Teen NY girls' mystery illness draws Brockovich In a small upstate New York town, a group of local high school girls are making national headlines for what many are calling a medical mystery. Thera Sanchez and Lydia Parker are only two of more than a dozen girls who have been experiencing symptoms of uncontrollable tics and verbal outbursts. Thera's mom told CNN she brought her daughter to the hospital after she started involuntarily ticking when she woke up from an afternoon nap. The nurse let her know she wasn't alone. "She had said, 'not to alarm you, but someone has to contact someone because you are the fourth girl to come in with this,'" her mother told CNN. Since then, the numbers have grown to 15 - and all of them, except one, are girls. Naturally, concerned parents are looking for answers. "These kids are just totally normal and then next thing you know they go blah, their arms are swinging and they can't control themselves," says James Dupont, whose daughter Brook has also been affected. Over the weekend the media craze surrounding the mystery grew when famous environmental activist Erin Brockovich sent her investigators to look for possible environmental causes. The team tested local ground water samples for chemicals that they believe may be left over from a 1970 train derailment that spilled thousands of gallons of industrial solvent just north of the school. "So far we haven't seen anything that is obvious or just stands out," Brockovich's investigator Bob Bowcock tells CBS News. It doesn't mean something won't come before us. But both school and state health officials have already concluded a three month investigation that determined "no environmental or infectious agents" could have caused the students' tics. Instead, local doctors who have examined 11 of the teens have determined the girls have a stress-induced "conversion disorder," which "starts as a mental or emotional crisis - a scary or stressful incident of some kind - and converts to a physical problem." But some parents refuse to accept that the causes are purely psychological. "Even if it was Conversion Disorder, and that was the symptoms of it, we don't know what caused it," says James Dupont, whose daughter Brook has suffered from a tic. In the minds of parents like Dupont, the small town medical mystery remains very much unsolved. However, Dr. Jennifer McVige, a pediatric neurologist who treated many of the girls after they were referred to her by their normal physicians, doubts the train wreck has anything to do with the symptoms displayed by the girls in upstate New York now. McVige has also said some form of Conversion Disorder is most likely to blame - and she says anything from a divorce in the family, to the normal stresses of teenage life can cause the condition.