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We are constantly making decisions in our lives, from picking an entrance gate at the station to choosing a place to live. Our expectations about the outcome drive these choices. But what if we become uncertain about a situation or are surprised by an outcome and our expectations are no longer correct? Thomas Meindertsma examined how the brain deals with uncertainty and surprise when making decisions. 'In uncertain situations, we get messier in our choices', he concludes. 'But this also leads to exploration, which helps us to adapt to a new environment.' He will defend his PhD thesis at the University of Amsterdam on Thursday, 7 April.

'We always have expectations about how the world works and about the possible outcome of our decisions', says cognitive neuroscience researcher Thomas Meindertsma. 'We base these expectations on previous experiences and our knowledge of the world, such as natural laws and regularity. If something big falls out of the window, for example, it always goes straight down, so you decide to step aside.'

According to Meindertsma, this is how we build expectations that guide our choices. Uncertainty and surprise are closely linked to these expectations. 'If we have strong expectations about the outcome of a decision, we will experience little uncertainty. But if we become uncertain about a situation or are surprised by an outcome, we will start to question our expectations. They might no longer be correct.' He investigated how the brain processes information in the event of uncertainty and surprise and how this influences decisions.

How do you measure what uncertainty and surprise do to the brain?

Meindertsma got subjects to perform a task in a scanner that can measure brain activity. Using a camera, he also recorded the pupil size; this made is a marker of the state of arousal of the brain. He then linked these measurements to the choices made by the subjects while performing their tasks. 'Using a computer model, we then mimicked the choice process of the test subjects and were able to determine how surprising the outcome of a decision was and what effect this had on them. For example, they might have been surprised because a certain regularity or structure in the task suddenly deviated from the norm. Subjects built up expectations while performing the task, but then suddenly encountered an unexpected outcome. When they were surprised in this way, the brain became more active and they began to adapt their decision-making method.'

The state of arousal of our brain can change very quickly

Meindertsma regards the effect of uncertain expectations on decision-making as the most striking result of his research. 'If people are uncertain or surprised about a result, this can directly influence their next choice. It changes the state of the brain and expectations and decisions are adjusted as a result.' He explains that this ties in with recent developments in neuroscientific research that show that the state of excitement of the brain not only varies slowly, as in the day/night rhythm, but also much faster. 'It therefore influences our cognitive performance over a period of a few seconds.'

Decisions become messy, but not necessarily bad

He discovered that in these uncertain situations, people become ‘messier’ in their choices. Things are still stored in the brain, but the selection process becomes increasingly ‘noisy’. 'People are going to make their choices in a less focused way. We thus apply our predictions, which we based on previous experiences and choices, poorly when being in a new situation.' Although people may not choose the best option as a result, Meindertsma also regards these messy choices as positive.

It’s how your brain helps you to adapt to a new situation

Uncertainty is a signal that your expectations may no longer be correct and you should not build on them too much. You need to seek out an alternative strategy and look around to see what else you could do. The messiness in decision-making allows for the exploration of other options that may also be good to follow.' According to Meindertsma, this can help people to adapt to a new situation. 'The increased state of arousal in your brain means that you will make your choices more randomly. This randomness allows us to explore our environment and build up new expectations that are in line with it. And then you can start applying these new expectations.'

It is therefore good to know that the random decisions you sometimes make in uncertain situations can be useful. 'These random decisions also have a function and can produce something that would otherwise not have been there. So you do need to cherish them a little.'

Details of thesis

Thomas Meindertsma, 2022, ‘How Surprise and Uncertainty Alter Brain State and Decisions’, supervisors: prof. T.H. Donner and prof. E.M. Wagenmakers

Time and location

Thursday 7 April, 13.00, Agnietenkapel, Amsterdam