Green Environments for Sustainable Brains: Parameters Shaping Adaptive Neuroplasticity and Lifespan Neurosustainability—A Systematic Review and Future Directions

The review investigates whether and how exposure to green environments is associated with adaptive neuroplasticity across the human lifespan. Situated in the context of growing urbanization and public health needs, it frames greening the built environment as environmental enrichment capable of promoting positive brain changes. It introduces the concept of neurosustainability—sustaining adaptive neuroplasticity through environmental design—and positions the synthesis to inform urban planning and architecture. The study aims to identify types and parameters of green environments (e.g., forests, urban green spaces, residential greenness) and their associations with total or regional brain changes to provide a neurobiological perspective for health-focused sustainable cities.

Background literature highlights WHO initiatives for health-centric urban sustainability and increasing interest in how green cities and architecture can support public health and well-being. Prior reviews link greenspace to health benefits, but evidence specifically on structural and functional brain changes is emerging. The paper situates neurosustainability as a novel framework focusing on maintaining adaptive neuroplasticity through environmental enrichment, noting a gap in understanding how specific green environment parameters relate to region-specific brain changes.

Protocol registered at INPLASY (INPLASY2024110103). Systematic searches in Scopus, PubMed, and Web of Science for records up to November 2024, following PRISMA guidelines. Search strategy combined terms for natural/green environments (e.g., "urban green", "greenness", NDVI, EVI, tree cover density, biophilia) AND neuroplasticity/brain metrics (e.g., hippocampal volume, cortical thickness, gray/white matter, amygdala, brain volume, atrophy). Inclusion: English journal articles (trials, cross-sectional, longitudinal) with human participants across ages/genders/health conditions; exposure to green environments; outcomes in structural or functional brain measures. Exclusion: grey literature and non-English. PICO: Population—humans; Intervention—exposure to natural/green environments; Comparison—none required (built environment comparisons accepted); Outcome—structural/functional brain plasticity. Screening and selection performed by the sole author; duplicates removed; forward/backward citation chasing applied. Risk of bias: PEDro scale for RCTs; ROBINS-I for non-randomised studies. Meta-analysis not feasible due to heterogeneity and limited study count; no sensitivity or missing-results bias assessments; certainty not assessed. Narrative synthesis organized by green environment type, parameters, brain changes, demographics, and effect measures. PRISMA: 925 records identified; after exclusions and duplicates, 528 screened; 23 studies included.

- Twenty-three studies (2017–2024) across Europe, USA, UK, East Asia show positive, region-specific associations between green environments and brain changes from prenatal to late adulthood. - Forests: More consistently associated with amygdala-related benefits and hippocampal subiculum changes than urban greens or blue spaces. Acute nature walks reduced amygdala activity (significant; stronger in women). One-hour forest walk increased subiculum volume (p=0.010; t(29)=-2.758). - Residential greenness: Consistently effective within 300–500 m buffers, especially when sky visibility (SVF) is present. Tree cover density (TCD) without sky views showed adverse associations in children; open green space with high SVF predicted positive prefrontal/temporal/parietal effects. - Parameterization: NDVI and TCD demonstrate stronger associations at ≤300–500 m buffers; effects often diminish at 1000 m+. SVF emerged as a key predictor of medial prefrontal GM. - Specific brain regions: Amygdala (structural integrity and reduced activity); hippocampal subiculum; orbitofrontal and prefrontal cortices; ACC; insula; precuneus; parietal, temporal, occipital cortices; cerebellum; ventricle grade; whole-brain FA. - Examples of quantitative associations: • Shang et al. (n≈34,454): Each 10% increase in greenness at 1000 m associated with total brain volume, GM, WM (e.g., GM β≈0.013, p=0.0004); broad natural environment increases showed mixed significance. • Pu et al. (n≈34,588): Green space (≈45% at 1000 m) explained variance in brain volume (39.4%), WM (49%), GM (21.7%); pollution/noise had antagonistic effects; precuneus association p=0.002. • Webb et al. (n=288 trauma survivors): NDVI within 100 m associated with greater amygdala reward reactivity (β=0.18; p=0.02) and resilient PTSD trajectory. • Kühn et al. (children): OGS with SVF positively associated with bilateral prefrontal/temporal cortex; higher TCD negatively associated with frontal/temporal regions at 200–500 m; SVF strongest predictor in medial PFC. • Min et al. (n=2542): Residential greenness (EVI, 750 m) associated with increased cortical thickness globally and in parietal/occipital regions in urban populations. • Dadvand et al. (children): NDVI within 100 m associated with increased GM in prefrontal/premotor and WM in cerebellum/prefrontal regions. • Binter et al. (two cohorts): Greater distance to major green space during pregnancy associated with higher whole-brain FA at age ~9 (β=0.001 per 7 m increase; mediated by traffic noise). - Urban green spaces show mixed results; effectiveness influenced by definitions, proximity, and antagonists (noise/pollution). Forests typically away from noise may partly explain stronger amygdala and hippocampal benefits. - No studies assessed green architecture or biophilic interiors, despite likely greater exposure duration and proximity.

