NeuroPace, Inc. is sponsoring an investigational device study of the RNS® System, the first closed loop responsive brain stimulator designed to treat refractory epilepsy. The RNS® System LTT study is an open-label multi-center prospective 7-year clinical investigation which follows completion of the RNS® System Pivotal or Feasibility study. Data regarding safety and efficacy are collected at 6-month intervals, and data regarding quality of life are collected at yearly intervals.