Abstract
Background
Animal and clinical studies have shown that exposure to enriched environments (providing enhanced sensory, social, cognitive and motor stimulation) can reduce aging-related neurodegenerative processes, especially in those genetically predisposed. ‘Walkable’, high-density, destination-rich urban areas represent real-life, large-scale enriched environments. They offer high levels of complexity, sensory stimulation, and opportunities for a variety of activities to entire populations. We examined cross-sectional and longitudinal associations of neighborhood characteristics with brain imaging volumetric and amyloid β burden measures, and the moderating effects of Apolipoprotein E (APOE) genotyping on these associations.
Methods
We geocoded residential addresses of participants (n=146) from the Melbourne stream of the AIBL study who had data on APOE genotyping and two Magnetic Resonance Imaging (MRI) brain volumetric (ventricle; grey matter; left and right hippocampus) and/or Positron Emission Tomography (PET) amyloid β burden (SURV) assessments 18 months apart. At baseline, 32 participants had mild cognitive impairment and 27 Alzheimer Disease. Objective measures of dwelling density, street intersection density, and mixes of land use (a measure of destination-richness) were computed for 0.5km- and 1km-radius areas around each participant's baseline residential address using Geographic Information Systems data. Mixed models examined confounder-adjusted associations of environmental attributes with levels of, and changes in, brain imaging outcomes, and the moderating effect of APOE genotyping (allele ε4 carriers vs. non-carriers).
Results
Dwelling density was negatively associated with ventricular volume and positively associated with right-hippocampal volume. Street intersection density and land use mix were negative associated with ventricular volume, and positively associated with right-hippocampal and grey matter volumes (Table 1). Decreases in grey matter volume were smaller in residents of areas with high land use mix. APOE ε4 carriers showed larger increases in ventricle volume and decreases in right-hippocampal volumes if living in neighborhoods with low street intersection density and land use mix, respectively. Significant increases in amyloid β burden were found only in APOE ε4 carriers from areas with below-average dwelling and intersection densities.
Conclusions
These preliminary findings indicate possible associations of urban environment characteristics with brain imaging measures, especially in those with a higher genetic risk. Further investigations are warranted.