Toward Our Understanding of Tourette Syndrome
Scientists Produce Images of Active Brain Areas Associated With Tics
Oct 23, 2000
Tourette syndrome is a rare neuropsychiatric disorder in which the patient is subject to random physical and vocal tics. At times, a patient may suddenly utter obscenities—in a manner that is both embarrassing and frightening. Generally beginning in childhood, the disorder can disrupt normal life and can give rise to chronic misunderstandings.
Scientists at Weill Cornell Medical College have taken a first big step in locating precisely where in the brain the tics of Tourette syndrome (TS) are generated. Along with colleagues in London, Drs. Emily Stern, David Silbersweig, and others used a positron emission tomography (PET) technique to produce images of the brains of sufferers of TS as they underwent their tics. The results are published in the August issue of Archives of General Psychiatry.
Tourette syndrome poses complex issues of what it means to have free will and what it means to be ill through no fault of one's own. A tic may be a simple vocalization (such as grunting or sniffing) or a movement of individual muscle groups. Or it may comprise whole words (including curses, as in coprolalia) or clusters of movements.
"Mild tics can be unintentional, involuntary actions that can occur without a patient's awareness," the authors write. "However, the more severe or complex tics are often intentional, 'unvoluntary' actions, in that they are briefly suppressible, performed to relieve a local tension, sometimes preceded or provoked by an uncomfortable sensation, or performed compulsively in association with irresistible urges. In these cases, the subjective sense of free will is disrupted: tics are performed against the patient's will, or the will to act is not under the patient's control."
The scientists found that tics are associated with activity in specific regions and circuits of the brain. These include:
- Areas of the basal ganglia, deep circuits that are involved in controlling movement, and have been implicated in disease models of TS—as has dopamine, a neurotransmitter that modulates activity in these circuits.
- The sensory-motor cortex, which is involved in the outflow of motor signals from the brain.
- Broca's area, the source of vocalization.
- Motor planning and executive regions of the prefrontal cortex, which are involved in the planning and initiation of behavior that is accompanied by a sense of willful action.
"We hope that these findings will provide a further foundation for the possible development of new therapeutic strategies," Dr. Stern said. "Such findings can also help to reduce the stigma associated with neuropsychiatric illness, as the general public realizes that patients with behavioral or mental disorders suffer from brain dysfunction similar to any other medical condition."
The study is only a beginning, based on one group of TS patients. "It will be important to perform follow-up studies to assess the generalizability of these findings," Dr. Stern said.
Follow-up projects are being performed at the Functional Neuroimaging Laboratory of New York Weill Cornell Medical Center. Scientists there are using functional magnetic resonance imaging (fMRI) to provide more detailed information and to localize brain dysfunction in such major neuropsychiatric disorders as schizophrenia, depression, and anxiety disorders.