Uncovering functional brain signature via random matrix theory

TL;DR

This paper introduces a novel random matrix theory-based method to detect sign-dependent brain modules, revealing previously hidden inhibitory and excitatory structures in neuronal data, with implications for understanding brain plasticity.

Contribution

The paper presents a new data-driven approach that identifies sign-dependent brain modules without arbitrary thresholds, uncovering hidden inhibitory and excitatory interactions.

Findings

Uncovered two negatively correlated modules in neuronal gene expression data.

Modules' size and interaction strength depend on photoperiod.

Identified a potential region of circadian-related functional plasticity.

Abstract

The brain is organized in a modular way, serving multiple functionalities. This multiplicity requires that both positive (e.g. excitatory, phase-coherent) and negative (e.g. inhibitory, phase-opposing) interactions take place across brain modules. Unfortunately, most methods to detect modules from time series either neglect or convert to positive any measured negative correlation. This may leave a significant part of the sign-dependent functional structure undetected. Here we present a novel method, based on random matrix theory, for the identification of sign-dependent modules in the brain. Our method filters out the joint effects of local (unit-specific) noise and global (system-wide) dependencies that empirically obfuscate such structure. The method is guaranteed to identify an optimally contrasted functional `signature', i.e. a partition into modules that are positively correlated internally and negatively correlated across. The method is purely data-driven, does not use any arbitrary threshold or network projection, and outputs only statistically significant structure. In measurements of neuronal gene expression in the biological clock of mice, the method systematically uncovers two otherwise undetectable, negatively correlated modules whose relative size and mutual interaction strength are found to depend on photoperiod. The neurons alternating between the two modules define a candidate region of functional plasticity for circadian modulation.