Reconciliation of weak pairwise spike-train correlations and highly coherent local field potentials across space

Chronic and acute implants of multi-electrode arrays that cover severalsquare millimeters of neural tissue provide simultaneous access topopulation signals such as extracellular potentials and the spikingactivity of one hundred or more individual neurons. While the recordeddata may uncover principles of brain function, its interpretationcalls for multiscale computational models with corresponding spatialdimensions and signal predictions. Such models can then facilitatethe search of candidate mechanisms underlying experimentally observedspatiotemporal activity patterns in cortex. Multi-layer spiking neuronnetwork models of local cortical circuits covering about $1\,\mathrm{mm}^2$have been developed, integrating experimentally obtained neuron-typespecific connectivity data and reproducing features of observed in-vivospiking statistics. Using forward models, local field potentials (LFPs)can be computed from the simulated spiking activity. To account forthe spatial scale of common neural recordings, we here extend a localnetwork and LFP model to an area of $4\times4\,\mathrm{mm}^2$. Theupscaling preserves the densities of neurons and local synapses, andintroduces distance-dependent connection probabilities and conductiondelays. As detailed experimental data on distance-dependent connectivityis partially lacking, we address this uncertainty in model parametersby testing different parameter combinations within biologically plausiblebounds. Based on model predictions of spiking activity and LFPs,we find that the upscaling procedure preserves the overall spikingstatistics of the original model and reproduces asynchronous irregularspiking across populations and weak pairwise spike-train correlationsexperimentally observed in sensory cortex. In contrast with the weakspike-train correlations, the correlation of LFP signals is strongand distance-dependent, compatible with experimental observations.Enhanced spatial coherence in the low-gamma band around $50\,\mathrm{Hz}$may explain the recent experimental report of an apparent band-passfilter effect in the spatial reach of the LFP