Abstract
Most neural stimulation techniques rely on macroelectrodes, which generate electric fields that impact neuronal groups rather than specific neurons, often resulting in unintended side effects.1,2 Ultramicroelectrodes (UMEs) offer enhanced spatial resolution, holding promise for precise targeting of specific neurons to optimize therapeutic outcomes while mitigating adverse effects. However, ultramicroelectrodes present challenges. For example, delivery of required charge may require current densities that can damage the electrode or adjacent tissue. Impedance measurements of UMEs were conducted and analyzed to understand stimulation currents and potential damage to the electrodes and tissue. The measurement-model technique was used to identify the optimal frequency range for regression analysis, to quantify the stochastic error structure, and to identify inconsistencies with the Kramers-Kronig relations. Understanding of the error structure is vital for interpretation.3 The regressions were weighted using the inverse of the variance for the stochastic error structures, and quality of fits were determined by the weighted chi-square statistic. Process modeling was used to understand and characterize the underlying physical and chemical processes that occur at the electrode-electrolyte interface and electrode-tissue interface during neural stimulation. Constant-phase element (CPE) parameters, Q and alpha, corresponding to the behavior of the electrode-tissue interface, were obtained from this model. In addition, parameters associated with a capacitive loop were identified. Work is in progress to identify the origin of this loop. References (1) Otto, K. J.; Schmidt, C. E. Neuron-Targeted Electrical Modulation. Science. March 20, 2020, pp 1303–1304. https://doi.org/10.1126/science.abb0216. (2) Orazem, M. E.; Otto, K. J., Alexander, C. L., Electrochemistry in Action-Engineering the Neuronal Response to Electrical Microstimulation. Electrochemical Society Interface 2023, 32 (1), 40–42. https://doi.org/10.1149/2.F06231IF. (3) Orazem, M. E.; Agarwal, P.; Jansen, A. N.; Wojcik, P. T.; Garcia-Rubio, L. H. Development of Physico-Chemical Models for Electrochemical Impedance Spectroscopy. Electrochim Acta 1993, 38 (14), 1903–1911.
Published Version
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