1 Department of Biomedical Engineering, University of California, Davis, Davis, California, USA.
2 Department of Psychology, Concordia University, Montreal, Quebec, Canada.
3 School of Health, Concordia University, Montreal, Quebec, Canada.
4 Department of Neurology, Max Planck Institute of Human Cognitive and Brain Sciences, Leipzig, Germany.
5 Department of Neurology, University of California, Davis, Davis, California, USA.
6 Department of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, California, USA.

There is a growing interest to study cerebellar contributions to aging outside of traditional sensory processing and motor tasks. While cerebellar aging analyses typically utilize functional connectivity (FC) to study functional differences with age, this study aimed to identify a marker of healthy aging based on resting state blood oxygenation level dependent (BOLD) signal dynamics in the cerebellum. To do this, we investigated both Amplitude of Low Frequency Fluctuations (ALFF) and fractional ALFF (fALFF), semi-quantitative metrics of the strength of the BOLD signal. We found that fALFF is a highly repeatable metric of cerebellar function that demonstrates a significant increase in BOLD signal fluctuations at 0.008-0.1 Hz in cerebellar regions Crus I and II with aging. Furthermore, cerebellar fALFF of these regions was associated with FC to cortical regions across separate scanning sessions. These results highlight age-related differences in spontaneous cerebellar dynamics, particularly in regions tied to the frontal cortex, motivating the use of fALFF as a potential biomarker of healthy aging and motivate the need to incorporate the cerebellum in existing models of brain network changes with age.