Impedance and Noise Characterizations of Utah and Microwire Electrode Arrays

Acquisition of Neural Action Potentials Using Rapid Multiplexing Directly at the Electrodes

“…All studies were conducted with the approval of the Institutional Animal Care and Use Committee at the University of Utah. The surgical procedure was similar to that outlined in [ 38 ]. Anesthesia was induced using 5% vaporized isoflurane in a specialized induction chamber and maintained at 1.5–3%.…”

“…Recently, we performed wideband spectral measurements of implanted electrodes [ 37 , 38 , 39 , 40 ] ( Figure 3 ). These measurements characterize the noise at high frequency as thermal in origin, on the basis of impedance magnitude and phase measurements.…”

“…Background biological noise is generally in the 5–10 µV rms range in the AP band [ 17 ], which would correspond to 75–150 nV rms / white noise across 0.5–5 kHz. Our studies [ 38 ] have also shown that high-frequency electromagnetic interference can be eliminated through proper referencing, grounding, and shielding, and that biological noise is confined to low frequencies (<10 kHz) [ 37 ]. Overall, thermal noise is the dominant concern at high frequencies and can be accurately predicted by impedance magnitude and phase measurements [ 38 ].…”

“…The in vivo measurements were performed under isoflurane anesthesia, which is known to suppress local cortical spiking activity [ 43 ], revealing the baseline noise floor. The real part of the measured impedance was used to predict the thermal noise (dashed lines), whereas the solid lines are direct spectral measurements [ 38 ]. For the in vitro measurements, the measured noise and predicted thermal noise match well across the spectrum.…”

“…For the in vitro measurements, the measured noise and predicted thermal noise match well across the spectrum. For in vivo measurements, there is excess low-frequency noise/activity attributed to biological sources other than local AP activity [ 37 , 38 , 39 , 44 ].…”