‘Tara’ follows bizarre trend in comedies

The family comedy has undergone some transformations, thanks mostly to cable television and its restless search for buttons and/or envelopes to push.

“United States of Tara,” a new Showtime series about a woman with multiple personalities, is solidly within this new tradition of the strange, alongside the network’s “Weeds” and HBO’s “Big Love” (which returns tonight at 9).

In “Tara,” which premieres tonight at 10, Toni Collette plays an artist, wife and mother of two who by turns becomes a troublesome teenager, a proper ’50s housewife and an improper good old boy.

Her condition – it’s called “dissociative identity disorder,” revised from multiple personality disorder, as Tara herself has occasion to point out – seems to be an open secret: Teen “T” goes to the mall with her daughter as a kind of peer (but with credit cards); Alice attends a parent-teacher meeting and makes a perfect cake for a bake sale; Buck goes bowling and beats up the daughter’s mean boyfriend.

Despite the left-field premise, the show’s concerns are those of a conventional sitcom. We have seen these folks before: rebellious older daughter (Brie Larson); sensitive, precocious younger son (Keir Gilchrist); and good-natured husband (John Corbett).

Series developer Diablo Cody (“Juno”) says she has done her homework on what is a controversial subject. She does include a skeptical voice – not every authority supports DID as an actual disease – but she puts it in the mouth of Tara’s sister (Rosemarie DeWitt), who is herself troubled.

The idea is that by going off her medications and letting the “alters” come out to play, Tara will be able to bring to light the suppressed memory of whatever trauma caused the fracture.

While their presence may provide novel dilemmas for her family – as when husband Max has to rebuff the sexual advances of Tara’s other selves not to cheat on her – Collette, and the show, is always most interesting when she’s just Tara. That is, the person with layers.