Stress Physiology, Measurement, and Impact on Immunity

Exam and Study Guide Updates

  • The stress chapter will be completed today, and the immunity chapter will start.

  • Students will not be responsible for the entire immunity chapter for the upcoming exam; details will be provided.

  • An exam discussion, including question types, will occur on Friday.

  • A study guide will be posted soon to help students prepare for the exam.

Physiology of Stress

  • Recap: Previously covered brain and nervous system responses, as well as the endocrine system's role in stress (e.g., histamine release).

  • Current Focus: Today's discussion will focus on cardiovascular responses to stress and methods for measuring stress.

Challenges in Measuring Stress

  • Defining stress is complex: It refers both to the "stimuli" causing responses and our "responses" to those stimuli.

  • Measurement is even more complicated due to the intricate definition.

Methods for Measuring Stress

1. Self-Report Measures (Self-Report Scales)

  • Method: Researchers ask individuals about their stress levels, sleep quality, recent stressors, etc.

  • Limitations:

    • Unreliability: Recollection can be inaccurate, particularly for past events.

    • Memory Bias: People tend to remember positive experiences more vividly and forget negative ones or their negative responses to them.

  • Improving Accuracy: Ecological Momentary Assessment (EMA)

    • Definition: EMA involves collecting data at specific times (e.g., daily, multiple times a week/day) using tools like journals or smartphone apps.

    • Process: An app might prompt users to report their stress levels or number of stressors encountered in real-time or within a recent period (e.g., last hour).

    • Benefit: This method yields relatively more reliable data due to immediate reporting.

2. Physiological Assessments

  • Principle: Some researchers prefer objective physiological measures over self-reports.

  • Indicators: Changes in heart rate, blood pressure, breathing frequency, and sweating (palmar).

  • Connection to Nervous System: These indicators are part of the autonomous nervous system's response, specifically sympathetic nervous system activation (e.g., increased heart rate, sweaty palms, frequent breathing).

  • Modern Technology: Wearable devices (smartwatches) can monitor heart rate, breathing, and oxygen levels, allowing for stress detection outside laboratory settings.

  • Hormonal Measures:

    • Health psychologists measure stress hormones like cortisol, epinephrine (adrenaline), and noradrenaline.

    • Elevated levels in the bloodstream indicate stress.

    • Measurement: Hormones are typically measured through saliva and urine analysis.

    • Limitations:

      • Blood levels of hormones decrease quickly after a stressful event, making detection challenging for brief stressors.

      • Urine samples are also affected by time, requiring precise timing for accurate measurement.

Cardiovascular Responses and Reactivity Hypothesis

  • Stress Impact: Stress affects blood pressure and heart rate.

  • Reactivity Hypothesis: Individuals who exhibit large increases in blood pressure and vascular resistance in response to stress have an increased risk of developing heart disease in the future.

  • Criticisms of Research:

    • Most data is collected in laboratory environments.

    • Questions arise about whether these findings apply similarly to real-life, natural contexts.

Respiratory Sinus Arrhythmia (RSA)

  • Definition: RSA measures how heart rate changes with breathing, indicating nervous system balance.

  • Mechanism: Heart rate tends to speed up slightly when inhaling and slows down when exhaling.

  • Measurement: RSA quantifies the variation in this pattern.

  • Significance:

    • High variation (high RSA) indicates a better-balanced nervous system.

    • A balanced nervous system is linked to better overall health and reduced susceptibility to stress-related diseases.

    • Individuals with high RSA tend to have better emotional well-being and lower risk of stress and anxiety.

    • High RSA is associated with better heart health, lower obesity risk, and reduced diabetes risk.

  • Conclusion: RSA serves as a good indicator of overall health and resilience.

How Stress Makes Us Sick: The Mind-Body Connection

  • Historical Context: Before the 1980s, the connection between physical health, mental health, and stress was largely unknown or doubted by biomedical researchers.

Robert Ader's Classical Conditioning Experiment (1980s)

  • Background: Classical Conditioning

    • Definition: An organism learns to associate a neutral stimulus with a naturally occurring response after repeated pairings.

    • Ivan Pavlov's Experiment:

      • Unconditioned Stimulus (UCS): Meat (naturally causes salivation).

      • Unconditioned Response (UCR): Salivation to meat.

      • Neutral Stimulus (NS): Metronome sound (initially no salivation).

      • Conditioning: Metronome sound (NS) paired with meat (UCS) multiple times.

      • Conditioned Stimulus (CS): Metronome sound (after conditioning).

      • Conditioned Response (CR): Salivation to metronome sound alone.

    • Food Aversion: Can occur with just one pairing (e.g., eating a food and getting poisoned can lead to long-lasting aversion to that food).

  • Ader's Experiment (Rats):

    • Goal: To negatively condition rats to an unhealthy drink.

    • Procedure:

      • Rats were given artificially sweetened water (neutral stimulus).

