According to the findings of a study conducted by the Barcelona Institute for Global Health (ISGlobal), more exposure to air pollution is related with stronger functional brain connectivity across numerous brain areas in preadolescents, although exposure to traffic noise is not.
The findings also identify the first years of life as the most sensitive period of exposure to air pollution. Traffic-related air pollution and noise are affecting an increasing number of people worldwide. “We already know that children are particularly vulnerable to the effect of these exposures, because of their immature metabolism and developing brain,” says ISGlobal researcher and senior author Monica Guxens. In fact, several studies by Guxens and others have found an association between exposure to traffic-related air pollution during early childhood and alterations in the brain structure.
In this study, the research team used magnetic resonance imaging (MRI) to explore whether higher exposure to air pollution or noise could also be associated with possible alterations in brain connectivity (i.e. the way in which different brain regions interact). “The use of MRI has opened up new possibilities in epidemiological research for investigating the structure and the functioning of the brain,” says Guxens.
The researchers analysed data from the Generation R Study, which included 2,197 infants born between April 2002 and January 2006 in Rotterdam, the Netherlands. They used land use models to estimate levels of nitrogen oxides (NOx and NO2) and particulate matter (PM) in the participants’ residences at various times: during pregnancy, from birth to 3 years, from 3 to 6 years, and from 6 years to the age of the MRI scan. Traffic noise levels were assessed using available noise maps. Participants between the ages of 9 and 12 were asked to undertake a resting MRI scan (i.e. with no external stimuli).
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The findings show that higher exposures to NO2 and PM2.5 absorbance (an indicator of black carbon particles) from birth to 3 years, and to NOx from 3 to 6 years of age were associated with higher functional brain connectivity among several brain regions in the preadolescents. The associations were identified in brain areas predominantly involved in two networks that have strongly opposing functions: the task negative (or “default-mode”) network tends to be activated in resting conditions and the task positive network tends to be activated during tasks that demand attention. “We still have to understand the consequences of this increased activity of both networks in resting conditions, but for now we can say that the brain connectivity in children exposed to higher levels of air pollution is different from what we would expect,” says Laura Perez-Crespo, first author of the study.
0-3 year olds most vulnerable to air pollution
The period from birth to three years had the most vulnerability to air pollution, and black carbon was the pollutant most related with alterations in brain connections. As the authors point out, diesel cars are the primary source of black carbon and nitrogen oxide pollutants in European cities. Despite the fact that multiple studies have shown that noise impacts cognitive development in children, noise exposure at home was not connected with variations in brain connection.
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