Political consultants have long tried to get inside voters' heads, and now, they are, sort of. And as it turns out, the brain can be pretty partisan.

Researchers at the University of California Los Angeles (search) are working with political consultants to put people on MRI (search) machines and measure blood flow to the brain when viewing campaign ads.

When Democrats were shown President Bush's re-election campaign ads featuring images of the Sept. 11, 2001, terror attacks, the part of the brain that reacts to danger lit up. Researchers believe it's because Democrats view that day as a good issue for Bush to get re-elected.

Conversely, ads for presumptive Democratic nominee John Kerry (search) seem to strike a nerve with Republicans.

"Our idea is that they have more of an emotional response to their favorite candidate and they use their reasoning apparatus to almost argue against the opponent when they see the face and picture of the opposing candidate," said Marco Iacobani of UCLA's Neuropsychiatric Institute (search).

Some critics say they are afraid the brain scans will be used to brainwash.

"What's the line between figuring out which ad works and figuring out, 'how do I manipulate this particular voter through a combination of words and images in order to convince him to believe something he may not really believe?'' asked Democratic analyst and Fox News political analyst Susan Estrich.

Researchers say, however, that MRI information would actually empower voters to make sure politics are on the brain.

Click here to watch a report by Fox News Channel's Trace Gallagher.