Physiological parameters (blood pressure and ICP) are documented in the CRF corresponding to each patient. BIS and NIRS data are stored on a portable computer and subjected to offline analysis. Parametric and non-parametric statistics will be used to compare MRI and PET. Physiological data will be recorded during stimulation with study-drugs. The sample size is based on previous publications where a MRI protocol was performed before and after drug administration in anesthetized patients. The exact form of applied statistics are not yet decided. This kind of study with new parameters from MRI and PET has never been done and statistical help will be consulted along the process.