Homeostatic plasticity and external input shape neural network dynamics

TL;DR

This paper demonstrates how external input strength and homeostatic plasticity influence neural network dynamics, explaining differences between in vitro and in vivo activity patterns and suggesting ways to replicate in vivo-like activity in vitro.

Contribution

It introduces a model showing how input strength modulates neural dynamics via homeostatic plasticity, bridging the gap between in vitro and in vivo activity patterns.

Findings

Low input leads to bursting activity in vitro.

Higher input results in reverberating, in vivo-like dynamics.

Weak stimulation can transform in vitro activity to resemble in vivo states.

Abstract

In vitro and in vivo spiking activity clearly differ. Whereas networks in vitro develop strong bursts separated by periods of very little spiking activity, in vivo cortical networks show continuous activity. This is puzzling considering that both networks presumably share similar single-neuron dynamics and plasticity rules. We propose that the defining difference between in vitro and in vivo dynamics is the strength of external input. In vitro, networks are virtually isolated, whereas in vivo every brain area receives continuous input. We analyze a model of spiking neurons in which the input strength, mediated by spike rate homeostasis, determines the characteristics of the dynamical state. In more detail, our analytical and numerical results on various network topologies show consistently that under increasing input, homeostatic plasticity generates distinct dynamic states, from bursting, to close-to-critical, reverberating and irregular states. This implies that the dynamic state of a neural network is not fixed but can readily adapt to the input strengths. Indeed, our results match experimental spike recordings in vitro and in vivo: the in vitro bursting behavior is consistent with a state generated by very low network input (< 0.1%), whereas in vivo activity suggests that on the order of 1% recorded spikes are input-driven, resulting in reverberating dynamics. Importantly, this predicts that one can abolish the ubiquitous bursts of in vitro preparations, and instead impose dynamics comparable to in vivo activity by exposing the system to weak long-term stimulation, thereby opening new paths to establish an in vivo-like assay in vitro for basic as well as neurological studies.