Dopamine agonists rather than deep brain stimulation cause reflection impulsivity in Parkinson's disease

Dopamine agonist therapy is the main risk factor for impulse control disorders in Parkinson's disease (PD). However, it is unclear whether bilateral deep brain stimulation of the subthalamic nucleus also causes impairment in decision making.

To assess the role of dopamine agonist therapy and deep brain stimulation on reflection impulsivity in non-demented patients with PD.

We recruited 61 PD patients, 20 treated with L-dopa in combination with a dopamine agonist, 14 taking L-dopa monotherapy, a further 16 PD patients with bilateral subthalamic nucleus deep brain stimulation treated with L-dopa in combination with a dopamine agonist, and 11 PD patients with bilateral subthalamic nucleus deep brain stimulation taking L-dopa but not a dopamine agonist. Results were compared with 18 healthy controls. Patients who had evidence of impulsive compulsive behaviour were excluded. Reflection impulsivity was assessed with the beads task, which is a validated information sampling task.

All patients treated with a dopamine agonist gathered significantly less information and made more irrational decisions than all other groups regardless of whether they had surgical treatment.

Our results imply that dopamine agonist therapy but not deep brain stimulation leads to "reflection impulsivity" in PD.