Maybe you noticed: Americans drink a lot of Coke and Pepsi. Researchers at Baylor University looked at what's going on in the brain when people drink cola—and how brand influences their preference for one drink or the other.

What the researchers wanted to know: How do brains respond to cola, and how does brand affect that?

What they did: The researchers carried out several taste tests. Each subject tasted drinks in cups, then was loaded into an MRI machine with a plastic tube in his or her mouth to deliver tiny squirts of Coke and Pepsi while the machine monitored brain activity. Sometimes the drinks were both anonymous, and sometimes only one of the two drinks was labeled—but the other, secretly, was always the same soda as the labeled drink. They ran the "semianonymous" trial for both Coke and Pepsi, with different people.

What they found: When people didn't know what either drink was, they were equally likely to pick Coke or Pepsi as the favorite. But when one cup or one tube-squirt was labeled as Coke, participants preferred it to the other, unlabeled drink (even though both contained Coke). Oddly, the same was not true for Pepsi. As for the pictures of brain activity: No matter what, a part of the brain that responds to rewards lighted up. This makes sense, since every test involved sugar water. But when one drink was labeled Coke, other parts of the brain lighted up, too—regions involved in memory and cognitive control. That suggests that when you know what you're tasting, you don't respond only to flavor; your brain also gets excited about other things it knows about the product.

What the study means to you: This is interesting basic research for neuroscientists who are interested in stimulus and preference—but it could also have applications for advertisers who want to know how brains react to brands.

Caveats: In the "semianonymous" test, the researchers didn't check whether people came into the experiment preferring Coke or Pepsi. Also, in the MRI part of the experiment, the subjects got only a tiny amount of the drink—not even a quarter teaspoon. (This was to avoid choking, since they were lying on their backs.)

Find out more: The website Neuroscience for Kids can teach the rest of us a thing or two, too.

Read the article: McClure, S.M. et al. "Neural Correlates of Behavioral Preference for Culturally Familiar Drinks." Neuron. Oct. 14, 2004, Vol. 44, pp. 379–387.

Abstract online: www.neuron.org