The Increase of the Functional Entropy of the Human Brain with Age

TL;DR

This study shows that the functional entropy of the human brain, measured via fMRI, increases with age, reflecting changes in neural activity distribution, with notable differences between sexes across the lifespan.

Contribution

It introduces a novel entropy-based measure of brain activity that correlates with age and sex, supported by empirical fMRI data and computational modeling.

Findings

Brain entropy increases by ~0.1 bits over lifespan

Males have lower entropy at birth but surpass females after age 50

Entropy differences between sexes are statistically significant

Abstract

We use entropy to characterize intrinsic ageing properties of the human brain. Analysis of fMRI data from a large dataset of individuals, using resting state BOLD signals, demonstrated that a functional entropy associated with brain activity increases with age. During an average lifespan, the entropy, which was calculated from a population of individuals, increased by approximately 0.1 bits, due to correlations in BOLD activity becoming more widely distributed. We attribute this to the number of excitatory neurons and the excitatory conductance decreasing with age. Incorporating these properties into a computational model leads to quantitatively similar results to the fMRI data. Our dataset involved males and females and we found significant differences between them. The entropy of males at birth was lower than that of females. However, the entropies of the two sexes increase at different rates, and intersect at approximately 50 years; after this age, males have a larger entropy.