      • Immediately after, they received an injection of a drug that made them nauseous.

      • This was intended to create a food aversion wherein the rats would feel nauseous upon seeing the sweetened water without the drug.

    • Unexpected Discovery: Over several weeks, many rats became very sick and died, even after the nauseating drug was stopped and only the sweetened water was given.

    • Mechanism: Ader found a significant reduction in the number of T cells (part of the immune system) in these rats.

    • Implication: The nausea-inducing drug negatively impacted their immune system, and after conditioning, their immune system responded to the sweetened water (conditioned stimulus) as if it were the harmful drug, leading to illness and death.

  • Challenging Beliefs: This experiment provided strong evidence against the prevailing belief that the mind and body were independent.

Confirmation and Further Research

  • Ader and Nicholas Cohen: Teamed up to confirm the findings, replicating the results across different contexts, animals, and substances.

  • Candace Pert: Demonstrated that the brain has receptors for immune molecules, allowing the brain to monitor and influence immune system activity.

  • Conclusion: Our brains control our immune system. Psychological conditioning (believing something is harmful) can influence the immune system's response, leading to physiological changes (e.g., immune suppression).

  • Conditioning Illustration:

    • Unconditioned Stimulus (UCS): Immune-suppressing drug.

    • Unconditioned Response (UCR): Immune suppression.

    • Neutral Stimulus (NS): Saccharin-flavored water.

    • Pairing: Repeated pairing of saccharin water (NS) with immune-suppressing drug (UCS).

    • Conditioned Stimulus (CS): Saccharin-flavored water.

    • Conditioned Response (CR): Immune suppression to saccharin-flavored water alone (even without physiological harm from the water itself).

Psychoneuroimmunology (PNI)

  • Pioneering Work: Ader, Cohen, and Pert's work validated George Solomon's earlier (10-year prior) theoretical article.

  • Solomon's Term: Coined "psychoneuroimmunology" (PNI).

  • Definition: A speculative theoretical integration of the links among emotions, immunity, and disease.

    • Psycho-: Psychological processes (emotions, stress perception).

    • Neuro-: Nervous system (brain, neural pathways) and Endocrine system (hormones).

    • Immunology: Immune system.

  • Core Idea: Our emotions and stress levels affect our immune system's responses, which in turn impact our overall health and susceptibility to disease.

  • Goal of PNI Research: To uncover the intricate ways behaviors and health are interrelated, focusing on the underlying immunological mechanisms.

Duration of Stress and Immune System Response

  • Short-Term Stressors: Can actually increase the immune system's response (e.g., a sudden loud noise).

  • Long-Term (Chronic) Stressors: Decrease or suppress the immune system's response (e.g., persistent worry about exams or classes).

How Stress Affects the Immune System: Two Hypotheses

1. Direct Effect Hypothesis

  • Core Idea: Stress directly weakens the immune system through biological pathways.

  • Mechanisms:

    • HPA Axis & SAM Axis Activation: Stress activates the Hypothalamic-Pituitary-Adrenal (HPA) axis and Sympathetic Adrenomedullary (SAM) axis.

    • Hormone Release: These systems release corticosteroids, epinephrine, and noradrenaline.

    • Immune Cell Receptors: T cells and B cells (key immune cells) have receptors for these stress hormones.

    • Impact: When these hormones bind to immune cells, it reduces the immune system's ability to fight infections; immune cells become preoccupied with receiving hormones, making the body vulnerable to pathogens.

    • Blood Clotting: Increased stress can lead to inappropriate blood clotting inside the body (blood clotting disorder).

      • Normal clotting occurs to stop bleeding from cuts.

      • Internal clots increase the risk of heart attacks and strokes.

      • Individuals in high-stress occupations (teachers, caregivers) are more prone to these clotting issues.

2. Indirect Effect Hypothesis

  • Core Idea: Stress weakens the immune system indirectly by promoting maladaptive behaviors.

  • Mechanism: Stress doesn't directly alter immune processes but encourages unhealthy coping mechanisms.

  • Maladaptive Behaviors:

    • Increased alcohol use.

    • Increased smoking.

    • Unhealthy eating habits (e.g., consuming sweets).

    • Reduced sleep due to stress.

  • Impact: These behaviors, rather than the stress itself directly, lead to increased health issues and a weakened immune system.

Allostatic Load

  • Definition: "Allostatic load" refers to the cumulative "wear and tear" on the body from long-term exposure to stress.

  • Neuroendocrine System Role: The neuroendocrine system plays a key role in mediating this load.

  • Accumulation: While single, isolated stressful experiences can be regulated, multiple, unpredictable, uncontrollable, long-lasting, or hard-to-manage stressors accumulate over time.

  • Impact: This buildup of allostatic load eventually makes individuals sick, impacting their overall health and well-being. The more stressors one faces, the stronger their cumulative effect on the body.