Intraoperative brain mapping is an important step in performing neurosurgery because it allows to spare the eloquent areas of the brain and increase the post-operative life quality for patients. However, the gold standard - electrical cortical stimulation - leads to seizures in up to 30% cases when language cortex is mapped intraoperatively in epilepsy patients. Modern neurosurgery is facing the need for a more innocuous method to intraoperatively map functionally critical cortical zones. The goal of this study is to create a setup for passive intraoperative functional mapping, and to compare informativeness and safety of both mapping procedures. We have created and tested a software and hardware setup for a high-resolution passive ECoG-based eloquent cortex mapping in a neurosurgical setting. Also, we have developed a mobile version of this platform that can be used in multiple hospitals and operating rooms across the country. We found precise localization of the Broca's area overlapping by more than 90% with the results of electrical cortical stimulation mapping in 3 out of 4 patients. In the fourth patient, the language cortex was not localized in the resection area, and the patient did not experience post-operative language deficiency. Passive mapping of the Broca’s area is a safe alternative to direct electrical stimulation. Further development of this approach includes mapping cortical activation in a patient in response to audited speech without the need to name the objects which may allow for mapping under anesthesia.