Yet despite the findings, he said, it's possible that personalities might have something to do with Parkinson's. "People can argue there are other ways of measuring personality, other personality traits we did not consider," he said.
It's also possible that personalities might change when people develop the disease, and families might think the changes began earlier, he said.
The findings are being released this week in Paris at the International Congress of Parkinson's Disease and Movement Disorders.
Also at the conference, French researchers are reporting that the drugs used to treat Parkinson's disease have varying effects on creativity.
The disease is thought to hurt creativity, although treatment with dopamine agonist therapy -- which reduces dopamine levels -- can boost it.
The study involved people who underwent deep-brain stimulation, a surgical treatment for Parkinson's disease that appears to help some people, although it's not entirely clear why.
Researchers found that those who had the treatment and underwent dopamine replacement therapy lost creativity if the therapy was too "drastically reduced."
The study is so small that "it's hard to extrapolate from this to the general Parkinson's population," said Dr. Hooman Azmi, director of movement disorders at Hackensack University Medical Center in New Jersey.
But, he said, the findings come from a "very well-respected" group of researchers. And previous studies have suggested that creativity is boosted as dopamine levels go up, he said.
By contrast, creativity dips in some people with Parkinson's.
"It doesn't just affect their movement," Azmi said. "It affects their whole brain function."
There's a potential problem, however. Dopamine can cause mania in some people and can lead to gambling addictions and other disord
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