Researchers have discovered that extended exposure to air that is polluted may lead to physical changes in a person's brain, as well as memory issues, learning issues and even depression. The findings of these researchers might have a notable and troubling implication for those who live and work in urban areas that are polluted. Prior studies have revealed the damaging effects of polluted air on a person's lungs and heart, although researchers from Ohio State's Department of Neuroscience working with colleagues in the University's Davis Heart and Lung Research Institute have now shown that polluted air is detrimental to a person's brain. The study, conducted using mice, is published in the journal, 'Molecular Psychiatry.'
Air pollution is defined as a mixture of solid particles and gases in the air. Car emissions, chemicals from factories, dust, pollen and mold spores may be suspended as particles. Ozone, a gas, is a major part of air pollution in cities. When ozone forms air pollution, it's also called smog. Indoor air pollution and urban air quality are listed as two of the world's worst toxic pollution problems in the 2008 Blacksmith Institute World's Worst Polluted Places report. In general any substance that people introduce into the atmosphere that has damaging effects on living things and the environment is considered air pollution.
Researchers from the State of Ohio, in earlier work with mice, discovered that fine air particulate matter causes widespread inflammation in the body that could be linked to diabetes, high blood pressure, as well as obesity. The health issues are chronic ones experienced by industrialized populations around the world today. The research moves the work further, opening up the potential of a link between air pollution and the increasing numbers of people who experience issues with their brains.
In the Ohio study, mice were exposed to either filtered air or polluted air for six hours each day, five days per week for ten months. The length of time is almost 50% of the lifespan of the mice. The polluted air contained fine particulate matter - the kind of pollution created by factories, cars and natural dust. The fine particulates are tiny, around 2.5 micrometers in diameter, or approximately one-thirtieth of the width of a human hair. The particles can reach deep into areas of the lungs or other organs in the body.
The concentration of particulate matter that the mice were exposed to was equal to what people might be exposed to in some cities and towns that are polluted. Following the ten month exposure to polluted or filtered air, the mice underwent a number of behavioral tests.
In a memory and learning test, the mice were placed in the middle of a well-lit arena and given two minutes to find an escape hole leading to a dark box where they feel more at ease. The mice were given five days of training to locate the escape hole, yet the mice who breathed the polluted air took longer to learn where the escape hole was located. The mice exposed to polluted air were also less-likely to remember where the escape hole was when they were tested at a later time.
In still another experiment, mice exposed to the polluted air showed more depressive-like behaviors than did the mice that breathed the clean, filtered air. The polluted-air mice also presented signs of increased levels of anxiety-like behaviors. In an attempt to try to understand how air pollution might lead to the observed changes in memory, learning and mood - the researchers continued on to examine the hippocampus in the brain, a main area associated with memory, learning and depression.
The researchers discovered distinct physical differences in the hippocampuses of mice who were exposed to the polluted air compared to the mice who were not. The researchers looked specifically at the branching structures called, 'dendrites,' at the end of nerve cells or, 'neurons.' The dendrites have small projections on them called, 'spines,' that transmit signals from one nerve cell to another.
Mice who were exposed to polluted air had fewer spines in portions of their hippocampuses, shorter dendrites, as well as overall reduced cell complexity. Prior research has shown that these types of changes are linked to decreased memory and learning abilities. In earlier work, researchers from the Ohio group discovered that chronic exposure to polluted air leads to widespread inflammation in the body, which is linked to a range of different health issues in human beings. The new study discovered evidence of low-grade inflammation in the hippocampus.
In the mice that breathed the polluted air, chemical messengers that cause inflammation called, 'pro-inflammatory cytokines,' were more active in the hippocampus than they were in the mice who breathed the filtered air. The hippocampus is especially sensitive to damage caused by inflammation.
The work was conducted in mice, and while it is not wise to extrapolate the findings of animal work to humans - it is difficult to ignore the potential significance the findings might have for people. Plainly, we need to better understand the effects of breathing polluted air on the human brain and in particular, the effects of polluted air on memory and learning in children as well as the longer term consequences such as the risk in later life of developing cognitive impairment and a number of other neurological conditions.