Last fall, when researchers had freestyle rappers go through an fMRI while rapping, they noticed that the prefrontal cortex -- the part of the brain responsible for self-editing -- shut down. This allowed, they said, words and ideas to arise unfiltered in the artists' lyrics. Their research, and similar studies done on jazz musicians during improvisation, implied that creativity itself is driven by that unrestrained state of mind.

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For those who fall somewhere short of the creative artist label, finding a way to tone down the prefrontal cotex's activity should still theoretically help boost outside-of-the-box thinking. To test this, researchers at the University of Pennsylvania hooked 48 participants up to electrodes and sent a weak electrical charge through either their right or left prefrontal cortex (the left is particularly associated with the self-editing effect).

The process, known as transcranial direct current stimulation (tCDS), interferes with cell-to-cell communication in the areas through which the charge passes. So in effect, the researchers were turning off their participants' filters.

With their cognitive controls inhibited, the participants were given a challenge: look at images of ordinary objects and come up with unusual uses for them. Rubber hose? Use it to climb a tree. Manila folder? How about kindling for a fire.

Both people who had current sent through their right prefrontal cortex, and those who didn't receive any electrical charge, were stumped by an average of 15 of the 60 objects. Those whose left prefrontal cortexes were deactivated, on the other hand, missed an average of only 8. They were also about a second faster in their responses.

"It was surprising to me how big the finding was" Sharon Thompson-Schill, one of the study's authors, told me. "What I thought we would see was something on the order of milliseconds, and no difference in accuracy," she explained. Instead, "we were cutting in half the number of times that people failed to come up with something."

The results don't apply to all thought processes that we might call "creative," said Thompson, but only to ones in which there isn't a clear goal you're trying to achieve -- as with musical freestyle or improvisation. When it comes to cognitive control, she explained, we tend to assume that more is always better, and attempts to enhance that ability are a stalwart of cognitive psychology. "Being able to dynamically turn on and off the amount of control you have could be a useful skill to acquire," said Thompson. "Whether you should slap an electrode on the side of your head to do it ... I wouldn't go so far as to say that."

"Noninvasive transcranial direct current stimulation over the left prefrontal cortex facilitates cognitive flexibility in tool use," is published in Cognitive Neuroscience.