Understanding the magnitude and structure of inter-neuronal correlations and their relationship to synaptic connectivity structure is an important and difficult problem in computational neuroscience. Early studies show that neuronal network models with excitatory-inhibitory balance naturally create very weak spike train correlations. Later work showed that, under some connectivity structures, balanced networks can produce larger correlations between some neuron pairs, even when the average correlation is very small. All of these previous studies assume that the local neuronal network receives feedforward synaptic input from a population of uncorrelated spike trains. We show that when spike trains providing feedforward input are correlated, the downstream recurrent neuronal network produces much larger correlations. We provide an in-depth analysis of the resulting "correlated state" in balanced networks and show that, unlike the asynchronous state of previous work, it produces "tight" excitatory-inhibitory balance, consistent with in vivo cortical recordings.
Author summaryCorrelation and synchrony between the activity of neurons in the brain is known to play a crucial role in the dynamics and coding properties of neuronal networks, and also mediates synaptic plasticity and learning. Therefore, it is important to understand the relationship between the structure of connectivity in a neuronal networks and the correlations between the activity of neurons in the network. Previous theoretical work shows that this relationship is constrained by the widely observed balance between excitatory (positive) and inhibitory (negative) input received by neurons in the network. We extend this previous theoretical work to account for the fact that inputs coming from outside the local neuronal network might come from neural populations that are themselves correlated or partially synchronous. Including this biologically realistic assumption changes the basic operating state of the network and produces a tighter balance between excitatory and inhibitory synaptic inputs that is consistent with in vivo recordings.