Chronic deep brain stimulation (DBS) of the subthalamic nucleus (STN) accomplishes favourable long-term improvements of motor symptoms in selected patients with advanced Parkinson’s disease.¹ However, disagreement exists about the occurrence of cognitive and behavioural sequelae and their clinical significance. In a large cohort study with 3 years follow-up, Funkiewiez et al² concluded that STN stimulation did not lead to global cognitive deteriorations. Rodriguez-Oroz et al,¹ on the other hand, reported cognitive and behavioural dysfunction in 15 of 49 (30%) patients 3–4 years after surgery. In 11 patients, the dysfunctions were moderate to severe. However, they remarked that the severity of the adverse events did not …