Brain Stimulators Move Toward Closed Loop Function

by James Cavuoto, editor

In a twofold effort to improve the performance of implanted neuro­stimulation devices such as deep brain stimulation (DBS) systems and also reduce the trauma of the implantation process, several neural engineering researchers and commercial vendors are looking at closed-loop stimulation strategies. The goal here is to provide feedback signals that modify stimulation parameters, locations, and other factors that can have a profound effect on overall system performance.

Many of these issues were discussed at the 2005 Neural Interfaces Workshop in Bethesda, MD earlier this month [see conference report, p7]. At the event, Jerrold Vitek from the Cleveland Clinic identified feedback control systems as one of the major challenges confronting the DBS industry in years ahead. Vitek advocates for a “smart” programming system that alters stimulation parameters based on feedback from sensors that detect kinematic or neural response to brain stimulation. He also envisions a new generation of three-dimensional or branched electrodes that would endow a DBS system with the ability to perform selective stimulation of different areas of subthalamic nucleus or globus pallidus based on actual performance in real time.

There are at least two neurotech startups that may be looking at closed loop stimulation systems for commercial development. Newly formed Medtrode Inc. of London, ON in Canada has recently teamed up with researchers from the Lawson Health Research Institute and the NRC Integrated Manufacturing Technologies Institute to commercialize a new laser micromachined multichannel electrode that incorporates both stimulation and recording sites. The 0.5 mm thick probe promises to reduce the complexity of the surgical implantation procedure by allowing neurosurgeons to identify the appropriate brain regions involved with a movement disorder intraoperatively. More promising, the device would allow surgeons to configure the stimulation field with chronic recordings—thus saving operating room time—and to tailor the simulation fields and thereby reduce side effects.

Another neurotech startup looking into new technologies for neurostimulation systems is BioNeuronics Inc., the Seattle, WA firm launched by ex-Northstar Neuroscience executive John Harris and Tulane neural engineer Dan DiLorenzo. Though the company has been quite tight-lipped about its future product directions, DiLorenzo has been issued patents for “closed-loop intracranial stimulation” that incorporates sensory feedback to modulate treatment parameters. It would not be surprising to see this intellectual property put to use by BioNeuronics in a neurostimulation system for treating Parkinson’s disease, epilepsy, or other neurological disorders.

A closed-loop stimulation system might look for feedback from sensors such as accelerometers, temperature sensors, or electromyographic signals to gauge the effectiveness of tremor reduction, for example. In this scenario, manufacturers of sensory stimulation systems or implantable sensors such as MicroStrain or Afferent Corp. might be well placed to participate in product development efforts with stimulation system vendors.

NeuroPace Inc. has already incorporated concepts of feedback control in its Responsive Neurostimulator System for treatment of refractory epilepsy. The system monitors electrocorticogram signals for evidence of epileptic activity.