For the first time, University of Washington researchers have combined electrodes on top of the brain to sense movement in the parts of the body that experience essential tremor, along with a deep brain electrode, to deliver stimulation only when it’s needed. The approach, developed by electrical engineers, UW Medicine researchers and ethicists at the Center for Sensorimotor Neural Engineering (CSNE) at UW, is described in a paper to be published in a forthcoming issue of the journal IEEE Transactions on Neural Systems and Rehabilitation Engineering.

It’s an important step toward developing fully–implanted, closed–loop deep brain stimulators to treat disorders like essential tremor and Parkinson’s disease – devices that one day might be controlled by the patient’s own thoughts or movements.

“We’d ultimately like to give individuals that ability and choice,” said co–author Margaret Thompson, a UW electrical engineering doctoral candidate and member of the CSNE team. “One side effect of deep brain stimulation can be difficulty speaking, for instance. So if you’re about to drink a glass of water, you might want to turn up the stimulation so your hand doesn’t shake. If you’re answering the phone, perhaps you’d want to turn it down so your speech isn’t affected.”

Delivering deep brain stimulation also can extend the battery life of these implanted devices, which currently last only three to five years. Lengthening battery life is important because replacing the battery requires surgery, which carries risks to the patient such as infection.

“We’re saving about half of the battery power, based on our subjects so far, which was one of our main motivations,” said senior author and UW electrical engineering professor Howard Chizeck. “But even more interesting are some early indications that suggest our closed–loop system results in better patient performance, with less tremor, better control of their hands and fewer side effects.”

The project originated in a partnership between the CSNE and medical device manufacturer Medtronic to test new ways of activating Medtronic’s Activa PC+S Deep Brain Stimulation system with essential tremor patients. This system not only delivers electrical stimulation like traditional DBS systems, but also has the capability to sense and respond to electrical signals generated by the brain itself. The UW team received an investigational device exemption from the U.S. Food and Drug Administration for these tests.

To treat essential tremor, a surgeon typically implants an electrode in the thalamus of a patient’s brain. It’s wired down the neck to another implanted device housed under the clavicle that contains a battery and the electronics that drive the system. This “open–loop” system, in clinical use today, delivers constant deep brain stimulation at levels set by a doctor.

In three patients who received the Medtronic Activa PC+S Deep Brain Stimulation system, UW Medicine surgeons also implanted a small strip of electrodes on top of the brain’s motor cortex, the part of the brain that controls movement. The electrode strip can be used to sense when a hand or other extremity affected by essential tremor is moving. In a key innovation, the team developed machine learning algorithms to “decode” neural signals coming from the brain and correlate them with essential tremor symptoms that warrant treatment by stimulation.

The neural biomarkers and algorithms used to “decode” them differ by disease. While a similar treatment approach has been documented for Parkinson’s disease, this is the first time neural signals have been used to selectively treat essential tremor.