Optimization of Transcranial Motor Evoked Potentials in Supratentorial Surgeries

Inclusion Criteria: * Informed consent signed by the subject * The patient has a supra-tentorial lesion requiring surgery * The patient is undergoing neurosurgery with the use of MEP monitoring during surgery to protect functional tissue\* (During routine preparation for the surgery, patients are checked for any relative contraindications as listed in the user manual of the ISIS IOM System (see p. 11, chapter 2.2.4 of the user manual). Every relative contraindication must be weighed against the risk and benefits of the measurement signals which are routinely needed for the surgical intervention. There are no absolute contraindications for the ISIS IOM System.) * The patient is older than 18 years Exclusion Criteria: * No need for MEP monitoring * Vulnerable subjects (pregnant, impaired consciousness) * People who do not want to participate in the study * Emergency procedures in which no consent was obtained before the operation * Multiple surgeries on the same patient * Preoperative non-affected arm or leg motor deficit (MRC \<5), that is to say, no motor deficit of the arm or leg ipsilateral to the surgery * Inhalational anesthesia * Persisting neuromuscular blockade * Impossibility to place the stimulating or recording electrodes in the appropriate site