Feeling a bit slow and depressed? It just might be the air.
Neuroscientists at Ohio State University have linked fine-particle air pollution to slow thinking, bad memory and depressive-like behaviours in mice. The exposed animals also were found to have abnormal brain cells, inhibiting the flow of electrical impulses that transmit information.
The research appears to break new ground on what's known about the health effects of air pollution. Most of the hundreds of past studies have focused on how bad air impairs respiratory or cardiac health, and on how death rates increase on polluted days.
Earlier research done on rats at Cedars-Sinai Medical Center in Los Angeles suggested that several genes associated with common brain tumours and degenerative brain diseases are more active in rats exposed to freeway pollution.
The Ohio State research team wanted to know how pollution affects mental health.
They took samples of ambient air in Columbus, Ohio, and concentrated it seven times. Groups of mice breathed the air six hours a day, five days a week for 10 months. The air was five times worse than the average for Mira Loma, a community in Riverside County, California, that has among the nation's worst fine-particle pollution.
When run through memory and learning tests, the exposed mice couldn't think as well as those supplied with clean, filtered air.
In one exercise, mice were put in a brightly lit circular maze and subjected to irritating noise from a fan, said Laura Fonken, lead author of the study published in the scientific journal Molecular Psychiatry.
Only one of several holes along the perimeter offered escape to a quiet, dark and secure area. The animals exposed to bad air took longer to find the escape hole and, in subsequent tests, were less likely to remember its location.
The mice were tested for depression with what Fonken call a "forced swimming test". Each mouse was placed in a bucket of water and timed to determine how long it took for the animal to give up swimming and start floating.
Those exposed to air pollution swam on average for about 90 seconds, while mice that had breathed clean air swam for 145 seconds.
Mice are natural swimmers, Fonken said. When they stop paddling, it signals "behaviour despair" and "learned helplessness", she said. In other words, they are depressed.
How do the scientists know for sure? Fonken said earlier research found that mice dosed with antidepressant drugs, including Prozac, don't give up as quickly and will swim significantly longer than mice without medication.
Another significant finding involved cells in the hippocampus, the part of the brain controlling emotion, learning and memory. The cells were underdeveloped in mice that breathed the polluted air.
Specifically, their brains had fewer tiny projections, called spines, that transmit neurological signals among cells. Their brains probably do not transmit electronic signals as well as do those of other mice.
Fonken, a neuroscience doctoral, said more research needed to be done. She also said government health standards for air pollution should be revised periodically, as new information becomes available.
Southern California fails to meet federal health standards for fine-particle pollution, which includes diesel soot, wood smoke and chemical compounds from various factory and vehicle emissions. The region faces a 2015 deadline to bring such pollution down to healthful levels.
As of November 1, the South Coast Air Quality Management District will impose mandatory no-burn days for home fireplaces and wood stoves. It will cover Orange County and the urban parts of Los Angeles, Riverside and San Bernardino counties.
The mental-health finding fits with results of studies at the University of California, Irvine, which found that mice subjected to Southern California's polluted air developed inflammation in their brains similar to that found in people with Alzheimer's and Parkinson's diseases, said Jean Ospital, the district's health effects officer.