Emory Report

 November 3, 1997

 Volume 50, No. 11

PET scans show Parkinson's
surgery normalizes brain activity

Brain scans of persons whose symptoms improve significantly after surgery for Parkinson's disease show a clear reversal in abnormal patterns of brain activity, Emory researchers reported at a recent Society for Neuroscience meeting.

"These results provide new insight into the brain mechanisms responsible for symptomatic improvement following surgery for Parkinson's disease," said Robert Turner, assistant professor of neurology at the School of Medicine.

The researchers sought to determine via the brain imaging technique known as positron emission tomography (PET) whether pallidotomy surgery for Parkinson's disease has the predicted effect of restoring a normal pattern of movement-related brain activity.

The neurologists showed with PET scans that improvements in physical symptoms such as tremor and rigidity corresponded with improvements in brain activity. Activity increased in brain regions normally responsible for controlling movement and decreased in areas that showed abnormally high activation with the movement disorder.

One of the next steps in this research will be to discover the significance of the unexpected increased activity observed in the brains of Parkinson's disease subjects, Turner said. The increased activity could be evidence of compensatory neural mechanisms working to overcome the primary deficits of Parkinson's, or they could actually cause some of the symptoms of Parkinson's. The fact that clinically effective pallidotomy caused a marked reduction in these activations suggests that the abnormal activities are closely linked to the pathological processes that cause symptoms of Parkinson's disease, he said.

Although brain imaging techniques have been used previously in this research, the current study is unique in that the Emory team focused on brain activity that correlated with speed of movement. One of the primary symptoms of Parkinson's disease is a marked slowness of movement; by focusing on brain areas involved in the control of movement speed, the team hoped to discover why this specific aspect of the control of movement is impaired in Parkinson's and why pallidotomy is an effective treatment.

This approach also allowed the group to identify changes in brain activity that actually may have caused the improvement in task performance after pallidotomy and to distinguish those from changes in activity merely caused by changes in performance.

Researchers have established that Parkinson's disease is caused by a loss of dopamine, which causes the basal ganglia to send abnormal signals to large portions of the frontal cortex. Most, if not all, of the symptoms of Parkinson's, including slowness of movement, are thought to arise from these signals.

In support of this concept, a group at Emory headed by neurology chairman Mahlon DeLong and Jerrold Vitek, director of the department's functional neurosurgery section, and other researchers, has shown that most Parkinsonian symptoms can be alleviated by pallidotomy-an excision of neurons in the basal ganglia. Pallidotomy is thought to work because it eliminates the source of abnormal inhibition of the frontal cortex and allows the patterns of neural activity needed to perform normal movements.

Pallidotomy as a treatment for Parkinson's disease has gained a great deal of attention recently because of its potential for addressing some of the shortcomings of traditional therapies, Turner said. The most common drug treatments for Parkinson's, which work by providing an artificial supply of dopamine to the basal ganglia, are usually effective when first administered. After years of use, however, these drugs sometimes lose their effectiveness and begin to produce serious side effects such as excessive unwanted movement and hallucinations.

Pallidotomy has been advocated as a therapy for patients whose symptoms are inadequately controlled or those with adverse reactions to drug therapies. Although the clinical effectiveness of pallidotomy is well established, the mechanisms underlying its effectiveness are only now being discovered. The present work contributes substantially to that understanding, Turner said.

-Lorri Preston

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