Why are conservatives conservative and liberals liberal?

Conservatives--particularly tough-on-crime, pro-military conservatives--have a more pronounced startle reflex, measured by eye-blink length after hearing a sudden loud noise. Furthermore, when showed threatening images--maggots in an open wound, a large spider on someone's face--conservatives displayed a greater galvanic skin response, caused by subliminal increases in sweat gland activity. These traits are linked to high activity in the amygdala, center of emotional processing and seat of the fear response. Liberals displayed these reactions as well--the fight-or-flight response is universal--but in conservatives, it was stronger, faster, and more pervasive. This also explains why liberals who are placed under stress, time pressure, or emotional duress are more likely to endorse conservative viewpoints they would not have otherwise espoused.

And then there are the liberals and the anterior cingulate cortex, or ACC. Its role in the brain is somewhat more complicated, but there is still general scientific consensus that it is involved in error detection and conflict monitoring, and ultimately cognitive control. Consider a 2007 work published in Nature Neuroscience, one of the earliest political neuroscience studies. The researchers hypothesized that liberals have more active ACCs, since they are more flexible and intellectually innovative, and more tolerant of uncertainty. Then they proved as much by having liberals and conservatives perform a classic test for conflict monitoring, of the sort that the ACC is thought to govern.

It's called a "Go-No-Go" task: Study subjects are put in a situation where they are required to quickly tap a keyboard when they see "M" on screen--and become habituated to doing so. But one fifth of the time, the screen instead flashes a "W," and respondents have to quickly change their behavior and not tap the keyboard. Liberals performed better at the task--they were less likely to commit a 'D'oh!' and tap the keyboard at the wrong time--and they also showed more anterior cingulate cortex activity when engaging in the corrective response. This study was subsequently replicated by another research team, using a Canadian sample, who also linked more brain firing in the task to egalitarianism, and less firing to right-wing authoritarianism.

It is not difficult to interpret this finding: Liberal's greater anterior cingulate cortex activity indicates their greater cognitive flexibility and willingness to update and change their beliefs and responses vis-a-vis changing cues and situations.