9 August 2012
A skull implant that can detect an epileptic seizure and deliver therapeutic electrical impulses can reduce the length of these events by 60% in rats. The device, tested on nine rats with a ‘petit mal’ form of epilepsy, is described today in Science1.
Most electrical stimulation devices, such as those that deliver deep-brain stimulation (DBS) to treat Parkinson’s disease and depression, operate continuously, delivering impulses regardless of the patient’s brain activity. But this can cause a range of undesirable side effects, such as headaches.
Seizure-responsive versions of DBS devices are coming to market, such as the Responsive Neurostimulator System developed by NeuroPace, based in Mountain View, California. The system is awaiting approval by the US Food and Drug Administration and will be aimed at adults with certain types of partial-onset seizures, which tend to be localized to certain regions of the brain. But as the name implies, DBS uses electrodes that penetrate the brain, which can also carry certain risks, such as a worsening of epilepsy symptoms.
In the latest study, György Buzsáki, a neuroscientist at the New York University School of Medicine, and his colleagues used a less invasive approach that involves transcranial electrical stimulation (TES) of neurons using electrodes implanted in the skull. This technique has been shown to be effective at modifying the brain’s cortical (outermost) neurons, which become abnormally excited during epileptic seizures. To detect the onset of a seizure, recording electrodes that detect neural activity were implanted on the brain’s surface.
The challenge for the researchers was to engineer a device that could detect a seizure and stimulate the brain amid noisy electrical activity from the body’s neighbouring muscles and from the TES electrodes themselves.
The difference between a continuous stimulator and an on-demand device is comparable to the difference between an implantable cardiac pacemaker and an implantable defibrillator, says Martha Morrell, chief medical officer of NeuroPace and a neurologist at the Stanford School of Medicine in California. Like DBS devices now in use, pacemakers basically comprise a battery hooked up to a pulse generator, she says. An on-demand device such as an implantable defibrillator requires integrated circuits capable of sensing and interpreting the signals to know when to trigger the impulse, she says, “so the technology is much more complicated”.
Buzsáki and his team got around some of the electrical-noise issues by fitting the device with an accelerometer which helps the device filter out muscle signals by revealing correlations between the signals and movements. And one of the advantages of event-triggered stimulation is that electricity can be delivered at higher currents than would be tolerated if delivered continuously, which makes the treatment more effective, he says.
The team now hopes try the device on other forms of epilepsy that lack effective treatments.