FIGURE 1.

(A) (from left to right) PCB-mounted HD-MEA chip, photomicrograph of the chip, and enlargement of a subsection of the array including about 100 electrodes with live-stained neurons highlighted in green. The stimulation electrode used in panel B is highlighted in red. The picture was taken using an immersion 60×-magnification lens at the periphery of the array, where the cell density is lower. (B) Illustration of the neuron, labeled in panel A, and corresponding electrode locations, with superimposed measured signals. (Left) Spontaneous EAPs obtained after spike sorting. (Center) EAPs after current stimulation of the selected neuron. (Right) EAPs after voltage stimulation. Current stimulation entailed a biphasic anodic-cathodic waveform of 20 μs per phase. Voltage stimulation entailed a biphasic anodic-cathodic waveform of 100 μs per phase. The smallest stimulation signal amplitudes that still evoked APs 27 times during 30 repetitions (90% efficiency) were used. (C) Signals from three of the readout electrodes in panels A and B (numbered boxes). (Left) Extracellular signals recorded during spontaneous neuronal activity composed of >100 detected EAPs. (Center and right) Extracellular signals recorded from the same electrodes during 30 repetitions of current and voltage stimulation.