Life is a series of battles against base urges. We invest our money, put on condoms, and avoid trans-fats because we know in the long run these buzz-kills will pay off. But the stronger the visceral desire the harder it is to resist. And it's been shown that hunger for one type of reward, such as sex, influences hunger for another, such as food or money. For example men who were asked to fondle bras, and thus had ramped-up libidos, made more impulsive economic decisions than men who handled t-shirts.

So impulsiveness has a spreading effect, but does inhibition? Based on earlier neuroscience research suggesting a general inhibitory network in the brain, three researchers conducted several behavioral tests to check for this inhibitory "spillover effect"—a term that takes on new meaning in their work. It's now in press at Psychological Science.

Often when you really need to pee—when you're doing the cross-legged-wee-dance—it's hard to focus on anything else. But this struggle for continence may actually enable certain types of decision-making. There's a standard test of restraint called the Stroop test. You look at a series of words for colors and quickly name the colors they're printed in, suppressing the instinct to read what the words say. If the word "blue" is printed in red ink, you say "red." Mirjam Tuk, Debra Trampe, and Luk Warlop found that people are faster at this task the more they need to pee.

In another test, subjects drank either 50 ml or 700 ml of water, and 45 minutes later made several decisions between small immediate rewards or larger delayed rewards. Those with the full bladders were more likely to act responsibly and wait for the larger reward. The effect was stronger in people with a more sensitive Behavioral Inhibition System (they agreed with statements like "I worry about making mistakes"), supporting the idea of a general inhibitory network.

Finally, the researchers reproduced the findings of the second study by merely reminding some of the subjects about urine with a word-search puzzle containing items like "toilet."

So the next time you need to discuss a tense issue with your boss while not telling him off, or you're headed to the candy store with a credit card, consider chugging a few cups of water beforehand. Your brain will thank your bladder.

P.S. Another new paper reports that tightening any muscle can boost your powers of resistance, but through a different mechanism.  

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