JONATHAN CAOUETTE may never make another movie in his career. In fact, whether he does or doesn’t is neither here nor there. Tarnation is basically the story of his life.

It’s a mind-bending experience, and there’s very little hope that anyone could possibly replicate it. This is a unique documentary, assembled from 20 years of home movies, and for reasons wildly beyond the director’s ken, it is one of the most important (and throw-away) self-portraits of a screwed-up artist ever made. My thankless task is explaining why you should possibly care.

At the age of 11, Caouette picked up a video camera and started filming his family falling to pieces. Only he didn’t have a clue what was going on. So we join him, circa 1985, giving a guided tour to his mother’s mental illness and the drugs that inspired his own. What follows is a comic catalogue of accidents, and surreal medical advice. Jonny’s mother, Renee, was a child model who fell off a roof aged 12. For some strange reason she was prescribed electric shock treatment and referred to 100 different psychiatric institutions. But being beautiful, she married in her teens. By the time she gave birth to Jonathan, her mind was in tatters. Dad swiftly left.

In 1975 Renee was raped in front of her son and inexplic-ably sent to jail for six weeks. Jonathan was moved and abused around foster homes until his grandparents legally adopted him in 1981.

The family story is fed to us much like titbits of Hansel and Gretel. In 1986, aged 13, Jonny smoked two joints dipped in PCP and toasted in formaldehyde and life has never been quite the same since.

The film basically tees off from this moment: a teenage boy with huge gaps in his teeth, vamping to camera like a lost dolly; and the film-maker, aged 31, crying on the telephone about his mother’s latest lithium overdose. What is extraordinary is how the past and present decide to overlap.

The older Jonathan is a gay New York sophisticate with messy feelings of guilt about his parents. But his younger self is the raw and real thing: damaged, exciting, and steeped in underground culture. You wonder how and why this Blue Velvet rebel grew a desire to care when his elders left him on a ledge.

One of the haunting details is how much the director stares at his shaving mirror through the years. He has no fears about self-love. Curiously that might be his saving, as well as his chief source of grace.

The older Caouette has the last angle. As survivors go, he’s a good-looking hunk. This is his story. His captions might read like a medical log, and his film might look like a scrapbook put together by an angry child. But the glue is the most interesting thing about the film: cool music, ironic lyrics and sophisticated television promises of better things.

I actually think that Caouette has accidentally made a musical. So many telling moments are shrouded by pop. You have to go with the rhythm, or you might leave with nothing at all.