Near-optimal information relay by the neuronal population of layer 4 barrel cortex

Abstract

Cortical function reflects the coordinated activities of populations of neurons, which, in turn, depend on the speed with which each neuron can respond to input, as revealed by dynamic gain analysis. In Layer 4 of the rodent barrel cortex, a finite population of interconnected, small, excitatory neurons rapidly and briefly relays input from the specific thalamus to the rest of the cortical column. Theory predicts that the determinants of a population’s dynamic gain - cell number, cell size and the correlation time of the background noise - control the speed with which the population can respond to input. Here, we demonstrate how these parameters are optimized such that a single thalamocortical input spike is reliably reflected in the output population response of layer 4. We show that the synaptic receptor dynamics that dominate the background noise in layer 4 are slower than in other layers. We further show that the speed with which the spike-generation machinery can respond depends on the activity of KV7 channels, suggesting that the relay function of layer 4 is under muscarinic control.