Take six jazz musicians and put them in MRI scanners. Add special plastic keyboards so that they can jam together (itself a feat in these confines) and see what happens. When this experiment was performed recently some interesting things were observed.
Inhibition switches off. Self-expression switches on. Sensory awareness is heightened. Specific areas of the brain controlling these functions either shut down or powered up. It was much the same type of pattern that happens when we enter a dream state.
It certainly mirrors my subjective sense of what happens during my own creative flows. Story-telling switches on. Feelings intensify. And at flow’s end there is the often surprising realization that hours have gone by. Check it out at the link.