Abstracts

Rationale: Recent studies have demonstrated that human epileptic brain is organized on sub-millimeter spatial scales. Here we describe a thin film subdural electrode array, recording system, and data acquired during epileptogenesis in the barrel cortex of rodents. Methods: To examine cortical networks at multiple spatial scales, thin film polyimide substrate electrodes were designed and implanted into the subdural space overlying a Ferrous Chloride lesion in rodent barrel cortex. The recordings were obtained from a 32 contact bi-scale electrode. Four macroelectrodes (1 mm dia.), each embedded with 7 microelectrodes (40 µm dia.), were placed over the epipial barrel cortex in controls, as well as, lesioned animals. Continuous video and electrophysiological recordings were obtained over the course of 4 days (DC – 9 kHz, sampling 32 kHz; Cheetah system, Neuralynx Inc.). The local field potential (LFP) recordings were analyzed for focal oscillations (0.01 – 1 kHz) occurring over 0.01 to 1 mm spatial scales. Results: Electrophysiological recordings in both normal and lesioned barrel cortex of rodents demonstrate LFP activity spanning 0.01 – 1 mm spatial and 0.001 – 600 Hz spectral scales. In the lesioned rodents high amplitude focal rhythmic activity was observed and quantified. Focal, sub millimetric electrographic subclinical seizure activity was recorded, in 1 lesioned animal with clinical seizures. Conclusions: High fidelity electrophysiological recordings over multiple spatial scales can be used to explore the organization of normal and epileptogenic cortex. The thin, flexible, polyimide film electrodes with lithographic deposition of metallic contacts provided stable multi-scale electrophysiological recordings. These electrodes have properties such as increased flexibility, reduced volume, and decreased immunological response, which should reduce artifacts associated with the brain-electrode interface. The integrated thin film electrodes, mounting apparatus, and head stage system provided a stable platform for long-term electrophysiology. The recordings in 1 of the 5 lesioned animals demonstrated sub-millimetric electrographic seizures similar to microseizures described previously in humans.  Funding: Mayo Clinic