Fig. 1.

Electrocorticograms with first seizures recorded by the RNS® System. (a) Patient 1 had her first seizure 7.5 months after implantation of the RNS System. Electrographic seizure onset (arrowhead) involves low-voltage fast activity arising from cortex overlying the periventricular nodular heterotopia (PVNH) with rapid spread to the hippocampus and then to the PVNH. (b) Patient 2 had his first seizure 49 days after implantation of the RNS System. Electrographic seizure onset (arrowhead) involves rhythmic alpha frequencies arising from the hippocampus without involvement of orbitofrontal cortex.