A new neuroimaging study published in Environmental Health has found that our brain functions change when exposed to small amounts of diesel exhaust, a component of traffic-related air pollution. The findings indicate even small amounts of exposure to diesel exhaust result in negative changes in brain function. The research reveals the neural impact that traffic-related air pollution can have after a limited amount of exposure.
The damaging effects on health caused by traffic-related air pollution, including respiratory and cardiovascular issues, are widely understood. Additionally, the negative impact on the central nervous system is newly recognized as a significant health problem. While the exact reasons behind traffic-related air pollution’s harmful effects on the nervous system are unclear, initial research suggests that the particles may be transmitted directly through the olfactory bulb or indirectly through inflammation.
These findings have serious implications, given that traffic-related air pollution is responsible for approximately five million deaths globally every year, causing significant harm to both the world’s health and productivity.
“For many decades, scientists thought the brain may be protected from the harmful effects of air pollution,” said senior study author Chris Carlsten of the University of British Columbia. “This study, which is the first of its kind in the world, provides fresh evidence supporting a connection between air pollution and cognition.”
In order to provide further evidence of the effects of traffic-related air pollution on the body’s systems, the research team utilized a safe method of diluted diesel exhaust and investigated brain changes using magnetic resonance imaging (MRI). Participants were exposed to either diesel exhaust or filtered air after light exercise, allowing for observation of short-term effects on brain connectivity.
For the study, 25 healthy individuals, non-smokers aged 19 to 49, were recruited. Recruitment was done via community posters, online notices, and email notifications. The study was conducted in a controlled, double-blinded crossover design at the Air Pollution Exposure Lab, located at Vancouver General Hospital, which is equipped with a state-of-the-art exposure booth that can mimic what it is like to breathe a variety of air pollutants.
Each participant was exposed to both filtered air and diesel exhaust at different times for comparison. Filtered air or diesel exhaust was present for 120 minutes during each exposure, with a particulate matter concentration of 300 μg/m3 or less. During the first 15 minutes of each hour, participants spent 15 minutes cycling at a slow to moderate speed. The study employed a blinded method for both the participants and the individuals collecting the MRI data. So neither the participants nor the MRI technicians knew who had received diesel exhaust or filtered air. The MRI protocol used a whole-brain anatomical MRI and a functional MRI (fMRI) scan during a resting state, which lasted six minutes.
The findings demonstrated that exposure to diesel exhaust led to a decrease in functional connectivity in the default mode network as compared to filtered air. Prior studies have indicated that enhanced functional connectivity is linked with physical activity, and the results for the filtered air condition align with this outcome. However, the same results were not observed for the diesel exhaust condition, indicating that the brain-related advantages of light exercising are not achievable under this condition.
“We know that altered functional connectivity in the DMN has been associated with reduced cognitive performance and symptoms of depression, so it’s concerning to see traffic pollution interrupting these same networks,” said Jodie Gawryluk, a psychology professor at the University of Victoria and the study’s first author. “While more research is needed to fully understand the functional impacts of these changes, it’s possible that they may impair people’s thinking or ability to work.”
Notably, the changes in brain functioning were temporary and participants’ connectivity returned to normal after the exposure.
Nevertheless, these findings are significant for the welfare of the general public. These alterations in brain function are linked to a decline in working memory, decreased job performance, and decreased productivity at work. The study could help to expand the knowledge base of direct proof of the neurocognitive effects caused by short-term exposure to traffic-related air pollution and should be seen as a public health crisis. Moreover, the results emphasize the importance of individuals limiting their exposure to air pollution, including using public transport, reducing car usage, and wearing protective masks in polluted areas.
“Air pollution is now recognized as the largest environmental threat to human health and we are increasingly seeing the impacts across all major organ systems,” Carlsten said. “I expect we would see similar impacts on the brain from exposure to other air pollutants, like forest fire smoke. With the increasing incidence of neurocognitive disorders, it’s an important consideration for public health officials and policymakers.”
The study, “Brief diesel exhaust exposure acutely impairs functional brain connectivity in humans: a randomized controlled crossover study“, was authored by Jodie R. Gawryluk, Daniela J. Palombo, Jason Curran, Ashleigh Parker and Chris Carlsten.