Between them, Janet Jackson and her brother Michael have sold more than 850 million albums worldwide. Those are serious numbers, but they mean little in the currency of pop, which is all about “What have you done for me lately?”

That’s a question Janet Jackson herself asked on her 1986 breakthrough album, “Control,” and she tries to respond this week on her 10th studio album, “Discipline” (Island Def Jam). It follows the latest release from Michael Jackson, “Thriller 25th Anniversary Edition” (Epic), an expanded version of his 1982 landmark. Both serve as reminders that two of the most formidable hitmakers in pop history are still in business. But, unfortunately for the House of Jackson, that’s about all they do.

Coincidental or not, Janet Jackson’s career hasn’t been the same since her overblown “wardrobe malfunction” at the 2004 Super Bowl. The two studio albums she released since then both failed to sell 1 million copies, a major fall-off for a singer who dominated the charts for nearly two decades. Blame Nipplegate if you must, but the bottom line is that the music on “Damita Jo” and the 2006 follow-up, “20 Y.O.,” wasn’t very good. Against a batch of R&B newcomers, from Rihanna to Beyonce, Jackson simply didn’t sound distinctive enough to warrant the mega-sales of her youth.   

The shortfall of inspiration continues on “Discipline.” She works with the usual A-list producers, including Rodney Jerkins, Ne-Yo and Jermaine Dupri, who sound as if they were under orders to update the “Control”-style electro-funk of Jimmy Jam and Terry Lewis.

Mechanized beats and layered vocals reign on tracks such as “Rollercoaster,” which most explicitly evokes the long-departed Jam and Lewis, and “Rock With U,” a not-so-subtle nod to Michael’s 1979 hit “Rock With You.” Cyber-Janet is best showcased on “Feedback,” which arrays strings and synthesizers around a robotic chant, and the prancing Stargate-produced extravaganza “2nite.”

For Cyber-Janet, intimacy ultimately equates with sex, the kinkier the better. The title track might as well come equipped with bondage straps and a riding crop. “You be the teacher, I’ll be the student,” she coos.

Early in her career, she was the somewhat underestimated girl-next-door with better producers (back then, Jam and Lewis were as hungry as Jackson to make a name for themselves). She had an exuberance that couldn’t be denied, whether she was chirping about racial unity or getting nasty. Once she grew up, the focus narrowed, and she started churning out soft-porn soundtracks.

Here’s the problem, though: Singing about sex isn’t necessarily sexy. For Jackson, the failure to recognize the difference has been costly.  Yesterday’s wardrobe malfunction has become today’s boring exhibitionism.

The news isn’t much better for Michael Jackson; it’s been nearly seven years since his last studio album, “Invincible,” was released. So the third major repackaging of “Thriller” (there also was an expanded reissue in 2001) is designed to remind us of the Jackson we knew, the gifted singer-songwriter-dancer who once made an album that has sold an extraordinary 104 million copies worldwide.

But the expanded track list is a waste of everyone’s time. Kanye West, will.i.am, Fergie and Akon take turns tinkering with various “Thriller” tracks, and the results are beyond forgettable. In his remix of “Billie Jean,” West even goes so far as to erase the track’s original bass line. That’s like wiping the smile off the “Mona Lisa.”

If a repackaged 100-million-seller can be deemed a flop, “Thriller 25” qualifies.