Stochastic Amplification of Fluctuations in Cortical Up-states

TL;DR

This paper investigates the emergence of a 20 Hz oscillation within cortical Up states, demonstrating through models and theory that stochastic amplification of fluctuations explains this collective phenomenon, which is absent in Down states.

Contribution

It introduces a novel explanation for intra-Up state oscillations based on stochastic amplification, supported by computational models and theoretical analysis.

Findings

A 20 Hz peak appears in Up states but not in Down states.

Oscillations are collective phenomena, not synchronized at the single-neuron level.

Stochastic amplification explains the emergence of intra-Up oscillations.

Abstract

Cortical neurons are bistable; as a consequence their local field potentials can fluctuate between quiescent and active states, generating slow 0.5-2 Hz oscillations which are widely known as transitions between Up and Down States. Despite a large number of studies on Up-Down transitions, deciphering its nature, mechanisms and function are still today challenging tasks. In this paper we focus on recent experimental evidence, showing that a class of spontaneous oscillations can emerge within the Up states. In particular, a non-trivial peak around 20 Hz appears in their associated power-spectra, what produces an enhancement of the activity power for higher frequencies (in the 30-90 Hz band). Moreover, this rhythm within Ups seems to be an emergent or collective phenomenon given that individual neurons do not lock to it as they remain mostly unsynchronized. Remarkably, similar oscillations (and the concomitant peak in the spectrum) do not appear in the Down states. Here we shed light on these findings by using different computational models for the dynamics of cortical networks in presence of different levels of physiological complexity. Our conclusion, supported by both theory and simulations, is that the collective phenomenon of "stochastic amplification of fluctuations" -previously described in other contexts such as Ecology and Epidemiology-- explains in an elegant and parsimonious manner, beyond model-dependent details, this extra-rhythm emerging only in the Up states but not in the Downs.