you perform better at school and work, it claimed.
That’s a novel idea and it’s based on some truth – but really? Can positive thinking about sleep quality fool both the body and mind into doing better than if they “knew” they were exhausted?
Like all attractive but false ideas, this notion of placebo sleep has a grain of truth in it. Research shows insomniacs misperceive their sleep, often overestimating the amount of time they spend awake. And if they feel they haven’t slept well, this may make them feel worse when awake.
Still, sleep – and the lack of it – has physiological impacts. And just telling yourself you’re well rested doesn’t mean you can override how your body is experiencing its lack.
How sleep works
Sleep is comprised of two core stages, non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. The former is divided into four sub-stages that typically become deeper.
In adults, a normal nocturnal sleep period involves four to five cycles of both types of sleep, each lasting about 90 to 100 minutes.
While NREM and REM sleep may serve slightly different functions – NREM sleep is thought to be important for tissue growth and repair, immunity to help fight disease and illness, and energy conservation, whereas REM sleep may be involved in brain development, memory and learning – most researchers generally agree both are equally important to maintain optimal waking functions.
Sleep loss, whether from staying up all night or simply not getting enough (for instance due to work, or a new baby, or staying up late), is widely associated with cognitive impairment, including increased reaction time and poor vigilance, concentration and decision-making.
It also has consequences for physiological functioning, such as changes to stress hormones (cortisol), metabolic factors (glucose metabolism, growth hormone secretion, appetite hormones) and immunity. These are critical for health and well-being, and for maintaining optimum performance at school and work.
The placebo sleep study suggests you can improve your cognitive performance by changing how you think about your sleep quality. But there are many holes in how the study authors reached that conclusion.
Researchers randomly assigned 164 students to either an above or below average sleep quality condition or a control condition. Participants were not aware the experiment was focusing on sleep quality.
All students were given a brief lesson on sleep and told that, on average, adults spend between a fifth and a quarter of their total sleep in REM sleep, and that people with less than 20% REM sleep perform worse on tests of learning and memory while those who get 25% or more perform better.
All were then briefly attached to equipment measuring their waking brainwave activity and told it would determine the amount of REM sleep they had the night before.
Although students were asked to report how they’d slept the night before, the actual amount wasn’t recorded. So, there’s no way of knowing if the results of the performance measures were because of the experiment and not simply due to the amount of sleep the students got the night before.
The group assigned to above average sleep quality were told they spent 28.7% of their total sleep time in REM sleep, while the below average group was told they spent 16.2%. When cognitive performance was assessed, students in the first group tended to perform better than those who thought they had less REM sleep.
Although the results indicated performance was correlated to how participants perceived their sleep quality, the differences between the two groups were only small. It’s unlikely such small differences would have a significant effect on performance in the real world.
The prosaic truth
Still, the authors interpreted this to indicate that mindset about sleep quality influences cognitive performance.
If you agree with that conclusion, it seems the way you think about how you slept can change the way we feel when awake. In other words, if you think you had a restless sleep the night before, you might feel worse during the day, and vice versa.
But while changing what you think about the sleep you’ve had may make you feel better, and maybe even perform better in tests and the like in the short term, biology and the drive for sleep will ultimately determine how well or poorly people perform during the day.
There’s no substitute for sleep when it comes to good health and optimal performance. There’s no fancy fix; the best thing you can do for this is have a regular routine that gives you seven hours of sleep every night.
Going to bed and getting up at the same time each day, natural light in the morning and exercise can all help improve sleep quality over the long term, and maximise cognitive performance at school and work. Perhaps the best lesson from this study is that you shouldn’t think too much about sleep, it’ll just make matters worse.
Gemma Paech has no conflicts of interest to disclose.
Siobhan Banks does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.