For many people living with epilepsy, medication is effective. “However, a third of patients with epilepsy are refractory to medications,” explains Dawn S. Eliashiv, MD, professor of neurology and co-director of the UCLA Seizure Disorder Center. “That means they failed or didn’t respond to two medications and still have seizures.”
Historically, the next step for these patients might involve surgery to remove the portion of brain tissue responsible for generating seizures. But surgery is not always possible and, even when it is, it may carry meaningful neurological risks.
A newer approach, responsive neurostimulation (RNS), allows neurologists and neurosurgeons to control seizures through technology, without removing brain tissue. In short, it offers new hope to patients with different epilepsy types who were not candidates for surgical resection.
Listening to the brain
RNS is a form of neuromodulation designed to detect and interrupt seizure activity at its earliest electrical stages. The NeuroPace RNS System was FDA approved in the United States in 2013 for treating patients whose seizures do not respond to medication.
In the procedure, physicians implant a small neurostimulator beneath the skull. Thin electrodes are placed in or near the areas of brain where seizures originate. These may be depth electrodes placed deep within brain structures or electrodes positioned on the surface of the brain. The device then acts as an internal observer.
“It has the ability to record brain waves directly from those structures,” Dr. Eliashiv explains. “Using algorithms that recognize the electrical patterns specific to that patient’s seizures, the device can detect when a seizure is beginning.”
When those patterns appear, the system responds instantly by delivering brief electrical pulses through the electrodes. The stimulation may halt the seizure in its earliest moments. Over time, however, neurologists believe this therapy does something even more interesting.
“It can stop seizures in some cases,” Dr. Eliashiv says, “but what we’ve learned is that it also modulates brain activity and decreases the tendency to have seizures over time.” The brain’s circuitry appears to gradually recalibrate.
The value of RNS becomes particularly clear in patients whose seizures originate in regions of the brain that surgeons cannot safely resect. A recent multi-center retrospective cohort study led by UCLA investigators, published in Seizure: European Journal of Epilepsy, assessed the safety and efficacy of RNS.
Researchers examined 20 patients with drug-resistant focal motor epilepsy who underwent implantation of RNS in the primary motor cortex. For these patients, traditional epilepsy resection surgery would carry a risk of profound post-surgical motor deficits, including loss of motor function.
The study offered encouraging results. About half of the patients experienced greater than 90% reduction in seizure frequency, placing them among what clinicians sometimes call “super-responders.” Just as important, the treatment offered a therapeutic pathway where none previously existed.
RNS therapy: A growing field
Even when epilepsy surgery is technically possible, it can carry neurological trade-offs depending on the region of brain involved.
“In the past, we might perform resections of the dominant temporal lobe,” Dr. Eliashiv notes. “Patients could have a good seizure outcome but then develop memory deficits or cognitive problems.”
For some patients, RNS offers a more conservative alternative. Rather than removing brain tissue, physicians implant electrodes and monitor brain activity while providing responsive stimulation.
Another advantage of RNS is diagnostic. When physicians are uncertain which side of the brain generates seizures, RNS can monitor both regions simultaneously.
“With RNS, we can implant electrodes on both temporal lobes and monitor over a long period of time,” Dr. Eliashiv says. “We can see where the seizures are actually coming from while also delivering therapy.”
This dual-role treatment, combined with long-term brain monitoring, is one of the system’s unique strengths.
RNS is part of a broader family of neuromodulation therapies for epilepsy. Other devices include the vagus nerve stimulation system, which stimulates the vagus nerve in the neck, and deep brain stimulation targeting structures within the thalamus. RNS differs in one critical respect: it is responsive rather than continuous.
“This device looks at brain patterns, recognizes the seizure pattern and then delivers a response,” Dr. Eliashiv explains. “That responsive quality is unique.”
Researchers are also exploring whether expanding the system’s targets, such as certain thalamic regions, might allow it to treat broader forms of epilepsy, including some generalized seizure disorders.
The emergence of RNS reflects a broader shift in neurology and neurosurgery. Increasingly, physicians are moving away from one-size-fits-all solutions toward individualized, data-driven treatments that adapt to each patient’s brain. For patients with refractory epilepsy, that shift carries enormous implications. In the United States alone, approximately 1.4 million people live with drug-resistant epilepsy.
Dr. Eliashiv believes clinicians should increasingly think about neuromodulation earlier in the treatment pathway.
“The big takeaway,” she says, “is to consider, for patients with refractory epilepsy, more options that include neuromodulation in general and RNS specifically.”
Responsive neurostimulation may continue to evolve. Researchers are actively investigating new targets in the brain, more sophisticated algorithms for detecting seizure activity and broader neurological applications. For now, however, it offers meaningful seizure control to patients who once had very few epilepsy treatment options.
