Efficiency and Cost of Economical Brain Functional Networks

TLDR

Brain anatomical and functional networks exhibit sparse, complex, small‑world architectures that enable efficient parallel information processing at low connection cost. The study examined how age and dopamine antagonism affect the efficiency and cost of human brain functional networks using resting‑state fMRI. Functional connectivity among 90 cortical and subcortical regions was estimated via wavelet correlation in the 0.06–0.11 Hz band and thresholded to build undirected graphs, enabling analysis of network efficiency and cost. Older adults showed a disproportionate decline in network efficiency relative to cost, especially in frontal and temporal regions, while dopamine antagonism similarly impaired global and local efficiency without interacting with age, demonstrating that aging and dopamine blockade differentially disrupt the economical small‑world architecture of brain functional networks.

Abstract

Brain anatomical networks are sparse, complex, and have economical small-world properties. We investigated the efficiency and cost of human brain functional networks measured using functional magnetic resonance imaging (fMRI) in a factorial design: two groups of healthy old (N = 11; mean age = 66.5 years) and healthy young (N = 15; mean age = 24.7 years) volunteers were each scanned twice in a no-task or "resting" state following placebo or a single dose of a dopamine receptor antagonist (sulpiride 400 mg). Functional connectivity between 90 cortical and subcortical regions was estimated by wavelet correlation analysis, in the frequency interval 0.06–0.11 Hz, and thresholded to construct undirected graphs. These brain functional networks were small-world and economical in the sense of providing high global and local efficiency of parallel information processing for low connection cost. Efficiency was reduced disproportionately to cost in older people, and the detrimental effects of age on efficiency were localised to frontal and temporal cortical and subcortical regions. Dopamine antagonism also impaired global and local efficiency of the network, but this effect was differentially localised and did not interact with the effect of age. Brain functional networks have economical small-world properties—supporting efficient parallel information transfer at relatively low cost—which are differently impaired by normal aging and pharmacological blockade of dopamine transmission.