These two winning strategies could explain Marco Rubio's surge in the GOP race

Although Sen. Ted Cruz (R-Texas) came out with a win in the Iowa Republican caucuses last week, Sen. Marco Rubio (R-Florida) has emerged as a strong GOP contender.

But the best way to measure a candidate's effect on voters may be to measure what's going on in voters' brains.

Last weekend, the author and communication coach Carmine Gallo wrote in Forbes how "neuroeconomics" professor Paul Zak of Claremont Graduate University is doing just that.

The purpose of Zak's studies is to identify what ideas or political messages trigger action - whether it's charitable giving or votes.

The winning formula

Based on Zak's research and his own experience, Gallo says he has identified what he calls the "winning formula" for action. It comes down to two things: attention and emotional resonance.

"Attention is a scarce brain resource, so attention is necessary to induce action," Zak told Gallo. But attention alone is not enough. To get someone to take action for a cause, you need to create empathy by forging emotional connections, something Zak calls emotional resonance.

In a recent experiment, Zak and his colleagues wired up a group of registered Republicans with sensors that detect their brain waves while they watched the January 14 and January 28 GOP presidential debates.

Here's what they found: During the earlier debate, real-estate mogul Donald Trump scored the highest among the study participants on measures of attention, but low on emotional resonance. None of the candidates scored very high on emotional resonance, either - which might have been because they were all competing for attention.

In the January 28 debate (in which Trump declined to participate), Zak and his colleagues found that Rubio "won" because he earned the highest combination of both attention and emotional resonance. As a result, Zak predicted that Rubio would do well in the Iowa caucuses - which he did, surprising with a strong third-place finish.

New Jersey Gov. Chris Christie (R) has criticized Rubio for being too "scripted." But recently, Rubio has been gaining voters' trust by opening up about his family and personal life on the campaign trail, as The New York Times has reported.

For example, when a voter lamented that his home was losing value, Rubio recounted the story of his neighbor foreclosing on his home. And when another voter talked about the burden of raising a child with autism, the senator talked about a friend's 2-year-old daughter who struggles with the disorder.

The emotional appeal of personal stories like these comes down to our brain chemistry.

Trust in the brain

In his previous research, Zak has found that the brain chemical oxytocin plays an important role in emotional resonance.

For example, in a 2013 study of data gathered in 2007, when George W. Bush was president and Democrats controlled Congress, Zak and his colleagues gave 88 college students - 42% of whom identified as Democrats and 23% as Republicans - a nasal spritz of either oxytocin or a placebo, and asked them to fill out a survey about their political attitudes and trust in various politicians.

Those who were given the oxytocin reported greater their trust in political figures and government. However, the increased trust was only among politicians in their party. In addition, the study participants were younger and more diverse than the general population.

Oxytocin has been called a "cuddle hormone" or "moral molecule" because of its role in promoting trust and social bonding. But this description is far too simplistic, as research suggests oxytocin may also be responsible for distrust or aggression toward people who are not part of one's social group.

Neuroscience is only just scratching the surface of what makes voters tick. But it may provide some insight into how Rubio, and others, can earn votes this primary season.

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