The sophistication of neuroscience experiments designed to elucidate the functionality of the mammalian central and peripheral nervous system is rapidly increasing, and so must the use of more complex electrodes that are used to interrogate the behavior of neural networks. Despite the rapid rise of optical techniques, the metal microelectrode remains the workhorse of experimental neuroscience, and implantable electrode arrays continue to be an important experimental tool. Unfortunately, the reliability of multielectrode arrays remains marginal. While some researchers have been able to record neural activity for many months, or years, more commonly the neuroscientist is hampered by short-term degradation in electrode insulation, increasing array electrical leakage, breakage of wires, and failure of percutaneous connectors. Often these failures obscure the neuroscience experimental goals, and the neuroscientist is left to guess whether changes in data are due to array deficiencies or biological effects.

Initiated by a DARPA grant, our group has developed a microelectrode array analytic and diagnostic instrument that can assess the “health” of implanted electrode arrays. Using a combination of CV, EIS, and pulsed-current measurements, the multiple electrode array analyzer uses 16 parallel potentiostatic modules to perform these measurement modalities in parallel, rather than multiplexing a single instrument. This parallel measurement capability is important because the duration of sessions with experimental animals is often very limited, and the researcher is unable to dedicate a significant portion to merely determining the status of the implanted electrodes. Parallel measurement of 16 electrodes dramatically reduces the time required to diagnose the condition of implanted electrodes at the onset of an experimental session. However, performing parallel measurements of CV and EIS for multiple electrodes pose unique instrumentation challenges that have been addressed in our design.

The performance of this instrument has been evaluated in experiments performed on Macaque with electrode arrays implanted in the brain in a location that is particularly vulnerable to cable breakage. Diagnoses of the electrodes, and connection system, have been performed that clearly show increased electrical leakage as differentiated from biological encapsulation of the electrode tips. The presentation will describe these experiments, the electrochemical data, and the functional diagnoses. 

Our long-term goal is the development and distribution of a diagnostic software module which permits frequent and rapid collection of in-vivo electrode electrochemical data, with the option of upload to a central database for sharing among researchers. Using this diagnostic means, the researcher can anticipate electrode array failures, and make appropriate experimental decisions.