Humanised Environmental Enrichment: Spatial Effects of Cities and Buildings on Adult Hippocampal Neurogenesis in Humans.

Adult hippocampal neurogenesis persists throughout the human lifespan, yet declines in Alzheimer's disease and major depression, associated in part with reduced brain-derived neurotrophic factor (BDNF) levels. For rodents, environmental enrichment, dichotomised primarily as physical activity and spatial complexity, robustly promotes adult hippocampal neurogenesis, but no framework has translated these findings to human environments. This review is the first to synthesise evidence across the full translational pathway, arguing that spatial complexity and physically active navigation in neighbourhoods and buildings constitute a humanised form of environmental enrichment. It proposes that standard indoor environments may represent a functionally impoverished condition for the human hippocampus, paralleling standard laboratory caging. An applied model is presented, mapping built environment features onto the neurobiological mechanisms regulating adult hippocampal neurogenesis, with BDNF as the central translatable biomarker linking environmental exposures to neurogenic outcomes. A methodological roadmap for future empirical validation is also outlined. This framework repositions the built environment as a modifiable determinant of adult hippocampal neurogenesis in humans, with implications for mitigating the risk of depression, cognitive impairment, and Alzheimer's disease.