It's one of the great paradoxes of television sitcom history: How did Alex P. Keaton —a character in the 1980s sitcomportrayed by actor Michael J. Fox—the son of mellow hippie parents, become an uptight Republican who idolizes both Richard Nixon and Ronald Reagan?

"In the past, people thought that [political leanings were] all environmentally influenced, a combination of biological dispositions as well as cultural shaping," says David Amodio, an assistant professor of psychology at New York University. However, a new study, led by Amodio, indicates that political bent "is not just a choice people have, but it seems to be linked to fundamental differences in the way people process information."

Amodio and colleagues report in Nature Neuroscience that they scanned the brains of 43 subjects during 500 trials of a task designed to test their ability to break from a habitual response. Prior to beginning the experiment, volunteers were asked to rate their political leanings based on a scale from –5 (extremely liberal) to +5 (very conservative). They were then given a computerized test in which they were shown one of two stimuli for 100 milliseconds (0.1 second). If an "M" popped on the screen, the respondent had 500 milliseconds (a half second) to press a key on the keyboard before him or her; if a "W" appeared, the person was told to do nothing.

The task, known as Go/No-Go, is an example of "conflict monitoring," which Amodio says, "came about as a way to explain how we realize that we need to pay more attention." In this version, subjects became accustomed to pressing the button when they saw an "M," which appeared 80 percent of the time during the trials. Thus, when a "W" cropped up, participants faced a conflict between their trained response and a new stimulus.

Amodio says that the anterior cingulate cortex (ACC), a forebrain region, "serves almost as a barometer for this degree of conflict."

"People who have more sensitive activity in that area,'' he notes, "are more responsive to these cues that say they need to adapt their behavior," reacting more quickly and accurately to the unexpected stimulus. On average, people who described themselves as politically liberal had about 2.5 times the activity in their ACCs and were more sensitive to the "No-Go cue'' than their conservative friends.

"They are more sensitive to the need for change and more sensitive to the need to change their behavior," Amodio says about the politically left-leaning subjects.

He plans to repeat the experiment with subjects who give views on specific hot-button political issues, such as gun control.