FRAGMENTED to the point of kaleidoscopic, alternately poetic and harrowing, "Tarnation" is, more than anything else, about the awesome power -- and the abject failure -- of memory.

A documentary, but one that is probably unlike almost anything you've ever seen, Jonathan Caouette's heartbreaking film takes as its source imagery a stream of family photos, Super 8 movies, home video, campy old film and television clips, and snippets of amateur audio, all blended together with on-screen titles and evocative period music using a Mac desktop computer and iMovie editing software, to tell the story of the filmmaker's strange and sad childhood, and his stranger and sadder family. It begins with the words, "Once upon a time in a small Texas town . . . " flashing on the screen. Like any good fairy tale, it soon turns horrific.

A childhood beauty, Caouette's mother, Renee LeBlanc, was in and out of mental institutions from about age 11 onward. After a fall from the roof of her house resulted in a six-month paralysis that may or may not have been psychosomatic, LeBlanc underwent two years' worth of twice-weekly electric shock therapy. Whether this was a failed attempt at a cure by LeBlanc's well-meaning parents, Adolph and Rosemary Davis, or whether the treatments in fact exacerbated the ensuing metal illness (or even brought it on, abetted by LeBlanc's teenage drug use) is never clear. What is clear is that the repercussions for Caouette -- who, as a young boy had the misfortune to see his mother get raped during a trip to Chicago while she was experiencing a psychotic episode, and who himself was physically and emotionally abused while briefly in foster care -- are deeply painful.

They are also, as sometimes happens, the inspiration for great art.

Where "Tarnation" succeeds is not in reconstructing the past. That, despite Caouette's throwing every scrap of personal history he can find at us, is just not possible. While it is fascinating to watch him, as a histrionic preteen, seemingly channel, for the camera, the persona of a grown female abuse victim who has just killed her husband, it also presents us with another enigma. Where does his hair-raising ability to step into the character of another come from? Caouette, it should be noted, worked as an actor after moving to New York as an adult.

Diagnosed as an adolescent with depersonalization disorder (which, it is implied, may have resulted from smoking two PCP- and formaldehyde-laced joints at an early age), Caouette tells us that life for him, "is a trip, like one long dream." "Tarnation," then, feels like a travelogue documenting that trip. It is incomplete, contradictory, as multifaceted (and as brilliant) as a diamond.

Characterized by a detachment from one's own mental processes, Caouette's condition results in the sensation of being an outside observer of one's life. This, in fact, is where "Tarnation" makes its most powerful impact. For, in a sense, there are two Jonathan Caouettes -- the filmmaker and the filmmaker's subject -- and the former underscores this idea over and over again by the frequent use of split-screen imagery of the latter.

Taking its title from a corruption of the word "damnation," "Tarnation" suggests, more than a physical place, a hellish state of mind that exists somewhere between Caouette's two heads. Floating above himself, the filmmaker doesn't just look down and backward, but forward.

Despite his history, he never lets himself feel sorry for himself, but he has every reason to be afraid (as do we, by implication). That's because, whatever our background and circumstances, when we look at our own twisted roots, what's scariest is not who we once were but who we might become.

TARNATION (Unrated, 88 minutes) -- Contains obscenity, brief nudity and disturbing thematic elements. At Landmark's E Street Cinema.

Jonathan Caouette shows himself as a young boy with his troubled mother, Renee LeBlanc, in his documentary, "Tarnation."