Patients with severe, current psychological problems (e.g., depression, high anxiety) or substance-abuse were excluded. Other exclusion criteria were the use of therapeutic anticoagulants, cognitive and/or psychiatric disorders in the medical history, nociceptive pain, an expected life expectancy less than 3 years due to other diseases (e.g., cancer), contra- indications for general anesthesia (e.g., severe cardio-pulmonal diseases), convulsive disorders and the presence of other neuromodulation systems.