Microphysiology of Epileptiform Activity in Human Neocortex

The authors report the use of dense two-dimensional microelectrode array recordings to characterize fine resolution electrocortical activity ("mu EEG") in epileptogenic human cortex. A 16-mm(2) 96 microelectrode array with 400-mu m interelectrode spacing was implanted in five patients undergoing invasive EEG monitoring for medically refractory epilepsy. High spatial resolution data from the allay were analyzed in conjunction with simultaneously acquired data from standard intracranial electrode grids and strips. mu EEG recorded from within the epileptogenic zone demonstrates discharges resembling both interictal epileptiform activity ("microdischarges") and electrographic seizures ("microseizures") but confined to cortical regions as small as 200 mu m(2). In two patients. this activity appeared to be involved in the initiation or propagation of electrographic seizures. The authors hypothesize that microdischarges and microseizures are generated by small cortical domains that form the substrate of epileptogenic cortex and play important roles in seizure initiation and propagation. and propagation.