English: The DPI neuron circuit. (A) Circuit schematic. The input DPI low-pass filter (yellow, ML1 − ML3) models the neuron's leak conductance. A spike event generation amplifier (red, MA1 − MA6) implements current-based positive feedback (modeling both sodium activation and inactivation conductances) and produces address-events at extremely low-power. The reset block (blue, MR1 − MR6) resets the neuron and keeps it in a reset state for a refractory period, set by the Vref bias voltage. An additional DPI filter integrates the spikes and produces a slow after hyper-polarizing current Ig responsible for spike-frequency adaptation (green, MG1 − MG6). (B) Response of the DPI neuron circuit to a constant input current. The measured data was fitted with a function comprising an exponential ∝e−t/τK at the onset of the stimulation, characteristic of all conductance-based models, and an additional exponential ∝e+t/τNa (characteristic of exponential I&F computational models; Brette and Gerstner, 2005) at the onset of the spike (Indiveri et al., 2010).