Understanding politics with brain blood flow patterns. Maybe some people will be critical of the use of MRI technology to test political ads.

[A man] lay inside an M.R.I. machine, watching commercials playing on the inside of his goggles as neuroscientists from the University of California, Los Angeles, measured the blood flow in his brain. Instead of asking the subject, John Graham, a Democratic voter, what he thought of the use of Sept. 11 images in a Bush campaign commercial, the researchers noted which parts of Mr. Graham's brain were active as he watched. The active parts, they also noted, were different from the parts that had lighted up in earlier tests with Republican brains.

Here's why I was eager to find out what science can tell us. Democrats were harshly critical of Bush for using 9/11 images in ads and asserted that they were outraged at the desecration of the images. But maybe the claim of outrage is being asserted because it is an effective political argument to counter what is actually an effective commercial that doesn't outrage people who have some potential to actually vote for Bush. So can you answer such questions from seeing blood flow patterns?

Mr. Graham, like other Democrats tested so far, reacted to the Sept. 11 images with noticeably more activity in the amygdala ["the part of the brain that responds to threats and danger"] than did the Republicans, said the lead researcher, Marco Iacoboni, an associate professor at the U.C.L.A. Neuropsychiatric Institute...

"The first interpretation that occurred to me," Professor Iacoboni said, "is that the Democrats see the 9/11 issue as a good way for Bush to get re-elected, and they experience that as a threat."

But then the researchers noted that same spike in amygdala activity when the Democrats watched the nuclear explosion in the [LBJ] "Daisy" spot, which promoted a Democrat.

Hmmm.... so what's the interpretation?

[Clinton strategist Tom] Freedman suggested another interpretation based on his political experience: the theory that Democrats are generally more alarmed by any use of force than Republicans are. For now, Professor Iacoboni leans toward this second interpretation, though he is withholding judgment until the experiment is over.

Freedman's interpretation is self-serving, but is there an alternative? Maybe not. What makes someone affiliate on a deep level with a political party? It can't be actual rational agreement with all the positions that party currently espouses. Maybe present day affiliation with the Democratic Party is founded on an emotional aversion to violence. Maybe people with steelier nerves (or an attraction to violence) are drawn into the Republican Party.

This is even more interesting:

One of the most striking results so far is the way subjects react to candidates after seeing a campaign commercial. At the start of the session, when they look at photographs of Mr. Bush, Mr. Kerry and Ralph Nader, subjects from both parties tend to show emotional reactions to all the candidates, indicated in the ventromedial prefrontal cortex, an area of the brain associated with reflexive reactions.

But then, after the Bush campaign commercial is shown, the subjects respond in a partisan fashion when the photographs are shown again. They still respond emotionally to the candidate of their party, but when they see the other party's candidate, there is more activity in the rational part of the brain, the dorsolateral prefrontal cortex. "It seems as if they're really identifying with their own candidate, whereas when they see the opponent, they're using their rational apparatus to argue against him," Professor Iacoboni said.

That seems to explain a lot about the way people behave in politics and why people talk past each other once they've bonded with their candidate. It also suggests why people in the middle (like me), who actually have the potential to vote for either candidate, get so sick of hearing the arguments both sides make.