RNS System LGS Feasibility Study

Inclusion Criteria: * Participant is 15 years of age or older for first cohort; 12 years of age or older for second cohort. Note that age requirements for eligibility differ by cohort, as follows: the age limit for Cohort 1 is 15 years of age and above and the age limit for Cohort 2 may decrease to 12 years, pending a DSMB letter of recommendation, based on review of interim data analysis and concurrence with NINDS. * Participant has medically intractable epilepsy defined as failure to achieve acceptable seizure control without unacceptable medication related side effects despite trials of 2 or more antiseizure medications. * Participant had an average of ≥ 5 drop seizures per month in the 2 months preceding enrollment. A drop seizure is defined as an epileptic seizure (atonic, tonic, tonic-clonic, or myoclonic) involving the entire body, trunk, or head that leads or could lead to a fall, injury, or slumping in a chair. * Participant's seizures are non-localized. * Participant's scalp recorded EEG has features of LGS, such as multifocal spike, slow spike and wave discharges, and paroxysmal fast activity. * Participant must (a) have a stable antiseizure medication (ASM) regimen for the 2 months preceding enrollment and (b) be willing to remain on the stable regimen, as medically able, through the Blinded Evaluation Period; rescue medication for acute seizure clusters are permitted. A stable ASM regimen is defined as no introduction or discontinuation of an ASM, and no change …