Knowing that there is a small chance of getting a
painful electric shock can lead to significantly
more stress than knowing that you will definitely be
shocked, finds a new UCL study funded by the Medical
Research Council (MRC).
The study, published in Nature Communications, found
that situations in which subjects had a 50% chance
of receiving a shock were the most stressful while
0% and 100% chances were the least stressful. People
whose stress levels tracked uncertainty more closely
were better at guessing whether or not they would
receive a shock, suggesting that stress may inform
judgements of risk.
The experiment involved 45 volunteers who played a
computer game in which they turned 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
odds changed throughout the experiment, generating
fluctuating levels of uncertainty.
Participants’ uncertainty that any individual rock
would have a snake under it was estimated from their
guesses using a sophisticated computational model of
learning.
This uncertainty matched the stress levels reported
by participants, which was also 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.”
This is the first time that the effect of
uncertainty on stress has been quantified, but the
concept is likely to be familiar to many people.
“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.”
Stress in the modern world is often seen as a
negative and counterproductive response, but the
study also found a potential benefit. People whose
stress responses spiked the most at periods of
greatest uncertainty 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). “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.”
For more information
Nature Communications
Computations of uncertainty mediate acute stress
responses in humans
Archy O. de Berker, Robb B. Rutledge, Christoph
Mathys, Louise Marshall, Gemma F. Cross, Raymond J.
Dolan & Sven Bestmann.
Link...
University College London - Institute of Neurology
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Medical Research Council
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