It is no secret that democrats and republicans often butt heads, but the reasons why the two groups rarely find a consensus may- or may not, for some cynics – surprise: The partisan brain is only capable of irrational thought.

According to a recent neurological study, the politically partisan brain digests opposing arguments almost solely with its emotional and unconscious sectors, while the rational part of the brain is left out of the process.

According to Dr. Drew Westen, the Republican Party uses the mind’s predisposition to respond emotionally in political situations, while the democrats have lost ground as they attempt to appeal to the rational side of voters.

With the help of M.R.I. scanners, Westen, director of clinical psychology at Emory University and lead author of the study, found that when it came to politics, emotional sensors in the brain, rather than the rational part, were most active when Democrats and Republicans with strong beliefs were spurred by political debate.

“Everything we know about cognition suggests that, when faced with a contradiction, we use the rational regions of our brain to think about it, but that was not the case here,” Westen.

Westen conducted the study at the height of the 2004 presidential election campaign by observing 30 adult men with staunch political beliefs – half of whom supported President George W. Bush, the other half U.S. Sen. John Kerry.

Study participants sat through a slide show featuring speeches from Kerry, Bush and figures who were not affiliated with politics, such as actor Tom Hanks. During the study, the participants were connected to an M.R.I machine that recorded the brain activity of their reactions.

The slide show featured clips of Bush and Kerry continuously making comments that contradicted themselves. For example, participants were shown a 1996 clip of Kerry saying changes in social security might be necessary, followed by a 2004 slide in which Kerry said he would never consider changing social security, calling it “a sacred trust with our elders.”

Westen admitted in an interview with WBUR that some of the statements in the slide show had been doctored slightly for the purpose of creating a strong contradiction, but researchers presented them as factual.

As seen through M.R.I results after the slide shows, participants had heightened brain activity in the area that controls negative emotion and increased activity in the cingulate, a region that controls emotions about forgiveness.

The portion of the brain that controls factual reasoning was almost inactive.

The study found that the participants were equally harsh in their disapproval of the opposing candidate, and they were also quick to forgive the candidate they supported.

“The interesting thing is that they weren’t consciously thinking,” Westen said. “The data suggested that when viewing the slides, participants are probably trying to unconsciously recruit memories to make them feel more emotionally comfortable.”

Although previous studies have found there is a strong emotional response to politics, Westen said this is the first study to monitor brain imaging.

Westen said, in an email interview, the Republican Party leadership realized emotions play a large role in political campaigns, but Democrats – with the exception of President Clinton, who Westen said is a different type of Democrat – mainly appeal to the rational sense, leading to what Westen labeled “an un-level playing field.”

Westen added that members of the Republican Party have used this realization to their advantage in their campaigns and advertisements.

“Republicans understand how mind works,” Westen said. “Democrats are tenaciously holding onto an 18th century view of a dispassionate mind where people think things out, they reason things out, and this is how they make their voting decisions.”

BU political science professor Michael Ebeid, who specializes in presidential elections, said he needs to see more concrete evidence to prove there is an actual difference in campaign strategies between the parties.

“I understand why one might draw this conclusion about electoral strategies of the major parties based on anecdotal impressions,” Ebeid said. “But of course it would have a much more solid foundation if it was supported with empirical evidence, such as content analysis of campaign speeches, platforms, et cetera.”

Westen further estimated that between 75 percent to 80 percent of the American population are rationally unable to listen to new political information because of their pre-determined beliefs, but he added political change is possible after a long amount of time.

“We are emotionally driven towards ideas that make us feel comfortable,” Westen said. “And that happens automatically and unconsciously. What we really have to do in cases like this is fight that process.”