Intertemporal choice in Parkinson's disease

The administration of dopamine agonists in Parkinson's disease has been associated with impulse control disorders, in particular, pathological gambling. In the present investigation, 17 patients with Parkinson's disease without impulse control disorders and 17 matched control participants were offered choices between monetary rewards (ranging between 11 and 80 euros) available immediately and larger rewards (between 25 and 85 euros) available after delays ranging from 7 to 186 days. Participants had a 1-in-6 chance of winning a reward that they chose on 1 randomly selected trial. Assuming a hyperbolic discounting model, k values were estimated from the pattern of participants' choices. Patients were tested twice, once on dopamine agonist medication and once after 12 hours without medication. Patients showed a considerably steeper discounting function than healthy controls independent of medication status, with k values more than 3 times larger than those of controls. This study shows that patients with Parkinson's disease without clinically apparent impulse control disorders nevertheless tend to make impulsive decisions in intertemporal monetary choice. The lack of difference between sessions could be a result either of the persistent effects of dopaminergic therapy or hint at a genuine medication-independent change in intertemporal choice behavior in Parkinson's disease. This needs to be addressed in further studies. The paradigm used is easy to apply and should be used more extensively to describe decision behavior in Parkinson's disease.