Why do Parkinson's Disease Patients Sometimes Make Wrong Decisions?

Our knowledge of the cerebral bases of decision making has grown considerably in the past decade. The dopamine system is closely involved in many aspects of the decisional process. It is therefore not surprising that the dysfunctions that occur in Parkinson's disease (PD) can alter some patients' decisions. Put simply, a decision is the final step of a process in which a subject weighs up the potential benefits and costs associated with each of the different options available for a given choice. The option that appears to have the best ratio of benefits to costs is chosen. In some PD patients, dopamine agonists destabilize the balance: the benefits are given an inappropriately high weighting relative to the costs, leading patients to take decisions they would not otherwise have taken. This might be one of the explanations for impulse control disorders observed in some PD patients. Dysfunction of the subthalamic nucleus (STN) induced by dopamine replacement or by deep brain stimulation is another mechanism that can alter decision making. The STN plays an active role in the decisional process, especially by slowing down the process when the difference between the options to be considered in a given choice is small (e.g. a win-win choice). Deep brain stimulation applied to the STN may interfere with its monitoring role and lead to an impulsive choice. Attention disorders and frontal lobe dysfunction, highly prevalent in the course of PD, are other factors that may alter a patient's decision making. Patients and caregivers need to be aware of this, since the consequences can sometimes be detrimental.