How does the environment contribute to increased excitability?

From the Guidelines

The environment significantly contributes to increased excitability through various sensory and physiological pathways, including excessive stimulation from noise, as evidenced by the adverse cardiovascular effects of traffic noise 1. Excessive stimulation from loud noises, such as traffic noise, can overwhelm the nervous system, triggering the body's stress response and raising cortisol levels.

• The World Health Organization (WHO) has classified traffic noise as the second worst environmental stressor affecting human health, exceeded only by air pollution 1.
• Traffic-related noise accounts for more than 1 million healthy years of life lost annually in the European Region, with disability-adjusted life-years (DALYs) lost from environmental noise totaling 61,000 years for ischemic heart disease, 903,000 years for sleep disturbance, and 654,000 years for annoyance 1.
• New research has found that traffic noise may also increase the risk for other major diseases, including stroke and diabetes, which would add substantially to the DALY estimate 1. Additionally, environmental enrichment has been shown to have a positive impact on reducing excitability and promoting improvements in mood and pain, as demonstrated by the reduction of pain and anxiety/depression-like behaviors in rats submitted to spared nerve injury during infancy 1.
• Environmental enrichment reduced pain and anxiety/depression-like behaviors in rats by mechanisms associated with a decrease in both IL-1β and TNF-α and an increase in IL-10 expression in the medial prefrontal cortex (mPFC), basolateral amygdala, and ventral hippocampus 1.
• Environmental enrichment also attenuated the pain threshold, depression-like phenotype, and memory deficit in a model of neuropathic pain, which involved the neuronal PAS domain protein 4 (NPAS4) hippocampal pathway, in addition to reducing inflammation and re-establishing hippocampal neurogenesis 1. However, other environmental factors such as poor air quality, cluttered or disorganized spaces, and social environments characterized by conflict or tension can also contribute to increased excitability.
• Poor air quality with high levels of pollutants or allergens can cause respiratory distress and inflammation that affects brain function and mood.
• Cluttered or disorganized spaces create visual overload that taxes cognitive resources and increases stress.
• Social environments characterized by conflict, tension, or high expectations can trigger emotional responses that increase physiological arousal. These environmental factors collectively impact the autonomic nervous system, neurotransmitter balance, and stress hormone production, shifting the body toward a state of hyperarousal and increased excitability. Overall, the environment plays a significant role in contributing to increased excitability, and reducing exposure to adverse environmental factors while promoting environmental enrichment can help mitigate this effect.

From the Research

Environmental Factors Contributing to Excitability

The environment plays a significant role in contributing to increased excitability in various organisms. Some of the key factors include:

• Temperature: Changes in temperature can affect the membrane potential of neurons, leading to alterations in excitability 2
• Light intensity: Variations in light intensity can influence the properties of plant leaves, leading to changes in their thickness resonant frequency 3
• Emotional sounds: Emotionally characterized sounds can modulate the excitability of the corticospinal motor tract, with unpleasant sounds leading to increased excitability 4
• Chemical stimuli: Bacteria can sense a wide range of environmental stimuli, including chemicals, and respond accordingly 5

Mechanisms of Environmental Influence

The mechanisms by which the environment influences excitability are complex and multifaceted. Some of the key mechanisms include:

• Ion channel conductance: Temperature affects the rates of diffusion through ion channels, leading to changes in membrane potential and excitability 2
• Neurotransmitter release: Emotional sounds can influence the release of neurotransmitters, leading to changes in excitability 4
• Gene expression: Environmental stimuli can influence gene expression in bacteria, leading to changes in behavior 5
• Physical environmental stimuli: The physical environment of healthcare settings can encourage the healing process and patients' feelings of well-being, with factors such as sunlight, windows, and seating arrangements having a positive effect 6

Organisms and Systems Affected

The environment can affect the excitability of various organisms and systems, including:

• Neurons: Temperature and emotional sounds can influence the excitability of neurons 2, 4
• Plants: Light intensity and watering can influence the properties of plant leaves 3
• Bacteria: Chemical stimuli and environmental conditions can influence the behavior of bacteria 5
• Healthcare settings: The physical environment of healthcare settings can influence the well-being of patients 6