Abstracts

Rationale: Focal drug resistant epilepsy affects approximately 65 million worldwide and 3 million patients in the United States. Approximately 1/3 of people diagnosed with focal epilepsy may be drug resistant and require an alternative treatment. Surgery is an important treatment option for patients if the region generating seizures can be identified and resected. The evaluation for respective epilepsy surgery, which can be curative, often utilizes subdural electrodes to better localize the seizure onset zone to guide surgical resection or direct brain stimulation. The subdural strips and grids are commonly composed of 4 mm diameter electrodes with a 1 cm pitch. These low resolution electrode arrays require a large portion of the brain to be exposed to allow placement. In addition to grid electrodes, the craniotomy is used to deliver a compliment of linear electrode arrays to targeted subdural locations adjacent to the edge of the craniotomy. Following electrode implantation, continuous intracranial EEG (iEEG) monitoring is conducted over the course of multiple days with the goal of recording the patient’s habitual focal seizure. Here we describe an innovative electrode configuration that enables collection of iEEG signals at multiple spatial scales to investigate the stimulation response of cortex. Methods: We designed, fabricated, and tested this multiscale thin-film polyimide electrode array that contained 128 platinum electrodes with 3 spatial scales covering a 100 mm2 surface area. The contact configuration consisted of 40 µm diameter electrodes nested within larger 1 mm diameter electrodes that were nested within 4 mm diameter electrodes. Electrochemical impedance spectroscopy and phantom signal recording were conducted on the benchtop to verify electrode functionality prior to in vivo testing in a rodent animal model. The analysis of the recordings and results of the in vivo recordings test show the ability to collect signals on all channels across multiple spatial scales. The electrodes were used to record over a wide dynamic range (0.01 – 1000 Hz) and characterized using spectral analysis. Results: These multiscale electrodes exhibited the expected impedance response with impedance magnitudes scaling inversely with geometric area. Prior to in vivo testing, the recording functionality was successfully verified across all electrode sizes with benchtop testing. Subsequently, cortical recordings were obtained from rodent and show the ability to collect cortical activity across multiple spatial scales that are not captured by conventional electrodes. In addition, this design had the ability to capture unique cortical activity within and across all electrode sizes. Conclusions: The study demonstrated the potential of multiscale electrodes for passive recording at different spatial scales. The results will be used to influence electrode design refinements and biocompatible device design requirements for multiscale brain mapping. Funding: No funding