Deeply personal and filled with love, Maya Forbes' Infinitely Polar Bear is nonetheless a hard movie to watch - hard to watch comfortably. Based on her experiences growing up with a father who was in and out of institutions, diagnosed with manic depression, Forbes' film throws a memoir-ish lasso around late-1970s Cambridge, Mass., where a family with a wildly careening dad, a mom trying to pursue a career, and two girls caught in the throes go about their lives.

Not an easy thing when Cam Stuart (Mark Ruffalo), the close-to-penniless scion of one of Boston's wealthiest clans, drinks and smokes to excess, rides a bike around in his underwear, dreams up outlandish schemes, and screams out whatever agitated idea is bursting in his head. When he's energized and elated, he's as unstoppable as Harold Lloyd in a madcap silent-era romp. But when Cam falls, the chasm is dark and wide - and horrific for those in his proximity.

It's textbook bipolar disorder, but because Forbes lived with and loved the real-life Cam, Infinitely Polar Bear keeps the emphasis on the breathless manic moments, the wayward industry of a man trying to do everything at once, spurred by his own sense of excitement and invention. It's exhausting, but it's also eccentric and charming. Sometimes, it borders on cute.

Yes, Ruffalo's Cam emerges from a psychiatric hospital in Lithiumed numbness. Yes, he throws ferocious fits in public, disappears in the middle of the night, turns the cramped, shabby apartment into a disaster zone. But, hey, it's hard not to love the guy.

Well, Forbes loved him, anyway. Yet even with Ruffalo's full-tilt, fully committed performance, it's not easy to share the filmmaker's affections. This is a movie seen through a child's viewfinder, the filter of memory; to adults, watching from the theater seats, the landscape of mental illness looks more troubling.

That said, it's impossible not to be won over by this cast. Zoe Saldana plays Maggie, the wife who, somewhat desperately, entrusts her daughters to her husband while she goes to New York to get an M.B.A. and, eventually, a job. Imogene Wolodarsky, Forbes' daughter, plays Amelia, the older of the two sisters, cringing in embarrassment at her father's public displays of, well, serious wackiness. As a stand-in for her filmmaker mom, whose mother (the Saldana character) was black, Wolodarsky brings an innate understanding to the role. She's reenacting family history here, acquitting herself with grace and guts.

Ashley Aufderheide is Faith, the younger of the pair - and the one who looks more like the biracial offspring of her parents. What the girls' blackness is, and what it means, is something both struggle with. As an African American woman in 1970s Boston, Maggie has her struggles, too.

Infinitely Polar Bear (the title comes from an entry Cam scrawled on an intake form, describing his condition) has a sweet, retro vibe, with its vintage cars (VW microbuses, a dubious Citroen sedan), vintage clothes, its home-movie palette of faded color. A mother grapples with daunting issues of self-worth and empowerment; a father grapples with issues that can subsume him completely; and two girls, armed with the resilience of childhood, grapple with what they've been given: love, anarchy, laughter, pain.

Infinitely Polar Bear *** (Out of four stars)


Directed by Maya Forbes. With

Mark Ruffalo, Zoe Saldana, Imogene Wolodarsky, Ashley Aufderheide. Distributed by Sony Pictures Classics.

Running time: 1 hour, 28 mins.

Parent's guide: R (profanity,

adult themes).

Playing at: Ritz Five and Carmike Ritz Center/NJ.EndText