Does bilateral stimulation of the subthalamic nucleus aggravate apathy in Parkinson's disease?

OBJECTIVE High frequency stimulation of the subthalamic nucleus (STN) dramatically decreases motor disability in patients with Parkinson"s disease (PD), but has been reported to aggravate apathy. The aim of this study was to analyse the effect of STN stimulation on motivation and reward sensitivity in a consecutive series of PD patients. METHODS Apathy and reward sensitivity (Apathy Scale, Stimulus-Reward Learning, Reversal, Extinction, and Gambling tasks) were assessed in 18 PD patients treated by bilateral STN stimulation ("on" and "off" conditions) compared with 23 matched patients undergoing long term treatment with levodopa ("on" and "off" conditions). RESULTS Apathy decreased under both STN stimulation and levodopa treatment, whereas explicit and implicit stimulus reward learning was unchanged. CONCLUSIONS Bilateral STN stimulation in PD patients does not necessarily have a negative effect on motivation and reward sensitivity and can even improve apathy provided patients have been appropriately selected for neurosurgery.