Abstract
Changes in biotic and abiotic factors can be reflected in the complex impedance spectrum of the microelectrodes chronically implanted into the neural tissue. The recording surface of the tungsten electrode in vivo undergoes abiotic changes due to recording site corrosion and insulation delamination as well as biotic changes due to tissue encapsulation as a result of the foreign body immune response. We reported earlier that large changes in electrode impedance measured at 1 kHz were correlated with poor electrode functional performance, quantified through electrophysiological recordings during the chronic lifetime of the electrode. There is a need to identity the factors that contribute to the chronic impedance variation. In this work, we use numerical simulation and regression to equivalent circuit models to evaluate both the abiotic and biotic contributions to the impedance response over chronic implant duration. COMSOL® simulation of abiotic electrode morphology changes provide a possible explanation for the decrease in the electrode impedance at long implant duration while biotic changes play an important role in the large increase in impedance observed initially.
Highlights
Tungsten micro-wire electrode arrays continue to be used as chronic implants for single-unit neuronal recording (Williams et al, 1999a,b; Rennaker et al, 2005; Rizk et al, 2009; Freire et al, 2011)
The electrode impedance varied over time increasing during the first few weeks of implantation followed by a drop in the impedance value in the latter phase of the implant duration
We examined the complex impedance trends of a 16 channel tungsten microwire array used in a chronic in vivo neural recording study
Summary
Tungsten micro-wire electrode arrays continue to be used as chronic implants for single-unit neuronal recording (Williams et al, 1999a,b; Rennaker et al, 2005; Rizk et al, 2009; Freire et al, 2011). Chronic in-vivo studies (Prasad and Sanchez, 2012) have confirmed a functional correlation between the electrode impedance value at 1 kHz and the overall neuronal yield during the implanted duration. The electrode impedance varied over time increasing during the first few weeks of implantation followed by a drop in the impedance value in the latter phase of the implant duration. Though these observations suggest that the electrode impedance is affected by some short-term and long-term factors, the underlying driving mechanisms are not fully understood. The impedance variation for tungsten microwires itself varied across different implanted animals
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