There are now scores of aging clocks in the literature, most of which have come and gone and see little adoption. Most research is focused on gathering more data for handful of mainstream clocks, but these clocks are intended to capture a measure of aging generally across the whole body, keyed to outcomes such as mortality risk. Evidence suggests that different organs and tissues can age at different rates, however. Thus there remains a need for the development and validation of tissue-specific aging clocks. Here, researchers review the present state of development for clocks intended to measure aging in the brain specifically.
Brain aging represents a critical risk factor for neurodegenerative diseases and cognitive decline, yet the measurement of biological brain age remains challenging. Brain aging clocks, which quantify the discrepancy between predicted brain age and chronological age, have emerged as powerful tools for assessing brain health and predicting disease outcomes. Recent advances have transformed these clocks from simple global metrics to sophisticated, multi-modal approaches that capture regional heterogeneity, measure the pace of aging, and achieve cellular resolution.
This review examines the methodological evolution of brain aging clocks, including the development of regional brain age gradients, pace-of-aging measurements, and multi-modal integration strategies. We then explore the cellular and molecular mechanisms underlying accelerated brain aging, with particular emphasis on cellular senescence, cell-type-specific aging patterns, vascular dysfunction and blood-brain barrier breakdown, mitochondrial decline, proteostasis failure, synaptic loss, and the accumulation of senescent cells in neurodegenerative conditions. Epigenetic clocks and emerging plasma biomarkers (neurofilament light, GFAP, phosphorylated tau), particularly DNA methylation-based approaches, are discussed in the context of their relationship with neuroimaging markers and cognitive outcomes.
Clinical applications are reviewed, including the prediction of neurodegenerative disease, the impact of socioeconomic and geographic disparities on brain aging, and emerging senotherapeutic interventions. Finally, we address current challenges in biomarker standardization, the need for longitudinal validation, and future directions toward precision aging medicine. Together, these advances position brain aging clocks as essential tools for understanding neural aging mechanisms and developing targeted interventions to promote healthy brain aging.
Link: https://doi.org/10.1016/j.exger.2026.113260
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