PD is characterized by the symptoms resting tremor, rigidity and bradykinesia. Later in the course of the disease, patients develop gait- and balance symptoms. In the first years of the disease, the patients' symptoms are treated well with levodopa. As the disease develops and the loss of dopamine-producing cells grows, the physiological buffer-capacity for levodopa is lost and patients develop motor fluctuations in the shape of on-off symptoms and dyskinesias. Patients with these symptoms may benefit from implantation of electrodes in the subthalamic nucleus, which is stimulated by an pulse generator on the chest.