http://www.youtube.com/watch?v=HpvrwXMDSNY

The most recent episode of South Park, “Ass Burgers,” and its preceding episode of last spring, “You’re Getting Old,” call for a little armchair psychology. What caused South Park creators Matt Parker and Trey Stone to set up, and then immediately destroy, a new direction for the show? Why did they tread meta territory so heavily, trash their own creation through the voice of one of its most-loved characters, bleakly refuse to laugh at the type of humor they’d cultivated over 15 years and then toss the whole enterprise away with the biggest and most intentional deux ex machina this side of the Coen Brothers?

The answer? Call it the seven year itch.

It’s become almost clich? to compare the top three most successful animated comedies on TV right now, but the comparison remains appropriate because of the unique placement that cartoons, as a genre, and their creators hold in the entertainment industry. People like “Simpsons” creator Matt Groening, “Family Guy” creator Seth MacFarlane and Parker and Stone are neither directors nor actors nor producers proper – though, of course, they may direct or produce or do voice acting on their shows – because those skills don’t translate over to more traditional Hollywood media.

Rather, they’re best (if wishy-washily) categorized as creatives. They’re equally capable of dreaming up, say, an album of show tunes or a Broadway musical as they are overseeing year after year of an animated show about middle-class life in America. In fact, they’re more than capable of branching out into new genres or formats – they appear hardwired to do so, and at surprisingly regular intervals.

Take Groening. The first episode of “The Simpsons” aired in December 1989. The show quickly became a cultural phenomenon and churned out dozens of classic episodes you can still hear quoted ad nauseum by aging fanboys if you happen to affect a Scottish brogue in the wrong bar.

All of that success, and still: In 1997, Groening began researching science fiction works for “Futurama,” a show that would hit the airwaves two years later. In 2007, “The Simpsons Movie” was released, which put Springfield on the big screen and expanded Homer’s misadventures to feature-film length.

MacFarlane exhibits a similar pattern. Apparently not content with just one cartoon sitcom family with an anthropomorphacized pet, he created “American Dad” in 2005, six years after Family Guy’s premiere in January 1999. It’s a little unclear how “The Cleveland Show” (which premiered in 2009) fits into this pattern, but then again, it’s a little unclear how “The Cleveland Show” belongs on television at all.

The syndrome is everywhere you look. Mickey Mouse made his debut in 1928, and Walt Disney began work on “Snow White,” his first feature film, in 1934. The first episode of the Jim Henson-inspired “Sesame Street” was in 1969, the BBC premiere of “The Muppet Show” in 1976. Whether it’s an expression of pent-up creativity, a re-self-affirmation of why the creator became famous in the first place or just a pet project that might never have seen the light of day if it weren’t implicitly tied to a better-known work, seven years (give or take, depending on whether you’re counting from conception, creation or air date) appears to be the time span granted to a project until a diversion, spin-off or final? is dreamed up.

Which brings us to Parker and Stone. In June, before the show went on its scheduled summer hiatus, “South Park” aired an episode that some speculated would serve as an unannounced series final?. In it, Stan Marsh, one of a few characters that occasionally serves as a proxy voice for Parker and Stone, experienced something of an existential crisis on his 10th birthday. Things that had seemed entertaining to him before seemed inane; that which had seemed funny was now dull. Nothing whatsoever interested him; rather, everything (literally, this being “South Park”) looked and sounded like shit. Other plot points, like Stan’s parents getting divorced, went weirdly unresolved. On one reading it was an indictment of all pop culture by Parker and Stone, but on another it was a mea culpa – an admission that they were part of the problem.

The first episode of “South Park” aired in August 1997. Seven years later, Parker and Stone created “Team America: World Police,” an ambitious, offensive, puppet-based send-up of American imperialism and ethnocentrism that had no overlap with Kyle, Stan, Cartman and Kenny’s paper-cutout world. Seven years later was this summer. It appears that Parker and Stone had two ideas (there are, after all, two of them) about how to branch out. Luckily, their musical, “The Book of Mormon,” became a critical and popular sensation, and when the pair returned to the animation studio to continue the show that made them famous, the edge had apparently dulled on their desire to blow up the cozy Colorado town.

So that’s why, last week, all the damage was undone. That’s why Barack Obama was dragged back into the “South Park” frame to replace the mouth-defecating duck occupying the Oval Office. That’s why Stan’s parents quickly and unceremoniously moved back in together, Steamy Nix paraphernalia a charred, forgotten memory. And that’s why, with Parker and Stone’s seven-year itch vigorously scratched by a summer on Broadway, no one should have expected anything different.