Electrocorticographic Frequency Alteration Mapping: a Clinical Technique

Received, May 25, 2006. Accepted, November 10, 2006. Creating transient lesions or inducing overt movements through the use of direct electrocortical stimulation (ECS), either extraor intraoperatively, has been an established practice in delineating eloquent cortex (3, 5, 26). This has been critical in minimizing the risk in neurological surgeries that involve seizure focus, tumor, or vascular malformation resections (1, 4, 11). To date, this is considered the “gold standard” and has been shown in a high number of patients to be predictive of functional outcome (11, 17). ECS, however, is still coarse in its ability to delineate regions of motor and speech cortex. Effective mapping requires that all electrodes be individually stimulated with varying amounts of electrical current and ongoing and consistent patient participation. In the setting of awake craniotomies, however, this is not always reliable. Moreover, stimulation is not without limitations. Discharges after stimulation have been found to occur in approximately 71% of all patients mapped (32). These discharges can induce seizures or provide misleading funcELECTROCORTICOGRAPHIC FREQUENCY ALTERATION MAPPING: A CLINICAL TECHNIQUE FOR MAPPING THE MOTOR CORTEX