Figure 4.

Voltage attenuation and impedance measurements for several electrodes. Plots show amplitude data from signals recorded with electrodes in dilute saline. Grey-to-blue lines show data recorded using the low input impedance head-stage for electrodes with low-to-high measured impedance values at 10 Hz. The manufacturer specified 1 kHz impedance value for each electrode is indicated in A. Values in italics and followed by an asterisk denote data from a glass insulated electrode. Orange lines show data recorded with the higher input impedance head-stage for one electrode with a large specified 1 kHz impedance of 8.4 MΩ. Parallel configuration data is shown with solid lines, series configuration data is shown with dashed lines. A and B denote parallel confugration recordings with no Z_a’ manipulations, and C shows the average parallel and series configuration values across 4 different values of Z_a’. Spike and LFP channel data (see Methods) are shown overlapping in A, but in B and C the vertical dashed line denotes the point where data to the left corresponds to the LFP channel data only, and data to the right corresponds to the spike channel data only. Frequency is shown on a log scale. For a list of the exact frequencies tested, please see the Signals used subsection in the Methods section. A: raw gain of the recorded over the actual signal. B normalized gain showing voltage attenuation across the electrode, given by the value in A for each recording divided by the raw gain of the reference recording, which was done with a steel pin with negligible impedance. C: Effective electrode impedance (Z_e’) calculations derived from the above data for each trace. Z_e’ is shown on a log scale.