K Hynna | PubMed Health

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Spike-based VLSI modeling of the ILD system in the echolocating bat.

The azimuthal localization of objects by echolocating bats is based on the difference of echo intensity received at the two ears, known as the interaural level difference (ILD). Mimicking the neural circuitry in the bat associated with the computation of ILD, we have constructed a spike-based VLSI model that can produce responses similar to those seen in the lateral superior olive (LSO) and some parts of the inferior colliculus (IC). We further explore some of the interesting computational consequences of the dynamics of both synapses and cellular mechanisms.

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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.

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