Mind Hacks has written about a new study of the neuroscience of jazz improvisation. Six pianists' brains were scanned while they performed a scale, a memorized jazz melody, or improvisations of either the scale or the melody. "For Scale's improvisation condition, subjects improvised in quarter notes only, selecting all notes from within one octave and from the C major scale notes alone..." "For Jazz's improvisation condition, subjects improvised using the composition's underlying chord structure as the basis for spontaneous creative output..."
The brain scans (fMRI's) showed that one area of the brain had reduced activity during improvisations. The dorsolateral prefrontal cortex is associated with self-censorship and other inhibiting behaviors, suggesting that jazz improvisation requires a lack of inhibition. Another area of the brain showed heightened activity during improvisation, the medial prefrontal cortex. This area is associated with actions of individuality or self-expression, "such as telling a story about yourself."
Thus jazz improvisation is about revealing yourself, and requires you to be less inhibited to do so. I wonder if other types of improvisation - aleatory, free improv, embellishments - would have similar results.
Charles J. Limb and Allen R. Braun, "Neural Substrates of Spontaneous Musical Performance: An fMRI Study of Jazz Improvisation" Public Library of Science One [an open source journal], Feb. 27, 2008.