Fig. 3.

Stimulation and recording with flexible gold ion-implanted electrodes. a Composite image of a cell strand (red) with stimulation (orange) and recording electrodes (yellow) on either side of the DEA electrodes (black). The center arrow illustrates the direction of action potential propagation. b Strength–duration curve for stimulation of the preparation with bi-polar current pulses (inset). The star indicates typical stimulation parameters used during the experiments. c Upper panel: AP_EC as recorded by one electrode during propagated electrical activity along the cell strand. The AP_EC exhibits an amplitude (V_pp) of 900 µV and, as calculated from the Gaussian fit to the first derivative (lower panel), a downstroke time (t_DS) of 940 ms and a maximal downstroke velocity of −2.2 V s⁻¹. The negative peak of the fit was used to determine the local activation time (t_AT). d AP_ECs recorded by all electrodes during propagated electrical activity. The initial 5 ms of the signals containing the stimulation artifact were blanked. e Plot of local activation times vs. position for each recording electrode. Conduction velocity (θ = 324 mm s⁻¹) is derived from the slope of a linear fit to the data. The insert indicates the presence of minimal t_AT variability (SD < 10μs, n = 170 serial stimulations) at Rec_El III during 170 successive measurements