Brain Implant Cuts Seizures

It sounds extremely promising," says Jaimie Henderson, a neurosurgeon at Stanford University who is not involved with Neuropace or with the clinical trials. "The demonstration that a system like this can be effective is a big step forward."

Some 30 to 50 percent of epilepsy patients cannot adequately control their seizures with medication, a figure that amounts to hundreds of thousands of patients in the United States. Some resort to surgery, in which the part of the brain where the seizure originates is removed. But not everyone has this option--the abnormal activity may start in brain areas responsible for language or vision and thus cannot be surgically destroyed without serious consequences.

The Neuropace system, called the Responsive Neurostimulator, is one of a handful of electrical stimulation devices that are available or in development for epilepsy patients. These devices are designed to counter the uncontrolled electrical storm of a seizure with an externally delivered current.

While other devices stimulate the nervous system continuously or in a predetermined pattern, the Neuropace implant is unique in that it monitors the brain, delivering jolts of electricity only when it detects the abnormal electrical activity that signals the onset of a seizure. "It's like dousing a spark before it becomes a flame," said Martha Morrell, Neuropace's chief medical officer, at a press conference at the American Epilepsy Society's annual meeting in Boston on Monday.

The device consists of a neurostimulator that's smaller than a deck of cards. It's surgically implanted into a hollowed out part of the skull, along with a set of electrical leads that can both record electrical activity and dispense jolts of electricity. The leads are placed either on the surface of the brain or deep in the brain tissue, depending on where a patient's seizures begin. Surgeons locate this spot, known as the "seizure focus," prior to surgery using a combination of brain imaging and electroencephalogram (EEG) recordings, which measure brain activity from surface electrodes on the skull, or electrocorticography (ECoG), in which activity is recorded directly from the surface of the brain.

The device, which contains a battery and a small computer, continuously monitors electrical activity. "As the [electrical activity] becomes higher in amplitude, the device is programmed to identify that as a significant event and deliver a stimulus," said Morrell at the conference. "The system then reevaluates the EEG and determines if further stimulus is needed."