While guest-hosting a BBC radio program last December, the Academy Award-winning actor said he would like to have British Deputy Prime Minister Nick Clegg "scanned" to discover why the two never see eye-to-eye on issues.
So Firth, 50, contacted scientists at the University College London to undertake the study.
"I took this on as a fairly frivolous exercise: I just decided to find out what was biologically wrong with people who don't agree with me and see what scientists had to say about it and they actually came up with something," said Firth.
That something has recently been published in the journal Current Biology and has revealed some interesting insights into how hardwired we are on our political views.
Using MRI scans of more than 90 college students — in addition to Labour MP Stephen Pound and Alan Duncan, the conservative minister of State for International Development — scientists concluded that conservatives have larger areas concerned with fear and anxiety while liberals have greater capacity for optimism and courage.
"The anterior cingulate is a part of the brain that is on the middle surface of the brain at the front, and we found that the thickness of the grey matter, where the nerve cells of neurons are, was thicker the more people described themselves as liberal or left wing and thinner the more they described themselves as conservative or right wing," Geraint Rees, director of the UCL Institute of Cognitive Neuroscience, told the BBC.
"The amygdala is a part of the brain which is very old and very ancient and thought to be very primitive and to do with the detection of emotions," he added. "The right amygdala was larger in those people who described themselves as conservative."
Suddenly, it makes a lot more sense why Republicans use scare tactics to frighten their base into action.
While Rees says a scan is not a wholly accurate way to measure one's political beliefs, there was "a strong correlation that reaches all our scientific tests of significance."