Pollution impairs brain function

Study finds even two hours of breathing diesel fumes can affect memory, behaviour, productivity

This article was written by Kevin Jiang and Joanna Chiu, and was published in the Toronto Star on January 27, 2023.

Physiological evidence of traffic pollution’s impact on our bodies — or more specifically, our minds — has been discovered by scientists in Canada.

A study, published in the journal Environmental Science, found that exposure to just two hours of diesel exhaust fumes led to a decrease in the brain’s functional connectivity — a measure of how well different regions of the brain interact with each other.

While the exact ramifications are as yet unknown, previous observational studies have linked weakened functional connectivity with worsened working memory, behavioural performance and productivity at work, the study authors wrote.

The study was the world’s first to expose humans to air pollutants in a lab setting, according to the authors from the University of British Columbia and University of Victoria.

In total, 25 adults between 19 and 49 were exposed to two hours of both filtered air and air contaminated with diesel exhaust.

“In our study, Joe is compared to Joe, so the only thing that is different is the exposure to diesel,” said senior study author Chris Carlsten, professor and head of respiratory medicine and Canada Research Chair in occupational and environmental lung disease at UBC.

“A crossover design where each individual serves as their own control has vastly more statistical power than if you looked at a hundred people,” Carlsten told the Star.

Participants received a functional MRI scan before and after each treatment, enabling researchers to monitor each subject’s brain activity. They were especially interested in a brain region called the default mode network (DMN), as it’s particularly sensitive to stresses like toxicity, aging and disease.

After analyzing the MRIs, the researchers recorded a significant decrease in functional connectivity inside the default mode network after breathing diesel exhaust compared to filtered air.

“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,” Jodie Gawryluk, psychology professor at the University of Victoria and the study’s first author, said.

“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.”

Additionally, Carlsten said his team is planning to publish another set of data from the same study that focused on cognition and reaction times.

“In addition to the MRI, we had participants take a standardized computer test called CANTAB, where a computer basically says, ‘Press the button if there’s a yellow square,’ and they have to do that as quickly as possible.

“Our preliminary results is that reaction time is slower under diesel conditions.”

Notably, the changes in the brain were temporary and the healthy participants’ brain function returned to their normal baseline after the exposure. However, Carlsten speculated that the effects could be longlasting when exposure is continuous.

“It would also be important for another study to look at effects from fire smoke as well, which is arguably a bigger problem in some places … Wood smoke is quite different to diesel exhaust,” he said.

Although the experiment was the first of its kind, it’s preceded by thousands of observational studies on the health impacts of traffic pollution, said Dr. Samantha Green, a Torontobased family physician and board member of the Canadian Association of Physicians for the Environment.

“The findings are not surprising to me, given the tremendous amount of observational research that already exists,” she said.

According to Green, traffic pollution has been linked to a broad spectrum of health disorders including issues with pregnancy, heart disease, various cancers and even an increased rate of dementia and Alzheimer’s disease.

Green believes the study represents a foundational step in taking air pollution research further, despite its relatively small sample size of 25 people.

Michael Brauer, a professor at UBC’s school of population and public health, and unaffiliated with the study, recommends individuals avoid areas with heavy traffic when walking or exercising if possible, install better air ventilation at home or even change commuting patterns.