A Dutch team has won the Ig Nobel prize after studying how we make better decisions on a full bladder

Mirjam Tuk is from the faculty of behavioural sciences at the University of Twente, Netherlands. She and her colleagues recently won an Ig Nobel prize in medicine for their research into the effects of controlling your bladder on your ability to control decisions in other areas. The Ig Nobels, in their 21st year, are awarded for improbable research that "first makes people laugh and then makes them think".

What led you to study this area? Did you drink a lot of coffee before a lecture?

The lecture that I was attending was on impulse control by one of my colleagues, Luk Warlop, in which he argued that hunger and sexual arousal could make people more impulsive. That triggered the question whether there were also visceral experiences or physiological states that could make people more controlled rather than more impulsive. I did have a full bladder at the time so that gave me some inspiration.

How did you test the theory?

In several experiments, I told people they were taking part in a water-tasting test. Half of the group drank full cups of water, while the other half only took sips. Those in the first group each drank nearly 700ml, while those in the other half each drank 50ml. Then they all did some other tests for 45 minutes. By this time, half of the group did have the need to go to the lavatory more urgently than the other. Then we did the tests about impulse control. I gave them a choice between a smaller reward very soon or a larger reward at a later point in time. It requires control over the impulsive desire to go for the more rational option. People who had to go to the lavatory urgently more often opted for the later but larger reward.

How full where their bladders?

I couldn't look in their bladders but some of them were crossing their legs. I asked them a question, on a scale of 1-7, about how urgently they wanted to go to the lavatory. The average was 4.5.

What is going on in this process?

We didn't do neuroimaging studies so this is speculation. I think as your bladder becomes fuller, the responsible neurological area is the anterior cingulate cortex and that area has to send stronger control signals to retain all the urine in your bladder. However, this area is also responsible for control of all sorts of other tasks, such as not displaying your first emotional response for example, and also more cognitive responses – so all these types of responses require the same type of control originating from the same neurological area. Some recent neurological research shows that control signals sent by this area are not completely domain-specific but unintentionally affect all these other forms of control.

Hadn't previous studies found restraint in one area makes it more difficult to exercise self-control in another?

Yes. We know, for example, resisting some nice chocolate cookies requires self-control; if you do it for quite some time and you get involved in another task that requires self-control you are less able to perform well in this task. It seems contradictory and I'm currently investigating this because I think there are two important differences. First, bladder control is a very automatic form of control compared with other forms of control such as resisting cookies – your bladder is almost impossible not to control.

Also my respondents were controlling their bladder at the same time as they were making their decisions, whereas many self-control studies show a deteriorating effect on performance on sequential control tasks. So it could be well be that the inhibitory spill-over aspect occurs for tasks so long as they occur simultaneously but not sequentially.

Could shops that install lavatories see sales increase?

I'm not sure. Bladder control is just one of many factors that may influence people's purchasing decisions.

People weren't just putting off decisions until they'd emptied their bladders?

The impact of impulse control is more like an inverted U-shape. At a certain point, you can only think about going to the lavatory and nothing else and I doubt that then people are better able to control their impulses.

So people with stronger pelvic floor muscles make better long-term decisions?

Who knows? If your muscles are stronger perhaps it requires fewer control signals from the brain.