Outdoor Air Pollution and Brain Structure and Function From Across Childhood to Young Adulthood: A Methodological Review of Brain MRI Studies.

Abstract

Outdoor air pollution has been recognized as a novel environmental neurotoxin. Studies have begun to use brain Magnetic Resonance Imaging (MRI) to investigate how air pollution may adversely impact developing brains. A systematic review was conducted to evaluate and synthesize the reported evidence from MRI studies on how early-life exposure to outdoor air pollution affects neurodevelopment. Using PubMed and Web of Knowledge, we conducted a systematic search, followed by structural review of original articles with individual-level exposure data and that met other inclusion criteria. Six studies were identified, each sampled from 3 cohorts of children in Spain, The Netherlands, and the United States. All studies included a one-time assessment of brain MRI when children were 6-12 years old. Air pollutants from traffic and/or regional sources, including polycyclic aromatic hydrocarbons (PAHs), nitrogen dioxide, elemental carbon, particulate matter ( n = 1), during childhood ( n = 3), or both ( n = 2), using personal monitoring and urinary biomarkers ( n = 1), air sampling at schools ( n = 4), or a land-use regression (LUR) modeling based on residences ( n = 2). Associations between exposure and brain were noted, including: smaller white matter surface area ( n = 1) and microstructure ( n = 1); region-specific patterns of cortical thinness ( n = 1) and smaller volumes and/or less density within the caudate ( n = 3); altered resting-state functional connectivity ( n = 2) and brain activity to sensory stimuli ( n = 1). Preliminary findings suggest that outdoor air pollutants may impact MRI brain structure and function, but limitations highlight that the design of future air pollution-neuroimaging studies needs to incorporate a developmental neurosciences perspective, considering the exposure timing, age of study population, and the most appropriate neurodevelopmental milestones.