"We don't understand that aspect of it completely," Hallett said of the potential for conversion disorder to spread through a group, a characteristic that once earned it the name "mass hysteria." "For some reason, the brain mimics things that they know. ... It's just one of the ways the brain reacts to psychological stress. We don't understand why, but it truly is involuntary just as patients say it is."
Lydia Parker, a senior at Le Roy High School, has symptoms so severe she spends most of the day in a wheelchair.
"I can't stand for more than about two minutes," said 17-year-old Parker. "And my vocal and tic and everything gets really bad at night."
Parker said she's glad Brockovich is drawing attention to the disorder, but she doesn't think the answer is in the school's water supply.
"I didn't eat the food, I didn't drink the water. … I brought my own Snapples," she said. "I don't even borrow pencils."
Parker said her younger brother goes to the same school and has no symptoms. "If it was something in the environment, it would have kicked in and a lot more people would have gotten it," she said. But she doesn't think it's stress is the answer, either.
"Conversion disorders are brought on by stress, she said. "Just being a senior isn't that stressful; you just have fun."
Hallett said he's not surprised the teens and their families were looking for another, nonpsychological explanation.
"It always seems to be the case that patients far prefer to have a [medical] diagnosis than a psychological one," he said.
The possibility of an environmental trigger has been bolstered by reports of similar symptoms in two teens living in Corinth, a town 250 miles from Le Roy. The girls started showing symptoms in May, around the same time they passed through Le Roy on their way to a softball tournament in Ohio.
"We have two girls out here that were showing these symptoms before those girls," said Randall Nicholson, whose daughter Alycia continues to have tics and even seizures. "Is it just a coincidence? Is this the same as what they have or are we dealing with two completely different animals here?"
Nicholson said it's been hard for his daughter, who just turned 16.
"She's so excited about getting to drive. How do you tell her, 'No, you can't."
If it is conversion disorder, there are treatments. Psychotherapy and stress management can improve the symptoms, which usually subside within a few weeks.
Miller said his daughter Katie has good days and bad days.
"On Wednesday I brought her to cheerleading practice and she was fine. But when she got home, she had verbal tics for almost an hour -- just loud verbal tics," he said. Katie is still attending school but spends half her time at home sleeping, exhausted from her uncontrollable symptoms, Miller said. "Yesterday she seemed better, but who knows today."