FIGURE 6.
Effects of uncompensated stray capacitance on Cm measures with the eCm method. (A) Capacitive currents evoked by voltage step. Model Rs was in headstage but ungrounded. (Top) Fully compensated, (middle) undercompensated, and (bottom) overcompensated. The effect of these extremes was evaluated during parameter estimations after reassembly of the model circuit. (B) The three panels show model cell parameter estimates during manual under- and overcompensation of fast capacitance compensation. Cm was modulated ±0.3%; Rs, ±1.8%; and Rm, < ±0.01%. The increase in Cm occurred during under compensation. Nominal component values of Rs: 10 MΩ, Rm: 300 MΩ, and Cm: 18 pF. Cm noise: 14.6 fF rms; system noise with model 3.75 pA rms, 10-kHz Bessel filter, PC clone, Axon 200 amplifier in capacitive feedback mode, and Axon 1322A A/D D/A board.