Findings support the hypothesis that green environments act as environmental enrichment promoting adaptive neuroplasticity across life stages, substantiating neurosustainability. Benefits are region-specific: forests preferentially modulate stress/emotion circuits (amygdala, hippocampal subiculum), while residential greenness—especially within 300–500 m and with sufficient sky visibility—supports cortical (prefrontal, parietal, occipital, temporal) and cerebellar structures. Antagonistic urban factors (noise, pollution) can diminish or reverse benefits, explaining weaker or mixed effects in urban green spaces compared to forests. The review bridges environmental neuroscience with urban planning and architecture, suggesting multi-scalar strategies: protect and provide access to forests; optimize neighbourhood-level tree cover with SVF; and integrate biophilic elements in buildings. It underscores public health implications for reducing stress-related disorders and cognitive decline and highlights equity and contextual considerations. The synthesis advances parameterized guidance (buffer sizes, NDVI/TCD ranges, SVF) for designing greener environments that sustain brain plasticity.

This review provides the first comprehensive synthesis linking exposure to green environments with adaptive neuroplasticity from prenatal through late adulthood, framing greening strategies as pathways to neurosustainability. Forests yield robust amygdala and hippocampal subregion benefits; residential greenness is consistently effective within 300–500 m buffers when sky visibility is assured; urban green spaces show mixed effects influenced by urban stressors. A critical gap is the absence of studies on green architecture and biophilic interiors despite high exposure potential. Urban and architectural design should integrate empirically supported parameters (e.g., buffer distances, vegetation indices, tree cover balanced with sky views) to enhance brain health. Future research should replicate studies to enable meta-analyses; expand to diverse geographies and climates; quantify sky-tree-building trade-offs; test skylights/indoor biophilia; evaluate architectural materials mitigating noise/pollution; examine private gardens; explore clinical populations and molecular mechanisms; and assess equity implications to ensure inclusive access to neuroprotective environments.

- Heterogeneity across studies in definitions of green environments (forest, urban green, residential greenness), quantification methods (NDVI, EVI, TCD, NLCD, CLC), buffer sizes, exposure durations, and targeted brain regions impeded meta-analysis. - Limited number of studies overall; evidence skewed toward adults and older adults, with fewer studies in children and only one prenatal exposure study. - Mixed or null findings for some regions (e.g., hippocampus total volume; some urban green measures) and variability by sex (amygdala reductions stronger in women). - Antagonistic urban factors (noise, pollution) confound and may counteract benefits; limited control of these in some designs. - No studies on green architecture or biophilic interiors, despite likely high exposure time, limiting translation to building-scale interventions. - Narrative synthesis only; certainty and sensitivity analyses not conducted; no assessment of bias due to missing results. Risk of bias generally satisfactory, with variability across ROBINS-I domains and one study rated ‘fair’ on PEDro.