With the increasing strive for complete resections of supratentorial low or high-grade gliomas, the necessity for intraoperative electrical stimulation methods to map and monitor functional important cortical or subcortical brain areas increased. While many brain functions can be assessed during awake surgery using electrical stimulation, motor function as well as visual function can be mapped and monitored in the asleep patient, as well. Several different methods reviewed in this article are available which lead to an improved functional outcome while increasing the extent of tumor resection and thereby potentially the oncological outcome of the patient.