Age-related and individual differences in brain complexity of resting-state fMRI signals in healthy elderly

Entropy-based complexity of neural signal characterizes intrinsic function of the human brain.

In this resting-state functional magnetic resonance imaging (rs-fMRI) study, we employed multiscale entropy (MSE) analysis to examine age-related and individual differences in the complexity of intrinsic network, brain function and cognition. Specifically, the MSE of blood oxygen level-dependent (BOLD) signals of rs-fMRI data from 90 prior-selected regions-of-interest (ROIs) were estimated in 28 young and 65 healthy older adults. The results showed that healthy older adults exhibited significant reduction in MSE of BOLD signals in fronto-parietal network but increase in MSE of BOLD signals in thalamus, indicating a higher degree of complexity in the aging brain with reduced information transfer between cortical and subcortical regions. Moreover, the MSE of BOLD signals in high-functioning older adults appear to be similar with the MSE of BOLD signals in the default mode and salience networks found in young adults, suggesting a preserved intrinsic network for individuals who age better than others. Our findings provide supportive evidence that complexity of brain activity is declined across the lifespan and associated with the individual variations in neurocognitive performance in the healthy older adults.