Republican candidate Donald Trump's acceptance speech Thursday night took a voyage through dark images of a country adrift and under threat — seemingly pushing all the buttons of fear that supposedly motivate conservative voters.
Was it a mistake?
Widely reported studies have shown that conservatives have more activity in a brain structure called the amygdala — which is most closely identified with fear and emotional responses, while liberals appear to have more brain cells in the anterior cingulate cortex, involved in decision-making.
So when Trump said: "The attacks on our police, and the terrorism in our cities, threaten our very way of life," it could be interpreted as an attempt to frighten voters, and a strong appeal to the right.
However, recent research casts real doubts on this idea that the brains of conservatives are structurally different from the brains of liberals.
"Basically, we don't know anything whatsoever. Absolutely nothing," said Evan Charney, a professor at Duke University whose expertise crosses the fields of public policy and brain science.
"Any claim to the contrary is based upon pseudoscience."
Some of the best-known work was done by Ryota Kanai, a former researcher at Britain's University of Sussex who has now formed a brain imaging company in Japan called Araya Brain Imaging. Kanai used functional magnetic resonance imaging (fMRI) to show self-described conservatives and liberals responding differently to various stimuli and showing basic differences in the sizes of their brain structures.
They even found that using a weak electrical current in what's called transcranial random noise stimulation could alter the way people think, making them more conservative, at least for a time.
Read Montague at Virginia Tech University found conservatives and liberals react differently to, say, disgusting images, which also suggests basic biological differences.
Charney disputes it.
"We don't know anything about the brain," he said.
And a study released earlier this month might help back him up. A team at Linköping University in Sweden found that the software used to generate the fMRI images was glitchy. Their study, published in the Proceedings of the National Academy of Sciences, showed the software created false readings 70 percent of the time - and it had been used in 40,000 brain studies going back 15 years.
Even if the images are right, they don't say much, Charney argues.
"We cannot infer what anyone is thinking or feeling by the activation of a particular region of the brain," Charney told NBC News.
"So activation of the amygdala, for example, could indicate fear, disgust, sexual arousal, interest, concern — any number of different kinds of responses," he said.
"I could give you 100 different fMRI studies in which activity in the same area of the brain has been interpreted 100 different ways, depending on what the author was trying to demonstrate and trying to prove."
To Charney, that means if Trump was trying to scare people, it will backfire.
"I think it was a profound mistake," Charney said. "I think he really overestimated the extent to which Americans really do feel the fear, the primal fear that he was depicting," he added.
"I think that is only going to appeal to a small segment of the Republican party. I feel he did nothing to expand his base to reach out to other voters."
And if Democrats try scaring people, it won't work there, either, Charney said. "I think there are going to be lots of appeals to fear in this election)," he said. "A lot of the current Democratic campaign is based on fear of Donald Trump."
But another expert said the tactics Trump is using are cleverly manipulating the electorate.
George Lakoff, professor of cognitive science and linguistics at the University of California Berkeley, says Trump is tapping into something much wider than fear.
"People think metaphorically," Lakoff said. It's not as simple as fear or curiosity — it's how they frame the world in general. And it's not unique to either Republicans or Democrats, he argues.
Related: Fact-Checking Trump
Lakoff uses the metaphor of the family.
Conservatives, Lakoff said, see the world in terms of paternal-type authority, which is why they tend to support police, hard work and hierarchical order.
"You have to be disciplined. If you are not working hard, it is your fault," Lakoff said.
"If you have that 'strict father' view, then you can appealed to by Trump."
And that, Lakoff argues, is why Trump's speeches could appeal to people who are not traditional conservatives. Many so-called moderates lean to a "strict father" morality even if they are liberal in some ways, and they'll respond to rhetoric about strength.
And people also respond to repeated assertions — even when those assertions are later proven wrong.
"He is framing Hillary (Clinton) as purposely and knowingly committing crimes for her own benefit, which is what a crook does," Lakoff said.
"Repeating makes many people unconsciously think of her that way, even though she has been found to have been honest and legal by thorough studies by the right wing."
And the fear works, too. "Fear tends to activate desire for a strong strict father — namely, Trump," Lakoff said.
Both liberals and conservatives can be motivated by fear. Conservatives may be fearful about potential attacks from outside the country, while liberals may fear threats to the environment or from out-of-control police.
In either case, voters are not thinking in terms of facts. They are thinking in metaphors, he argues. What differs is the metaphor that people use.
So checking facts and debunking claims does little to change people's thinking, Lakoff said.
"The liberal media doesn't understand what's going on," he added.
"Even if he loses the election, Trump will have changed the brains of millions of Americans, with future consequences," Lakoff said.