Illustration of a woman pulling thread through brain

Sleep and decision making: here’s why deep sleep reduces risky behaviour

Posted by for Wellbeing

A new study found that the answer to better choices might lie in your slow wave phase. 

A little bit of jeopardy every now and then can make life exciting, but do you find you constantly make precarious decisions that don’t serve you well? Maybe you repeatedly choose to skip breakfast even though you know you end up starving and shaky, or you always seem to end up drinking too much on a weekday despite having important meetings the next morning. Now, new research shows why some of us seem hard-wired to enjoy the thrill of risky behaviour – and it’s all down to our sleep.

In the study, by psychologists at the University of Bern in Switzerland, researchers studied the normal sleeping patterns of 54 healthy adults. They then asked them to complete a risk assessment test that involved playing a computer game where they drive a car down a road on which a wall would appear at a random distance – with the chance to win increasing amounts of money if they didn’t hit the wall, but also risking a crash if they did. 

It appeared that there was a correlation between those who crashed – or got close to it – and the level of slow-wave activity in the brain. Slow-wave sleep is otherwise known as deep sleep, and it was particularly lacking from the right prefrontal cortex of those who had risky behaviour traits.

Researchers explained that the right prefrontal cortex plays a large role in cognitive control functions, meaning that increased brain activity – and decreased sleep depth – in the area can be an indication of a lack of self-regulation, which in turn reflects preferences towards risk-taking.

Other studies have shown that activity in the right prefrontal cortex while awake can also impact risky decision-making. And sleep deprivation studies, including a 2017 paper published in Annals of Neurology, found that reducing the amount of slow-wave sleep intensity in that area of the brain led to an increase in risk-taking financial behaviour. Even more concerningly, the change in behaviour went unnoticed by the participants. 

A woman deeply sleeping in bed
Deep sleep improves your decision making, finds a new study

So what does this mean for us? Firstly, if you are someone who often finds themselves berating the decisions they made, it’s useful to know that it could be down to your sleeping habits rather than intrinsically favouring silly choices.

But it’s also a call to focus on improving quality sleep, as well as quantity. Researchers in this study didn’t change any of the sleeping habits of the participants, saying that we all have a unique sleep ‘fingerprint’, meaning our bodies tend to consistently favour different waves and depths of sleep. So it was our natural fingerprint that was associated with risk-taking habits. But it doesn’t mean it’s unchangeable.

“There is a saying that people need a good night’s sleep before making important decisions. However, what does a good night of sleep mean? Most people would probably say that a good night of sleep means sleeping long and deep enough. Here we demonstrate that sleep depth is a decisive factor,” writes lead researcher Mirjam Studler. They suggest that evidence-backed brain stimulation techniques, “such as transcranial magnetic stimulation, transcranial direct current stimulation and auditory closed-loop stimulation” could help enhance slow-wave activity.

The first two activities may require being hooked up to a machine in the lab – but the latter recommendation could be useful to us at home in future. The activity involves listening to ‘clicks’ during sleep that acts as a sleep pacemaker and enhances slow-wave activity. It’s not quite available in your bedroom yet but it doesn’t seem far away. In the meantime, other habits like pre-10pm bedtimes and building restful times during waking hours are shown to increase deep sleep. An early night may make you less regretful of all that spending. 

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Chloe Gray

Chloe Gray is the senior writer for stylist.co.uk's fitness brand Strong Women. When she's not writing or lifting weights, she's most likely found practicing handstands, sipping a gin and tonic or eating peanut butter straight out of the jar (not all at the same time).