Space-rate coding in an adaptive silicon neuron

Neurophysiology is largely the study of spike rates of single neurons, under controlled conditions, with the hope that these results reflect how populations of neurons compute. However, the population response differs radically from the single-neuron response if the membrane voltage's rate of change drops dramatically when it is close to the spike-firing threshold. By delaying spiking, this slew-rate adaptation has been shown to regulate spike rate and prolong synaptic integration at the single-neuron level. We show here that it sharpens sensitivity and shortens latency at the population level. Thus, slew-rate adaptation enables neurons to process information faster than their interspike interval by using space-rate coding, instead of time-rate coding. This study also suggests how neural populations can modulate their gain and synchrony by regulating active conductances. Our results are extrapolated from experiments and analysis performed on a single silicon neuron, with Ca- and voltage-dependent potassium-channel analogs.