The number of people who have resided inside Cynthia Byrtus' head for the past 30 years could fill a movie theater. In fact Byrtus says she has kept a count of her multiple personalities and the number has reached 351.

After years of therapy, she says she has integrated all but 40 of those personalities into the real Cynthia Byrtus. "I'm down to double digits," she says with a smile.Byrtus has become something of an expert on multiple personality disorder (MPD). The former Salt Lake resident now lives in Boulder, Colo., where she works as a trainer for the Social Movements Research Group, a small consulting company that studies deviant social movements. She also is on the staff of the Institute of Police Technology and Management at the University of North Florida.

It is childhood abuse, including ritual abuse, that most often causes MPD, she says. The disorder becomes the child's way of coping with unspeakable trauma - what the child himself can't face alone he unconsciously invents a separate personality, or many personalities, to endure for him.

Byrtus, who in 1985 ran a private residential treatment program in Salt Lake for multiples, was back in town last weekend to present a workshop, at Olympus View Hospital, for patients with multiple personality disorder.

"There's a lot of hype and misnomer about MPD," says Byrtus. "People think that multiples go around out of control," on the verge of committing some heinous crime. But the average person wouldn't even know that the average multiple has MPD, she says.

The subtleness of the disorder can prove to be a stumbling block for multiples themselves, though, says Byrtus. A person with MPD usually can't recognize when he is beginning to switch over to another personality and therefore can't switch back of his own volition. That's where Byrtus comes in.

She now travels around the country training doctors and patients how to recognize "switching" and how to regain control.

For Byrtus herself the switching usually feels something like this: a pressure in her head, stiffness in her neck, dizziness, watery eyes.

Other multiples may notice other signs - blurry vision, pressure behind the eyes, chills, ringing in the ears, an inability to concentrate. They may suddenly feel more childlike, or actually feel shorter; they may experience sudden mood swings, a detached sensation in the body, a feeling that objects and people look different, or that their own face or voice has changed.

Any number of things can trigger a personality switch, says Byrtus - including smells, sounds, life stresses and seeing either the past perpetrator of the childhood trauma or someone who looks like the perpetrator.

Bringing the switching to a conscious level, she says, helps to bring it under control. Sometimes it's also necessary for multiples to talk themselves into a level of comfort. "You can say to yourself, `I'm a big girl now, I think I can handle this.' "

"When they were little it was necessary for them to switch," she explains. "But when they're bigger they don't need to. They can use other coping skills. Life is much easier to handle when you're 37 than when you're 4."

Byrtus was accompanied on her Salt Lake trip by Jim McCarthy, director of Social Movements Research Group, who says that the average perpetrator of ritual abuse is white and middle or upper class, as is his victim.