Regional- and cell type-specific changes of the human brain during aging

As individuals age, cognitive decline becomes more prominent, concomitant with an elevated susceptibility to neurodegenerative diseases and dementia. Additionally, symptoms of chronic neuropsychiatric diseases tend to worsen with age. It is crucial to highlight that the aging process does not affect individuals uniformly, and its effects can vary, even within the same person. This review aims to summary the impact of healthy aging on the human brain, focusing on the variations from different brain regions and cell types. Depending on specific brain regions, the brain exhibits thinning, volume reduction, regional shrinkage, disrupted tissue integrity, decreased cell complexity, or iron accumulation during aging. Moreover, the brain cells exhibit morphology and function changes during aging. Neurons undergo changes characterized by reduced dendrites, dendritic spines, and axons with less compact myelin sheaths, leading to a significant loss of synapses. Comparatively, glia often transform into a reactive phenotype.