|Dr. Maysam Ghovanloo examines a test chip with circuitry designed to improve deep brain stimulation in patients with neurological disorders. (Photo: Jennifer Weston)|
Parkinson’s disease (PD) is one of several neurological disorders with symptoms such as tremor, rigidity, stiffness, slowed movement and walking problems. In some cases these disorders do not respond to medications. However, the patients can still benefit from a surgical procedure known as deep brain stimulation (DBS). DBS uses a surgically implanted, battery-operated medical device called a neurostimulator to deliver electrical stimulation to targeted areas in the brain that control movement, blocking the abnormal nerve signals that cause tremor and PD symptoms.
The stimulation devices that are currently in use are based on cardiac pacemakers that have been modified for use in the brain. While these devices provide adequate stimulus for symptom relief, they are so bulky that they have to be implanted in the upper chest area and connected to the head with a long cable that is placed under the skin. Statistical research conducted at the Johns Hopkins University has shown that the subcutaneous cable is the main source of patient discomfort and system malfunction.
Using a combination of novel microstimulation methodologies and low-power circuit design techniques, Dr. Maysam Ghovanloo, assistant professor of electrical and computer engineering at North Carolina State University, is creating a device that eliminates the long, subcutaneous cable between the stimulator and its electrodes and delivers a better-controlled train of electrical impulses for stimulating the brain. The small-sized, low-power, head-mounted deep brain stimulation system will reduce patient morbidity and mechanical failures while improving the safety, efficacy and efficiency of stimulation delivery as well as patient comfort.
“Significant advancements in electronics, computing, microfabrication, wireless communications, biocompatible materials and neurosciences have made possible the development of a new generation of neuroprosthetic devices that are aimed at restoring sensory, motor and cognitive functions lost through injury or disease. This research takes advantage of these technologies to develop state-of-the-art implantable microelectronic devices,” says Ghovanloo.
Current DBS devices are susceptible to failures, including breaks in the lead wires, migration of the subcutaneous wire and shifting of the stimulation electrodes. Studies of DBS patients have shown that the long wires and connectors attached to the chest-implanted devices are the primary cause of mechanical failure.
Ghovanloo’s more efficient head-mounted design reduces the possibility of these problems because the stimulator will be small enough to be placed under the scalp inside a cap that will be located directly above the place where the electrodes enter the skull. The head-mounted device does not require long subcutaneous wires, and the smaller stimulation device and rechargeable battery eliminate the current bulky chest-implanted device.
One key component of the new device is a novel switched-capacitor-based stimulation (SCS) circuitry, developed by Ghovanloo, that gives better control over the electrical charge delivered to the neural tissue. Existing devices either provide high power efficiency through voltage-controlled pulses for longer battery life with very little control over the injected current or provide good control over the stimulus current with greater power consumption, resulting in shorter battery life. The SCS circuitry, on the other hand, provides both good control over the injected charge into the neural tissue and reduced power consumption.
To evaluate his experimental device designs, Ghovanloo is collaborating with Dr. Oleg Favorov, associate professor of biomedical engineering in the joint Department of Biomedical Engineering at NC State and the University of North Carolina at Chapel Hill (UNC-CH), and Dr. Richard W. Murrow and Dr. Mark Tommerdahl, both of the Department of Neurology at UNC-CH. The study compares the different stimulation delivery methods, including the SCS-based circuitry developed by Ghovanloo. Once the optimum circuitry, stimulus waveforms and range of stimulus parameters are determined, miniaturized, fully integrated system-on-a-chip (SoC) prototypes of the head-mounted device can be built and tested.
Ghovanloo’s research into implantable microelectronic devices (IMDs) for the treatment of neurological disorders such as Parkinson’s disease, essential tremor and dystonia can be applied to a variety of other diseases, disorders and disabilities.
“Developing new technologies to better and more effectively aid people with disabilities is one of the major challenges that scientists and engineers aspire to undertake in the 21st century,” says Ghovanloo. “These devices can be designed to address many other nerve-related problems, including hearing loss, blindness and paralysis. While these applications are still in the early stages, they are very promising for the future.”