Intrinsically-generated fluctuating activity in excitatory-inhibitory networks

TL;DR

This paper investigates how intrinsic fluctuations in excitatory-inhibitory neural networks influence activity, revealing that excitation qualitatively changes fluctuation dynamics and can induce different stable regimes, with implications for spiking neuron models.

Contribution

The study introduces a tractable excitatory-inhibitory network model showing how excitation qualitatively alters fluctuation regimes compared to purely inhibitory networks.

Findings

Excitation increases mean firing rates during fluctuations.

Two distinct fluctuation regimes are identified based on coupling strength.

Signatures of these regimes are observed in integrate-and-fire neuron networks.

Abstract

Recurrent networks of non-linear units display a variety of dynamical regimes depending on the structure of their synaptic connectivity. A particularly remarkable phenomenon is the appearance of strongly fluctuating, chaotic activity in networks of deterministic, but randomly connected rate units. How this type of intrinsi- cally generated fluctuations appears in more realistic networks of spiking neurons has been a long standing question. To ease the comparison between rate and spiking networks, recent works investigated the dynami- cal regimes of randomly-connected rate networks with segregated excitatory and inhibitory populations, and firing rates constrained to be positive. These works derived general dynamical mean field (DMF) equations describing the fluctuating dynamics, but solved these equations only in the case of purely inhibitory networks. Using a simplified excitatory-inhibitory architecture in which DMF equations are more easily tractable, here we show that the presence of excitation qualitatively modifies the fluctuating activity compared to purely inhibitory networks. In presence of excitation, intrinsically generated fluctuations induce a strong increase in mean firing rates, a phenomenon that is much weaker in purely inhibitory networks. Excitation moreover induces two different fluctuating regimes: for moderate overall coupling, recurrent inhibition is sufficient to stabilize fluctuations, for strong coupling, firing rates are stabilized solely by the upper bound imposed on activity, even if inhibition is stronger than excitation. These results extend to more general network architectures, and to rate networks receiving noisy inputs mimicking spiking activity. Finally, we show that signatures of the second dynamical regime appear in networks of integrate-and-fire neurons.