"Well, what if we did this in the mind as opposed to the brain? So instead of blood vessels and dendrites, what if it was consciousness and dream production? And that would allow us to have characters that represent emotions. And that felt like, man, that's exactly what animation does best - strong, opinionated, caricatured personalities. And that just got me excited."
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Source : "It's All In Your Head: Director Pete Docter Gets Emotional In 'Inside Out'". "Fresh Air" with Dave Davies, www.npr.org. February 19, 2016.