Neuropsychological functioning was assessed in patients with Parkinson 's disease ( PD ) at baseline and after @ months in a prospective , randomised , controlled study comparing best medical therapy ( BMT , n = @ ) and bilateral deep brain stimulation ( DBS , n = @ ) at either the subthalamic nucleus ( STN , n = @ ) or globus pallidus interna ( GPi , n = @ ) , using standardised neuropsychological tests .