A new study suggests that significant early childhood exposure to traffic-related air pollution (TRAP) is associated with structural changes in the brain at the age of 12.
The Cincinnati Children’s Hospital Medical Center study found that children with higher levels of TRAP exposure at birth had reductions at age 12 in gray matter volume and cortical thickness as compared to children with lower levels of exposure.
“The results of this study, though exploratory, suggest that where you live and the air you breathe can affect how your brain develops, says Travis Beckwith, PhD, a research fellow at Cincinnati Children’s and lead author of the study.
“While the percentage of loss is far less than what might be seen in a degenerative disease state, this loss may be enough to influence the development of various physical and mental processes.”
These brain images of 12-year-old children show regions of the brain in red, orange and yellow that are most affected by traffic related air pollution (TRAP). Those regions denote a reduction in cortical thickness linked to elemental carbon attributed to traffic. Of these images, the darker the color, the stronger the effect. Image is credited to Cincinnati Children’s Hospital Medical Center.
Gray matter includes regions of the brain involved in motor control as well as sensory perception, such as seeing and hearing. Cortical thickness reflects the outer gray matter depth. The study found that specific regions in the frontal and parietal lobes and the cerebellum were affected with decreases on the order of 3 to 4 percent.
“If early life TRAP exposure irreversibly harms brain development, structural consequences could persist regardless of the time point for a subsequent examination,” says Dr. Beckwith.
The researchers on the study, which is published online in PLOS One, used magnetic resonance imaging to obtain anatomical brain images from 147 12 year olds.
These children are a subset of the Cincinnati Childhood Allergy and Air Pollution Study (CCAAPS), which recruited volunteers prior to the age of six months to examine early childhood exposure to TRAP and health outcomes.
The volunteers in the CCAAPS had either high or low levels of TRAP exposure during their first year of life. The researchers estimated exposure using an air sampling network of 27 sites in the Cincinnati area, and 24/7 sampling was conducted simultaneously at four or five sites over different seasons. Participating children and their caregivers completed clinic visits at ages 1, 2, 3, 4, 7 and 12.
Previous studies of TRAP suggest that it contributes to neurodegenerative diseases and neurodevelopmental disorders. This work supports that TRAP changes brain structure early in life.
Senior author of the study is Kim Cecil, PhD, a scientist at the Cincinnati Children’s Imaging
Air pollution is the main environmental contributor to the global burden of disease (GBD 2013 Risk Factor Collaborators 2015). Over the last few years, interest in investigating the associations between air pollution and cognitive function has increased (Suades-González et al. 2015), both for children (Calderón-Garcidueñas et al. 2012; Chiu et al. 2013; Sunyer et al. 2015) and adults (Ailshire and Crimmins 2014; Gatto et al. 2014).
Environmental exposures in utero and during early life may permanently modify the body’s structure, physiology and metabolism (Gluckman and Hanson 2004). The structure and function of the brain as well as consequent lifelong developmental potential are established in the early years in a process that is extremely sensitive to external influence (Boucher et al. 2009; Luna et al. 2001).
Both positive (e.g., responsive caregiving, early learning) and negative (e.g., nutritional deficiencies, air pollution; Black et al. 2016) environmental factors may determine whether children would be able to reach their full neurodevelopmental potential at adulthood.
Working memory and attention are essential for normal cognitive development. Working memory is a cognitive system that is responsible for temporarily holding information for its manipulation. Its function is crucial for many competencies of cognition, such as learning, reasoning, problem solving, and language comprehension (Vuontela et al. 2003).
Most of the development of working memory occurs during childhood, though development of working memory continues until adulthood (Østby et al. 2011; Ullman et al. 2014). Attention involves different processes, such as selectively attending to a particular source of stimulation or voluntarily controlling actions (Anderson 2002).
Attention is a basic function required for superior cognitive abilities (e.g., executive functions or memory). The conflict network, also called executive control or executive attention, is one of the three functionally and anatomically differentiated networks that form attention (Posner and Petersen 1990).
The conflict network is involved in high-level forms of attention, such as the detection and resolution of conflicts among various options and responses, error detection, response inhibition, as well as in the regulation of thoughts and feelings (Fan et al. 2005).
Attention starts to develop early in infancy, and the conflict network presents a longer development period that extends into adolescence (Konrad et al. 2005; Rueda et al. 2015, 2005).
Studies that focused on exposures to air pollution, particularly particulate matter (PM) and , during the prenatal period and the first years of life found associations with reduced psychomotor development (Guxens et al. 2014; Kim et al. 2014), as well as with autism spectrum disorder (Kalkbrenner et al. 2015; Volk et al. 2013) and impairment in cognitive development (Calderón-Garcidueñas et al. 2015; Chiu et al. 2016).
However, for similar outcomes, other studies reported no associations (Guxens et al. 2014, 2016; Harris et al. 2015). Children from New York, New York City, showed structural brain alterations related to prenatal air pollution levels, whereas no significant correlation was observed for postnatal exposure at 5 years of age via measures of the cortical thickness or cerebral surface (Peterson et al. 2015).
The evidence is still scarce, given the lack of studies focusing on the exposure during the most vulnerable stages of brain development (i.e., prenatal and first one or two postnatal years). Therefore, further research is required to assess how the exposure to traffic-related air pollutants at particular time windows affect brain development.
This study was conducted within the framework of the Brain Development and Air Pollution Ultrafine Particles in School Children (BREATHE) project. In previous publications, we reported a deceleration over a year in the development of working memory and reduced attentiveness among children attending schools with a high concentration of traffic-related air pollution in comparison with children in less-polluted schools (Basagaña et al. 2016; Sunyer et al. 2015). Reduced attentiveness was also associated with short-term exposures to such pollutants (Sunyer et al. 2017).
These previous studies evaluated the exposure only during the study period, when the children were 7–10 y old, and omitted the exposure in prenatal and early postnatal periods. Moreover, the conflict network was not assessed before within BREATHE, although the conflict network is of great importance in academic achievement (Checa and Rueda 2011; Posner et al. 2006).
Therefore, we aimed to assess whether the exposure to PM with an aerodynamic diameter () at different time windows (prenatal and first years of life) was associated with impaired cognitive development (working memory, attentiveness, and conflict network) in 7- to 10-y-old children and to identify the most vulnerable periods of exposure for the development of these cognitive abilities.
