Mass media campaigns have proven to influence people’s health-related decision making—for better or for worse. Effective messaging has helped millions quit smoking, exercise more, and eat better, while failed campaigns have backfired, sometimes even causing those with unhealthy habits to dig deeper into their vices.

“We don’t always know what’s going to persuade us,” says Emily Falk, an associate professor at the Annenberg School for Communication. “In the moment, it might feel like one set of advertisements is appealing, but that doesn’t always translate into downstream behavior.”

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In a soon-to-be-published study in the journal Social Cognitive and Affective Neuroscience, a team of researchers led by Falk discovered a new way to help predict the success of public health campaigns. Instead of just asking someone’s opinion, they looked inside people’s brains and measured their neural reactions when they viewed specific advertisements.

Using functional magnetic resonance imaging (fMRI), the researchers recorded the brain activity of 50 smokers from Michigan who viewed a total of 40 anti-smoking images, including some that the Food and Drug Administration was considering using as warning labels. Researchers focused on the medial prefrontal cortex (MPFC) region of the brain, which helps people gauge how valuable or relevant information is to them.

The more activity in the MPFC, the more motivating the image would be to stop a person from smoking, the researchers believed.

To test this hypothesis, they compared the fMRI results from the small sample of smokers to a large anti-smoking email campaign sent in partnership with the New York State Smokers’ Quit Line. One of the same 40 images was sent to each of the 800,000 smokers, along with the slogan “Stop Smoking. Start Living.” Each email included a link to online smoking cessation resources.

The researchers found that the same anti-smoking images that caused powerful MPFC responses were also most effective at getting New York smokers to click the get-help link.

This information is a convincing demonstration of how looking at brain activity can help when creating a public health campaign, Falk says. But that still doesn’t mean it can take the place of self-reported data.

“Asking people does give us some important information, too,” Falk says. “Essentially what’s best is to do both.”

Falk is continuing this research by studying not only what changes a single person’s behavior, but what he or she might choose to share with others—in essence, how ideas might spread.

“A lot of things that kill people come from behaviors that we can prevent,” Falk says. “If we could figure out how to get people to feel motivated and follow through to act in healthier ways, then we could potentially save a lot of lives.”

Falk collaborated with colleagues from the University of Michigan and the Medical University of South Carolina on the study, and also Matthew Brook O’Donnell, research assistant professor at Annenberg. Funding was provided by the Michigan Center of Excellence in Cancer Communication Research and the National Institutes of Health New Innovator Award.