Conservatives and liberals may have one less thing in common: neurology.

ProCon.org has gathered 13 peer-reviewed studies of behavioral and neurological studies and come to the conclusion that differences between Republicans and Democrats are more than skin-deep.

"Basically, the different sides have been yelling at each other for millennia, and we're trying to figure out what could be the root cause of this," said Steven Markoff, ProCon.org's founder.

The studies looked at things like differences between groups' perception of eye movement, and aversion to threatening noises. Researchers also noted that Democrats had larger anterior cingulate cortexes, which are associated with tolerance to uncertainty, while Republicans had larger right amygdalas, which are associated with sensitivity to fear.

"Everybody seems to basically agree, and these are people that have scientific backgrounds," Markoff said of the repetition in the studies. "That to me is probably the biggest eye-opener."

Although Markoff concluded the studies combine to mean that the different groups communicate in different ways, psychiatrist Greg Appelbaum said the studies point toward conservatives' tendency to avoid something called self-harm, while liberals avoid collective group harm.

That said, Appelbaum the studies are not representative of all Republicans or Democrats, given that researchers are weaving different small studies together to draw conclusions, and several different opinions designate whether someone is liberal or conservative.

"It's important to keep in mind that this is a big, multidimensional space," Appelbaum said.

He also said someone's brain makeup doesn't necessarily predispose that person to think one way or another politically, calling it a "chicken or the egg issue." In fact, it's possible that a person's political thinking can change their physiological traits.

It makes sense to consider a person who plays video games and has good reaction times, he said. Does that person play the games because he (or she) is good at them and gets positive reinforcement or does that person hone the abilities by playing video games?

Regardless of the caveats, Markoff said the collection of studies generate an interesting discussion.

"The real reason ProCon is here is to foster critical thinking, and I can't think of anything more interesting from a critical thinking standpoint," he said.