The advertising industry has long recognized the value of repetition when you have a product to sell. Brain researchers are just now figuring out why that is, and their conclusions hold some lessons for political campaigns.

The advertising industry has long recognized the value of repetition when you have a product to sell. Brain researchers are just now figuring out why that is, and their conclusions hold some lessons for political campaigns.


Facts that we hear or see first land in the part of the brain called the hippocampus, Sam Wang, a Princeton professor of neuroscience, and Susan Aamodt explain in a recent column in The New York Times. Each repetition of the fact resonates again in the hippocampus and it is reprocessed and gradually moved to the cerebral cortex, where it is available for easy retrieval.


Along the way, the fact is subject to "source amnesia," the authors say, which disconnects the fact from the circumstances in which it was learned. That process can also disconnect it from other knowledge, including the understanding that the "fact" isn't really true.


"With time, this misremembering only gets worse," the authors write. "A false statement from a noncredible source that is at first not believed can gain credibility during the months it takes to reprocess memories from short-term hippocampal storage to longer-term cortical storage. As the source is forgotten, the message and its implications gain strength."


Experiments done with students have tested these findings, but there's evidence in the political world as well. Polls showed the "Swift boat" attacks on Sen. John Kerry in 2004 made a larger impression on voters over several weeks, as they were repeated and the challenges to their veracity faded. Barack Obama is a Christian, but references to him as a Muslim have been repeated often enough that 10 percent of voters think it's true.


You don't have to be a neuroscientist to understand the principle. President George W. Bush explained it in 2005: "In my line of work, you got to keep repeating things over and over and over again for the truth to sink in, to kind of catapult the propaganda."


Voters who are the target of campaign propaganda should learn from the science. Just because you've heard it a lot, doesn't make it true.