FIGURE 4.

(A) Fitting of an electrode model to the experimental data of measured voltage values upon applying a current stimulus to an electrode. For bright Pt (Pt), a current stimulation was performed with a biphasic anodic-cathodic waveform with an amplitude of 140 nA, a duration of 1 ms per phase and a readout amplifier gain of 2. For Pt-black (PtB) the amplitude was 560 nA, the duration 2.5 ms per phase, and the readout amplifier gain was equal to 2. The different waveforms durations and amplitudes are due to the readout channel saturation in case of bright Pt as a consequence of the higher impedance. In both cases, only the first half of the waveform, i.e., the positive part was used for the fits and is displayed. (B) Capacitance values of 10 Pt and PtB electrodes are presented. The values were computed as a result of the fitting in panel A by setting the capacitance as an unknown value. (C) Charges required for efficient voltage and current stimulation of the same neuron. For current stimulation, the waveform had a duration of 20 μs per phase, while the duration for voltage stimulation was 100 μs per phase. The stimulation protocol included 30 repetitions of every stimulation amplitude in a randomized manner. For current stimulation, the charge was computed as q = I × t, i.e., the product of applied current and time. For voltage stimulation, the charge was computed as q = C × Δv, i.e., the product of the computed capacitance and the voltage change upon stimulation.