Awake brain mapping of cortex and subcortical pathways in brain tumor surgery

Awake surgery is not a new technique: this is a new philosophy. Indeed, in surgery for diffuse gliomas performed in awake patients, the goal is not anymore to remove a "tumor mass" according to oncological boundaries (which in essence do not exist in infiltrating neoplasms), but to resect a part of the brain invaded by a chronic tumoral disease, according to functional limits both at cortical and subcortical levels. Therefore, intraoperative electrical mapping is accepted as the gold standard in order to gain information about the functionality of the underlying tissue when performing neurooncological surgery. This review should give the reader an overview of principles and indications of mapping of eloquent cortex and subcortical pathways with practical considerations for cerebral tumors. In gliomas, awake mapping has been demonstrated as increasing the surgical indications in socalled "critical areas" with nonetheless a significant decrease of postoperative morbidity while maximizing the extent of resection. Beyond clinical implications, awake surgery represents a unique opportunity to study neural networks underpinning sensorimotor, visuospatial, language, executive and even behavioral functions in humans. This led to propose new models of connectomics, breaking with the localisationist view of brain processing, and opening the window to the concept of neuroplasticity. In summary, awake mapping enables to make a link between surgical neurooncology and cognitive neurosciences, to improve both survival and quality of life of glioma patients.