ST. PAUL, Minn -- In what's being called a novel finding, researchers using brain scans have uncovered evidence of cerebral dysfunction in women with sensory conversion disorder, better known as hysteria. The study's findings open up a new window to understanding hysteria, an unexplained neurological disorder in which a patient complains of symptoms, but doctors can't find anything medically wrong with them. The study is published in the December 12, 2006, issue of Neurology, the scientific journal of the American Academy of Neurology.

The study involved three women with sensory conversion disorder who complained of numbness in their left hand or foot. Researchers used an MRI to study how the brains of these three women respond to stimulation of their numb body parts.

In all three cases, the study found stimulation of the numb hand or foot failed to activate the side of the brain which responds to touch. However, that part of the brain did respond when researchers stimulated both the numb body part and the other normal feeling hand or foot.

"The principal finding is that stimulation of the numb body part did not activate the somatosensory region of the brain, while stimulating both limbs did," said the study's author Omar Ghaffar, MD, MSc, with Sunnybrook Health Sciences Centre in Toronto, Ontario, Canada. "To our knowledge, this represents a novel result that may help explain the differing results in the few studied articles devoted to this topic."

Ghaffar says one possible explanation for why this happens could be that bilateral stimulation acts as a distraction, shifting the patient's attention, and thereby overcoming the inhibition.

"Future studies plan to build on these findings by scanning more subjects and healthy controls," said Ghaffar. "In addition, a study examining the role of distraction in conversion disorder is underway."