Molecular mechanisms underpinning cognitive reserve and resilience

The concept of cognitive reserve (CR) and resilience originates from clinicopathological observations that amyloid-β deposition, tau pathology and neurodegeneration do not uniformly translate into clinical dementia, highlighting inter-individual differences in the brain’s capacity to tolerate pathology. Although CR and resilience lack a single accepted definition, they broadly describe the ability to maintain cognition in the presence of age-related or pathological brain changes. This review synthesises current molecular, cellular, and brain network mechanisms of cognitive reserve and critically examines key controversies. We also identify convergent biological pathways across multiple levels of organisation. Available evidence implicates that CR is not attributable to a single factor but reflects interactions among environmental exposures, genetic background, epigenetic regulation, cellular homeostasis, glial function, and large-scale brain network organisation. Lifestyle factors are associated with reduced pathology accumulation, preserved brain structure, and maintenance of cognition despite pathology, depending on the mechanism and outcome considered and are understood to exert their effects through epigenetic modulation of neuroplasticity, neurotrophic signalling, metabolic regulation, and inflammatory pathways. At the cellular level, preservation of dendritic spine integrity, synaptic signalling balance, mitochondrial energetic flexibility, and adult hippocampal neurogenesis supports efficient circuit function under pathological stress. Glial cells play central roles in mediating adaptive plasticity, neuroinflammatory control, and metabolic support, with dysregulation accelerating cognitive decline. Collectively, these findings frame CR as an emergent property of coordinated biological processes operating across molecular, cellular, and network scales, with important implications for developing reserve-enhancing therapeutic and lifestyle-based interventions that complement traditional pathology-focused approaches.