Flexible Ultra-resolution Subdermal EEG Probes

Scalp Electroencephalogram (EEG) is a popular, noninvasive method to record neural activity, commonly used in the clinical setting as a gold-standard for diagnosing many disorders, including epilepsy. The spatial resolution of scalp EEG is of critical concern for targeting surgical interventions and resultant patient outcomes. However, high-resolution spatial information is filtered and obscured by noise as electrical signals propagate through layers of tissue. We present a novel paradigm of high-density subdermal EEG arrays, capable of being implanted under the scalp to increase spatial resolution of EEG recordings while minimizing invasiveness compared to traditional implantable recording electrode arrays such as electrocorticography (ECoG) surface grids. In addition, our device can be chronically implanted, as opposed to traditional scalp EEG electrodes that need to be removed periodically for re-application of conductive electrode gel. We demonstrate the design, fabrication and electrical characterization of high-density subdermal EEG arrays realized in Parylene C polymer platform using an optimized microfabrication process. Devices are realized in a range of electrode diameters (200 microns - 1000 microns) and pitch (1 mm - 3.5 mm), to study the effects of electrode size and spacing on the spatial frequency content and redundancy of recorded neural signals. Electrochemical Impedance Spectroscopy (EIS) measurements, show an impedance of <;10 kΩ (for 600 micron diameter) at 1 kHz. These high-density subdermal EEG probes will be used to validate our theoretical models of sampling and reconstructing neural activity from electric potentials.