Bridging social isolation, loneliness, and brain aging: A narrative review of mechanisms and translational interventions.

Abstract

Social isolation and loneliness (SIL) are increasingly recognized as potent determinants of cognitive decline in aging and Alzheimer's disease-related dementias (ADRD). Yet, despite their prevalence, the neurobiological pathways through which SIL accelerates brain aging remain incompletely understood, and effective interventions are scarce. This narrative review synthesizes human and animal research to present a translational framework linking SIL to brain aging across cognitive-affective, socio-behavioral, physiological, and neural domains. Converging evidence indicates that SIL and cognitive impairment constitute a self-reinforcing loop: isolation amplifies age-related deficits in cognitive control, emotional regulation, and stress resilience, while these impairments heighten social threat sensitivity and blunt social reward, perpetuating isolation. Cross-species findings implicate interconnected neural networks, including the prefrontal and insular cortices, hippocampus, and associated reward and stress-regulatory systems, as critical hubs mediating this loop. Large-scale human neuroimaging consortia reveal convergent neural signatures of SIL within these networks, supported by mechanistic findings from animal models that identify shared molecular cascades involving neuroinflammation, glucocorticoid imbalance, myelin disruption, and dysregulated oxytocin and dopaminergic signaling. Importantly, evidence from animal resocialization paradigms and human multimodal interventions demonstrates that SIL-related neural and behavioral alterations are partially reversible, highlighting enduring plasticity in the aging brain. Together, these findings define SIL and cognitive decline as a dynamic, mutually reinforcing cycle that accelerates brain aging through convergent molecular and circuit mechanisms. Targeting these pathways, by enhancing cognitive control, modulating reward systems, reducing stress reactivity, and strengthening social connectedness, offers a promising translational route to preserve resilience and cognitive vitality across the lifespan.