Exposure to air pollution in childhood is associated with reduced brain connectivity

The research showed reduced functional connectivity within and between certain cortical and subcortical brain networks. These networks are systems of interconnected brain structures that work together to perform different cognitive functions, such as thinking, perceiving and controlling movement. These findings are consistent with previous studies suggesting that air pollution may be associated with changes in the functional connectivity of brain networks, particularly in children. However, it is not yet fully understood how air pollution affects the development and maturation of these brain networks.

The study analysed data from 3,626 children from the Generation R cohort in Rotterdam, the Netherlands. Exposure to air pollution at the participants' residence, including particulate matter (PM_2.5 and PM₁₀), nitrogen dioxide (NO₂) and nitrogen oxides (NO_X), was estimated using statistical models that combine actual measurements with environmental characteristics. Brain connectivity was then assessed both between and within networks, including 13 cortical networks and three subcortical regions: the amygdala -- responsible for processing emotions and triggering survival responses -, the hippocampus -- key for memory formation and spatial orientation -, and the caudate nucleus -- involved in movement regulation, memory and decision-making.

The children were evaluated using resting state neuroimaging, meaning their brains were scanned while not performing any active task, at two time points: around the age of 10 and again at an average age of 14. Exposure to air pollution was analysed over two periods: from birth to three years of age and in the year before the neuroimaging assessment.

"This is one of the first studies to explore how air pollution affects brain connections at rest, using brain scans taken multiple times in a large group of children from birth," says Michelle Kusters, ISGlobal researcher and first author of the study.

Persistent Associations During Adolescence

The results show that greater exposure to air pollution from birth to three years old is associated with lower connectivity between the amygdala and the cortical networks involved in attention, somatomotor function -- which coordinates body movements -- and auditory function. Additionally, higher exposure to PM₁₀ particles in the year before the neuroimaging assessment was associated with lower functional connectivity between the salience and medial-parietal networks, which are responsible for detecting stimuli in the environment and for introspection and self-perception.

"These associations persist throughout adolescence, which may indicate persistent disruptions in the normal development of brain networks due to pollution exposure. This could affect emotional processing and cognitive functions," explains Mònica Guxens, ICREA researcher at ISGlobal and lead author of the study. "However, more research is needed to confirm these findings and to understand their exact impact on brain development," she adds.

Changes in Brain Volume

Another recent study by the same team examined the relationship between exposure to air pollution during pregnancy and childhood, and changes in brain volume through adolescence. The study was based on data from 4,243 children from the same Generation R cohort, who underwent repeated assessments of white matter, cortical grey matter, the cerebellum, and seven subcortical volumes.

The results revealed that exposure to air pollution during pregnancy, particularly to fine particles (PM2.5) and copper, was associated with a smaller volume of the hippocampus, a crucial brain structure for memory function, at age 8. However, as the children grew, "compensatory growth" in the hippocampus was observed, suggesting that brain plasticity, particularly in this area, may counteract some of the initial negative effects of pollution exposure. Despite the early effects on hippocampal volume, no significant associations were found between air pollution and other brain volumes, such as white matter, cortical grey matter, or the cerebellum.

Importance of Policy Changes

According to the research team, these findings together underscore the potential long-term impact of early-life air pollution exposure on brain connectivity and development. "While some brain regions may exhibit compensatory growth, the persistent disruptions observed in functional networks highlight the need for further research into the mechanisms behind these changes. Given the widespread exposure to air pollution, these results reinforce the importance of policies aimed at reducing pollution levels, particularly in urban environments, to safeguard children's brain development," says Michelle Kusters.