Bilateral subthalamic or pallidal stimulation for Parkinson's disease affects neither memory nor executive functions: A consecutive series of 62 patients

There is a renewal of interest in surgical approaches including lesions and deep brain stimulation directed at motor subcorticofrontal loops. Bilatera l lesioning presents a far greater risk of adverse effects, especially cogn itive impairment. Furthermore, the main advantages of the stimulation proce dure over lesioning are adaptability and reversibility of effects. The aim of this study was to assess the influence of bilateral stimulation of the s ubthalamic nucleus or internal globus pallidus on memory and executive func tions in Parkinson's disease. Sixty-two patients were assessed before and a fter 3 to 6 months of chronic bilateral stimulation of the subthalamic nucl eus (n = 49) or internal globus pallidus (n = 13). The neuropsychological t ests used were the Mattis Dementia Rating Scale, the Grober and Buschke Ver bal Learning Test, the Wisconsin Card Sorting Test, category and literal fl uency, graphic and motor series, the Stroop Test, and the Trail Making Test . Mood was evaluated by the Beck Depression Inventory. Only 4 of 25 cogniti ve variables were affected by deep brain stimulation. Under stimulation, pe rformance improved for Parts A and B of the Trail Making Test, but there wa s a deterioration in literal and total lexical fluency. There was also a mi ld but significant improvement in mood. It may therefore be concluded that stimulation of the subthalamic nucleus or internal globus pallidus does not change the overall cognitive performance in Parkinson's disease and does n ot greatly affect the functioning of subcorticofrontal loops involved in co gnition in humans. This relative absence of cognitive impairment in bilater al deep brain stimulation is likely because of the accurate positioning of the electrodes, allowing the effects of stimulation to be confined to senso rimotor circuits.