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
"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
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,
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
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
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
to November 3, 1997 Contents Page