Full bladder, better decisions? Controlling your bladder decreases impulsive choices

Sexual excitement, hunger, thirst -- psychological scientists have found that activation of just one of these bodily desires can actually make people want other, seemingly unrelated, rewards more. Take, for example, a man who finds himself searching for a bag of potato chips after looking at sexy photos of women. If this man were able to suppress his sexual desire in this situation, would his hunger also subside? This is the sort of question Mirjam Tuk, of the University of Twente in the Netherlands, sought to answer in the laboratory.

Tuk came up with the idea for the study while attending a long lecture. In an effort to stay alert, she drank several cups of coffee. By the end of the talk, she says, "All the coffee had reached my bladder. And that raised the question: What happens when people experience higher levels of bladder control?" With her colleagues, Debra Trampe of the University of Groningen and Luk Warlop of the Katholieke Universiteit Leuven, Tuk designed experiments to test whether self-control over one bodily desire can generalize to other domains as well.

In one experiment, participants either drank five cups of water (about 750 milliliters), or took small sips of water from five separate cups. Then, after about 40 minutes -- the amount of time it takes for water to reach the bladder -- the researchers assessed participants' self-control. Participants were asked to make eight choices; each was between receiving a small, but immediate, reward and a larger, but delayed, reward. For example, they could choose to receive either $16 tomorrow or $30 in 35 days.

The researchers found that the people with full bladders were better at holding out for the larger reward later. Other experiments reinforced this link; for example, in one, just thinking about words related to urination triggered the same effect.

"You seem to make better decisions when you have a full bladder," Tuk says. So maybe you should drink a bottle of water before making a decision about your stock portfolio, for example. Or perhaps stores that count on impulse buys should keep a bathroom available to customers, since they might be more willing to go for the television with a bigger screen when they have an empty bladder.

The results were a little surprising from a theoretical point of view; a lot of research in psychology has supported the concept of "ego depletion" -- that having to restrain yourself wears out your brain and makes it harder to exert self-control over something else. But Tuk says this seems to work in a different way, maybe because bladder control is largely an automatic, unconscious process.