Characteristics of electrode impedance and stimulation efficacy of a chronic cortical implant using novel annulus electrodes in rat motor cortex

• Published in: Journal of neural engineering 2013-08, Vol.10 (4), p.046010-046010
• Main Authors: Wang, Chun, Brunton, Emma, Haghgooie, Saman, Cassells, Kahli, Lowery, Arthur, Rajan, Ramesh
• Format: Article
• Language: English
• Subjects: Animals; behaviour response; biphasic stimulation; Brain; chronic cortical implant; Deep Brain Stimulation - instrumentation; Electric Impedance; electrode impedance; Electrodes, Implanted; Equipment Design; Equipment Failure Analysis; Evoked Potentials, Motor - physiology; Longitudinal Studies; Motor Cortex - physiology; Movement - physiology; neural prosthesis; penetrating annulus electrodes; Rats; Rats, Sprague-Dawley; Reproducibility of Results; rodent primary motor cortex; Sensitivity and Specificity
• ISSN: 1741-2560; 1741-2552
• DOI: 10.1088/1741-2560/10/4/046010

Objective. Cortical neural prostheses with implanted electrode arrays have been used to restore compromised brain functions but concerns remain regarding their long-term stability and functional performance. Approach. Here we report changes in electrode impedance and stimulation thresholds for a custom-designed electrode array implanted in rat motor cortex for up to three months. Main Results. The array comprises four 2000 µm long electrodes with a large annular stimulating surface (7860-15700 µm2) displaced from the penetrating insulated tip. Compared to pre-implantation in vitro values there were three phases of impedance change: (1) an immediate large increase of impedance by an average of two-fold on implantation; (2) a period of continued impedance increase, albeit with considerable variability, which reached a peak at approximately four weeks post-implantation and remained high over the next two weeks; (3) finally, a period of 5-6 weeks when impedance stabilized at levels close to those seen immediately post-implantation. Impedance could often be temporarily decreased by applying brief trains of current stimulation, used to evoke motor output. The stimulation threshold to induce observable motor behaviour was generally between 75-100 µA, with charge density varying from 48-128 µC cm-2, consistent with the lower current density generated by electrodes with larger stimulating surface area. No systematic change in thresholds occurred over time, suggesting that device functionality was not compromised by the factors that caused changes in electrode impedance. Significance. The present results provide support for the use of annulus electrodes in future applications in cortical neural prostheses.