Abstract: Principles from the analogous field of cardiac electrophysiology are translated to neuro electrophysiology whereby electrically competent catheters and introducing devices are threaded intravascularly through large vessel access (e.g., leg or arm) into the arterial or more typically the venous system to or within the brain tissue, possibly targeting a specific region that needs to be functionally mapped. After passive recording and mapping of important activity exactly to a 3-dimensional, high resolution brain image taken either before or during the procedure, electrical stimulation paradigms are triggered to both evoke responses to help map regions vital to the epileptic network or pathologically functioning networks in other neurological and/or psychiatric conditions, and then to map brain function in specific regions during motor, sensory, emotional, psychiatric and cognitive testing, in order to localize these functions in relation to the epileptic network.