Just two hours of exposure to air pollution may impair human brain function, according to a study.
The researchers found that exposure to diesel exhaust for just two hours causes a decrease in the brain's functional connectivity - a measure of how different areas of the brain interact and communicate with each other.
The study, published in the journal Environmental Health, provides the first evidence in humans, from a controlled experiment, of altered brain network connectivity induced by air pollution.
"For many decades, scientists thought the brain may be protected from the harmful effects of air pollution,” said senior study author Chris Carlsten, a professor at the University of British Columbia (UBC) in Canada.
"This study, which is the first of its kind in the world, provides fresh evidence supporting a connection between air pollution and cognition,” Carlsten said.
The researchers briefly exposed 25 healthy adults to diesel exhaust and filtered air at different times in a laboratory setting.
They measured the brain activity before and after each exposure using functional magnetic resonance imaging (fMRI).
The team also analysed changes in the brain's default mode network (DMN), a set of inter-connected brain regions that play an important role in memory and internal thought.
The fMRI revealed that participants had decreased functional connectivity in widespread regions of the DMN after exposure to 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 is concerning to see traffic pollution interrupting these same networks," said Jodie Gawryluk, a professor at the University of Victoria in Canada and the study's first author.
"While more research is needed to fully understand the functional impacts of these changes, it is possible that they may impair people's thinking or ability to work,” Gawryluk said.
The researchers noted that the changes in the brain were temporary and participants' connectivity returned to normal after the exposure.
Carlsten speculated that the effects could be long lasting where exposure is continuous. He said that people should be mindful of the air they are breathing and take appropriate steps to minimise their exposure to potentially harmful air pollutants like car exhaust.
"People may want to think twice the next time they are stuck in traffic with the windows rolled down," said 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," he said.
While the current study only looked at the cognitive impacts of traffic-derived pollution, Carlsten said that other products of combustion are likely a concern.
"Air pollution is now recognised 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 is an important consideration for public health officials and policymakers,” he added.