It is being reported that an implantable brain device to help Parkinson's disease patients may come with an unsettling little side effect - the inability of those patients with the device to act rationally in certain situations.

"The benefit of the (DBS) therapy was so powerful when we first started doing this, it took us some time to understand the more subtle cognitive side effects," said Dr. Scott Sherman, a UA neurologist who has been working since 1998 with local patients receiving the treatment.

"But even with what we know about the impulsive behavior now, the effects of deep brain stimulation can be really amazing for patients and far outweigh the side effects," Sherman said. "So this is not a reason to avoid the therapy. But as we understand how this affects the brain, we are more aware of what can happen, and we can make adjustments to benefit the patient's quality of life."

Doctors are now noticing that in some Parkinson's patients with the devices, that they can sometimes not think rationally in certain situations, something that can put them at risk of potentially doing something that they may regret.

In a study it was proven that when the brain stimulation was turned off, the Parkinson's patients with the devices acted totally normally, regaining the ability to think appropriately under stressful situations.

"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 a brain degenerative disorder that results from degradation of nerve cells in the brain that produce dopamine. When these cells are destroyed, people experience tremors, muscle rigidity and difficulty walking and balancing -- symptoms that only worsen with time.