Implants

Prèlude

Implantable devices have been a part of epilepsy treatment and diagnostics for a long time.

Although mostly intraoperative and not persistently intracranial, the experiments of Jasper and others showed how electrical stimulation of the cortex could affect cortical function.

Implantable devices range from diagnostic to therapeutic to diagnostic-therapeutic.

Vagus nerve stimulation (VNS) was introduced in the late 1990s and the devices made by Livanova (formerly Cyberonics) have become more featureful with time. It has a responder rate around 40–50%.

Neuravista was an investigational implant in the 2000s which was meant to capture long-term electrocorticography (ECoG) over the putative seizure onset zones in patients with focal epilepsy. An online processor examined the signal and classified it into either safe, seizure imminent, or ambivalent states, which were represented on a hand-held monitor as different colors. The purpose, besides feasibility proof, was to allow patients to have better warning when seizures would occur so that they could take precautions. The secondary goal was collecting long-term ECoG data for further analysis. The company went bankrupt but the data are still available for collaborators.

Responsive neurostimulation (RNS), represented by a single extant product called Neuropace, is similar to Neurovista in that it is a chronic indwelling ECoG recorder and processor. Whereas Neuravista was geared toward alerting patients to upcoming seizures, Neuropace is designed to disrupt nascent seizures with cortical stimulation. The latter approach was driven by observations in phase 2 monitoring that either spontaneous or accidentally-induced seizures could sometimes be disrupted by additional current stimulation. Responder rates for Neuropace can be up to 60–70%.

Deep brain stimulation for epilepsy (DBS) stereotactially inserts depth electrodes in the anterior nuclei of both thalami. An on-off stimulation paradigm (not unlike in VNS) causes neuromodulatory effects. Unlike RNS and like VNS, the seizure onset zone does not need to be known to use this device.