Uncertainty is stressful, but that’s not always a bad thing

The most stressful situation is the uncertain one we can do nothing about

hand squeezing stress ball

Life is full of stressful situations. But the ones we can predict stress us out less, and may even help us learn, a new study suggests.


Interviewing for a new job is filled with uncertainty, and that uncertainty fuels stress. There’s the uncertainty associated with preparing for the interview — what questions will they ask me? What should I put in my portfolio? And then there’s the ambiguity when you’re left to stew. Did I get the job? Or did someone else?

Scientists have recently shown that these two types of uncertainty — the kind we can prepare for, and the kind we’re just stuck with — are not created equal. The uncertainty we can’t do anything about is more stressful than the one we can. The results help show exactly what in our lives freaks us out — and why. But the findings also show a positive side to the stress we feel when not knowing what’s ahead — the closer our stress levels reflect the real ambiguity in the world, the better we perform in it.

“There is a bias in the public perception” against stress, says Claus Lamm, a cognitive neuroscientist at the University of Vienna in Austria.  But stress “prepares us to deal with environmental challenges,” he notes, preparing us to fight or flee, and it keeps us paying attention to our surroundings.

For decades, scientists have been trying to figure out just what makes us stressed and why. It turns out that unpredictability is a great stressor. Studies in the 1960s and 1970s showed that rats and humans who can’t predict a negative effect (such as a small shock) end up more frazzled than those who can predict when a zap is coming.  In a 2006 study, people zapped with unpredictable electric shocks to the hand rated the pain as more unpleasant than when they knew what to expect.

What is going on in the brain when judging the uncertainty of a situation and translating it to stress? Lamm and his group recently sought the answer to answer this question by combining measures of electrical activity in the brain (via electroencephalogram) with functional magnetic resonance imaging to show blood flow patterns in 25 participants getting rounds of shocks on their hands. A visual cue told the participants what to expect — sort of. Sometimes the participant knew with 100 percent certainty that either a painful shock or nothing at all was coming. Sometimes there was only 50 percent certainty. No matter what, the shock would happen (or not) in the next 15 seconds, leaving the people in the scanner with nothing to do but wait.

During that waiting period, the brain prepares for a shock in different ways, depending on whether the jolt is certain or uncertain, Lamm and his colleagues reported last February in Human Brain Mapping. During the first two seconds, the brain is processing the visual cue. “You have an initial quick evaluation,” Lamm explains, categorizing whether the stimulus is going to be aversive and whether it is certain or uncertain. If the possibility for a zap was ambiguous, there was a quick increase in blood flow to participants’ visual processing areas. This suggests the brain is getting ready to take in more information and pay more attention — to get a better read on if that shock is really coming or not.

If the zap is definitely going to happen, the last two seconds before delivery saw increased activity in the posterior insula. The insula participates in processing someone’s current state, including pain processing and emotional awareness — “basically reading out the physiological signals of your body,” Lamm says. Pain is coming, brace yourself.

When participants weren’t sure if the shock was coming, the last two seconds of waiting were accompanied by increased brain activity in areas related to sensing the environment and maintaining attention — such as the parietal lobe, orbitofrontal cortex and angular gyrus. The brain was on high alert, continuing to look for any information that could determine when and if the pain would arrive.

But this is only one kind of stress —and one kind of uncertainty. “We know a lot about what happens if you take someone and give them a stressful experience,” says Archy de Berker, a neuroscientist at University College London. “But in a way, that approach is missing out on a whole step: What is it about the experience that makes it stressful?” Is it the ambiguity? Or is it the shock to the hand? Is it both?

But there’s also more than one kind of ambiguity to prepare for. Remember the job interview scenario: You can reduce some of the uncertainty by preparing for your interview. But once the interview has passed, you’re stuck with irreducible uncertainty — that endless wait for the call that may never come.

To separate out these two forms of uncertainty, de Berker recruited 45 participants for a different hand-shock experiment. For each trial, the participant was presented with one of two rocks and asked if there was a snake under it. At first, the snake might be under rock “A” 100 percent of the time. Then it might change, and the snake might be under rock “A” only 60 percent of the time, spending the rest of the time under rock “B.” For some trials, the participant could easily learn to predict where the snake would be, while for others the rock-turner was always uncertain. But one thing remained certain: If they saw the snake, they’d get a shock, even if they predicted the outcome correctly.

As the participants played this painful game, de Berker and his colleagues monitored their skin conductance and pupil size — measures of physical stress. They also asked the participants how stressed out they felt.

The amount of ambiguity the participants had about whether the snake was under the rock was associated with their stress. If they could easily predict when the shock would come, reducing their uncertainty, they shocks were easier to take. But if the outcome remained difficult to predict — if no amount of learning was going to help — the participants were much more stressed out.

But if the participants had a good feel for just how uncertain the odds were — if their measures of stress tracked well with the amount of ambiguity — they ended up with an unexpected benefit: They performed better on the rock and snake task (though they still got shocked for their pains). The scientists published their results March 29 in Nature Communications.

The study “reveals more quantitatively how stress (both self-reported and measured with physiological arousal) is driven by… ‘irreducible uncertainty,’ uncertainty about the state of the world that we can’t control,” says Ross Otto, a neuroscientist at New York University. It’s that irreducible uncertainty — the fact that the job applicant just doesn’t know if he’s got the job until the call comes through, and there’s nothing he can do about it — that really gets to us.

But the part of the stress we can control represents the positive side of an unpleasant feeling. “We always tend to think of stress as a negative effect, you don’t want to be stressed,” Lamm says. “But in the end, if you’re not stressed you will not perform. You need a certain level of arousal to meet challenges.”

Bethany was previously the staff writer at Science News for Students. She has a Ph.D. in physiology and pharmacology from Wake Forest University School of Medicine.

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