In a storytelling convention that’s at least as old as the 1966 sci-fi film Fantastic Voyage —another example that springs to mind is Madeleine L’Engle’s great novel A Wind in the Door —Inside Out cuts between two parallel storylines, one taking place around Riley, the other inside her.
Miniaturized interlopers have also found comic results ("Innerspace") and harrowing ones ("Fantastic Voyage") after being injected into bodies.
This isn't the first film to depict small beings inside others (beyond the likes of "Fantastic Voyage" and any number of demonic possession flicks there's been "Everything You Wanted to Know about Sex" (or at least one segment of that Woody Allen film), "Meet Dave" and "Osmosis Jones," among a few others).
Tipping its hat to The Wizard of Oz, Fantastic Voyage and numerous other fantasy journeys, this animated adventure thoroughly amuses and challenges on its subconscious quest.
When something goes wrong and Joy and Sadness are inadvertently ejected from the "Control Room," we begin perhaps the strangest road trip since Fantastic Voyage: a trek through Riley's subconscious.