Diesel fumes can disrupt the functioning of an important neural network in the brain. (Image credit: Peter MacDiarmid/Staff via Getty Images)
A new study suggests that even short-term exposure to diesel fumes can alter brain function by disrupting signaling in key neural networks.
Previous studies have shown that people exposed to polluted air may have a higher risk of developing mental illness and neurodegenerative disorders. Now, a new study published January 14 in the journal Environmental Health shows that exposure to diluted diesel exhaust led to reduced “functional connectivity” in an important brain network compared to exposure to filtered air.
Functional connectivity measures how effectively different areas of the brain communicate with each other; after exercising in fresh air, participants experienced a temporary increase in connectivity in a particular neural network, whereas after exposure to diesel pollution, connectivity remained unchanged. Although the study did not analyze cognitive outcomes, this network is associated with internal thinking and introspection, and disruptions in its functioning have been associated with various mental disorders and concentration problems.
The study's authors say it's the first study to examine the brain's response to air pollution in such a controlled format. “These researchers have greatly expanded our knowledge of the effects of pollution,” said Hao Yan Tang, lead researcher at the Lieber Institute for Brain Development in Baltimore, who was not involved in the study.
The scientists used functional magnetic resonance imaging (fMRI) to image brain activity in 25 adults; fMRI works by detecting increased blood flow to active neurons, which provides indirect evidence of brain activity. The participants were then exposed to either filtered air or air mixed with diesel exhaust for two hours on a stationary bike at a relaxed pace.
Another fMRI was performed immediately after the intervention. All participants completed the intervention and control scenarios at different times, and neither the participants nor the researchers knew which group they belonged to.
The researchers looked at how diesel exposure affected the default mode network (DMN), which is responsible for self-reflection and internal thoughts rather than external stimuli, said Dr. Michael Lipton, a professor of radiology at Albert Einstein College of Medicine and medical director of the MRI service at Montefiore Medical Center, who was not involved in the study. Research shows that people with mental health conditions such as anxiety and depression show clear changes in the DMN, Tan added.
DMN connectivity temporarily increased after exposure to filtered air, which the researchers attributed to the exercise the participants performed. Previous studies have linked mild exercise to increased DMN connectivity. However, DMN connectivity did not change after exposure to diesel fuel.
The new study has its limitations, including a small sample size and the fact that in real life, people are exposed to higher concentrations of pollutants for longer periods. The study also cannot explain how diesel could have caused the observed changes in connectivity.
“Diesel exhaust is known to cause systemic inflammation, which can affect the brain and alter the DMN,” senior study author Dr. Chris Carlsten, a professor and chair of respiratory medicine at the University of British Columbia, told Live Science in an email. “However, this remains speculative.” Lipton added that he’s not sure that such short-term exposure can cause significant inflammation in the brain.
Tan said the study is a good first step toward better understanding how air pollution negatively impacts the brain. It’s also important to understand that, regardless of the biological mechanisms underlying the effect, there are other reasons why air pollution doesn’t affect everyone equally, he added. For example, socioeconomically disadvantaged communities are more likely to
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