In a recent review published in a magazine Trends in neuroscience, The researchers examined current evidence highlighting that midlife is a critical period of brain aging, influencing cognitive trajectory and brain health. They recommend using models that account for nonlinear changes across broad age groups to distinguish between processes that are unique to midlife and those that occur uniformly throughout the lifespan.
Review: The “middle-aged” brain. Image credit: Monkey Business Images / Shutterstock
background
Midlife, from approximately 40 to 60-65 years of age, is a transition period into old age and predicts future health outcomes, including the risk of dementia. However, research has not progressed as much as in older age groups. Recent studies have revealed a complex and nonlinear biological aging process in the brain, especially during midlife. Additionally, gene expression and structural changes may predict cognitive decline accelerated by menopause in women. Understanding these processes may reveal new biomarkers and interventions for cognitive decline. In this review, researchers considered evidence from human and animal studies at multiple levels of analysis. They argued that midlife is a critical period in brain aging and may predict future cognitive health.
Cognitive changes in the midlife brain
The Baltimore Longitudinal Study of Aging suggests that cognitive decline in midlife follows a diverse, nonlinear pattern, particularly affecting memory, reasoning, and reaction time. In particular, episodic memory exhibits instability during the transition from midlife to old age, likely influenced by changes in social dynamics and career trajectories. Processing speed declines also intensify during this period, and the effects of practice diminish around age 60, which may indicate early cognitive impairment. Genetic factors such as the apolipoprotein E (APOE) ε4 allele can exacerbate memory decline in midlife. Neuroimaging studies have revealed nonlinear changes in hippocampal structure and function, suggesting transition points in the emergence of cognitive decline. These trends are also reflected in mouse studies, confirming the importance of midlife on cognitive trajectories.
Structural and functional changes
Middle age brings about both linear and nonlinear changes in the brain, and major changes in structures such as the hippocampus and white matter tracts occur around the age of 50 to 60. These changes affect cognitive function, particularly episodic memory, and are associated with overall cognitive status. Functional connectivity of brain networks also tends to be nonlinear, leading to decreased system separation and loss of functional specialization. These changes may explain individual differences in cognitive aging trajectories and highlight the complex biological dynamics at play during midlife.
Cellular and molecular changes
Research on biological aging is increasingly employing large-scale “omics” assays, revealing linear and nonlinear trajectories across a variety of molecular processes. Biological “clocks” constructed from features such as deoxyribonucleic acid (DNA) methylation predict chronological age, but some clocks exhibit nonlinear patterns. Molecular processes such as gene expression and noncoding ribonucleic acid (RNA) expression also exhibit nonlinear changes, particularly during midlife. These changes observed in mTOR (short for mammalian target of rapamycin), mitochondria, synapses, and inflammation-related pathways may underlie an individual's aging trajectory and highlight the complex dynamics of aging. ing. Furthermore, midlife brain changes may be influenced by systemic factors and other organs, suggesting a holistic approach to understanding the aging process.
Peripheral regulators of the midlife brain
During midlife, significant changes occur outside the brain, particularly in the systemic circulation, including inflammatory pathways. These changes influence the trajectory of cognitive aging and predict cognitive decline and the development of dementia later in life. Research has shown that markers of inflammation and immune responses in midlife predict cognitive decline and the development of dementia up to 20 years later. Additionally, changes in peripheral metabolite levels during midlife, likely influenced by gut microbiota composition, may also influence neuroinflammation and cognition. Importantly, the biological age of peripheral organs can influence brain aging, highlighting the interconnectedness of systemic and cognitive aging processes in midlife.
Menopause and middle-aged women
Menopause in women occurs at approximately age 50, accelerating epigenetic aging and affecting cognition, although this varies from person to person. The transition to menopause is associated with declines in cognitive function, particularly verbal episodic memory, along with changes in hippocampal volume, brain metabolism, and white matter integrity. Early menopause is correlated with accelerated brain aging and is likely influenced by hormonal changes. Hormonal fluctuations during the menstrual cycle also affect hippocampal volume. Studies in rats suggest that menopause affects hippocampal pathways and immune responses. Menopause appears to act as a breaking point in various brain aging processes, although the effects vary depending on the species. Overall, menopause is an important aspect of midlife and deserves further investigation in brain aging research.
conclusion
In conclusion, midlife is characterized by unique biological processes that influence future brain and cognitive health. The complex trajectories in brain connectivity, gene expression, and systemic factors highlight the importance of longitudinal studies to improve our understanding of these processes. Promising interventions such as exercise provide a means to reduce cognitive decline. The observed sex differences in the aging process highlight the need for a comprehensive research approach. Nonlinear analysis methods, in parallel with studies of broad age groups, may help distinguish midlife-specific changes from lifelong aging markers, providing insights into brain aging and cognitive health in aging populations. There is.
