Abstracts

Rationale: Resective surgery remains the most effective, yet underutilized treatment for drug resistant focal epilepsy. High procedure costs coupled with patient discomfort associated with prolonged intracranial EEG monitoring likely contribute to underutilization of resective surgery. Current intracranial electrodes are largely handmade, bulky, costly, and pose several risks to patients. Furthermore, recent research supports that biomarkers of the epileptic networks occur on sub-millimeter spatial scales that are not probed by standard clinical subdural and depth electrodes. Here we describe thin, flexible, polyimide substrate electrodes, that can be easily manufactured and show promise towards improving human brain mapping. Methods: To examine biological impact on mammalian brain, 25 µm-polyimide substrate electrodes containing 64 microelectrode contacts (40 µm diameter) were implanted into porcine subdural space alongside standard clinical subdural electrodes for one week. The tissue underlying the two types of electrodes was removed, fixed, stained, and examined for immunological responses. To examine the electrophysiological fidelity of thin film electrodes, acute recordings were obtained from polyimide and standard, clinical electrodes in an acute seizure model in porcine cortex and in 5 patients undergoing resection for drug resistant epilepsy. Results: Histological analysis showed reduced immunological reaction to prolonged polyimide substrate implants compared to standard silicone substrate, clinical electrodes. Electrophysiological recordings obtained from polyimide electrodes showed the feasibility of high-fidelity, micro-scale electrophysiology. For standard macro-electrodes, polyimide substrate macroelectrode EEG was comparable to that from standard clinical electrodes, while also displaying easier deployment of polyimide electrodes through burr holes and underneath the dura. Conclusions: Thin, flexible polyimide substrate electrodes with lithographic deposition of metallic contacts provide multi-scale electrophysiological data and macroeletrode recordings similar to standard clinical electrodes with markedly reduced immunological response. In addition, the flexibility and reduced volume of polyimide electrodes should reduce pain and edema associated with subdural grid implantation. The increased number of channels per grid whose signals can be carried by a single electrode tail exiting the brain should provide reduced infection risk. Combined, these properties suggest that the replacement of current silicone electrodes with polyimide substrate electrodes for the acquisition of intracranial EEG could provide enhanced clinical electrophysiological value with reduced cost, infection risk, and patient discomfort. Funding: none