Flickr CC: Amy McTigue

The anticipation of pain can cause more stress than knowing for certain that you're about to be given an electric shock, a UCL study has found.

In research published in Nature Communications, a team found that even a small chance of getting an electric shock is "significantly" more stressful than knowing for sure that you will be shocked. A 50 percent chance of getting shocked caused the most stress, with 0 and 100 percents the least stressful.


In the study, 45 volunteers played a game in which they had to overturn virtual rocks. They were then asked to guess whether or not they thought they had a snake underneath them -- when there was, they received a small electric shock.

As participants got to grips with the game, they learned which rocks were most likely to give them an electric shock, but because the chances of this oscillated throughout the game, uncertainty was high -- and it also "matched the stress levels reported by participants". "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," said lead author Archy de Berker. "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."

The team also saw physiological stress match self-reported levels, with increased perspiration and dilated pupils.

They compare it to the stress felt when applying for a job. "You feel more relaxed if you think it's a long shot or if you're confident it's in the bag," said study co-author Robb Rutledge. "The most stressful scenario is when you really don't know. The uncertainty 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."

It's not all bad news, though -- participants with the highest stress levels also showed better judgement, and were able to ascertain far better which rocks housed secret snakes. "From an evolutionary perspective, our finding that stress responses are tuned to environmental uncertainty suggests that it may have offered some survival benefit," said co-author Sven Bestmann. "And appropriate stress responses might be useful for learning about uncertain, dangerous things in the environment."