Physiologic Effects of Deep Brain Stimulation in Patients with Parkinson’s Disease

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Chen, Robert, MA, MBBChir, MSc, FRCPC Institution: Toronto Western Hospital, Toronto, Ontario, Canada

Abstract

Dr. Robert Chen and his colleagues at Toronto Western hospital will use their second Year of PDF funding to expand their understanding of neuroanatomy by working with PD patients who have undergone deep-brain stimulation at their institute. They will compare the benefits of electrodes placed in 1) thalamus; 2) globus pallidus and 3) subthalamic nucleus to determine in which sites the most effective symptomatic relief is provided. They also hope to shorten the time required to program and adjust the devices. As those who have DBS implants know, as symptoms progress, the stimulations require adjustments. The advantage is that they CAN be adjusted, unlike the lesions made in the “otomy” procedures, Which are permanent. Shortening the Time needed for adjustments would please the patients (their costs would be reduced) and the institute personnel (who could spend their time more profitably as well.

Progress Report (as of 8/2002)

Deep brain stimulation (DBS) is a promising new treatment for patients with Parkinson’s disease. This involves placing electrodes into the small but well-defined target areas within a region of the brain known as the basal ganglia. The electrical impulses used for DBS are generated by a pulse generator (similar to a heart pacemaker) usually implanted in the chest wall. However, how DBS leads to improvement in the symptoms of Parkinson’s disease and the best location in the brain to apply DBS is currently unknown. In a series of studies, we examined how DBS of different target areas in the basal ganglia affects the motor cortex, which is the part of the brain that mediates movement. In ten patients with Parkinson’s disease with stimulator in the internal globus pallidus (GPi) and 12 patients with Parkinson’s disease with stimulator in the subthalamic nucleus (STN), we tested the effects of stimulating the motor cortex with a magnetic coil with the stimulators turned on, off, or to half the normal strength. In patients with GPi stimulator we found significant changes with stimulation which is likely related to improvement in dyskinesia. In patients with STN stimulators, turning the stimulator on lead to normalization of a measure known as “intracortical inhibition” which may be related to improvement in the speed of movement. These studies suggest that although GPi and STN stimulation are both used to treat Parkinson’s disease, they have different effects on the motor cortex and this may be related to their different clinical effects. Both of these studies have been published in the scientific journal Neurology (Chen R, Garg RR, Lozano AM, Lang AE. Effects of internal globus pallidus stimulation on motor cortex excitability. Neurology 2001, 56:716-723; Cunic D, Roshan L, Khan F, Lonzano AM, Lang AE, Chen R. Effects of subthalamic nucleus stimulation on motor cortex excitability in Parkinson’s disease. Neurology 2002, 58:1665-1672). We are continuing other studies on DBS including a detailed analysis brain electrical rhythms to examine the effects of DBS on other brain areas. We hope that the studies will result in greater understanding of the function of the basal ganglia, how the basal ganglia is abnormal in Parkinson’s disease, and how DBS works. This should advance our knowledge of Parkinson’s disease, and may lead to improved treatment in the future.

 

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