The Congested Brain

Along with the warm sun shining in your face, the wind tussling your hair, you inhale the smell of…car exhaust? Yet, you are not concerned because you live in New York City, where air pollution is as common as seeing planes in the sky. You move on with your day, running to school, strolling through the city, getting your lunch. However, as you continue to inhale and exhale pollution, there is a possibility that this smoke could cause massive, detrimental effects on the brain, one of the most vital organs in the human body.

The brain is composed of interconnected neurons and glial cells that send and relay signals, like a computer program that takes the information in the search bar and returns numerous results. When the brain is active, it controls, processes, and interprets these signals to connect the rest of the body with the nervous system, helping to maintain bodily functions. When it is inactive, the brain is unable to interpret these signals, and thus cannot transfer them to the rest of the body. The brain’s functions are vital, and air contamination, especially from car exhaust, can severely limit its performance.

Exhaust consists of organic compounds, metals, and ambient particulate matter, a complex mixture of solid and liquid particles in the air. Inhaled ambient particles can enter the nervous system through the olfactory nerve or nasal nerve cavities, and induce inflammatory responses in the brain. These responses can cause tissue damage and neurodegeneration, affecting the signaling pathways within the brain. Specifically, a recent study published by Environment Health examines the damaging effects of air pollution on the parts of our brains that allow us to think.

In this experiment, each participant was exposed to 300 micrograms (µg) of diesel and controlled filter air, almost half of the daily average of 625 µg of exhaust inhaled. Before and after exposure, their default mode network (DMN)—a complex intrinsic system involved in cognitive thinking—was measured using functional magnetic resonance imaging (fMRI). fMRI is a neuroimaging technique that reveals active portions of the brain through blood oxygen levels. This approach works because active neurons in the brain require more oxygen than inactive ones. fMRI has a plethora of different sub-methods to determine brain activation, but this experiment utilized the brain functional connectivity process.

Brain functional connectivity is a statistical association that determines the electrical wave pattern emitted by specific activated sectors of the brain to the body. Commonly, brain functional connectivity deciphers DMN activation because the DMN system relies on particular parts of the brain, like the amygdala or medial prefrontal cortex. This characteristic makes it easier for the fMRI to determine the association between the active sectors of the brain and body.

Patients’ functional connectivity was measured after two hours of exposure in both the control and experimental groups. In individuals exposed to diesel exhaust, post-exposure measurements contained lower oxygen levels compared to pre-exposure data. In individuals exposed to clean air, oxygen levels were the same pre- and post-exposure. These results concluded that while exposure to diesel fuel decreased DMN functional connectivity in the brain, exposure to controlled clean air had no significant effects on DMN functional connectivity. 

If DMN functional connectivity were the same, electrical waves in distinct brain segments would have the same wave frequency, indicating a relationship between brain activation and the body. This discovery reveals that the signals from the brain can be transmitted throughout the nervous system. On the other hand, altered DMN connectivity indicates the waves do not have the same frequency, and there is no correlation between the activity of neurons within set parts of the brain and the body. Essentially, altered DMN connectivity shows that the brain sections associated with particular signals do not conduct them to the rest of the body.

Disruptions within these systems can cause autism, depression, and bipolar disorder, a diverse range of neurological conditions where the brain cannot process the requests signaled by neurons to the rest of the body. The changes in brain activity during this experiment did not drastically impact the participants’ well-being long term, as the DMN decreased functional changes were merely temporary. However, there is no conclusive evidence that diesel air would cause more permanent damage to the brain in a continuous setting.

Currently, more observations are required to understand the magnitude of the effect traffic pollution can have on the brain and DMN functional connectivity. Air contamination is a major environmental threat to human health, as scientists are discovering detrimental impacts across all major organ systems. Researchers suggest measures to help reduce exhaust levels such as encouraging others to take public transportation, avoiding idling cars, and carpooling. Hopefully, decreasing quantities of exhaust could help prevent the spread of air pollution and stop damage to our brains and the rest of our bodies in the long run.