Closed-Loop Neurostimulators: A Survey and A Seizure-Predicting Design Example for Intractable Epilepsy Treatment

TLDR

Existing open‑loop and closed‑loop implantable neurostimulators are reviewed and compared by application, size, system features, and performance, and signal‑processing algorithms are examined with design trade‑offs and quantitative examples. The study presents an inductively powered seizure‑predicting microsystem for monitoring and treating intractable epilepsy. The microsystem consists of two miniboards—a 24‑channel on‑chip neurostimulator that records, processes, and stimulates, and a wireless communication board—together with a multilayer flexible coil that receives inductive power. The review yields guidelines for algorithm selection and evaluation, and the microsystem successfully controls chronic seizures in freely moving rats.

Abstract

First, existing commercially available open-loop and closed-loop implantable neurostimulators are reviewed and compared in terms of their targeted application, physical size, system-level features, and performance as a medical device. Next, signal processing algorithms as the primary strength point of the closed-loop neurostimulators are reviewed, and various design and implementation requirements and trade-offs are discussed in details along with quantitative examples. The review results in a set of guidelines for algorithm selection and evaluation. Second, the implementation of an inductively-powered seizure-predicting microsystem for monitoring and treatment of intractable epilepsy is presented. The miniaturized system is comprised of two miniboards and a power receiver coil. The first board hosts a 24-channel neurostimulator system on chip fabricated in a [Formula: see text] CMOS technology and performs neural recording, on-chip digital signal processing, and electrical stimulation. The second board communicates recorded brain signals as well as signal processing results wirelessly. The multilayer flexible coil receives inductively-transmitted power. The system is sized at 2 × 2 × 0.7 [Formula: see text] and weighs 6 g. The approach is validated in the control of chronic seizures in vivo in freely moving rats.