SEP Changes During Deep Anesthesia

Inclusion Criteria: * Location Helios Klinikum Wuppertal: neurological healthy patients, which undergo an elective surgery under general anaesthesia * Location Department of Neurosurgery, University Hospital Düsseldorf: all patients with intracranial interventions and the possibility to place a stripe electrode without complications on cortex (it is decided by the surgeon while surgery because of the situs and tumorlocation) Exclusion Criteria: * periodical consumption of drugs and pharmaceuticals which influence cortical excitability * intraoperative contraindication for required depth of anaesthesia * neurological pre-existing illness * advanced hepatic insufficiency