Hold Your Horses: Impulsivity, Deep Brain Stimulation, and Medication in Parkinsonism

TLDR

Deep brain stimulation of the subthalamic nucleus improves motor symptoms in Parkinson’s disease but can induce cognitive side effects such as impulsivity. DBS disrupts the ability to slow decisions under conflict, causing patients to speed up high‑conflict choices—a form of impulsivity that is independent of dopaminergic medication—while medication impairs learning from negative outcomes, indicating separate mechanisms for impulsivity as predicted by a basal‑ganglia computational model.

Abstract

Deep brain stimulation (DBS) of the subthalamic nucleus markedly improves the motor symptoms of Parkinson's disease, but causes cognitive side effects such as impulsivity. We showed that DBS selectively interferes with the normal ability to slow down when faced with decision conflict. While on DBS, patients actually sped up their decisions under high-conflict conditions. This form of impulsivity was not affected by dopaminergic medication status. Instead, medication impaired patients' ability to learn from negative decision outcomes. These findings implicate independent mechanisms leading to impulsivity in treated Parkinson's patients and were predicted by a single neurocomputational model of the basal ganglia.