Epileptiform and non-epileptiform paroxysmal activity from isolated cortex after functional hemispherectomy

The relationship of acute complete cortical isolation to paroxysmal cerebral activity was examined in 16 patients with electrocorticography (ECOG) before and after functional hemispherectomy (FH). Burst-suppression activity appeared over isolated cortex in all cases, the severity of which could be increased by systemic administration of propofol or methohexital. Interictal epileptiform activity (EA) recorded from frontal or parietal-occipital cortex before FH invariably persisted after FH (11 cases). No EA was recorded before or after FH in 3 cases while in 2 cases EA appeared following FH which had not been present before FH. The intensity of burst-suppression activity was not related to the presence or absence of post-excision EA. In total, 30 disconnected cortices were recorded from; relative abundance of EA was increased in 10, unchanged in 17, and decreased in 3 cases. Unrelated to the induction of burst-suppression activity, cortical isolation may decrease the threshold for expression of interictal EA.