NeuroPace, Inc. is sponsoring an investigational device feasibility study of the RNS® System, the first closed loop responsive brain stimulator designed to treat medically refractory epilepsy. The RNS® System Feasibility study is a multi-center investigation being conducted at 12 epilepsy centers through the United States. The first 4 subjects at each site are entered into an open label protocol, and subsequent subjects at that site are entered into a randomized, double-blinded, sham-stimulation controlled protocol. The study is designed to demonstrate safety and evidence of effectiveness of the RNS® System to support commencement of a pivotal clinical investigation.