The relation between burst and suppression periods in transcranial and direct cortical recorded EEG with cortical amplitudes median nerve somatosensory evoked potentials is studied.

60 patients are included in this study: 15 patients undergoing brain tumor surgery, 15 spine surgery (University Hospital Düsseldorf) and 30 patients during general surgical procedures (Helios Klinikum Wuppertal).

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