Breathing in air pollution could have an impact on the way your brain is wired, with scientists at the University of British Columbia (UBC) and the University of Victoria discovering that inhaling car exhaust can change a brain's connectivity within two hours.

The findings are based on a randomized, double-blind trial of 25 healthy adults, who were exposed to car pollution in a laboratory setting. At another stage, participants were also exposed to clean filtered air.

Brain scans were taken before and after each scenario. After participants were exposed to air pollution, their brains showed reduced connectivity in the default mode network (DMN), a set of inter-connected brain regions that are most active when we engage in internal thoughts, such as introspection and remembering.

These findings have not been observed among humans before, and while the current study did not test the effects that this could have on brain power, other research has.

Past studies, for instance, have linked altered brain connectivity to decreased working memory and work performance.

"It's concerning to see traffic pollution interrupting these same networks," says neuropsychologist Jodie Gawryluk from the University of Victoria.

"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."

The good news is that the changes observed in the study were temporary and reversed back to normal once clean air was flowing through the lungs.

Nevertheless, the findings do indicate a possible route by which chronic exposure to air pollution can have deleterious effects on the brain.

With up to 99 percent of the world breathing unsafe levels of air pollution, the consequences to public health could be profound.

In China, recent studies have linked air pollution to worse tests scores in language and math, whittling away at about a year's worth of education on average.

"For many decades, scientists thought the brain may be protected from the harmful effects of air pollution," explains respiratory physician Chris Carlsten from UBC.

"This study, which is the first of its kind in the world, provides fresh evidence supporting a connection between air pollution and cognition."

In 2020, markers related to Alzheimer's disease were observed in the brains of young adults, children, and even infants who lived in Mexico City – an urban hub that experiences extreme air pollution. (Recent data shows its air quality greatly improved during COVID-19 lockdown periods where vehicle movements and therefore exhaust fumes were reduced.)

Other research in the same city also revealed a possible trigger for that damage: metal nanoparticles of air pollution within the brains of many locals.

In 2022, scientists confirmed that these particles, once breathed in, can sometimes bypass the protective barrier of the brain, which was once thought to keep toxic material out.

The current study only relied on the fumes of car exhaust, but there may be other forms of air pollution that work even faster and with worse effects.

Before leaded gas was banned in the United States, for instance, researchers predict the toxic fumes were breathed in by 170 million Americans or more, resulting in a cumulative IQ score loss of 824 million points (nearly 3 points per person).

Gas might not contain lead today, but that doesn't mean it's safe for your lungs, or your brain.

"People may want to think twice the next time they're stuck in traffic with the windows rolled down," warns Carlsten.

"It's important to ensure that your car's air filter is in good working order, and if you're walking or biking down a busy street, consider diverting to a less busy route."

For much of the world, however, polluted air is inescapable. We need to know what that is doing to our brains in the long run.

The study was published in Environmental Health.