In vivo and in vitro electrochemical impedance spectroscopy analysis of acute and chronic intracranial electrodes

Invasive intracranial electrodes are used in both clinical and research
applications for recording and stimulation of brain tissue, providing
essential data in acute and chronic contexts. The impedance
characteristics of the electrode–tissue interface (ETI) evolve over time
and can change dramatically relative to pre-implantation baseline.
Understanding how ETI properties contribute to the recording and
stimulation characteristics of an electrode can provide valuable insights
for users who often do not have access to complex impedance
characterizations of their devices. In contrast to the typical method of
characterizing electrical impedance at a single frequency, we demonstrate
a method for using electrochemical impedance spectroscopy (EIS) to
investigate complex characteristics of the ETI of several commonly used
acute and chronic electrodes. We also describe precise modeling strategies
for verifying the accuracy of our instrumentation and understanding
device–solution interactions, both in vivo and in vitro. Included with
this publication is a dataset containing both in vitro and in vivo device
characterizations, as well as some examples of modeling and error
structure analysis results. These data can be used for more detailed
interpretation of neural recordings performed on common electrode types,
providing a more complete picture of their properties than is often
available to users.