Here is an interesting video featuring Charles Limb, a musician, surgeon, and TED presenter, about how the brain works during creative endeavours. While the main focus is on jazz music and rappers I think it still relates to the creative process of writing, especially free form writing which is also spontaneously produced. It gets especially interesting around the seven minute mark when they show what happens with the brain during the creative process.
In a nutshell the brain is divided into different areas for different functions. Their hypothesis is “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 not inhibited, so that you’re willing to make mistakes, so that you’re not constantly shutting down all of these new generative impulses.” Now does that sound like what we strive to achieve during our writing challenges or what?