The summary is that people which were more creative, according to their definition, had higher connectivity between hemispheres in the prefrontal cortex. Very important to remember is that creativity differs for different researchers so in this case it's Creativty Index (CGI) 
Creativity Index (CCI) is from Composite Creativity Index (CCI) which is defined in  as " One such cognitive process – divergent thinking – is the process by which one extrapolates many possible answers to an initial stimulus or target data set. We sought to link well established measures of divergent thinking and creative achievement (Creative Achievement Questionnaire – CAQ) to cortical thickness in a cohort of young, healthy subjects. Three independent judges ranked the creative products of each subject using the consensual assessment technique (Amabile, 1982) from which a “composite creativity index” (CCI) was derived. "
"Seemingly countless self-help books and seminars tell you to tap into the right side of your brain to stimulate creativity. But forget the "right-brain" myth—a new study suggests it's how well the two brain hemispheres communicate that sets highly creative people apart."