We’ve all gone through it at one point: not knowing is simply killing you. Whether it’s the result of a test, whether your crush likes you or not or whether your kids are coming back safely from camp, uncertainty can cause physical pain. Now, a study confirms just that, showing that uncertainty often causes more stress than the actual pain.

Photo by CollegeDegrees360.

The study, published in Nature Communications, placed participants in a situation where they had a some chance of receiving a shock, and measured their levels of stress. They found that the 50% chance of receiving a shock was easily the most stressful situation, while 0% and 100% chances were the least stressful. The concept is familiar to most people, but it’s the first time it was actually quantified.

“When applying for a job, you’ll probably feel more relaxed if you think it’s a long shot or if you’re confident that it’s in the bag,” says co-author Dr Robb Rutledge (UCL Institute of Neurology and Max Planck UCL Centre for Computational Psychiatry and Ageing Research). “The most stressful scenario is when you really don’t know. It’s the uncertainty that makes us anxious. The same is likely to apply in many familiar situations, whether it’s waiting for medical results or information on train delays.”

The experiment they created was pretty simple: they had the 45 participants play a simple game. They would turn over rocks that might have snakes under them. They had to guess whether or not there would be a snake, and when there was they received a mildly painful electric shock on the hand. Over time they learned which rocks were most likely to harbour snakes, but those percentages changed too, adding more uncertainty.

The uncertainty was gauged by a sophisticated computational model of learning, and the participants’ level of stress was tracked using measurements of pupil dilation and perspiration.

“Using our model we could predict how stressed our subjects would be not just from whether they got shocks but how much uncertainty they had about those shocks,” explains lead author Archy de Berker (UCL Institute of Neurology). “Our experiment allows us to draw conclusions about the effect of uncertainty on stress. It turns out that it’s much worse not knowing you are going to get a shock than knowing you definitely will or won’t. We saw exactly the same effects in our physiological measures – people sweat more and their pupils get bigger when they are more uncertain.”

From an evolutionary perspective, the study makes a lot of sense. It is often said that stressed people aren’t as efficient, but the study found that stressed people were better at judging whether or not individual rocks would have snakes under them.

“From an evolutionary perspective, our finding that stress responses are tuned to environmental uncertainty suggests that it may have offered some survival benefit,” explains senior author Dr Sven Bestmann (UCL Institute of Neurology).

The study also explains some minor grievances in our lives:

“Appropriate stress responses might be useful for learning about uncertain, dangerous things in the environment. Modern life comes with many potential sources of uncertainty and stress, but it has also introduced ways of addressing them. For example, taxi apps that show where a car is can offer peace of mind by reducing the uncertainty about when it will arrive. Real-time information boards at bus stops and train platforms perform a similar role, although this can be undermined by unspecified delays which cause stress for passengers and staff alike.”

Journal Reference: http://dx.doi.org/10.1038/ncomms10996