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Stimulating Parkinson’s Research
UNLV’s Brach Poston is exploring how low levels of electrical stimulation may contribute to improved motor performance in people with neurodegenerative diseases such as Parkinson’s disease.
And how did he choose this scientific path? Foresight.
After earning a master’s degree in exercise physiology from UNLV and a doctorate at the University of Colorado, Boulder, Poston began a postdoctoral program at Arizona State University. There he learned about brain stimulation, immediately recognizing its potential as the next “big thing” in his field.
“I was introduced to the methods of transcranial magnetic stimulation [TMS] and transcranial direct current brain stimulation [tDCS],” Poston says. “I saw tDCS as a promising [way] to help people, and I was fortunate enough to be admitted to a postdoc program at the National Institutes of Health [NIH], where I was able to learn about this type of stimulation.”
Poston spent the next year and a half studying how to use multiple noninvasive brain-stimulation techniques. After reviewing studies from other scientists, he became convinced that, as he puts it, “tDCS was most likely to be the best noninvasive stimulation option for aiding those with Parkinson’s disease.”
Parkinson’s is a disease of the basal ganglia, an area of the brain that is vital to motor control and the production of dopamine. Dopamine is more known for its involvement in reward mechanisms and reinforcement learning in the brain, but it also plays a crucial role in mobility. When a person completes a complex movement, action, or task, dopamine is required to enable the basal ganglia to assist his or her motor cortex with movement planning, execution, and learning.
When using tDCS to treat Parkinson’s patients, clinicians connect saline-soaked sponges to rubber electrodes that are distributed across the scalp. They then pass a weak electric current from one electrode to the other. The idea is to use the current to excite or inhibit activities that are thought to originate in specific areas of the brain. For Parkinson’s disease patients, these areas often include the motor cortex, a part of the brain’s cerebral cortex associated with muscular activity.
Preliminary findings by Poston and others have shown promise: tDSC does appear, in fact, to improve performance of simple motor tasks performed by hands and arms. These tasks can include using a pinch-grip movement to generate force against an object, retrieving small objects like buttons or coins, or performing an arm movement to a target.
The electric current doesn’t cause the action to happen, Poston explains; it simply augments the normal increase in the “excitability of cortical neurons” when a task is practiced. When someone wants to lift an object — picking up a glass, for example — cortical neurons become excitable and act to execute that movement. When you practice a particular action, such as throwing a ball, the neurons become more excitable over time. This leads to improved accuracy and efficiency of movement.
The lower levels of dopamine common among Parkinson’s patients cause impairments in the communication between the basal ganglia and the motor cortex, a breakdown that reduces cortical neurons’ excitability during movement execution — thus the slower movements, reduced muscle activity, and less accurate movements experienced by Parkinson’s disease patients. By augmenting excitability among cortical neurons when tasks are being attempted, tDCS boosts motor control in the short term.
Although tDCS today is used only on outer areas of the brain, Poston believes — based on study results involving animal models — the technique might one day be used to elicit effects within deeper brain structures.
Poston’s first studies at UNLV sought to identify the optimal method for one-time tDCS treatment among people with the disease. His findings helped identify optimal placements of electrodes, correct electric current strengths, and optimal durations for stimulation.
With these parameters established, Poston moved on to explore using daily stimulation to treat patients during a two-week period. “During a single treatment, we and other research groups have typically seen a 10 to 15 percent performance improvement, with the effects lasting up to 90 minutes,” he says. “Daily application could produce a cumulative effect, and we hope to be able to elicit performance improvements of approximately 30 percent, which were seen in studies among young adults, when we apply stimulation over a two-week period.”
Poston also broke some new ground last summer by using tDCS on the cerebellum. This hasn’t been done in Parkinson’s disease before but has been shown to increase motor performance in both younger and older adults. The rationale for this is that, because the cerebellum has been shown to compensate for impaired basal ganglia activity in Parkinson’s disease, applying tDCS to excite the cerebellum may enhance this compensation.
Poston’s previous and current studies focus exclusively on the hands and arms, but he says he now has the funding that will enable him to test tDCS while a person is walking. Doing this will involve Parkinson’s disease patients walking on a treadmill. The goal is to determine how tDCS treatments affect patients’ stride length, velocity, and movement variability.
So far, Poston says his results are positive and that, in the future, he expects the treatment to become a more widely used adjunctive therapy. He also says that affordable, wearable tDCS devices have a realistic potential to become available for home use, a place where patients or caregivers could easily apply the stimulation as needed.
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