Lifespan Trajectories of the Brain’s Functional Complexity Characterized by Multiscale Sample Entropy

Resting state functional magnetic resonance imaging (rs-fMRI) is a widely used imaging modality that can capture spontaneous neural activity of the brain. The human brain is a complex system, and emerging evidence suggests that the complexity of neural activity may serve as an index of the brain’s capacity of information processing. In this study we used multiscale sample entropy (MSE) to analyze the complexity of rs-fMRI timeseries of 504 healthy subjects between the age of 6 to 85 years. We constructed the global and regional trajectories of brain’s functional complexity over the lifespan and analyzed its correlation with executive function. We observed a nonlinear trajectory of fMRI-complexity over the lifespan with a peak age occurring at 23 (95% CI 21.27, 26.38 years) years of age. Males reach the peak age of complexity at 26 years (95% CI 19.95, 33.14 years) whereas females at 23 (95% CI 20.16, 29.18 years). We found significant correlations between complexity and Number-Letter Switching of Trail Making Test in parietal and medial temporal lobes while Inhibition and Inhibition/Switching of Color Word Interference Test also revealed a significant negative correlation with rs-fMRI complexity in lateral and medial frontal cortex. These results help to understand behavior of fMRI-complexity with aging and reveals association with executive function of the brain. As a non-invasive biomarker, fMRI-complexity could provide novel approach to understand information processing capacity in the brain and deficits thereof in illness.