Resting-state functional magnetic resonance imaging signal variations in aging: The role of neural activity.

Resting-state functional magnetic resonance imaging (rs-fMRI) has been extensively used to study brain aging, but the age effect on the frequency content of the rs-fMRI signal has scarcely been examined. Moreover, the neuronal implications of such age effects and age-sex interaction remain unclear. In this study, we examined the effects of age and sex on the rs-fMRI signal frequency using the Leipzig mind-brain-body data set. Over a frequency band of up to 0.3 Hz, we found that the rs-fMRI fluctuation frequency is higher in the older adults, although the fluctuation amplitude is lower. The rs-fMRI signal frequency is also higher in men than in women. Both age and sex effects on fMRI frequency vary with the frequency band examined but are not found in the frequency of physiological-noise components. This higher rs-fMRI frequency in older adults is not mediated by the electroencephalograph (EEG)-frequency increase but a likely link between fMRI signal frequency and EEG entropy, which vary with age and sex. Additionally, in different rs-fMRI frequency bands, the fMRI-EEG amplitude ratio is higher in young adults. This is the first study to investigate the neuronal contribution to age and sex effects in the frequency dimension of the rs-fMRI signal and may lead to the development of new, frequency-based rs-fMRI metrics. Our study demonstrates that Fourier analysis of the fMRI signal can reveal novel information about aging. Furthermore, fMRI and EEG signals reflect different aspects of age- and sex-related brain differences, but the signal frequency and complexity, instead of amplitude, may hold their link.