Parkinson's disease (PD) is related to abnormal functioning of an area of the brain known as the basal ganglia. A model of how the basal ganglia works, known as the rate model, proposed about 15 years ago, has led to new surgical treatment for PD and other movement disorders. However, there is emerging evidence that the model is inadequate. A new model, known as the oscillation model of the basal ganglia, proposes that the frequencies of oscillations are important and that PD is due to an imbalance of oscillations at beneficial and harmful frequencies. Our project is designed to test the oscillatory model by examining the effects of medications and movement on the frequency content of electrical activities recorded directly from the basal ganglia in patients undergoing deep brain stimulation (DBS) surgery. The clinical effects of DBS at frequencies specific for each individual will be determined in a subsequent study. The results will lead to greater understanding of the functional organization of the basal ganglia and may help develop new treatment for PD and other movement disorders.
Dr. Chen directly tested the oscillation model of the basal ganglia by studying patients undergoing deep brain stimulation. In summary, the novel finding is that stimulation at individualized "gamma" frequency is as effective as the clinically used (higher) frequency for PD motor symptoms. However, no worsening of motor symptoms was detected with stimulation at beta or theta frequencies.
Results of this study were presented as a poster at the 2009 Society for Neuroscience Meeting.
Drs. Chen and Moro obtained follow-on funding from the Canadian Institutes of Health Research (a Canadian federal government funding agency similar to the NIH in the United States) to pursue these studies. They are also collaborating with Medtronic Inc. In current studies in PD patients with externalized DBS electrode leads, the researchers are applying (via an external stimulator) short bursts of stimuli instead of single stimuli to test the hypothesis that short bursts of stimuli will be able to better synchronize the basal ganglia and worsen motor symptoms with beta frequency stimulation, and improve motor symptoms with gamma frequency stimulation. They also are testing the effects of random stimulation. If DBS works by removing "noisy" signals, random stimulation should improve motor symptoms but if it is necessary to set a certain frequency, it should not work.
The team plans future studies to further examine the effects of stimulation at the gamma frequency.