Inside the shopping brain.

If the holiday shopping season turns out to be as grim as many forecasters are warning, among the reasons will be a little brain region called the insula. Maxed-out consumers have been heeding the advice to take scissors to their credit cards, since paying with cash controls the eventual cost of a purchase (carrying a credit-card balance can double an item's original price) and limits impulse buys (most of us have less cash on hand than we do a credit limit, so if we have to count out greenbacks for Juicy Couture, we'll pass it up). But there's another, more fundamental reason why we buy less when we pay with cash. When you hand over a stack of 20s, you have less of something tangible: your billfold is lighter. That causes a brain region that registers negative feelings (bad smells, unfairness, social ostracism) to become more active than when you charge a purchase. Humans have evolved to pay attention to the messages the insula sends, with the result that it hurts to pay cash. There is no such feeling of loss when you pay with plastic, so the insula doesn't react. Credit cards anesthetize the otherwise painful act of paying.