Seizures induced by direct electrical cortical stimulation - Mechanisms and clinical considerations

Direct electrical cortical stimulation (CS) is widely used to map eloquent cortex. It can be applied extraoperatively in patients undergoing intracranial EEG recordings using chronically implanted electrodes (subdural, depth or a combination), or it can be used intraoperatively. Seizures can be induced by CS but there is controversy regarding the utility of CS induced seizures in defining the epileptogenic zone and hence practice varies considerably between centres. Some centres use seizures induced by direct CS routinely to aid in defining the epileptogenic zone. In contrast, others do not rely on such information and explicitly avoid stimulating seizures during cortical mapping. Intra- and extraoperative techniques have been used to stimulate seizures with varying results, which may in part reflect these methodological differences. We here aim to review current views, definitions and studies on seizures induced by direct electrical CS. In addition we discuss mechanisms and methodological considerations of this procedure.