Brain Fog in the Air

Memory is fundamental to almost all aspects of daily life, especially for Stuyvesant students. Remember when you had to memorize a hundred names and dates for your history test? Or all the train stops on the way home? Growing up in New York City, we are constantly bombarded with new things to see and remember as we walk down the crowded streets. The price of living in such a fun-packed urban city is exposure to urban air pollution, which consists of small particles and toxic gasses. There has been extensive research conducted on the negative impacts of air pollution, and recently, more attention has been placed on how air pollution affects neurological functions, including memory. Memory naturally deteriorates with age, but recent research suggests that increased exposure to air pollution could accelerate the processes of cognitive decline.

While memory formation and recall are still not fully understood, we know that the process relies on the complex connections that exist in a web of nerve cells, or neurons. Information is sent in the form of electrical and chemical signals between neurons, which communicate with each other through junctions called synapses. The electrical impulses from a neuron are converted into a chemical signal by triggering the release of ions and neurotransmitters. These neurotransmitters move across the synaptic cleft and bind with the receptor of another neuron, converting back into an electrical signal and moving along the path. One crucial aspect of memory is long-term potentiation (LTP), a process by which the repeated stimulation of neurons results in increasing synaptic strength. This allows for more effective communication between neurons. The ability of a particular synapse to change its strength is called synaptic plasticity. As a memory is repeatedly recalled and the neuron receives more signals, additional receptors are placed. This gives the neuron a higher sensitivity to those chemical signals, increasing its ability to send the message along and strengthen the synapses.

Short-term memory, occasionally called “working memory,” is linked to the prefrontal cortex, and functions as a temporary storage system for processing immediate information (lasting only a few seconds to a minute). This type of memory has a highly limited capacity, so it is susceptible to interference and decay. The prefrontal cortex and short-term memory aid in quick decision-making, problem-solving, and the storage of small pieces of information for immediate use, like when you review a term on a flashcard only to forget it immediately after the test. Unless you put effort into processing the thought, the information will be lost. Still, its efficient operation is crucial for our daily cognitive functioning, enabling us to process new information as we navigate various tasks and challenges in our everyday lives.

There are many ways that air pollution can damage these processes. The main method is by inducing neuroinflammation, or inflammation of the brain. Small particles suspended in the air can be inhaled and infiltrate the bloodstream. The particles can eventually reach and penetrate the blood-brain barrier (BBB), the protective layer between the bloodstream and the brain. This results in neurological damage, which kills neurons and triggers inflammation. When the body undergoes inflammation, immune cells can have what is known as a respiratory burst, releasing highly reactive oxygen species (ROS) to attack pathogens. While ROS help defend the body, an excessive amount can overwhelm the body’s natural antioxidant system. This may lead to an imbalance of oxygen species in the body, creating a state of oxidative stress. Oxidative stress can cause damage to areas of the brain necessary for memory creation and retrieval—such as the prefrontal cortex and hippocampus—by killing neurons and breaking neural connections. It can also disrupt the functioning of neurotransmitters, interfering with LTP and leading to memory impairment over time. Damage caused by oxidative stress can increase the intensity of the inflammatory response, which in turn releases more ROS and worsens oxidative stress, creating a positive feedback loop. Though there are many ways that neuroinflammation and oxidative stress can come about—through infections, bodily inflammation, or severe mental stress—there are experiments showing a connection between oxidative stress and exposure to air pollution.

An experiment was performed by Dr. Ana C.T. Zanchi and her team in 2009 to investigate the effects of air pollution exposure on the short-term memories of mice. These mice were split into four groups: all filtered air exposure (control), prenatal (pre-birth) exposure to filtered air and postnatal (post-birth) exposure to non-filtered air, prenatal exposure to non-filtered air and postnatal exposure to filtered air, and all non-filtered air exposure. The pre- and post-natal distinction was made to test whether or not a mother’s exposure to substantial amounts of air pollution affected the unborn child. After 150 days of this controlled exposure, the mice were given a spontaneous object recognition test to determine their short-term memory discriminative. The mice were placed in a room for a habituation phase to briefly familiarize them with an object before more objects were added or swapped. A healthy recognition of the object was identified if the mouse had a higher level of exploration with new objects, meaning they had recognized the old object and found the new one more interesting due to its novelty. This approach is often used in clinical research relating to memory and is essential to understanding cognitive function and bridging the gap between animal and human minds. It was determined that the groups that were exposed to non-filtered air, particularly the ones that had only non-filtered air exposure, had significantly lower short-term memory discriminants. Furthermore, after taking blood and cortex samples from the mice, the researchers found that the non-filtered air group had an increase in malondialdehyde, a marker for oxidative stress. This shows a correlation between exposure to air pollution, the weakening of short-term memory, and oxidative stress. Dr. Zanchi repeated a version of this experiment in 2021 and achieved similar results.

Memory plays a substantial role in our daily lives, from helping us understand the past to shaping the actions that determine our future. As the concentration of pollution in our atmosphere increases, concerns about the negative implications for memory become more pressing. As we navigate the complex relationship between cognitive health and environmental factors, it becomes clear that safeguarding air quality is not only important to averting climate change but also for the protection of our cognitive function. Our abilities to remember, learn, and progress are linked to the air we breathe. In this urban and industrial age, controlling air pollution is crucial to preserving memory, the very essence of human experience.