Effects of Microelectrode-based Brain Stimulation in Humans

Overview

The currently available treatments of Parkinson's disease (PD) and Essential Tremor (ET) are inadequate and accompanied by adverse side effects making the treatment much less effective. This includes treatments with pharmaceuticals as well as electrical brain stimulation (DBS; Deep Brain Stimulation). To address this challenge, we have systematically worked to identify and overcome the shortcomings with current brain stimulation. Essential has been to achieve an understanding of the mechanisms behind the ubiquitous tissue reactions (often referred to as "foreign body reactions"), with loss of nerve cells near implanted electrodes and how to accomplish minimal tissue reactions/damage, which is necessary to enable therapeutically efficient low-intensity stimulation at precise locations. A further challenge relates to individual differences at the level of neuronal networks, making the exact sites in the brain that cause therapeutic and adverse side effects when stimulated not known in advance and thus requiring individual determination. Our strategy has therefore been to develop highly biocompatible microelectrodes (thinner than a human hair and highly flexible) and a guiding investigational device for controlled insertion of a cluster of such microelectrodes in deep target tissue. This enables individualized selection of appropriate stimulation sites. This technique, termed by us "High Definition Brain Stimulation" (HDBS), proved remarkably successful in animal models of both Parkinson's disease and pain by reliably providing powerful symptom relief without noticeable adverse side effects. For this first in human (FIH) investigation of microelectrode-based brain stimulation, we have systematically minimized all identified and foreseeable risks through optimization of the microelectrodes, the design of the investigational device for HDBS and development of simple minimally invasive surgical insertion methods. Extensive monitored safety tests in animals have confirmed the picture of negligeable tissue reactions/damage and absence of bleeding in the target area. Biological safety is also ensured by using only well-established materials documented for chronic implantation in the brain, established sterilization methods, identified safe stimulation intensities, and that the insertion procedures are adapted to well-established precision neurosurgical instruments and routines. The study is an early (FIH) feasibility clinical investigation which will be conducted in up to 12 patients with Parkinson's disease and/or Essential Tremor who are already scheduled for implantation of established DBS. The HDBS device will be inserted into awake patients in the same track as planned for the established DBS electrode. The evaluation will follow a protocol that includes stimulation of predetermined subsets of microelectrodes at up to 4 predetermined levels (depth) in the brain. The stimulation intensity for each subgroup is gradually increased until either a therapeutic effect or an undesirable side effect has been achieved. If an unacceptable effect is elicited, stimulation is immediately interrupted and a new subset of electrodes will be tested. After completion of the evaluation, the HDBS cluster electrode is removed and the implantation of an established permanent DBS electrode is completed. The evaluation will take up to 2.5 hours per patient. The patient's verbal responses, gestures, changes (if any) in tremors, rigidity, speech ability (such as slurring) or facial expressions before, during and after stimulation will be linked to the stimulation parameters (stimulation intensity, subgroup of microelectrodes, depth in the brain and time of reaction) and documented in writing and through video recordings. The analysis will only be made on anonymized data. The primary objective of this early feasibility, FIH, clinical investigation is to clarify whether HDBS (High Definition Brain Stimulation), through individualized stimulation of appropriate subgroups of implanted biocompatible microelectrodes, can provide a powerful therapeutic effect with minimal negative side effects also in humans. In addition, it is intended to simultaneously obtain important information that can be used by the neurosurgeon to improve the subsequent placement of the already scheduled permanent DBS electrode in the individual patient and thereby improve the treatment. Consequently, the secondary objective is to clarify whether HDBS can be used by the neurosurgeon to improve the placement of a permanent DBS electrode. The project paves the way for permanent HDBS with completely new opportunities for powerful, sustainable therapy with minimal side-effects in Parkinson's disease, Essential Tremor and other intractable neurologic disorders. Moreover, the HDBS technology enables new and potent opportunities for brain research.