Indoor Air Pollution and Decision-Making Behavior: An Interdisciplinary Review

Abstract

The human brain is constantly exposed to air pollutants, some of which might be disruptive or even lethal to certain neurons implicated in abstract features of cognitive function. In this review, we present new evidence from behavioral and neural studies in humans, suggesting a link between indoor fine particulate matter and decision-making behavior. To illustrate this relationship, we use qualitative sources, such as historical documents of the Vietnam War to develop hypotheses of how aerial transmission of pollutants might obstruct alternative choices during the evaluation of policy decisions. We first describe the neural circuits driving decision-making processes by addressing how neurons and their cognate receptors directly evaluate and transduce physical phenomena into sensory perceptions that allow us to decide the best course of action among competing alternatives. We then raise the possibility that indoor air pollutants might also impact cell-signaling systems outside the brain parenchyma to further obstruct the computational analysis of the social environment. We also highlight how particulate matter might be pathologically integrated into the brain to override control of sensory decisions, and thereby perturb selection of choice. These lines of research aim to extend our understanding of how inhalation of airborne particulates and toxicants in smoke, for example, might contribute to cognitive impairment and negative health outcomes.

Keywords: cognitive behavior; indoor air management; neural circuits; particulate matter; smoke toxicants; vietnam war.

Figure 1. Footage from the Lyndon Baines Johnson Library.

Film clips depict the President of the USA with several of his secretaries and advisors discussing lay theories of peace for ending the prolonged and violent conflict in Vietnam. The film clips also show secretaries and advisors to the President smoking cigarettes in the West Wing of the White House. We now know that increased exposure to smoke toxicants results in negative health outcomes, independent of local concentrations of other indoor air pollutants. Although pulmonary and cardiovascular obstructive diseases are traditionally associated with human exposure to smoke, smoke particulates (> 1 µm) also injure large-scale brain networks that drive decision-making behavior. Thus, high levels of smoke plumes, for example, could have increased the risk of cognitive impairment by directly reducing LBJ’s cortical blood flow. Blood flow as measured by phase-contrast MRIs is an index of local neural activity. (A) LBJ and Secretary of State Dean Rusk; (B) Creighton W. Abrams United States Army General; (C) Walt Rostow National Security Advisor to LBJ; (D) from left to right: Walt Rostow, Earle Wheeler (Chairman of the Joint Chiefs of Staff), Clark M. Clifford (Secretary of Defense), and Maxwell D. Taylor (Chairman of the Foreign Intelligence Advisory Board). Images used for this composite are available through the photo archive of the LBJ Library (http://www.lbjlibrary.net/collections/photo-archive.html) through the public domain and are free for use by anyone for any purpose without restriction under copyright law.

Figure 2. Neural Circuits and Cognition.

The cognitive faculties of the human brain are underpinned by intricate and highly interconnected neural circuits. (A): Neurons from the following brain areas (in pink color) are thought to broadcast local chemical signals to a wider brain network to generate a subjective computational analysis of the social environment; (B) Cortex: different regions of the cortex (e.g., dorsal prefrontal cortex and orbitofrontal cortex) have specific cognitive functions and distinct computational properties; (C) hippocampus; (D) nucleus accumbens; (E) amygdala; (F) hypothalamus. These chemical signals are likely correlated with diverse aspects of behavior, including decision-making, declarative memory, intrinsic reward, anxiety, fear learning, and homophily cooperation, respectively. Obviously, chemical signals from other brain areas (e.g., periaqueductal gray and anterior insula) as well as peripheral nerves interact with the above neural circuits to provide complementary inputs to discern the best course of action among competing alternatives [1]. Human nerve cells (A) are from Lichtman Lab/Harvard University, Connectomics Team//Google. (B-F) Coronal brain sections (Nissl stained, ~14667-14712 µm) are from a 34-year-old male. Image Credit: Allen Institute (Interactive Atlas Viewer). Content for research and academic publication may be used without further permission as stated (https://alleninstitute.org/legal/terms-use/).

Figure 3. Schematic Diagram Depicts Progressive Action Phases Thought to be Involved in the Generation of Decision-Making Behavior.

Continuous signals from the environment are perceived by sensory systems which are then processed, coded, and experienced as segmented units by the brain. These experiences evoke complex patterns of neural activity which are then transmitted to cortical and subcortical cell type-specific areas. Some experiences such as personal, physical threats are most likely processed within neural circuits of the eyes (e.g., VG3 amacrine cell-signaling), not the brain [29]. Thus, some decisions are made in single automatic trials which are crucial for human and animal survival. Decision-making behavior is influenced by internal states (e.g., health status and reward values), personal evolutionary history (e.g., genetics and epigenetics), the behavior of others around us, and likely by the genes that those individuals carry. As a result, people’s choices do not always perfectly reflect the true state of the local environment. The figure was drawn and edited by Dr. German Torres and Dr. Joerg R. Leheste.

Figure 4. Schematic Diagram Depicts How High Levels of Particulate Matter Might Contribute to Cognitive Impairment and Motor Disability in Humans.

PM2.5 enters the brain via respiratory and olfactory epithelia, the integumentary system, and visual and/or auditory afferent pathways. Exposure to sulfates, nitrates, and/or volatile organic compounds negatively affects the electrical and chemical signals of the functioning neuron. This exposure is exacerbated by prolonged indoor living, inadequate air filtration, droplet shedding, and exhalation of gut bioeffluents, including those produced during talking and coughing. As a result, indoor pollution levels progressively distort people’s behavior creating situations where, in extreme cases, everyone selects exactly the same choice (Good or Bad) at the expense of rational reasoning and evidence from multiple sources. The figure was drawn and edited by Dr. German Torres and Dr. Joerg R. Leheste.