Voltage Biasing, Cyclic Voltammetry, & Electrical Impedance Spectroscopy for Neural Interfaces

The overall goal of this procedure is to monitor the quality of the electrode tissue interface of implanted neural recording prosthetic systems, as well as to improve recording quality and long-term functionality. This is accomplished by first collecting daily electrochemical impedance spectroscopy, and neural recording data. Cyclic V telemetry or CV data are collected to gain further detail on the quality of the electrode tissue interfaces that show no neural activity and display high impedance.

Then a corrective 1.5 volt voltage bias is applied for four seconds. This is followed by continued data collection and additional voltage biasing as needed. Ultimately, lower impedance and the improvement or revival of recorded neural activity is possible using these methods.

The main advantage of this technique over existing methods like drug delivery or service modification, is that voltage biasing can have a robust effect on improving the functionality and performance of neural recording prosthetic systems after tens to hundreds of days after implantation. This method can help answer key questions in the neural engineering field, such as how to improve the functional lifetime of implantable electrode systems. The implications of this technique extend toward therapy or diagnosis of a multitude of neurological deficits.

This is important as the prevalence and treatment options of these deficits increase On the meth auto lab. PG stat adapted with FA two and channel mucks add-ons. Build a head stage adapter to connect the channel mucks to the head stage.

Now connect the working and sensing electrodes to the channel mucks add on. Then connect the reference and counter electrodes attached to the animal subject to the part of the head stage adapter connected to the current return path. Start the frequency response analyzer software and verify that the procedure file is set to test two multis sign waveforms each consisting of 15 signs simultaneously ranging from 10 hertz to 30 kilohertz.

Also, make sure the applied voltage is 25 millivolts or less. Now open and edit the project file. The project uses the procedure file loops through each channel and saves the result.

Connect the animal subject with a passive head stage lacking amplification. Active head stages will not pass input signals. Execute the project file depending on the settings.

Recordings from each channel take between 10 seconds and a few minutes. Now display and interpret the result. Pass the output text files with MATLAB and make a nyquist or bode plot.

Frequency dependent shifts in phase indicate a tissue response. Start the general purpose electrochemistry system software. Verify that the procedure file settings are set to sweep the voltage at 50 millivolts per second and are within the limits of hydrolysis.

Run at least three scans for the system to reach equilibrium and save the results from the final scan. The scan rate can be increased to one volt per second to reduce measurement time. However, the shape of the IV curve will likely change if the scan rate is faster than the charge transfer reactions occurring at the electrode tissue interface.

Next, open and edit the project file. The project uses the procedure file loops through each channel and saves the results. Connect the animal subject with a passive head stage and execute the project file at one volt per second.

Collection takes 10 seconds per channel while using a scam rate of 50 millivolts per second. Takes about three minutes per channel. Finally, display and interpret the results.

Pass the output text files with MATLAB and plot the IV relationship. The charge carrying capacity is quantified by integrating the area of the catheter current within the CV E.The most critical decision in this protocol is deciding when to apply a voltage bias. This is enabled by the impedance cyclical telemetry and recordings data.

Start the general purpose electrochemistry system software and verify that the procedure file is set to use the steps and sweeps method. Step the voltage at 1.5 volts for durations of four seconds. Next, open and edit the project file, which uses the procedure file to loop through each channel and save the result.

Connect the animal subject with a passive head stage and execute the project file recordings from each channel. Take about 10 seconds, then collect EIS CV and recordings data and interpret the results in a typical workflow. Recordings and EIS are collected either daily or weekly across all channels while CV and rejuvenation can be used.

If spiking activity is no longer detectable, EIS changes over the course of days to weeks after an electrode is implanted. The blue data was collected immediately after implantation and the green data four months later. When EIS data is displayed as a nyquist plot, a semicircle at higher frequencies near the origin is indicative of the tissue response at the electrode site.

CV analysis produces a current voltage curve that shows some hysteresis. The most relevant CV statistic is the charge carrying capacity, the area inside the IV curve normalized by the electrode site area. Electrodes with large charge capacity are preferred for micro stimulation.

During rejuvenation, a voltage pulse is applied. That usually results in increased charge capacity and decreased impedance magnitudes spiking can also be restored in channels that previously had spikes. While rejuvenation has only short-term effects on impedance and signal to noise ratio, this technique can be applied daily.

In data collected daily from a Guinea pig implanted with a 16 channel array, rejuvenation had a robust effect on lowering the one kilohertz impedance magnitude by an order of magnitude after each application. As a result of recovered signals and lower impedance, SNR increased after each rejuvenation session. Ultimately, all signals were lost following 160 days after implantation and rejuvenation was no longer effective.

Once mastered, this technique can be done in approximately one hour. While attempting this procedure, it is important to ensure that the proper connections are made and that the impedance spectroscopy results indicate a significant tissue response prior to voltage bio treatments.