Anyone who is old enough to remember when MTV actually played music videos has grumbled about the deteriorating quality of the network's reality-laden TV schedule. Now, those crotchety complaints are finally being validated by the financial sector.

UBS analyst John Janedis on Tuesday downgraded the stock of MTV's parent company, Viacom (NASDAQ: VIAB), citing "ongoing ratings weakness at the house that Snooki built as one of the primary obstacles for the media giant's future growth potential."

"From a content perspective, our sense is that returning series at MTV are under-performing," Janedis wrote, "which will translate to further make goods [adjustments to advertisers] and a drag on ad growth in F13."

MTV did not return a request for comment.

Janedis also expressed concerns about ad growth at the kids' network Nickelodeon, another Viacom property. Downgrading Viacom's stock from buy to neutral, the analyst said he expected the stock would trade sideways until some of his points could be addressed. The UBS downgrade is third downgrade this year for Viacom, with the first two coming from Goldman Sachs and Miller Tabak.    

The fickle world of youth culture puts MTV in a difficult position for predicting future growth. The network must continually -- and rapidly -- redefine itself if it hopes to tap into the tastes of its target demographic of 12- to 34-year-olds. Often, that redefinition involves a seemingly haphazard process of trial and error, one that stirs impassioned debates over MTV's relevance andstubborn pining for its long-abandoned directive as an outlet for music videos.

And yet, regardless of how one measures success, it's difficult to argue with MTV's ability to innovate. Launching "The Real World" in 1992 made it a pioneer in the genre of cheap-to-produce reality shows that now permeates television, while animated programs such as "Beavis and Butt-head" earned MTV its ironic, self-referential stripes by connecting with the same audience it subtly mocked. By the early days of YouTube, the network lost some of that swagger. Reality snoozers like "The Hills" and "The College Life" ushered in a 23 percent drop in ratings, while insiders speculated that young people were too busy consuming entertainment online to bother with the decades-old network.

Not so, if 2011 is any barometer. MTV bounced back in a big way last year, when the freshly minted cast of "Jersey Shore" led a new roster of ratings boosters that included the envelope-pushing "Teen Mom" and "The Real World: Las Vegas." Meanwhile, a slew of controversy seemed only to increase the network's cache. The short-lived scripted show "Skins," which showcased  a barely legal cast of drug and alcohol users, had parental groups up in arms, while the aforementioned "Jersey Shore" brought criticism from Italian-American groups. Before we knew what hit us, everyone was talking about MTV again.

But 2011 was ages ago in MTV years. Ratings are down at the network this year, and Snooki and the gang are due to succumb to the ravages of excessive tanning any day now. Meanwhile, with MTV relying on two "Jersey Shore" spinoffs to keep it afloat, the network clearly has a longevity problem on its hands. UBS would seem to agree.