Michael Frank did what any thoughtful person would. He asked a patient suffering from Parkinson's disease if he would like to sit in a more comfortable chair across the room.
However, instead of taking a moment to think about it, the patient immediately stood up and tried to get to the chair -- completely ignoring the fact he was unable to walk.
"He couldn't walk without a wheelchair, and I had to help to prevent him from falling down," says Frank, an assistant professor of psychology at the University of Arizona at Tucson. "He saw the chair, thought it was a good idea, and got up to walk toward it without really thinking about his condition."
This kind of impulsive behavior may be a side effect of deep brain stimulation that is used to treat Parkinson's disease. Deep brain stimulation helps some patients control debilitating tremors, but new research suggests it may also impair decision making.
In a new study to be published in the journal Science, researchers found that when Parkinson's patients received brain stimulation, they had trouble making hard decisions. However, when the stimulation was turned off, patients responded like the healthy individuals in the control study.
"From a scientific point of view, this research provides light on how some of the circuitry involved in decision making works in the brain," says study co-author Scott Sherman, a professor of neuroscience at the University of Arizona.
"For Parkinson's patients, this study highlights the fact that there are side effects to most interventions," he says. "Even though patients know they have balance problems and are at risk for falling, they may still act impulsively. Patients may gain more mobility with deep brain stimulation, only to experience more falls."
Parkinson's disease is caused by the degradation of nerve cells in the brain that produce dopamine, a signaling chemical that is necessary for smooth and controlled muscular movement.
When these dopamine-containing cells are destroyed, people experience tremors, muscle rigidity and difficulty walking and balancing -- symptoms that only worsen with time.
However, because the disease progresses slowly, medications, physical therapy and surgical procedures can help most people live for many years after diagnosis. Deep brain stimulation is one surgical treatment option available for patients who do not experience relief from medications.
Doctors implant a neurostimulator, which is similar to a heart pacemaker, to deliver electrical stimulation to a specific area of the brain, called the subthalamic nucleus, or STN, effectively blocking the abnormal nerve signals that cause tremors.
For many patients, this device provides considerable relief and also helps researchers study the parts of the brain that are important in the decision-making process.
"Deep brain stimulation is a surgical technique that has been an important advance in the treatment of movement disorders such as Parkinson's disease," says Sherman. "This has allowed our research group to take advantage of an unusual situation of patients having stimulating electrodes implanted in the brains and to carry out a scientific study that explores how certain brain regions control the decision making process."