Josh Hafner

USA TODAY

Ted Cruz pitches himself as an overcomer, an underdog, an outsider who beats the odds.

While the Republic candidate has won four states in this nomination race so far, a neurologist says he still faces a big obstacle with voters: his own face.

In an interview with Quartz, George Washington University's Richard E. Cytowic said the unusual movements of Cruz's face may make him seem less sincere to the human brain than other candidates.

"The normal way a face moves is what's called the Duchenne smile, named after the 19th century French neurologist. So the mouth goes up, the eyes narrow and the eyes crinkle at the outside, forming crows feet," said Cytowic, a professor of neurology.

"Cruz doesn't give a Duchenne smile. His mouth goes in a tight line across or else it curves down in an anti-Duchenne smile. So he doesn't come across as sincere at all."

That doesn't mean Cruz is actually less sincere than, say, the Duchenne-smiling Trump or Rubio, Quartz notes. It is completely normal to perceive him that way, according to Cytowic, perhaps making Cruz's political success all the more noteworthy.

Cruz also makes jabbing motions and other unusual body motions while speaking, Cytowic said, which can feed negatively into the split-second judgments the brain makes when analyzing anyone, including candidates.

That's because when the brain makes choices, he said, it seeks to simplify the decision-making process.

In doing so, familiar or pleasing physical attributes like the Duchenne smile can actually do more to sway a voter's preference for a candidate than his or her stated policies.

So while many voters may think they choose their candidates based solely on rational factors like policy, Cytowic said, that's unfortunately not the case.

"Looks trump policy—no pun intended," he said. "Sad, but true."

See Quartz's video interview here.

Follow Josh Hafner on Twitter: @joshhafner