# Equivalence between synaptic current dynamics and heterogeneous propagation delays in spiking neuron networks

## TL;DR

This paper demonstrates a formal equivalence between synaptic current dynamics and propagation delays in spiking neuron networks, providing a unified framework to understand their impact on collective neural behavior.

## Contribution

It introduces a mean-field reduction that shows local synaptic filtering and transmission delays are formally equivalent in affecting network dynamics.

## Key findings

- Derived an effective Markovian model for population dynamics.
- Proved equivalence between synaptic filtering and delays across various conditions.
- Applicable to finite neuron networks and different firing regimes.

## Abstract

Message passing between components of a distributed physical system is non-instantaneous and contributes to determine the time scales of the emerging collective dynamics like an effective inertia. In biological neuron networks this inertia is due in part to local synaptic filtering of exchanged spikes, and in part to the distribution of the axonal transmission delays. How differently these two kinds of inertia affect the network dynamics is an open issue not yet addressed due to the difficulties in dealing with the non-Markovian nature of synaptic transmission. Here, we develop a mean-field dimensional reduction yielding to an effective Markovian dynamics of the population density of the neuronal membrane potential, valid under the hypothesis of small fluctuations of the synaptic current. The resulting theory allows us to prove the formal equivalence between local and distributed inertia, holding for any synaptic time scale, integrate-and-fire neuron model, spike emission regimes and for different network states even when the neuron number is finite.