Memory in neural activity: long-range order without criticality

TL;DR

This paper demonstrates that long-range order in neural activity can arise from memory effects without requiring the brain to be at a critical point, challenging the criticality hypothesis.

Contribution

It introduces a cortical dynamics model showing that memory-induced long-range order can exist independently of criticality, with robustness across parameters.

Findings

Long-range order (LRO) can be induced by memory without criticality.

LRO manifests in power-law distributions of neural avalanches.

LRO is robust over a wide parameter range.

Abstract

The "criticality hypothesis", based on observed scale-free correlations in neural activity, posits that the brain operates at a critical point of transition between two phases. However, the validity of this hypothesis is still debated. Here, employing a commonly used model of cortical dynamics, we find that a phase of long-range order (LRO) in neural activity may be induced by memory (time non-locality) without invoking criticality. The cortical dynamics model contains fast and slow time scales that govern the neural and resource (memory) dynamics, respectively. When the resource dynamics are sufficiently slow, we observe an LRO phase, which manifests in avalanche size and duration probability distributions that are fit well by power laws. When the slow and fast time scales are no longer sufficiently distinct, LRO is destroyed. Since this LRO phase spans a wide range of parameters, it is robust against perturbations, unlike critical systems.