Abstract

Mean-field models of the brain approximate spiking dynamics by assuming that each neuron responds to its neighbors via a naive spatial average that neglects local fluctuations and correlations in firing activity. In this paper we address this issue by introducing a rigorous formalism to enable spatial coarse-graining of spiking dynamics, scaling from the microscopic level of a single type 1 (integrator) neuron to a macroscopic assembly of spiking neurons that are interconnected by chemical synapses and nearest-neighbor gap junctions. Spiking behavior at the single-neuron scale ℓ≈10μm is described by Wilson's two-variable conductance-based equations [H. R. Wilson, J. Theor. Biol. 200, 375 (1999)], driven by fields of incoming neural activity from neighboring neurons. We map these equations to a coarser spatial resolution of grid length Bℓ, with B≫1 being the blocking ratio linking micro and macro scales. Our method systematically eliminates high-frequency (short-wavelength) spatial modes q(->) in favor of low-frequency spatial modes Q(->) using an adiabatic elimination procedure that has been shown to be equivalent to the path-integral coarse graining applied to renormalization group theory of critical phenomena. This bottom-up neural regridding allows us to track the percolation of synaptic and ion-channel noise from the single neuron up to the scale of macroscopic population-average variables. Anticipated applications of neural regridding include extraction of the current-to-firing-rate transfer function, investigation of fluctuation criticality near phase-transition tipping points, determination of spatial scaling laws for avalanche events, and prediction of the spatial extent of self-organized macrocolumnar structures. As a first-order exemplar of the method, we recover nonlinear corrections for a coarse-grained Wilson spiking neuron embedded in a network of identical diffusively coupled neurons whose chemical synapses have been disabled. Intriguingly, we find that reblocking transforms the original type 1 Wilson integrator into a type 2 resonator whose spike-rate transfer function exhibits abrupt spiking onset with near-vertical takeoff and chaotic dynamics just above threshold.

Highlights

  • Effective modeling of brain dynamics requires assimilation of activity over multiple scales

  • Synaptic and ion-channel noise can have a significant impact on neuron dynamics, and this has stimulated investigation of stochastic adaptations of these model equations using both additive noise and Markov-chain approaches [6,7,8,9,10,11]

  • We present a scheme to scale systematically the dynamics of a single spiking neuron to the bulk environment of an assembly of such neurons

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Summary

Introduction

Effective modeling of brain dynamics requires assimilation of activity over multiple scales. The process of spike generation is governed by voltagedependent changes in Na+ and K+ ion-channel conductances that shape the growth, deceleration, and subsequent recovery of the membrane voltage. Synaptic and ion-channel noise can have a significant impact on neuron dynamics, and this has stimulated investigation of stochastic adaptations of these model equations using both additive noise and Markov-chain approaches [6,7,8,9,10,11].

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