A Voxel-Based Morphometry Study Reveals Local Brain Structural Alterations Associated with Ambient Fine Particles in Older Women

Abstract

Objective: Exposure to ambient fine particulate matter (PM_2.5: PM with aerodynamic diameters < 2.5 μm) has been linked with cognitive deficits in older adults. Using fine-grained voxel-wise analyses, we examined whether PM_2.5 exposure also affects brain structure. Methods: Brain MRI data were obtained from 1365 women (aged 71-89) in the Women's Health Initiative Memory Study and local brain volumes were estimated using RAVENS (regional analysis of volumes in normalized space). Based on geocoded residential locations and air monitoring data from the U.S. Environmental Protection Agency, we employed a spatiotemporal model to estimate long-term (3-year average) exposure to ambient PM_2.5 preceding MRI scans. Voxel-wise linear regression models were fit separately to gray matter (GM) and white matter (WM) maps to analyze associations between brain structure and PM_2.5 exposure, with adjustment for potential confounders. Results: Increased PM_2.5 exposure was associated with smaller volumes in both cortical GM and subcortical WM areas. For GM, associations were clustered in the bilateral superior, middle, and medial frontal gyri. For WM, the largest clusters were in the frontal lobe, with smaller clusters in the temporal, parietal, and occipital lobes. No statistically significant associations were observed between PM_2.5 exposure and hippocampal volumes. Conclusions: Long-term PM_2.5 exposures may accelerate loss of both GM and WM in older women. While our previous work linked smaller WM volumes to PM_2.5, this is the first neuroimaging study reporting associations between air pollution exposure and smaller volumes of cortical GM. Our data support the hypothesized synaptic neurotoxicity of airborne particles.

Keywords: MRI; PM2.5; VBM; air pollution; brain.

Figure 1

GM areas negatively associated to PM_2.5 exposure (q < 0.05 FDR corrected) in the VBM linear regression models are presented in color. Images are oriented according to the neurological convention.

Figure 2

WM areas with decreased volumes associated to increased PM_2.5 exposure (q < 0.05 FDR corrected) in the VBM linear regression models are presented in color. Images are oriented according to the neurological convention.

Figure 3

GM areas positively associated to PM_2.5 (q < 0.05 FDR corrected) according to VBM linear regression are presented in color. Images are oriented according to the neurological convention.