At TEDx MidAtlantic, held in November 2010 in Washington, DC, medical researcher Charles Limb presented his lab's recent research using fMRI to explore dynamic brain response in musicians as they performed. He describes work published in 2008 working with jazz pianists, as well as more recent work studying rap performers. Their basic strategy was to record the fMRI scan during two modes of performance: playing memorized music and playing improvized music, and then identifying from the data the brain regions that showed activity unique to improvisation.
Their key finding was that during improvisation, a region of the brain linked to planned actions and self-censoring exhibited a slowdown in activity. They also found an increase in activity in a brain region associated with self-expression. Limb remarks that: "We think that at least a reasonable hypothesis is that, to be creative, you have to have this weird dissociation in your frontal lobe. One area turns on, and a big area shuts off, so that you're willing to make mistakes, so that you're not constantly shutting down all of these new generative impulses."